Chapter-1 Introduction to Biological importance of ...shodhganga.inflibnet.ac.in/bitstream/10603/37071/5/chapter 1.pdf · are three major divisions in organic chemistry ... and benzisoxazole

Chapter-1

Introduction to Biological importance of

Benzimidazoles and Benzisoxazoles

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1.1 Introduction to Heterocyclic Chemistry

The organic compounds have enormous diversity of structures; many of these structures

contain ring systems. If the ring system is made up of atoms of carbon and at least one

element other than carbon, the compound is classified as heterocyclic. The elements that

present most commonly, together with carbon, in ring systems are nitrogen, oxygen and

sulfur. About half of the known organic compounds have structures that incorporate at

least one heterocyclic component. A cyclic organic compound containing all carbon

atoms in ring formation is referred to as a carbocyclic compound. And, if at least one

atom other than carbon forms a part of the ring system then it is designated as a

heterocyclic compound.1-4

Heterocyclic chemistry is a vast and expanding area of chemistry because of the obvious

applications of compounds derived from heterocyclic rings in pharmacy, medicine,

agriculture and other fields. The chemistry of heterocyclic compounds is as relevant as

that of alicyclic or aromatic compounds. Their study is of great interest both from the

theoretical as well as practical standpoint.

The literature on heterocyclic compounds is very vast. They may be classified into

alicyclic and aromatic heterocyclic compounds. The alicyclic heterocycles are the cyclic

analogues of amines, ethers, thioethers, amides, etc. The aromatic heterocyclic

compounds in contrast are those which have a heteroatom in the ring and behave in a

manner similar to benzene in some of their properties. A heterocyclic ring may comprise

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of three or more atoms which may be saturated or unsaturated. Also the ring may contain

more than one heteroatom; this may be similar or dissimilar.

Heterocyclic compounds have a wide range of applications: they are predominant among

the types of compounds used as pharmaceuticals,

as agrochemicals, as veterinary

products, used as optical brightening agents, as antioxidants, as corrosion inhibitors and

as additives with a variety of other functions.5

Also, many dyestuffs and pigments have

heterocyclic structures.6

One of the reasons for the widespread use of heterocyclic

compounds is that their structures can be subtly manipulated to achieve the required

modification in function. Many heterocycles can be fitted into one of a few broad groups

of structures that have overall similarities in their properties but significant variations

within the group. Such variations include differences in acidity or basicity, difference in

susceptibility to attack by electrophiles or nucleophiles, and different polarity. The

possible structural variations include the change of one heteroatom for another in a ring

and the different positioning of the same heteroatoms within the ring.

The number of possible heterocyclic systems are reported in the field of synthetic organic

chemistry. An enormous number of heterocyclic compounds are known and the number

is increasing very rapidly. The literature on the subject is correspondingly vast and there

are three major divisions in organic chemistry namely, aliphatic, aromatic and

heterocyclic, the last one is the biggest. Over six million compounds are recorded in

chemical abstracts and approximately half of them are heterocyclic.

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An example of the way in which heterocycles are used is provided by an account of the

development of a new systemic fungicide (1), 7

the pyrimidine ring was incorporated into

this structure because a related compound (2) proved to be too lipophilic. The water

solubility and the transport of the fungicide through the plant were improved by replacing

a benzene ring by the more polar heterocycle.

Many heterocyclic compounds are biosynthesized by plants and animals and are

biologically active. Over millions of years these organisms have been under intense

evolutionary pressure, and their metabolites may be used to advantage: for example, as

toxins to ward off predators, or as coloring agents to attract mates or pollinating insects.

Some heterocycles are fundamental to life, such as haeme derivatives in blood and the

chlorophyll present in the plants is essential for photosynthesis. Similarly, the paired

bases found in RNA and DNA are heterocycles, as the sugars in combination with

phosphates provide the backbones and determine the topology of these nucleic acids.

Dye stuffs of plant origin include indigo blue, used to dye jeans. A poison of detective

novel fame is strychnine, obtained from the plant resin curare. The biological properties

of heterocycles in general make them one of the prime interests of the pharmaceutical and

biotechnology industries.

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There are many thousands of other heterocyclic compounds, both natural and synthetic

which have major importance, not only in medicine but also in other activities known to

man. Small wonder than that, their chemistry forms a major part of both undergraduate

and post graduate curricula.

Some heterocyclic compounds are shown below.

A brief introduction to applications of benzimidazole and benzisoxazole derivates in the

area of medicinal chemistry is discussed in the following sections.

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1.2 Introduction to Benzimidazoles

Benzimidazoles are involved in a great variety of biological processes. Some of their poly

functional derivatives have been proved to possess antibacterial, fungicidal and

antihelmintic activities. Therefore, substituted benzimidazoles have attracted the interest

of various research groups, especially, it has been reported that the introduction of the

substitution at 1, 2 and 5 positions of the benzimidazole ring is very important for their

pharmacological effects.

One of the main goals of medicinal chemistry research and drug discovery is to provide a

rational basis for the design of new medicinal agents. Organic compounds and their

reactions have been utilized by people since antiquity. When leaves or tree bark or plant

roots were mixed with water to make a medicinal potion. A complex mixture of organic

products is actually extracted for its biologically active components. In 1960s, a broad

spectrum group of drugs, known as benzimidazoles, were discovered with a big- gang

having specific activity. Due to the increasing demand for bioactive molecules, organic

chemists are increasingly required to synthesize new compounds of biological interest.

There has been an unlimited expansion of molecular diversity in synthetic organic

compounds by the application of combinatorial methodology. The benzimidazole nucleus

is an important pharmacophore in drug discovery8 and it is a fused aromatic imadozole

ring where a benzene ring is fused to 4 and 5 positions of an imidazole ring.

Benzimidazoles are very useful intermediates for the development of molecules of

pharmaceutical or biological interest. Substituted benzimidazole derivatives have found

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applications as in diverse therapeutic agents including antiulcer, antihelmintic,

antihypertensive, anticoagulant, antiallergic, analgesic, anti-inflammatory, antipyretic,

antibacterial, antifungal, antiviral, antiparasitic, antioxidant, anticancer and

antianxiolytic. Because of their significant medicinal importance, the synthesis of

substituted benzimidazoles is listed with various effects on human body and are used to

treat multiple system disorders.

Presence of benzimidazole nucleus in numerous categories of therapeutic agents such as

antimicrobials, antivirals, antiparasites, anticancer, anti-inflammatory, antioxidants,

proton pump inhibitors, antihypertensives, anticoagulants, immunomodulators, hormone

modulators, CNS stimulants as well as depressants, lipid level modulators, antidiabetics,

etc. has made it an indispensable anchor for development of new therapeutic agents.

Varied substitutents around the benzimidazole nucleus have provided a wide spectrum of

biological activities. Importance of this nucleus in some activities like, Angiotensin I

(AT1) receptor antagonism and proton-pump inhibition is reviewed separately in

literature. Even some very short reviews on biological importance of this nucleus are also

known in literature. However, owing to fast development of new drugs possessing

benzimidazole nucleus many research reports are generated in short span of time. So,

there is a need to couple the latest information with the earlier information to understand

the current status of benzimidazole nucleus in medicinal chemistry research. In the

present chapter, various derivatives of benzimidazole with different pharmacological

activities are described on the basis of substitution pattern around the nucleus with an aim

to help medicinal chemists for developing SAR on benzimidazole derived compounds for

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each activity. This discussion will further help in the development of novel

benzimidazole compounds.

Benzimidazole nucleus can be termed ‘Master Key’ as it is an important core in many

compounds acting at different targets to elicit varied pharmacological properties. Though

all seven positions in the benzimidazole nucleus can be substituted with a variety of

chemical entities, most of the biologically active benzimidazole compounds are based on

the functional groups bearing at 1, 2 and/or 5 (or 6) positions. Accordingly, the

compounds may be mono-, di- or tri-substituted derivatives of the nucleus. In the present

study, various benzimidazole based compounds are designed, synthesized and evaluated

and categorized on the basis of their biological activities. The major activities include

antihypertensive, anti-inflammatory, antibacterial, antifungal, anthelmintic, antiviral,

antioxidant, antiulcer, antitumor, pyschoactivity, etc.

1.2.1 Antimicrobial activity

Antimicrobial agents constitute a diverse group of chemical entities acting against varied

kinds of microbes including bacteria, protozoa, helminths (worms), fungi and viruses.

Various research groups have evaluated antibacterial, antiprotozoal, anthelmintic and/or

antifungal activities concomitantly while evaluation of antiviral compounds remains

solitary. Hence, in the present section compounds having antibacterial, antiprotozoal,

antihelmintic and antifungal activities are discussed collectively under the heading of

antimicrobials while antiviral compounds are discussed independently. Most of the

research activities on development of antimicrobials from benzimidazole nucleus have

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been taken up after the year 2000. Iwahi and Satoh have reported 2-(substituted pyridyl

methylsulfinyl) benzimidazole (3) as antibacterial agent against Campylobacter pylori.9

Modifications in (3) led to development of similar compound (4) having antibacterial

activity against C. pylori equivalent to omeprazole.10

Coupling of 2-

alkylthiobenzimidazole with β-lactam ring has produced compound (5) wherein

antibacterial and antifungal activities were dependent upon nature of R group.11

Holloway et al. have discovered 2-iminobenzimidazoles as antibacterial agents acting

through inhibition of Trypanothione reductase (a bacterial enzyme).12

1-Substituted

benzimidazole compounds have been found to exhibit poor antimicrobial properties.13

However, substitution at both 1- and 2-positions of benzimidazole has produced potent

antimicrobials. Semicarbazide, thiosemicarbazide and carbamate substituent at 1-position

along with a methyl group at 2-position has yielded compounds which have potent

bactericidal activities.14-16

Attachment of other heterocylces like chromane, β -lactam, thiadiazole and oxadiazole to

benzimidazole nucleus resulted in hybrid compounds (6-8) having potent antibacterial

and/or antifungal properties.17-21

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Fusion of 5- or 6-membered heterocycle at N1–C bond of benzimidazole nucleus has

produced tricyclic derivatives of benzimidazole like triazino[1,2-a]benzimidazole (9)

bearing fluorophenyl group as moderately antibacterial,22

1,2,4-triazolo[2,3-

a]benzimidazole bearing short alkyl and alkenyl groups (10) as potent

antimycobacterial23

and pyridobenzimidazole derivatives (11) as antifungal.24,25

Recently,

Kuarm et al. have reported benzimidazo[1,2-c]quinazolin-5-yl chromene derivative (12)

as antibacterial agent.26

Replacement of chloro groups with bromo groups converted the

molecule to antifungal. Varied 2, 5- and 2, 6-disubstituted benzimidazole derivatives

have also been explored for antimicrobial activities.

A critical analysis of these variedly substituted derivatives has revealed that either of the

1 and 2 positions of benzimidazole nucleus should bear a bulky electronic and lipophillic

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group while the other should have a small alkyl substituent for the optimum antimicrobial

activity. Further, a small lipophillic group containing a heteroatom at 5/6-position incurs

additional activity.

1.2.2 Antioxidant activity

The drugs possessing antioxidant and free radical scavenging activity have been

implicated in treatment of various diseases like cancer which are directly related to lack

of antioxidant capacity of organism. Cole et al. (1974) reported 5-hydroxybenzimidazole

and 5-hydroxy-2-methylbenzimidazole as effective antioxidants.27

Incorporation of

thiadiazoles, triazoles and their open chain counterparts, that is, thiosemicarbazides at 1-

position of benzimidazole incurs antioxidant activity. Further substitution of varied aryl

and alkyl substituents on these heteronuclei at 1-position has also yielded potent

antioxidants (13-15). Amongst these, semicarbazide derivatives produced stronger

inhibitory effects on lipid peroxidation levels as well as DPPH model.28, 29

Fused thiazolo[3,2-a]benzimidazoles substituted at 3-position by amino methyl group

(16) inhibited the oxidation of adrenaline to adrenochrome by preventing the formation of

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superoxide radical.30

Anisimova et al. reported a series of 2-(heteroaryl)imidazo[1,2-

a]benzimidazoles possessing 1-methylbenzimidazol-2-yl and 5-bromo-2-thienyl at R2

with varied dialkylaminoalkyl substituents at R1 as antioxidants in in vitro model of

ascorbate dependent lipid peroxidation model.31

Subsequently, the same research group

disclosed N-acylmethyl derivatives of 9H-2,3-dihydroimidazo and 10H-2,3,4,10-

tetrahydropyrimido[1,2-a]benzimidazole with varied substitutents at 1-position to possess

weak antioxidant activity.32

In continuation on their work on imidazobenzimidazole,

hydroxyl group in aroyl moiety are reported to possess high antioxidant activity.33

However, 2,2,2-trichloro-1-hydroxyethyl group at 3-position weakens the antioxidant

potential which complies with their earlier reports.34

A halogenophenyl group at 2-

position incurs moderate antioxidant activity with fluorine producing the maximally

active compound from the series.35

Recently, cyclization of dialkylaminoethyl at 1-position to 4-substituted piperazines and

piperidines (17) have been investigated for antioxidant activity.36

Schiff’s bases of

benzimidazole (18) has been found to exhibit high lipid peroxidation inhibitory activity

which increased with lipophilicity. A 4-carboxamidobenzimidazole analog (19) was

identified as potent hydroxyl radical scavenging property through poly (ADP-Ribose)

polymerase (PARP) inhibition.37

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1.2.3 Anti-inflammatory activity

Control of inflammation has become prime importance due to its association with

numerous diseased states like Alzheimer’s disease, asthma, atherosclerosis, Crohn’s

disease, gout, multiple sclerosis, osteoarthritis, psoriasis, rheumatoid arthritis, diabetes

mellitus, carcinoma, bacterial or viral infections, etc. which result in chronic

inflammation.38,39

The most common and widely explored points for control of

inflammation include inflammatory mediators like plasma proteases, prostaglandins,

leukotrienes, histamine, serotonin, nitric oxide, interleukins 1–16 (IL-1 to IL-16), tumour

necrosis factor-α (TNF-α), chemokines (CXC, CC and C subsets) and colony stimulating

factors (CSF).40–42

These mediators are produced through various processes involving

cyclooxygenases, caspases and kinases like cyclin dependent kinases (CDK1 and CDK5),

mitogen activated protein kinase 38 (MAP38), c-Jun N-terminal kinase (JNK), serine

threonine kinases (IKK1 and IKK2), interleukin receptor associated kinase 4 (IRAK-4),

Janus kinases (JAK1- JAK3 and Tyk2), kinase insert domain receptor (KDR),

lymphocyte specific kinase (Lck), spleen tyrosin kinase (Syk) and TNF-α kinase

(TNFK).43,44

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A large number of chemical entities derived from diverse group of heterocyclic nuclei are

reported to inhibit or block the inflammatory process at one or other stages. The search

for anti-inflammatory compounds derived from benzimidazole nucleus is as old as the

age of modern medical chemistry. Though a good number of research groups have

reported various benzimidazole derivatives having well to excellent anti-inflammatory

activity but no such molecule has made its way to the clinics so far. A number of

compounds targeting the kinases are currently undergoing clinical trials related to

inflammation and autoimmunity.45

Benzimidazole nucleus substituted at 1-position with varied heterocycles has produced

potent anti-inflammatory compounds. Sabat et al. have synthesized a series of 1-

(substituted pyrimidin-2-yl) benzimidazoles of which compound (20) has elicited anti-

inflammatory effect by blocking activity of Lck.46

Another similar compound (21) in

which pyrimidine is replaced by thiophene has been identified as moderately potent

inhibitor of IKK-3 kinase with pIC50 of 5.4.47

Based on extensive SAR studies, it has

been found that replacement of the amide moiety in (21) by the nitrile group increases

inhibitory effect on IKK-3. Further, substitution at 6-position in the benzimidazole has

resulted in compound (22) as potent inhibitor of JAK3 which is expressed in high levels

in natural killer cells, platelets, thymocytes, mast cells and inducible T and B cells.48

Buckley et al. have brought another similar 1,6-disubstituted compound as highly potent

IRAK4 inhibitor having good TNF-α inhibition.49

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Based on the moderate anti-inflammatory and analgesic activities of thiabendazole (a

well known anthelmintic), the Pharmaceutical Research Centre at Kanebo Ltd. (Japan)

have developed a series of 2-(2-pyridinyl) benzimidazoles by isosteric replacement of

thiazole ring in the lead.50–52

From a series of fifty five compounds, 2-(5-ethyl-2-

pyridinyl) benzimidazole (23) (KB-1043) is found to have anti-inflammatory, analgesic

and antipyretic activities better than phenylbutazone and tiaramide. Moreover, it has

slightly less gastrointestinal irritation and therapeutic index 2–3 times better than the

reference compounds. Recently, Achar et al. have synthesized novel 2-(substituted

phenyl) aminomethyl benzimidazoles and evaluated using carrageenan-induced paw

edema model. The compound (24) has emerged as potent compound (81% protection)

and the activity is further improved (89% inhibition) by placement of bromo group at 6-

position (25).53

A high throughput screening (HTS) of small molecules followed by SAR studies at

Amgen Inc. has identified (26) as potent inhibitor of IRAK4.54

A recent patent also

discloses similar N-acyl 2-aminobenzimidazole derivative with varied aroyl and

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heteroaroyl substituents at 2-position exemplified by compound (27) as potent IRAK4

inhibitor.55

Another HTS at Abbott Corporate has identified a new series of 1,2-

disubstituted benzimidazole derivatives through binding studies of CXCL10 to CHO cell

membranes.56

The compound (28) proved maximally active. Further, substitution with

methoxy group at 4-position of benzimidazole nucleus retained the activity, which

however decreased with substitution at 5- and 6-positions.

A structure based design of 2-methyl-N-substituted benzimidazole bearing varied sugar

moieties (29) has been reported to have significant anti-inflammatory activity dependent

on the kind and the linked-position of the sugar conjugated to the nucleus.57

Simultaneous

substitutions at 2- and 5-positions of benzimidazole nucleus have fancied many research

groups to develop novel anti-inflammatory drugs. Taking benoxaprofen as lead, Dunwel

et al.58

have synthesized (30) by bioisosteric replacement of benzoxazole nucleus with

benzimidazole. However, it did not reduce the inflammation in rat paw edema model

probably due to lower solubility or altered drug-receptor interactions. Subsequently,

Evans et al. from the same laboratory synthesized an exhaustive series of 72

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benzimidazole derivatives and tested on rat adjuvant arthritis screen.59

Only two

compounds (31 and 32) have been found to exhibit activity comparable to indomethacin.

The activity exhibited by compounds derived from varied substituents all around the

benzimidazole nucleus has prompted many research groups to synthesize fused

benzimidazole compounds. Toja et al. have synthesized for the first time fused imidazole

derivatives (benzimidazoles or naphthimidazoles) substituted at 1 and 2 positions as non-

acidic anti-inflammatory agents.60

SAR studies on about 50 compounds revealed that

electron rich groups such as –OCH3, –OC2H5, –NHCH3, –N(CH3)2 on para position in

phenyl ring at 2-position of the nucleus increases the activity. Compounds with

substituent at 1-position exhibit stronger anti-inflammatory potency. In addition to good

anti-inflammatory, analgesic and antipyretic activities, all active compounds also lack

ulcerogenic properties. The compounds (33) and (34) have emerged as the most potent

compounds. Sondhi et al. have synthesized and screened some tricyclic benzimidazole

derivatives and revealed that pyrimido[1,6-a]benzimidazole derivative (35) controls the

inflammation and pain not better than ibuprofen but pyrazolo[1,2-a]benzimidazole (36)

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analogs exhibit the activity equivalent to ibuprofen.61,62

A similar pyrimido[1,2-

a]benzimidazole derivative has also been found to have very weak anti-inflammatory and

analgesic activities.63

Further exploration of pyrimidobenzimidazoles has led to a series of

pyrimido[5`,4`:5,6]pyrimido[1,2-a]benzimidazol-5-ones as potent orally active specific

inhibitors of LcK. SAR studies have revealed the compound (37) as the most potent

compound.64

Very recently, Shen et al. have discovered a novel compound (38) by fusion

of an imidazole nucleus with phenyl ring of an active metabolite isolated from

fermentation broth of fungus Curvularia verruculosa having strong inhibitory activity

against TNF-α transcription.65

A series of 1-acyl-2-alkylthio-1,2,4-triazolo[3,2-

a]benzimidazole derivatives is reported from which the compound (39) exhibits the most

potent anti-inflammatory and analgesic activities reiterating the importance of amino

group at 2-position of benzimidazole nucleus.66

It has also exhibited a superior

gastrointestinal (GI) safety profile compared to indomethacin.

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The salient structural features of a typical benzimidazole based anti-inflammatory

compound as suggested by critical analysis of chemical structures of various such

compounds is that either of the 1 and 2 positions of the nucleus should bear a bulky,

lipophilic aryl/heteroaryl moiety appropriately substituted with alkyl, electronic or

heterocyclic groups while the tolerable substituents at 5 or 6-position of the nucleus

should have small electronic groups like halogens, nitro, amino, methyl or lower alkoxy

to mildly substituted or unsubstituted aryl or aralkyl groups.

1.2.4 Antihypertensive activity

Benzimidazole nucleus has been explored well for development of antihypertensive

drugs. Many benzimidazole based compounds act as antihypertensives by intercepting

with Renin–Angiotensin System (RAS). Angiotensin II (Ang II) is an octapeptide which

is active pressor produced by RAS cascade. Angiotensinogen, a polypeptide, is cleaved

by rennin to produce a decapeptide, Ang I, which is further acted upon by Angiotensin

converting enzyme (ACE) to generate Ang II. The latter acts on angiotensin receptor 1

(AT1) resulting in vasoconstriction, Na+ retention and aldosterone release to cause

hypertensive action. The various strategies to control these actions of Ang II include

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blocking production of Ang II through use of Renin and ACE inhibitors or blocking

binding of Ang II to AT1 receptors. Inhibition at the receptor level has proved maximally

safe, specific and effective. Hence, most of the research and development activities on

producing antihypertensives have been targeted towards development of AT1 receptor

blockers.67

One of the first reports discloses 2-butyl-benzimidazole-7-carboxylic acid

derivative (40) as a potent AT1 receptor antagonist.68

Optimization of the functional groups around the nucleus has produced CV-11974 which

reduces blood pressure in dose-dependent manner by blocking AT1 receptors in a non-

competitive manner due to slow dissociation from AT1 receptors.69-71

It is significantly

more active than losartan and EXP3174.72

Esterification of 7-carboxyl group has

culminated in discovery of orally active and long acting AT1 receptor blocker,

candesartan cilexitil73-77

which is now commercially available. It has triggered a spurt in

research activities to explore all seven positions of the benzimidazole nucleus by various

research groups to develop more potent compounds. In general, it has been found that the

position 4 must remain unsubstituted for favourable interaction of N-3 of the nucleus

with H-bond donor site in AT1 receptor while position 1 is reserved for biphenyl moiety.

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Replacement of biphenyl moiety with other moieties in the compounds (41-43) has

produced the compounds with varied potencies.78-82

Replacement of tetrazole moiety with varied acidic heterocylces like oxathiadiazole,

oxatriazole, oxadiazolone, oxadiazolidindione, thiazolone, oxathiadiazolone, etc. has

produced compounds with varied activity.83-85

However, none of the compounds were

found to be potent. Incorporation or substitution of tetrazole with a carboxyl group in the

molecule has produced insurmountable and orally active antagonists.86

A –COOH group

at 7-position provides potent compounds. Further esterification of this acidic function

improves the oral bioavailability as indicated by clinical use of candesartan cilexitil.

Recently, Kuroita et al. have disclosed 5-methyl-2-oxo-1,3-dioxol-4-yl methyl esters

analogs (44) as potent orally active antagonists of Ang II.87-89

Telmisartan is an orally

active, potent and insurmountable AT1 selective antagonist that is formed by a bulky

lipophillic group at 6-position.90,91

Substitution with pyridazinone moiety also produces a

potent benzimidazole derived compound (45).92

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1.2.5 Antiviral activity

Antiviral properties of various benzimidazole derivatives have been evaluated using

different virus strains, such as human cytomegalovirus (HCMV), human herpes simplex

virus (HSV-1), human immunodeficiency virus (HIV), and hepatitis B and C virus (HBV

and HCV). Numerous nucleoside analogs of benzimidazole derivatives have been

synthesized during 1950–1990s as selective inhibitors of HCMV amongst which 5, 6-

dichloro-l-(β-D-ribofuranosyl) benzimidazole (DRB) is the most explored nucleus. It

inhibits viral RNA synthesis by blocking RNA polymerase II.93, 94

Incorporation of chloro

and bromo group at 2-position of DRB provided TCRB and BDCRB, respectively having

dramatically improved therapeutic index. A ribosyl moiety at 1-position proved to be

very important for the activity.95

The non-nucleoside derivatives of DRB prepared by

replacing β-D-ribofuranosyl with a benzyl and phenethyl group were found inferior in

activity against HCMV but active against HIV-1.96

Enviradine and enviroxime are the

other non-nucleoside analogs which came into clinical use in the early 1980s as potent

broad spectrum inhibitors of RNA viruses.

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Amongst a series of benzimidazole derivatives bearing amidino group at 5-position and

varied heteronuclie such as pyridine, N-methyl-pyrrole or imidazole, the compound with

pyridine ring at 2-position (46) showed distinct and selective antiviral activity towards

RNA replicating enteroviruses. In contrast, pyrrole substituted compound (47) showed

prominent activity against other types of viruses especially adenovirus.97

SAR study on

2-naphthyl benzimidazoles with varied substituents at 5,6-positions of benzimidazole ring

and 4-position of naphthyl ring (48) suggested that electron releasing groups on

benzimidazole enhances the activity. An amino group on naphthalene ring yields a potent

antiviral compound. Replacement of amino with nitro and acetyl groups decreases the

activity significantly.98

Taking this 2-aryl benzimidazole as a lead, 2-biphenyl derivatives

of benzimidazoles were developed but most of the compounds except (49) and (50)

showed poor activities against all viruses tested.99

1H-Benzimidazole-4-carboxamide

derivatives bearing furyl at 2-postion and aryl moiety at carboxamide nitrogen possess

good inhibitory activity.100,101

Barreca et al. reported 1-benzyl-1,3-dihydro-2H-

benzimidazol- 2-ones as potential non-nucleoside reverse transcriptase inhibitors

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(NNRTIs) active against HIV-1.102

A 6-chloro-1-(2,6-difluorobenzyl)-substituted

derivative (51) was found to possess significant activity against HIV-1. Subsequently

molecular modeling studies, led to the rational discovery of N1-arylsulfonyl-1,3-dihydro-

2H-benzimidazol-2-one (52) as a novel template for design of new NNRTIs active

against wild-type and mutant strains of HIV-1.103

1.2.6 Antitumor activity

Cancer is one of the leading health hazards which is affecting a wide majority of people

in world population. Various anticancer agents (also referred as antitumor,

antiproliferative and antineoplastics) reported for treatment of varied kinds of cancers act

through different mechanisms. However, the major side effect associated with these

agents is cytotoxicity towards normal cells due to lack of selectivity for the abnormal

cells. Therefore search on anticancer agent has been in continuum since many years.

Benzimidazole being an isostere of purine based nucleic acid and an important scaffold in

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various biologically active molecules is widely explored for development of anticancer

agents.

Pyrrolo[1,2-a]benzimidazoles (53–55) is one of the early classes of anticancer agents

acting through cleavages of G and A bases and reductive alkylation of DNA.104–108

The

variedly substituted benzimidazole derivatives (56–58) are reported as cytotoxic against

lung and breast cancers.109,110

Ni et al. have developed some 2-(substituted quinolinon-3-

yl)benzimidazoles as serine/threonine checkpoint kinase (CHK-1) inhibitors for treatment

of cancer.111

The compound (59) has emerged as potent compound with subnanomolar

IC50 value. Neff et al. have reported another series (60) of CHK-1 inhibitors but all

compounds are found to have inhibitory activity significantly less than that of (59).112

Recent developments on 2-substituted benzimidazoles have revealed varied heterocycles

at 2-position to yield potent anticancer agents to various carcinoma cell lines. These

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include pyrimidine derivatives (61), 113

pyrazoline derivatives (62),114

and thiazole

derivatives (63).115

Further, 2-substituted benzimidazoles with chloro or carboxy group at

5-position having 4-amino-thioxothiazole (64), 4-oxothiazolidine (65), 4-

fluorobenzylidene (66) and cycloalkylidene are reported as potent antitumor agents.116

Planar fused benzimidazole analogs have the potential to get inserted into the space

between the base pairs of DNA resulting in DNA cleavage. Based on this mechanism, a

benzimidazo[1,2-a]quinoline derivative (67) has exerted potent activity on all cell lines

tested with IC50 values of 0.8–30 μM.117

Recently, more fused planar benzimidazole

derivatives have been reported to exhibit potent cytotoxicity. The examples include (68)

(pyrimido [1, 2-a] benzimidazole-3(4H)-one)118

and (69) (1,3-diarylpyrazino[1,2-

a]benzimidazole).119

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Huang et al. have synthesized their benzimidazole isosteres amongst which (70) was

found as the most potent anticancer synthetic precursor of bis(benzimidazoles) against

human A-549, BFTC-905, RD, MES-SA, and HeLa carcinoma cell lines.120

Benzimidazolyl- 1,2,4-triazino[4,5-a]benzimidazol-1-one (71) is another

bis(benzimidazole) analog having significant activity against multidrug- resistant P-

glycoprotein expressing cell lines.121

Two benzimidazole nuclei linked through a

thiophene ring have displayed moderate to strong antiproliferative effect toward a panel

of eight carcinoma cell lines. The most active compound (72) of the series is reported to

enter into live HeLa cells within 30 min, but did not accumulate in nuclei even after 2.5

h.122

Chapter-1

27

Taking Hoechst-33258 (a head-to-tail bis-benzimidazole wherein benzo ring a

benzimidazole nucleus is connected to the imidazole ring of the other nucleus through a

bond) and a head to head bis-benzimidazole (73), wherein two benzimidazole nuclei are

connected at either their benzo or imidazole rings through a bond as leads, Yang et al.

have designed and synthesized another series of symmetrical head-to-head bis-

benzimidazoles and found (74) to possess good antitumour activity.123

Very recently,

Singh and Tandon have modified Hoechst-33258 to synthesize another series of head-to-

tail bis-benzimidazole bearing aryl group at 2- position.124

The derivatives bearing

electron withdrawing groups like F (75) and Cl on the aryl ring exhibited potent

anticancer activity over the compounds bearing electron releasing groups.

Chapter-1

28

1.2.7 Anticoagulant activity

Thrombin causes proteolytic cleavage of fibrinogen, induces platelets activation and

triggers a wide range of effects secondary to thrombosis, for example, vascular smooth

muscle cell and fibroblast proliferation, monocyte chemotaxis, and neutrophil adhesion.

Inhibition of thrombin is an important mechanism for inhibition of coagulation.

Benzimidazole nucleus acts as an appropriate template to place the varied substitutents

required for interaction with thrombin. Hauel et al. have designed a series of

benzimidazole derivatives and arrived at BIBR 953 having excellent inhibitory potency

and tolerability.125

It was double prodrug BIBR 1048 that has exhibited good

pharmacokinetic properties and is in clinical evaluation. 1,2-Disubstituted benzimidazole

derivatives (76) possessing basic amine moieties have been reported as active site

directed thrombin inhibitors.126

Berlex Biosciences have reported tetra substituted

benzimidazole with naphthylamidine group at 1-position (77) as anticoagulant due to

factor Xa (fXa) inhibition. The activity is independent of the substituent at C-2 whereas

substitution of a nitro group at 4-position on the benzimidazole template affords potent

fXa inhibitor with excellent thrombin selectivity.127

Replacing the naphthylamidine

with differently substituted biphenylamidines caused a disappointing change in in vitro

profile. However, simplification of the naphthylamidine group to yield a

propenylbenzene group dramatically improved the potency and selectivity over the

unsubstituted naphthalene analogs.128

Chapter-1

29

Ueno et al. have conducted SAR studies leading to benzimidazole derivative (78) as

potent and selective factor Xa inhibitor possessing excellent anticoagulant activity with

no fatal acute toxicity.129

Inhibitor of factor VIIa/Tissue Factor (fVIIa/TF) complex is

another class of compounds for treatment of thromboembolic disease. The research group

at Celera Genomics has designed and optimized a series of benzimidazole derivatives

wherein compound (79) has emerged as safe anticoagulant but having less residence time

due to excessive glucuronidation.130

Further research into the compounds has led to

development of selective dicarboxylic acid analog (80) with pharmacokinetic profile

amenable to once daily subcutaneous dosing in humans.

Chapter-1

30

1.2.8 Psychoactive activity

The H3 receptors in CNS are associated with central disorders such as impaired cognitive

functions. A series of H3-antagonists composed of an imidazole ring connected through

an alkyl spacer to a 2-aminobenzimidazole moiety was designed and synthesized. Its

QSAR and quantitative structure-property relationship (QSPR) analysis suggested a three

carbon atoms chain length (81) optimum for the antagonistic activity.131

Replacement of

imidazole ring with piperidine and chlorophenoxy substituents retained the affinity for

H3 receptor inferring the importance of 2-aminobenzimidazole in receptor interactions.

The piperidine analog (82) showed good affinity for H3-receptor.132

1, 2-Disubstituted-5-

fluorobenzimidazole derivatives with aza-heterocycles (83) were evaluated to have potent

H3 antagonist activity.133

2-Aminobenzimidazole scaffold was also selected for

Chapter-1

31

development of H1-antihistaminic agents therapeutically used for insomnia. The varied

compounds evolved starting from a series of 2-aminobenzimidazoles include (84-

86).134,135

1.3 Introduction to Benzisoxazoles

Benzisoxazole is an aromatic organic compound with molecular formula C7H5NO

containing a benzene-fused isoxazole ring structure. Benzisoxazole has no household use.

It is used primarily in industry and research.

Being a heterocyclic compound, benzisoxazole finds use in research as a starting material

for the synthesis of larger, usually bioactive structures. It is found within the chemical

structures of pharmaceutical drugs such as the antipsychotic risperidone and

anticonvulsant zonisamide.

Chapter-1

32

Its aromatic nature makes it relatively stable, although as a heterocycle, it has reactive

sites which allow for functionalization.

1.3.1 Benzisoxazoles as antimicrobial agents

6-Fluoro-4-piperidinyl-1,2-benzisoxazole derivatives 87 were evaluated for their efficacy

as antimicrobials136

in vitro by disc diffusion and microdilution method against

pathogenic strains such as Bacillus substilis, Escherichia coli, Pseudomonas fluorescens,

Xanthomonas campestris pvs, X. oryzae, Aspergillus niger, A. flavus, Fusarium

oxysporum, Trichoderma species, F. monaliforme, and Penicillium species.

In their attempt for synthesizing new antimicrobial compounds, they have synthesized,6-

fluoro-4-piperidiny 1,2-benzisoxazole amides 4(I–VI) and evaluated their efficacy as

antimicrobials in vitro by disc diffusion and microdilution methods against various

pathogenic strains. Nystatin was used as standard drug against fungi, streptomycin and

tetracycline and were tested against bacteria. In all determinations, tests were performed

in duplicate and the results were reported as mean of three determinations. The results

showed that, from the 6-fluoro-4-piperidinyl-1,2-benzisoxazole amide series, compounds

with chloro and ethoxy groups in the second position of the benzene ring showed

Chapter-1

33

significant inhibition. Interestingly the compound bearing pyridine ring in second

position showed significant activity whereas at third position, least inhibition was

observed.

1.3.2 Benzisoxazoles as anticonvulsant agents

Several 3-(sulfamoylmethyl)-1,2-benzisoxazole derivatives 88 were synthesized from 3-

(bromomethyl)-l,2-benzisoxazole by reaction with sodium bisulfite followed by

chlorination and amination. Some of them displayed marked anticonvulsant activity137

in

mice. The introduction of a halogen atom at 5th position of the benzisoxazole ring caused

increased activity and neurotoxicity; the substitution of a sulfonyl group caused

decreased activity. The activity of monoalkylated compounds might be the result of

biotransformation.

The study of N-substituted compounds revealed that the introduction of simple

monoalkyl substituents did not abolish activity, but when the substituent was an amino,

dimethylamino, benzyl or larger, the activity was generally lost. With the exception of

diethylamino and N-(methylpiperanyl) derivatives, the disubstituted compounds were

inactive in the anticonvulsant test.

Chapter-1

34

1.3.3 Benzisoxazoles as Inhibitors of Chaperone Heat Shock Protein 90

Heat shock protein 90 (Hsp90) is a molecular chaperone that is responsible for activating

many signaling proteins and is a promising target in tumor biology. Gopalsamy, et al

have identified small-molecule benzisoxazole derivatives as Hsp90 inhibitors.138

Crystallographic studies show that these compounds bind the ATP binding pocket

interacting with the Asp93.

All the compounds bind to the ATP binding pocket of Hsp90, they were found to be very

selective for Hsp90 inhibition and was not active when tested against a panel of kinases

like B-Raf, PKC, PKC-θ, PI3K-R, PDK-1, MK2, IKK-2, ActRIIB, and m-TOR (IC50

>20 µM). Overall, they have identified benzisoxazole derivatives 89 as potent and

selective inhibitors of molecular chaperone Hsp90. The hit to lead optimization was

guided by structure-based design facilitated by the cocrystallization efforts. Inhibitors

with improved physical properties resulting in enhanced potency in the cellular systems

were disclosed.

Chapter-1

35

1.3.4 Benzisoxazoles as antipsychotic agents

A series of 3-(l-substituted-4-piperidinyl)-1,2-benzisoxazoles 90 are synthesized and

tested for neuroleptic activity139

by climbing mice assay and inhibition of spiroperidol

binding. Structure activity relationships were studied by variation of the substituent on

the benzisoxazole ring with concomitant variation of four different 1-piperidinyl

substituents. Maximum neuroleptic activity was realized when there was a 6-fluoro

substituent on the benzisoxazole ring. The 1-piperidinyl substituent appeared less

significant, although in most cases, the (1,3-dihydro-2-oxo-2H-benzimidazol-l-yl) propyl

group imparted maximum potency. The most potent compound in both assays was 6-

fluoro-3-[1-[3-(1,3-dihydro-2-oxo-2H-benzimidazol-l-yl)propyl]-4- piperidinyl]-1,2-

benzisoxazole.

From the structure-activity relationships it becomes apparent that, for any given 1-

piperidinyl substituent, a fluorine in the 6-position of the benzisoxazole nucleus results in

maximum activity. It also appears that the presence of methoxy or hydroxy groups

greatly diminishes activity, with the 5,6-dimethoxy compounds being quite weak.

Intermediate in potency were the unsubstituted analogues and the 6-chloro derivatives,

Chapter-1

36

with the nuclear unsubstituted compounds being somewhat more potent. The two

compounds bearing 5-fluoro substituent showed activity similar to that of their 6-chloro

counterparts.

1.3.5 Benzisoxazoles as antithrombotic agents

A series of 3-(2-thienyl)- and 3-(1-imidazolyl)-1,2-benzisoxazoles 91 as well as some

isomeric benzoxazoles were synthesized and tested in vitro for their inhibitory effect on

arachidonic acid-induced human platelet aggregation.140

The most active compound (7-

methoxy-3-(2-thienyl)-1,2-benzisoxazole SC) was nearly 20-30-fold more potent than

acetylsalicylic acid in inhibiting platelet aggregation. Structure-activity relationships

within the series are briefly discussed.

In an attempt to understand the contribution of the cyclic structure at position 3 of the

benzisoxazole nucleus on biological activity, authors have synthesized some non-

thiophenic derivatives differing in the degree of aromaticity. Permutation of the

thiophene nucleus by a nitrogen ring such as imidazole resulted in a marked decrease in

anti-aggregating activity. On the other hand, the introduction of a π electron-rich group

Chapter-1

37

such as the para methoxy phenyl moiety retained to a large extent, the pharmacological

activity. It has long been accepted that one of the most widely employed criteria for the

quantitative assessment of aromaticity is the resonance energy. Available values for

benzene, thiophene and imidazole are respectively 152, 121 and 59 kJ mol-1, indicating

that imidazole has a lower degree of aromaticity than the other 2. However, the marked

increase in activity exhibited by the thiophene derivative SC, compared to the para-

methoxy phenyl analogue seems to indicate that aromaticity is not the only factor

involved in the biological response. The thiophenic sulfur atom might be important for

activity.

1.3.6 Benzisoxazoles as antiglycating agents

Shantharam, et al have synthesized a series of urea/thiourea derivatives of Gly/Pro

conjugated benzisoxazoles 92 and has been screened for their in vitro antiglycation

activity141

. Several compounds showed promising activity with IC50 < 5 μM compared to

standard rutin (IC50 = 41.9 μM). Further, it was found that compounds containing

methoxy and bromine substituents have exerted highly potent activity.

They have successfully synthesized a series of urea/thiourea derivatives of Gly/Pro

conjugated benzisoxazole with different functionalities. Some of the representatives of

Chapter-1

38

the series were identified as highly potent antiglycating agents. The antiglycating activity

of the synthesized compounds showed that urea and thiourea moieties play a major role

in enhancing the activity.

Further, it is interesting to note that OCH3 and Br act as active moieties in inhibiting the

glycation. Thus, nature of the substituent was found to be crucial to improve the activity.

This study extends the knowledge of different substituents at phenyl ring and also various

amino acids which might be of interest for the identification of more antiglycation agents.

1.4 Scope of the present work

Heterocyclic compounds have a wide range of applications: they are predominant among

the types of compounds used as pharmaceuticals,

as agrochemicals, as veterinary

products, used as optical brightening agents, as antioxidants, as corrosion inhibitors and

as additives with a variety of other functions. In particular, benzimidazoles are involved

in a great variety of biological processes. Some of their poly functional derivatives have

proved to possess antibacterial, fungicidal and antihelmintic activities. Therefore,

substituted benzimidazoles have attracted the interest of various research groups.

Similarly, benzisoxazole finds use in research as a starting material for the synthesis of

larger, usually bioactive structures. It is found within the chemical structures of

pharmaceutical drugs.

A series of pyridine conjugated benzimidazole derivatives were synthesized according to

Scheme 1 and evaluated for their antibacterial, antioxidant and anti-inflammatory

activities. The results showed that most of the tested compounds exhibited good to

moderate antimicrobial activity against some strains of Gram negative bacteria

Chapter-1

39

(Escherichia coli, Klebsiella pneumoniae, Salmonella typhi, Shigella flexineri) and Gram

positive bacteria- Bacillus subtilis. Further, the molecules were evaluated for antioxidant

assays such as DPPH scavenging, super oxide radical scavenging and hydroxyl radical

scavenging assays. Most of the compounds showed potent antioxidant activities. Also,

the synthesized compounds were screened for anti-inflammatory activities such as

lipoxygenase inhibition and indirect haemolytic assays, where compounds revealed good

activity.

Reagents and reaction conditions: i) NaOCH2CF3 ii) NaNO2, H2SO4 iii) H2SO4,

CH3OH. iv) NaBH4, Methanol. v) SOCl2, DCM. vi) Mercaptobenzimidazole, Methanol.

vii) 8 (R-X/R-SO2Cl), Toluene, 50% KOH, TBAB.

Scheme 1

Chapter-1

40

A series of benzisoxazole derivatives were synthesized according to Scheme 2 and

evaluated for their antibacterial, antioxidant and anti-inflammatory activities. The results

indicated that most of the compounds exhibited moderate antimicrobial activity against

Gram negative (Escherichia coli, Klebsiella pneumoniae, Salmonella typhi, Shigella

flexineri) and Gram positive (Bacillus subtilis) bacterial cultures. The molecules were

evaluated for antioxidant activities using 2,2-diphenyl-1-picrylhydrazyl, super oxide

radical and hydroxyl radical scavenging assays and most of them showed good

antioxidant activities. Also, the synthesized compounds were screened for anti-

inflammatory activities such as lipoxygenase inhibition and indirect haemolytic assays.

Reagents and reaction conditions: (a) MeONa/THF, 0 °C-RT, 8 h. (b)

LiOH/MeOH/H2O, 0°C-RT, 3h. (c) 5 (6-fluoro-3-(piperidin-4-yl)benzo[d]isoxazole

hydrochloride), EDC.HCl/HOBt/DIPEA/CH2Cl2, 0 °C-RT, 8h. (d) HCl/ether, 0 °C-RT,

1h. (e) 8 (RCOCl/RSO2Cl), TEA/EDC, 0 °C-RT, 3-4 h.

Scheme 2

Chapter-1

41

References:

1. Katritzky, R.; Boultan, J. A. (Eds). Academic press, New York, “Advances in

Heterocyclic chemistry”, 1963-1980, 1.

2. Weissberger,.; Wiley Interscience. New York, “The Chemistry of heterocyclic

compounds”, 1950-1975, 1.

3. Katritzky. R.; Academic press, New York, “Physical methods in Heterocyclic

Chemistry”, 1963 -1973, 1

4. Newkome,G.R.; Pandler,W.W. “Contemporary Heterocyclic Chemistry”, John

Wiley, New York, 1982.

5. Czarnik, A. W. top 20 ethical pharmaceuticals prescribed in the USA in 1994,

17 are heterocyclic compounds: “Acc. Chem. Res”, 1996, 29, 112.

6. Meth-Cohn, O. Reviews of several applications of Heterocyclic Compounds can

be found in “Comprehensive Heterocyclic Chemistry,” Vol 1, ed., Pergamon

Press, Oxford, 1984.

7. Clough, J. M.; Godfrey, C. R. A. the discovery of this fungicide is described by

“Chem. Br”, 1995, 466.

8. Spasov, A. R.; iezhitsa, I. N.; Bugaeva, L. I.; Anisimova, V. A. Khim-Farm.

Zhurn, 1999, 33, 6.

9. Iwahi, T.; Satoh, H. U.S. Patent 5013,743, 1991.

10. Masaki, M.; Yamakawa, T.; Nomura, Y.; Matsukura, H. U.S. Patent 5576,341,

1996.

11. Desai, K. G.; Desai, K. R. Bioorg. Med. Chem. 2006, 14, 8271.

Chapter-1

42

12. Holloway, G. A.; Baell, J. B.; Fairlamb, A. H.; Novello, P. M.; Parisot, J. P.;

Richardson, J.; Watsona, K. G.; Street, I. P. Bioorg. Med. Chem. Lett. 2007, 17,

1422.

13. Guven, O. O.; Erdogan, T.; Goker, H.; Yıldız, S. Bioorg. Med. Chem. Lett.

2007, 17, 2233.

14. Fahmy, H. H.; El-masry, A.; Abdelwahed, S. H. A. Arch. Pharm. Res. 2001, 24,

27. 100.

15. Nofal, Z. M.; Fahmy, H. H.; Mohamed, H. S. Arch. Pharm. Res. 2002, 25, 250.

16. Nofal, Z. M.; Fahmy, H. H.; Mohamed, H. S. Arch. Pharm. Res. 2002, 25, 28.

17. Siva Kumar, B. V.; Vaidya, S. D.; Kumar, R. V.; Bhiryd, S. B.; Manr, R. B. Eur.

J. Med. Chem. 2006, 41, 599.

18. Ansari, K. F.; Lal, C. J. Chem. Sci. 2009, 121, 1017.

19. Ansari, K. F.; Lal, C. Eur. J. Med. Chem. 2009, 44, 4028.

20. Ansari, K. F.; Lal, C. Eur. J. Med. Chem. 2009, 44, 2294.

21. Gill, C.; Jadhav, G.; Shaikh, M.; Kale, R.; Shawalkar, A.; Nagargoje, D.;

Shiradkar, M. Bioorg. Med. Chem. Lett. 2008, 18, 6244.

22. Dolzhenko, A. V.; Chui, W.; Dolzhenko, A. V.; Chan, L. J. Fluor. Chem. 2005,

126, 759.

23. Mohamed, B. G.; Hussein, M. A.; AbdeI-Alim, A. M.; Hashem, M. Arch.

Pharm. Res. 2006, 29, 26.

24. Kitamura, A.; Someya, K.; Hata, M.; Nakajima, R.; Takemura, M. Antimicrob.

Agents Chemother. 2009, 53, 670.

Chapter-1

43

25. Takeshita, H.; Watanabe, J.; Kimura, Y.; Kawakami, K.; Takahashi, H.;

Takemura, M.; Kitamura, A.; Someya, K.; Nakajima, R. Bioorg. Med. Chem.

Lett. 2010, 20, 3893.

26. Kuarm, B. S.; Reddy, Y. T.; Madhav, J. V.; Crooks, P. A.; Rajitha, B. Bioorg.

Med. Chem. Lett. 2011, 21, 524.

27. Cole, E. R.; Crank, G.; Salam-Sheikh, A. J. Agr. Food Chem. 1974, 22, 918.

28. Kus, C.; Ayhan-Kilcigil, G.; Eke, B. C.; Iscan, M. Arch. Pharm. Res. 2004, 27,

156.

29. Kus, C.; Ayhan-Kılcıgil, G.; Ozbey, S.; Betu, F.; Kaynak, I.; Kaya, M.; Coban,

T.; Can-Eke, B. Bioorg. Med. Chem. 2008, 16, 4294.

30. Dianov, V. M. Pharm. Chem. J. 2007, 41, 308.

31. Anisimova, V. A.; Tolpygin, I. E.; Spasov, A. A.; Kosolapov, V. A.; Stepanov,

A. V.; Kucheryavenko, A. F. Pharm. Chem. J. 2006, 40, 261.

32. Anisimova, V. A.; Spasov, A. A.; Kucheryavenko, A. F.; Panchenko, T. I.;

Ostrovskii, O. V.; Kosolapov, V. A.; Larionov, N. P. Pharm. Chem. J. 2002, 36,

528.

33. Anisimova, V. A.; Tolpygin, I. E.; Spasov, A. A.; Kosolapov, V. A.; Stepanov,

A. V.; Orlova, A. A.; Naumenko, L. V. Pharm. Chem. J. 2007, 41, 126.

34. Anisimova, V. A.; Spasov, A. A.; Kosolapov, V. A.; Tolpygin, I. E.; Porotikov,

V. I.; Kucheryavenko, A. F.; Sysoeva, V. A.; Tibirkova, E. V.; Eltsova, L. V.

Pharm. Chem. J. 2009, 43, 491.

Chapter-1

44

35. Anisimova, V. A.; Spasov, A. A.; Tolpygin, I. E.; Minkin, V. I.; Chernikov, M.

V.; Yakovlev, D. S.; Stukovina, A. Y.; Goryagin, I. I.; Grechko, O. Y.;

Kirillova, N. V.; Kosolapov, V. A.; Tibirkova, E. V.; Salaznikova, O. A.;

Naumenko, L. V.; Gurova, N. A. Pharm. Chem. J. 2010, 44, 345.

36. Anisimova, V. A.; Spasov, A. A.; Tolpygin, I. E.; Chernikov, M. V.; Yakovlev,

D. S.; Goryagin, I. I.; Gurova, N. A.; Salaznikova, O. A.; Naumenko, L. V.;

Kosolapov, V. A.; Eltsova, L. V.; Kolobrodova, N. A. Pharm. Chem. J. 2010,

44, 241.

37. Kalai, T.; Balog, M.; Szabo, A.; Gulyas, G.; Jeko, J.; Sumegi, B.; Hideg, K. J.

Med. Chem. 2009, 52, 1619.

38. Medzhitov, R. Cell 2010, 140, 771.

39. Grivennikov, S.; Greten, F. R.; Karin, M. Cell 2010, 140, 883.

40. Nathan, C. Nature 2002, 420, 846.

41. Cronstein, B. N.; Weissmann, G. Annu. Rev. Pharmacol. Toxicol. 1995, 35, 449.

42. Feghali, C. A.; Wright, T. M. Frontiers Biosci. 1997, 2, 12.

43. Bhagwat, S. S. Purinergic Signal. 2009, 5, 107.

44. Dinarello, C. A. Cell 2010, 140, 935.

45. Sondhi, S. M.; Singhal, N.; Johar, M.; Reddy, B. S. N.; Lown, J. W. Current.

Med. Chem. 2002, 9, 1054.

46. Sabat, M.; VanRens, J. C.; Laufersweiler, M. J.; Brugel, T. A.; Maier, J.;

Golebiowski, A.; De, B.; Easwaran, V.; Hsieh, L. C.; Walter, R. L.; Mekel, M.

J.; Evdokimov, A.; Janusz, M. J. Bioorg. Med. Chem. Lett. 2006, 16, 5973.

Chapter-1

45

47. Bamborough, P.; Christopher, J. A.; Cutler, G. J.; Dickson, M. C.; Mellor, G.

W.; Morey, J. V.; Patel, C. B.; Shewchuk, L. M. Bioorg. Med. Chem. Lett. 2006,

16, 6236.

48. Chen, J. J.; Thakur, K. D.; Clark, M. P.; Laughlin, S.; George, K. M.; Bookland,

R. G.; Davis, J. R.; Cabrera, E. J.; Easwaran, V.; De, B.; Zhang, Y. G. Bioorg.

Med. Chem. Lett. 2006, 16, 5633.

49. Buckley, G. M.; Ceska, T. A.; Fraser, J. L.; Gowers, L.; Groom, C. R.;

Higueruelo, A. P.; Jenkins, K.; Mack, S. R.; Morgan, T.; Parry, D. M.; Pitt, W.

R.; Rausch, O.; Richarda, M. D.; Sabin, V. Bioorg. Med. Chem. Lett. 2008, 18,

3291.

50. Tsukamoto, G.; Yoshino, K.; Kohno, T.; Ohtaka, H.; Kagaya, H.; Ito, K. J. Med.

Chem. 1980, 23, 734.

51. Ito, K.; Kagaya, H.; Fukuda, T.; Yoshino, K.; Nose, T. Arzneimittel-forschung

1982, 32, 49.

52. Ito, K.; Kagaya, H.; Satoh, I.; Tsukamoto, G.; Nose, T. Arzneimittel-forschung

1982, 32, 117.

53. Achar, K. C. S.; Hosamani, K. M.; Seetharamareddy, H. R. Eur. J. Med. Chem.

2010, 45, 2048.

54. Powers, J. P.; Li, S.; Jaen, J. C.; Liu, J.; Walker, N. P. C.; Wang, Z.; Wesche, H.

Bioorg. Med. Chem. Lett. 2006, 16, 2842.

55. Frenkel, A. D.; Lively, S. E.; Powers, J. P.; Smith, A.; Sun, D.; Tomooka, C.;

Wang, Z. U.S. Patent. US 7635774, 2009.

Chapter-1

46

56. Hayes, M. E.; Wallace, G. A.; Grongsaard, P.; Bischoff, A.; George, D. M.;

Miao, W.; McPherson, M. J.; Stoffel, R. H.; Green, D. W.; Roth, G. P. Bioorg.

Med. Chem. Lett. 2008, 18, 1573.

57. El-Nezhawy, A. O. H.; Gaballah, S. T.; Radwan, M. A. A.; Baiuomy, A. R.;

Abdel- Salam, A. M. E. Med. Chem. 2009, 5, 558.

58. Dunwel, D. W.; Evans, D.; Smith, C. E.; Williamson, W. R. N. J. Med. Chem.

1975, 18, 692.

59. Evans, D.; Hicks, T. A.; Williamson, W. R. N.; Dawson, W.; Meacockz, S. C.

R.; Kitchen, E. A. Eur. J. Med. Chem. 1996, 3, 635.

60. Toja, E.; Selva, D.; Schiatti, P. J. Med. Chem. 1984, 27, 610.

61. Sondhi, S. M.; Rajvanshi, S.; Johar, M.; Bharti, N.; Azam, A.; Singh, A. K. Eur.

J. Med. Chem. 2002, 37, 835.

62. Sondhi, S. M.; Rani, R.; Singh, J.; Roy, P.; Agrawal, S. K.; Saxena, A. K.

Bioorg. Med. Chem. Lett. 2010, 20, 2306.

63. Shaaban, M. R.; Saleh, T. S.; Mayhoub, A. S.; Mansour, A.; Farag, B. M.

Bioorg. Med. Chem. 2008, 16, 6344.

64. Martin, M. W.; Newcomb, J.; Nunes, J. J.; Boucher, C.; Chai, L.; Epstein, L. F.;

Faust, T.; Flores, S.; Gallant, P.; Gore, A.; Gu, Y.; Hsieh, F.; Huang, X.; Kim, J.

L.; Middleton, S.; Morgenstern, K.; Oliveira-dos-Santos, A.; Patel, V. F.;

Powers, D.; Rose, P.; Tudor, Y.; Turci, S. M.; Welcher, A. A.; Zack, D.; Zhao,

H.; Zhu, L.; Zhu, X.; Ghiron, C.; Ermann, M.; Johnston, D.; Saluste, C. P. J.

Med. Chem. 2008, 51, 1637.

Chapter-1

47

65. Shen, Y.; Boivin, R.; Yoneda, N.; Du, H.; Schiller, S.; Matsushima, T.; Goto,

M.; Shirota, H.; Gusovsky, F.; Lemelin, C.; Jiang, Y.; Zhang, Z.; Pelletier, R.;

Ikemori- Kawada, M.; Kawakami, Y.; Inoue, A.; Schnaderbeck, M.; Wang, Y.

Bioorg. Med. Chem. Lett. 2010, 20, 3155.

66. Mohamed, B. G.; Abdel-Alim, A. M.; Hussein, M. A. Acta Pharm. 2006, 56, 31.

67. Naik, P.; Murumkar, P.; Giridhar, R.; Yadav, M. R. Bioorg. Med. Chem. 2010,

18, 8418.

68. Kubo, K.; Inada, Y.; Kohara, Y.; Sugiura, Y.; Ojima, M.; Itoh, K.; Furukawa,

Y.; Nishikawa, K.; Nakat, T. J. Med. Chem. 1993, 36, 1772.

69. Kubo, K.; Kohara, Y.; Imamiya, Y.; Sugiura, Y.; Inada, Y.; Furukawa, Y.;

Nishikawa, K.; Naka, T. J. Med. Chem. 1993, 36, 2182.

70. Vanderheyden, P. M. L.; Fierens, F. L. P.; Vauquelin, G.; Verheijen, I. J. Clin.

Basic Cardiol. 2002, 5, 75.

71. Ojima, M.; Inada, Y.; Shibouta, Y.; Wada, T.; Sanada, T.; Kubo, K.; Nishikawa,

K. Eur. J. Pharmacol. 1997, 319, 137.

72. Shibouta, Y.; Inada, Y.; Ojima, M.; Wada, T.; Noda, M.; Sanada, T.; Kubo, K.;

Kohara, Y.; Naka, T.; Nishikawa, K. J. Pharmacol. Exp. Ther. 1993, 266, 114.

73. Ogihara, T.; Nagano, M.; Higaki, J.; Kohara, K.; Mikami, H. J. Cardiovasc.

Pharmacol. 1995, 26, 490.

74. Kubo, K.; Kohara, Y.; Yoshimura, Y.; Inada, Y.; Shibouta, Y.; Furukawa, Y.;

Kato, T.; Nishikawa, K.; Naka, T. J. Med. Chem. 1993, 36, 2343.

75. Morimoto, S.; Ogihara, T. Cardiovasc. Drug Rev. 1994, 12, 153.

Chapter-1

48

76. Inada, Y.; Wada, T.; Shibouta, Y.; Ojima, M.; Sanada, T.; Ohtsuki, K.; Itoh, K.;

Kubo, K.; Kohara, Y.; Naka, T.; Nishikawa, K. J. Pharmacol. Exp. Ther. 1994,

268, 1540.

77. Kohara, Y.; Imamiya, E.; Kubo, K.; Wada, T.; Inada, Y.; Naka, T. Bioorg. Med.

Chem. Lett. 1903, 1995, 5.

78. Thomas, A. P.; Allott, C. P.; Gibson, K. H.; Major, J. S.; Masek, B. B.; Oldham,

A. A.; Ratcliffe, A. H.; Roberts, D. A.; Russell, S. T.; Thomason, D. A. J. Med.

Chem. 1992, 35, 877.

79. Palkowitz, A. D.; Steinberg, M. I.; Zimmerman, K. M.; Thrasher, K. J.; Hauser,

K. L.; Boyd, D. B. Bioorg. Med. Chem. Lett. 1995, 5, 1015.

80. Xu, J. Y.; Ran, Q.; Hua, W. Y.; Wu, X. M.; Wang, Q. J.; Zhang, J. Chinese

Chem. Lett. 2007, 18, 251.

81. Wienen, W.; Hauel, N.; Van Meel, J. C. A.; Narr, B.; Ries, U. J.; Entzeroth, M.

Br. J. Pharmacol. 1993, 110, 245.

82. Yagupolskii, L. M.; Fedyuk, D. V. Tetrahedron Lett. 2000, 41, 2265.

83. Kohara, Y.; Kubo, K.; Imamiya, E.; Wada, T.; Inada, Y.; Naka, T. J. Med.

Chem. 1996, 39, 5228.

84. Soll, R. M.; Kinney, W. A.; Primeau, J.; Garrick, L.; McCaully, R. J.; Coltsky,

T.; Oshiro, G.; Park, C. H.; Hartupee, D.; White, V.; McCallum, J.; Russo, A.;

Dinish, J.; Wodian, A. Bioorg. Med. Chem. Lett. 1993, 3, 757.

Chapter-1

49

85. Ferrari, B.; Tailadas, J.; Perreaunt, P.; Berhart, C.; Gougat, J.; Guiraudou, P.;

Cazaubon, C.; Roccon, A.; Nisato, D.; Le Fur, G.; Breliere, J. C. Bioorg. Med.

Chem. Lett. 1994, 4, 45.

86. Cho, N.; Kubo, K.; Furuya, S.; Sugiura, Y.; Yasuma, T.; Kohara, Y.; Ojima, M.;

Inada, Y.; Nishikawa, Y.; Naka, T. Bioorg. Med. Chem. Lett. 1994, 4, 35.

87. Kuroita, T.; Sakamoto, H.; Ojima, M. U.S. Patent. US 2009/0270464, 2009.

88. Kuroita, T.; Ojima, M.; Ban, J. U.S. Patent. US 2009/0054502, 2009.

89. Kuroita, T.; Sakamoto, H.; Igawa, H.; Sasaki, M.; Asano, K.; Maekawa, T.; Fuji,

K. U.S. Patent. US7803940, 2010.

90. Ries, U. J.; Mihm, G.; Narr, B.; Hasselbach, K. M.; Wittneben, H.; Entzeroth,

M.; VanMeel, J. C. A.; Wienen, W.; Hauel, N. H. J. Med. Chem. 1993, 36,

4040.

91. Wienen, W.; Entzeroth, M.; van Meel, J. C. A.; Stangier, J.; Busch, U.; Ebner,

T.; Schmid, J.; Lehmann, H.; Matzek, K.; Kempthorne-Rawson, J.; Gladigau,

V.; Hauel, N. H. Cardiovas. Drug Rev. 2000, 18, 127.

92. Dorsch, D.; Mederski, W. W. K. R.; Beier, N.; Lues, I.; Minck, K. O.; Schelling,

P. Bioorg. Med. Chem. Lett. 1994, 4, 1297.

93. Tamm, I.; Nemes, M. M.; Osterhout, S. J. Exp. Med. 1960, 111, 339.

94. Chodosh, L. A.; Fire, A.; Samuels, M.; Sharp, P. A. J. Biol. Chem. 1989, 264,

2250.

95. Townsend, B. L.; Devivar, R. V.; Turk, S. R.; Nassiri, M. R.; Drach, J. C. J.

Med. Chem. 1996, 38, 4098.

Chapter-1

50

96. Porcari, A. R.; Devivar, R. V.; Kucera, L. S.; Drach, J. C.; Townsend, L. B. J.

Med. Chem. 1998, 41, 1252.

97. Starcevic, K.; Kralj, M.; Ester, K.; Sabol, I.; Grce, M.; Pavelic, K.; Zamola, G.

K. Bioorg. Med. Chem. 2007, 15, 4419.

98. Vitalea, G.; Cartaa, A.; Lorigaa, M.; Pagliettia, G.; La Collab, P.; Busonerab, B.;

Collub, D.; Loddob, R. Med. Chem. 2008, 4, 605.

99. Vitale, G.; Corona, P.; Loriga, M.; Carta, A.; Pagliettia, G.; Collab, P. L.;

Busonera, B.; Marongiu, E.; Collu, D.; Loddo, R. Med. Chem. 2009, 5, 507.

100. Cheng, J.; Xie, J. T.; Luo, X. J. Bioorg. Med. Chem. Lett. 2005, 15, 267.

101. Zhang, Z. L.; Sun, Z. J.; Xue, F.; Luo, X. J.; Xiu, N. Y.; Teng, L.; Peng, Z. G.

Chinese Chem. Lett. 2009, 20, 921.

102. Barreca, M. L.; Rao, A.; Luca, L. D.; Zappala, M.; Monforte, A. M. J. Med.

Chem. 2005, 48, 3433.

103. Barreca, M. L.; Rao, A.; Luca, L. D.; Iraci, N.; Monforte, A. M.; Maga, G.;

Clercq, E. D.; Annecouque, C. P.; Balzarinic, J.; Chimirri, A. Bioorg. Med.

Chem. Lett. 2007, 17, 1956.

104. Schulz, W. G.; Islam, I.; Skibo, E. B. J. Med. Chem. 1995, 38, 109.

105. Islam, I.; Skibo, E. B.; Dorr, R. T.; Alberts, D. S. J. Med. Chem. 1991, 34, 2954.

106. Skibo, E. B.; Schulz, W. G. J. Med. Chem. 1993, 36, 3050.

107. Skibo, E. B.; Islam, I.; Heileman, M. J.; Schulz, W. G. J. Med. Chem. 1994, 37,

78.

108. Boruah, R. C.; Skibo, E. B. J. Med. Chem. 1994, 37, 1625.

Chapter-1

51

109. El-Naem, Sh. I.; El-Nazhawy, A. O.; El-Diwani, H. I.; Abdel Hamid, A. O.

Arch. der Pharm. 2003, 336, 7.

110. Ramla, M. M.; Omar, M. A.; Tokuda, H.; El-Diwani, H. I. Bioorg. Med. Chem.

2007, 15, 6489.

111. Ni, Z. J.; Barsanti, P.; Brammeier, N.; Diebes, A.; Poon, D. J.; Ng, S.; Pecchi,

S.; Pfister, K.; Renhowe, P. A.; Ramurthy, S.; Wagman, A. S.; Bussiere, D. E.;

Le, V.; Zhou, Y.; Jansen, J. M.; Ma, S.; Gesner, T. G. Bioorg. Med. Chem. Lett.

2006, 16, 3121.

112. Neff, D. K.; Dutra, A. L.; Blevitt, J. M.; Axe, F. U.; Hack, M. D.; Buma, J. C.;

Rynberg, R.; Brunmark, A.; Karlsson, L.; Breitenbucher, J. G. Bioorg. Med.

Chem. Lett. 2007, 17, 6467.

113. Abdel-Mohsen, H. T.; Ragab, F. A. F.; Ramla, M. M.; El Diwani, H. I. Eur. J.

Med. Chem. 2010, 45, 2336.

114. Shaharyar, M.; Abdullah, M. M.; Bakht, M. A.; Majeed, J. Eur. J. Med. Chem.

2010, 45, 114.

115. Luo, Y.; Xiao, F.; Qian, S.; Lu, W.; Yang, B. Eur. J. Med. Chem. 2011, 46, 417.

116. Refaat, H. M. Eur. J. Med. Chem. 2010, 45, 2949.

117. Hranjec, M.; Pavlovi, G.; Marjanovi, M.; Kralj, M.; Zamola, G. K. Eur. J. Med.

Chem. 2010, 45, 2405.

118. Neochoritis, C. G.; Tzitzikas, T. Z.; Tsoleridis, C. A.; Stephanatou, J. S.;

Kontogiorgis, C. A.; Hadjipavlou-Litina, D. J.; Papadopoulou, T. C. Eur. J.

Med. Chem. 2011, 46, 297.

Chapter-1

52

119. Demirayak, S.; Kayagil, I.; Yurttas, L. Eur. J. Med. Chem. 2011, 46, 411.

120. Huang, S. T.; Hseib, I. J.; Chena, C. Bioorg. Med. Chem. 2006, 14, 6106.

121. Styskala, J.; Styskalova, L.; Slouka, J.; Hajduch, M. Eur. J. Med. Chem. 2008,

43, 449.

122. Stolic, I.; Miškovic, K.; Magdaleno, A.; Silber, A. M.; Piantanida, I.; Bajic, M.;

Obrovac, L. G. Bioorg. Med. Chem. 2009, 17, 2544.

123. Yang, Y. H.; Cheng, M. S.; Wang, Q. H.; Nie, H.; Liao, N.; Wang, J.; Chen, H.

Eur. J. Med. Chem. 2009, 44, 1808.

124. Singh, M.; Tandon, V. Eur. J. Med. Chem. 2011, 46, 659.

125. Hauel, N. H.; Nar, H.; Priepke, H.; Ries, U.; Stassen, J. M.; Wienen, W. J. Med.

Chem. 2002, 45, 1757.

126. Takeuchi, K.; Bastian, J. A.; Gicord-Moore, D. S.; Harper, R. W.; Miller, S. C.;

Mullaney, J. T.; Sall, D. J.; Smith, G. F.; Zhangy, M.; Fisher, M. J. Bioorg. Med.

Chem. Lett. 2000, 10, 2347.

127. Zhao, Z.; Arnaiz, D.; Griedel, B.; Sakata, S.; Dallas, J.; Whitlow, M.; Trinh, L.;

Post, J.; Liang, A.; Morrissey, M.; Shaw, K. J. Bioorg. Med. Chem. Lett. 2000,

10, 963.

128. Shaw, K. J.; Guilford, W. J.; Griedel, B. D.; Sakata, S.; Trinh, L.; Wu, S.; Xu,

W.; Zhao, Z.; Morrissey, M. M. Bioorg. Med. Chem. Lett. 2002, 12, 1311.

129. Ueno, H.; Katoh, S.; Yokota, K.; Hoshi, J. I.; Hayashi, M.; Uchida, I.; Aisaka,

K.; Hase, Y.; Cho, H. Bioorg. Med. Chem. Lett. 2004, 14, 4281.

Chapter-1

53

130. Kolesnikov, A.; Rai, R.; Young, W. B.; Mordenti, J.; Liu, L.; Torkelson, S.;

Shrader, W. D.; Leahy, E. M.; Hu, H.; Gjerstad, E.; Janc, J.; Katz, B. A.;

Sprengeler, A. P. Bioorg. Med. Chem. Lett. 2006, 16, 2243.

131. Mor, M.; Bordi, F.; Silva, C.; Rivara, S.; Zuliani, V.; Vacondio, F.; Rivara, M.;

Barocelli, E.; Bertoni, S.; Ballabeni, V.; Magnanini, F.; Impicciatore, M.; Plazzi,

P. V. Bioorg. Med. Chem. 2004, 12, 663.

132. Rivara, M.; Zuliani, V.; Cocconcelli, G.; Morini, G.; Comini, M.; Rivara, S.;

Mor, M.; Bordi, F.; Barocelli, E.; Ballabeni, V.; Bertonib, S.; Plazzia, P. V.

Bioorg. Med. Chem. 2006, 14, 1413.

133. Aslanian, R.; Zhu, X.; Vaccaro, H. A.; Shih, N. Y.; Piwinski, J. J.; Williams, S.

M.; West, R. E. Bioorg. Med. Chem. Lett. 2008, 18, 5032.

134. Coon, T.; Moree, W. J.; Li, B.; Yu, J.; Zamani-Kord, S.; Malany, S.; Santos, M.

A.; Hernandez, L. M.; Petroski, R. E.; Sun, A.; Wen, J.; Sullivan, S.; Haelewyn,

J.; Hedrick, M.; Hoare, S. J.; Bradbury, M. J.; Crowe, P. D.; Beaton, G. Bioorg.

Med. Chem. Lett. 2009, 19, 4380.

135. Erb, K. L.; Ravula, S. B.; Yu, J.; Kord, S. Z.; Moree, W. J.; Petroski, R. E.;

Wen, J.; Malany, S.; Hoare, S. R. J.; Madan, A.; Crowe, P. D.; Beaton, G.

Bioorg. Med. Chem. Lett. 2010, 20, 2916.

136. Priya, B. S.; Basappa.; Swamy, S. N.; Rangappa, K. S. Bioorg. Med. Chem.

2005, 13, 2623.

137. Uno, H.; Kurokawa, M.; Masuda, Y.; Nishimura, H. J. Med. Chem. 1979, 22,

180.

Chapter-1

54

138. Gopalsamy, A.; Shi, M.; Golas, J.; Vogan, E.; Jacob, J.; Johnson, M.; Lee, F.;

Nilakantan, R.; Petersen, R.; Svenson, K.; Chopra, R.; Tam, M. S.; Wen, Y.;

Ellingboe, J.; Arndt, K.; Boschelli, F. J. Med. Chem. 2008, 51, 373.

139. Strupczewski, J. T.; Allen, R. C.; Gardner, B. A.; Schmid, B. L.; Stache, U.;

Glamkowski, E. J.; Jones, M. C.; Ellis, D. B.; Huger, F. P.; Dunn, R. W. J. Med.

Chem. 1985, 28, 761-767.

140. Nuhrich, A.; Varache-Lembege, M.; Renard, P.; Devaux, G. Eur. J. Med. Chem.

1994, 29, 75-82.

141. Shantharam, C. S.; Suyoga Vardhan, D. M.; Suhas, R.; Sridhara, M. B.; Channe

Gowda, D. Eur. J. Med. Chem. 2013, 60, 325-332.