Purin-6-One Derivatives as Phosphodiesterase-2 Inhibitors

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Purin-6-One Derivatives as Phosphodiesterase-2 Inhibitors Purin-6-One Derivatives as Phosphodiesterase-2 Inhibitors

Wei Yuan South-Central University for Nationalities China

Xin-Yun Zhao South-Central University for Nationalities China

Xi Chen South-Central University for Nationalities China

Chang-Guo Zhan University of Kentucky chang-guozhanukyedu

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Purin-6-One Derivatives as Phosphodiesterase-2 Inhibitors NotesCitation Information Published in Journal of Chemistry v 2016 article ID 6878353 p 1-10

Copyright copy 2016 Wei Yuan et al

This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

Digital Object Identifier (DOI) httpsdoiorg10115520166878353

This article is available at UKnowledge httpsuknowledgeukyedups_facpub73

Research ArticlePurin-6-One Derivatives as Phosphodiesterase-2 Inhibitors

Wei Yuan1 Xin-Yun Zhao1 Xi Chen1 and Chang-Guo Zhan2

1College of Chemistry and Materials Science South-Central University for Nationalities Wuhan 430074 China2Department of Pharmaceutical Sciences College of Pharmacy University of Kentucky 789 S Limestone Lexington KY 40536 USA

Correspondence should be addressed to Xin-Yun Zhao 45551525qqcom and Xi Chen ccnuchenyahoocom

Received 12 December 2015 Revised 14 January 2016 Accepted 17 January 2016

Academic Editor Jose L A Mediano

Copyright copy 2016 Wei Yuan et alThis is an open access article distributed under theCreative CommonsAttribution License whichpermits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

A series of purin-6-one derivatives were synthesized and their in vitro inhibitory activity against phosphodiesterase-2 (PDE2) wasevaluated by using a fluorescence polarization assayThree compounds that are2j 2p and 2q showed significant inhibitory activityagainst PDE2 with IC

50values of 173 018 and 343 120583M respectively Structure-activity relationship (SAR) analysis was performed

to explore the relationship between the chemical structures of these compounds and their inhibitory activity Compounds 2j 2pand 2q were further selected for molecular docking study The docking results suggested that these ligands bind with hydrophobicpockets of the catalytic active site of PDE2 where a Tyr655 residue was found to be important in binding with compound 2p themost potent inhibitor identified in this study Our present study provides useful information for the future design of novel PDE2inhibitors

1 Introduction

Mammalian cyclic nucleotide phosphodiesterases (PDEs)could catalyze the hydrolysis of ubiquitous intracellular sec-ond messengers cyclic adenosine monophosphate (cAMP)andor cyclic guanosine monophosphate (cGMP) into inac-tive 51015840-AMP andor 51015840-GMP to modulate a number ofphysiological processes Numerous studies have proved thatPDEs were excellent drug targets for the development oftherapeutic agents against various diseases [1 2] The humangenome encodes 11 PDE families (PDE1 to PDE11) to producea series of PDE isoenzymes [3ndash5] There is only one genecoding for PDE2 namely PDE2A PDE2Ahas been describedto degrade both substrates cAMP and cGMP Its enzymaticactivity can be allosterically activated by cGMP AdditionallyPDE2A is preferentially expressed in the mammalian heart[6] and brain tissues [7] Animal behavioral models haveindicated that PDE2 inhibition plays a key role in the controlof memory and anxiety [8ndash10] It could also be considered asa promising therapeutic target for cognition enhancement inAlzheimerrsquos disease [11]

Among the as-reported PDE2 selective inhibitors thereare four inhibitors particularly interesting to many scien-tists As shown in Figure 1 EHNA was the first reportedPDE2 inhibitor with IC

50value of 1 120583M [12] BAY 60-7550

and PDP (Figure 1) exhibited excellent inhibitory activitiesagainst PDE2A with IC

50values of 47 and 06 nM respec-

tively [8 13] ND7001 was under development by Neuro3D and advanced into clinical phase I in 2005 showingpotent inhibitory activity against PDE2 [14] with IC

50value

of 57 nM However according to the reports of ThomsonReuters Pharma developments of BAY 60-7550 and ND7001were ceased due to their poor pharmacokinetics perfor-mances [15]

Despite various X-ray crystal structures for PDE2 havingbeen reported [16 17] the shape of the binding pocket ofPDE2 remained uncertain until 2013 when Huang et al havereported the X-ray crystal structure of PDE2A complexedwith BAY 60-7550 [18] The crystal structure revealed thatthis compound binds to the PDE2 active site using not onlythe conserved glutamine-switch mechanism for substratebinding but also a binding induced hydrophobic pocketwhich is lined by Leu770 His773 Thr805 Leu809 Ile866and Ile870 (Figure 2) It has never been reported before Thebinding mode of BAY 60-7550 with the active site of PDE2in crystal state is depicted in Figure 2 As shown in thisfigure the ndashNH-COndashmoiety of BAY 60-7550 forms bidentatehydrogen bonding to the invariant glutamine (Gln859) andthe imidazotriazin-4-one core stack against the side chain ofPhe862 and Phe830 In addition the phenyl ring is filled into

Hindawi Publishing CorporationJournal of ChemistryVolume 2016 Article ID 6878353 10 pageshttpdxdoiorg10115520166878353

2 Journal of Chemistry

N

N N

N

OH

EHNA

N

N O

Ph

HN

N N N

O

OH

HN

N N

NO

O

ND7001

BAY 60-7550

PDP

H3C

NH2

OCH3

OCH3

OCH3

OCH3

H3CO

CONH2

Figure 1 Structures of EHNA BAY 60-7550 PDP and ND7001

His773

Leu770

Ile866

Thr805Ile870 Leu809

Tyr655

Gln859

Tyr827Phe830 Leu858

Met847

Met845

29

27

BAY 60-7550

Figure 2 The interaction of BAY 60-7550 with the catalyticdomain of PDE2 (PDB ID 4HTX)The BAY compound is renderedwith green color scheme Residues that form key interactionswith BAY compound are rendered with orange color scheme Theenvironmental protein surrounding is rendered in orange For theconvenience of display some residues are not shown

the binding induced hydrophobic pocket which significantlycontributes to the binding of BAY 60-7550 with PDE2

Inspired by the information mentioned in Figure 2 aseries of purin-6-one derivatives were designed and synthe-sized by keeping the core scaffolds purin-6-one and changingthe substituents at 2- and 9-positions on the purin-6-oneFluorescence polarization assay was performed to test theinhibitory effect in vitro using recombinant human PDE2 inthe presence of 10 120583M of inhibitors For those compoundswith higher inhibitory activity IC

50values against PDE2

were also determined Ligand-protein docking studies were

performed to investigate the bindingmodes of these purin-6-one derivatives with the PDE2 catalytic domain Our presentstudies provide useful information for the design of novelPDE2 inhibitors

2 Results and Discussion

21 Chemistry All compounds synthesized in this studyhave been summarized in Table 1 The general syntheticroutes of these target compounds are depicted in Scheme 1The key intermediates 5-amino-1-substituted-imidazole-4-carboxamides 1(1a 1c 1d 1i 1n and 1p) were firstly synthe-sized (Scheme 1) using amines 2-amino-2-cyanoacetamideand triethyl orthoformate as raw materials Their syntheticroute was modified from the work of Banerjee et al [19] byadding pyridine as catalyst under the refluxing conditionsThe yield of 1a (R = CH

2CH2OH) was higher (732) than

that reported (42) in the work of Banerjee et alThemeltingpoint and 1H NMR of 1c (R = CH

2C6H5) were found to be

consistent with those reported by Shaw and Alhede [20 21]Compounds 1n and 1p were synthesized by using 3-amino-4-phenyl-butan-2-ol and 3-amino-6-phenyl-hexan-2-ol asstarting materials Target compounds were synthesized byrefluxing intermediates 1 and the corresponding esters inthe presence of sodium methoxide Purin-6-one derivative2c was then reacted with allyl bromide to give N1-alkylated(2c-1) and O6-alkylated (2c-2) products in the presence ofNaH Compounds 2n and 2o were further oxidized to 2rand 2s under DMSO using SO

3pyridine complex [22]Their

structures were confirmed by 1H NMR 13C NMR IR andmass spectroscopyThe single-crystal structure of compound2a was also determined by our X-ray crystallography [23]

22 Inhibitory Activity of Purin-6-One Derivatives againstPDE2 and SAR Studies The in vitro inhibitory activityagainst the recombinant human PDE2 was evaluated for finalcompounds by using fluorescence polarization assay Theinhibition ratios of target compounds against PDE2 in thepresence of 10 120583M of inhibitor were summarized in Table 1Results from Table 1 indicated that varying substituent at the2- and 9-position will lead to remarkably different inhibitoryactivities Keeping R = minusCH

2CH2OH replacing R1 (3-

methoxybenzyl) in compound 2a with 34-dimethoxybenzyl(compound 2b) will increase inhibitory ratio from 48(2a) to 78 (2b) When R and R1 were respectively tobe ndashCH

2C6H5and 2-methylbenzyl (compound 2c) the

inhibitory ratio value decreased to 35 It was postulated thatlarge nonpolar groups at R substituent will be unfavorable forPDE2A inhibition This assumption is further confirmed bythe inhibitory values (18ndash42) of compounds 2d and 2fndash2hR groups of which were nonpolar group minus(CH

2)3C6H5 The

only exception is compound 2e the inhibitory ratio is 78which is the same as the inhibitory value of 2b Increasingthe chain length of R in compound 2e to ndash(CH

2)4C6H5leads

to compound 2i which has an inhibitory activity essentiallyidentical to that of 2e Further adding a methoxyl group to3-position of phenyl ring of R1 in 2i results in compound2j which has a significant stronger inhibitory activity witha value of 95 In contrast adding a methyl group to

Journal of Chemistry 3

Table 1 Molecular structures and PDE2 inhibitory activity of purin-6-one derivatives (see Scheme 1 compounds 2andash2q)

Compound R R1 Inhibition (at 10120583M inhibitor)2a ndashCH

2CH2OH 3-Methoxybenzyl 48

2b ndashCH2CH2OH 34-Dimethoxybenzyl 78

2c ndashCH2C6H5

2-Methylbenzyl 352d ndash(CH

2)3C6H5

34-Dimethoxyphenyl 442e ndash(CH

2)3C6H5

Benzyl 782f ndash(CH

2)3C6H5

2-Methylbenzyl 352g ndash(CH

2)3C6H5

4-Chlorophenyl 182h ndash(CH

2)3C6H5

24-Dichlorophenoxyethyl 422i ndash(CH

2)4C6H5

Benzyl 782j ndash(CH

2)4C6H5

3-Methoxybenzyl 95 (1731a)2k ndash(CH

2)4C6H5

2-Methylbenzyl 242l ndash(CH

2)4C6H5

24-Dichlorophenoxyethyl 342m ndash(CH

2)4C6H5

4-Chlorophenyl 302n ndash(CH

3CHOH)CHCH

2C6H5

Benzyl 732o ndash(CH

3CHOH)CHCH

2C6H5

2-Methylbenzyl 702p ndash(CH

3CHOH)CH(CH

2)3C6H5

Benzyl 100 (184a)2q ndash(CH

3CHOH)CH(CH

2)3C6H5

4-Chlorophenyl 99 (3427a)2r ndash(CH

3CO)CHCH

2C6H5

Benzyl 752s ndash(CH

3CO)CHCH

2C6H5

2-Methylbenzyl 782c-1 1-Allyl-9-benzyl-2-(2-methyl-benzyl)-19-dihydro-purin-6-one 562c-2 6-Allyloxy-9-benzyl-2-(2-methyl-benzyl)-9H-purine 9aIC50 (nM)

R1COOCH3

H2N

H2N

H2N

H2N

H2NCN

NH2++

+

OO

OO

EtO

OEt

HN

OEt

RNH2Pyridine

acetonitrile N

N

N

NNN

N

R

RR

1

R1

1

234

56

78

9

CH3ONa

reflux

SO3pyridine

DMSO

Alkylated2n2o 2r2s 2c

2c-2

2c-1

2andashq

Scheme 1 Synthesis of purin-6-one derivatives

the 2-position of phenyl ring of R1 in 2i (compound 2k) leadsto amuch less potent inhibitory with a value of only 24Thedifference of R1 groups and inhibitory values between 2j and2k clearly demonstrates that adding a moderately nonpolargroup at the 3- or 5-position of benzyl at R1-position isfavorable

Based on the discussion above we further compare thestructure of 2b and 2d It could be found that the presenceof a hydroxyl (eg ndashCH

2CH2OH) in R group is more

favorable than a nonpolar R substituent (eg ndash(CH2)3C6H5)

without a hydroxyl In addition comparing the inhibitionratio of 2d (44) to that of 2j (95) one can find that

4 Journal of Chemistry

the bulkiness of R group should also be important to thePDE2A inhibition Combining these two points we triedto introduce a bulky ndash(CH

3)CH(OH) group to the existing

R group of 2i The resulting compound that is 2p showsexcellent inhibitory activities with inhibition ratio of 100However when the ndash(CH

3CHOH)CH(CH

2)3C6H5group

of compound 2p was replaced with a less bulky groupthat is ndash(CH

3CHOH)CHCH

2C6H5

(compound 2n) thecorresponding inhibition ratio drops to 73 Hence thepresence of hydroxyl and bulky size of R group are bothimportant for inhibition activity

Beltman et al have reported a series of cGMP analoguesand evaluated the inhibitory activities of these compoundsagainst PDE2The N1-methylated cGMP analogues generallyexhibited weak inhibitory activity as compared to thosecGMP analogues with a hydrogen on N1 SAR study sug-gested that N1-methylation of cGMP analogues will resultin the loss of a hydrogen bond or increase the steric hin-drance with the binding pocket of PDE2 which will leadto reduced inhibitory activities [24] This study concernsthe importance of maintaining bidentate hydrogen bondsformed between the 120574-amide of Gln859 and the carbonylO6 NH moiety of the inhibitors To testify this idea we alsosynthesized N1-allylated derivative of compound 2c namely2c-1 Interestingly we observed a remarkably improvedinhibitory activity of compound 2c-1 (N1-allylation) whichis contrary to Beltmanrsquos reports As can be seen from Table 1the inhibitory ratio of 2c-1 is higher (57) than that (35)of 2c Although 2c-1 loses a hydrogen donor at its N1-position because of the allylation at this place the loss ofthe hydrogen bonding interaction can be compensated bythe hydrophobic interaction formed between the allyl groupand the surrounding hydrophobic pocket of PDE2 Hencefor purine-6-one derivatives it is not necessary to form abidentate hydrogen bond between the N1-H and 120574-amideof Gln859 to maintain optimal PDE2 inhibitory activity Onthe other hand when the O6-position of 2c is attached withan allyl group the resulting compound 2c-2 shows a muchweaker inhibitory activity (9) as compared to that (35)for 2c Our present study shows that the carbonyl oxygenat 6-position of purin-6-one scaffold (the scaffold consistsof atoms 1 to 9 See Table 1 for numbering of these atoms)probably plays a key role in binding with PDE2

The values in Table 1 show that compounds 2j 2p and2q have potent inhibitory activities These three compoundswere then selected for further inhibitory activity tests atvarious concentrations in order to calculate IC

50value which

showed a submicromolar inhibitory activity

23 Molecular Modeling The results from the preliminaryactivities prompted us to pay attention to three of the morepotent compounds (2j 2p and 2q) with higher inhibitoryactivity against PDE2 In an effort to gain an understandingof the structural basis for the empirical structure-activityrelationships observed we further studied the binding modeof the compounds (2j 2p and 2q) through moleculardocking For this purpose the crystal structure of PDE2 incomplex with BAY 60-7550 (PDB ID 4HTX) was selectedas the receptor for molecular docking Before docking

Table 2 Calculated binding free energies in comparison withavailable experimental data (all in kcalmol)

Compound ΔGbindcal(a) IC

50(120583M) ΔGbind

exp(b)

2j minus911 1731 minus782p minus980 0184 minus922q minus885 3427 minus74(a)Binding free energies predicted by AUTODOCK(b)Binding free energies derived from the experimental IC50 values

the complex-ligand and water molecules were removed fromthe complex structure except for four water molecules anda hydroxide ion that bound with the metal ions Zn2+ andMg2+ at the catalytic pocket Then hydrogen atoms wereadded by using the Leap tools implemented in AMBERsoftwareThemolecular structures of 2j 2p and 2qwere con-structed by GaussView followed by geometrical optimizationat PM3 level For the receptor and each ligand the nonpolarhydrogen atoms were merged and Gasteiger charges wereadded Then AUTODOCK42 program was used to searchfor the most favorable binding mode of the ligands andPDE2 catalytic domain During the docking process atomsin the receptor were kept constant 100 docking runs wereperformed for each ligand and the conformations with thelowest binding free energies were selected for analysis

Molecular docking revealed that all of these inhibitorsbind with PDE2 in a similar binding mode (Figure 3) Fromthis figure it could be found that each of the PDE2 inhibitorswas fitted in a cavity formed by Phe830 Phe862 Ile826Gln859 Met845 Met847 Leu770 His773 Leu809 Ile866and Ile870 residues In the PDE2-ligand binding complexes(Figure 3) the commonpurin-6-one scaffold of the inhibitorsis lodged in the hydrophobic pocket surrounded by the sidechains of Ile826 Ile866 Phe830 andPhe862 residues causinga high degree of surface complementarities Hydrogen bondswere formed between the purin-6-one and the 120574-amide ofGln859 In addition R groups of ligands were clapped bythe hydrophobic H pocket formed by His773 Leu809 Ile866and Ile870 residues which was also observed in the crystalstructure of PDE2 in complex with BAY 60-7550 R1 groupof the inhibitors formed additional hydrophobic interactionwith the peripheral residues Met847 Leu858 and Ile866

In addition to the common features mentioned abovethe hydroxyl group of R1 substituent of inhibitor 2p formsan extra hydrogen bonding interaction with the side chainof Tyr655 (see Figure 3(b)) which will enhance the bindingof 2p with PDE2 Compared to the binding mode of 2p2j (Figure 2(a)) and 2q (Figure 2(c)) do not interact withTyr655 implying that their binding affinities with PDE2 willbe weaker than that of 2p As can be seen from Table 2 thebinding free energies (ΔGbind

cal) predicted by AUTODOCKare consistent with the corresponding experimental bindingfree energies (ΔGbind

exp) suggesting that the present bindingmodes of these compounds are reliable

It is worth noting that the interaction with Tyr655 hasnever been reported before Hence this residue can beconsidered as a new site for the development of novel PDE2

Journal of Chemistry 5

His773

Leu770

Ile866

Thr805

Ile870Leu809

Tyr655

Gln859

Tyr827Phe830

Leu858

Met847

Met845

27

29

Compound 2j

(a)

His773

Leu770

Ile866

Thr805

Ile870 Leu809

Tyr655

Gln859

Tyr827Phe830

Leu858

Met847

Met845

30

26

Compound 2p

30

(b)

His773

Leu770

Ile866

Thr805

Ile870 Leu809

Tyr655Gln859

Tyr827Phe830

Leu858

Met847

Met845

3129Compound 2q

(c)

Figure 3 Binding mode of compounds 2j (a) 2p (b) and 2q (c) in the active site pocket of PDE2 Each ligand is rendered as balls and sticksand the surrounding residues are rendered as sticks For the convenience of display some residues and atoms are not shown See Figure 2 forthe color codes of the atom types

inhibitors Compound 2p can be regarded as a good startingstructure for the design of new PDE2 inhibitors

3 Conclusions

Aseries of purin-6-one derivativeswere designed and synthe-sized as potential PDE2 inhibitors SAR studies suggested thatthe carbonyl oxygen at 6-position of purin-6-one derivativesplayed a key role inmaintaining the inhibitory activity againstPDE2 enzyme Three more potential compounds 2j 2pand 2q were identified to have submicromolar IC

50values

Molecular docking of compounds 2j 2p and 2q into thecatalytic domain of the PDE2 revealed a similar bindingprofile with PDE2 to that of BAY 60-7550 Residue Tyr655which has been never reported before was found to bepotential binding target for PDE2 inhibitors The bindingmode analysis indicates that optimization of 2p compound

is promising to be a leading structure for the design of novelPDE2 inhibitors

4 Experimental Section

41 Chemistry 1H NMR spectra were recorded on a VarianNMR 600MHz instrument or Mercury plus 400MHz andthe chemical shifts 120575 are in ppm and tetramethylsilaneas internal standard Graphical 1H NMR spectra of thecompounds 2bndash2s in this work are collected in the Supple-mentaryMaterial available online at httpdxdoiorg10115520166878353 Mass spectra were determined using TraceMS2000 organic mass spectrometry and signals are given inmz Melting points were recorded on Buchi B-545 meltingpoint apparatus Elemental analysis (EA) was carried outwith aVario EL III CHNSO elemental analyzer Conventionalheating was carried out on Corning stirrerhotplates with oil

6 Journal of Chemistry

baths Thin layer chromatography (TLC) inspections werecarried out on a silica gel GF

254plates Triethyl orthoformate

2-cyano-2-amino-acetamide and other chemical reagentsotherwise noted were commercially available Solvents weredried in a routine way and redistilled Esters were preparedusing acid as raw materials in the presence of acetyl chlorideand alcohol

411 General Procedures for Synthesis of the Intermedi-ate 5-Amino-4-carboxamide-1-substituted-1H-imidazole (1)20mmol of 2-amino-2-cyanoacetamide was suspended in30mL absolute acetonitrile and 23mmol of triethyl ortho-formate and 003 g pyridine as a catalyst were added tothe suspension with stirring The suspension was heatedto reflux temperature using an oil bath preheated to 100∘Cand the suspension was held at boiling temperature for 1 hand then 20mmol of substituted amine was then addedover a 3 to 5min period and boiling was continued for anadditional 15min The reaction was quickly cooled to roomtemperature and then solvent was evaporated and the residuewas recrystallized from DMF-ethanol to give the product

(1) 5-Amino-1-(2-hydroxyethyl)-1H-imidazole-4-carboxamide(1a) Mp 1426∘C Yield 732 1H NMR (400MHzDMSO-d

6) 120575 706 (s 1H CH) 672 658 (pair of s br 2H

CONH2) 568 (s 2H ArNH

2) 503 (s 1H OH) 383 (t 2H

119869 = 52Hz CH2O) 361 (t 2H 119869 = 6Hz CH

2N) EI-MSmz

(relative intensity) 1709 (M+1 55) 1698 (97) 1258 (91) 1098(74) 1087 (100) 448 (67)

(2) 5-Amino-1-benzyl-1H-imidazole-4-carboxamide (1c)Mp2508∘C Yield 76 1HNMR (600MHz DMSO-d

6) 120575 719ndash

737 (m 6H ArH+CH) 664 679 (pair of s 2H CONH2)

584 (s 2H ArNH2) 507 (s 2H ArCH

2) EI-MS mz

(relative intensity) 2162 (M+ 23) 912 (100) 651 (26) 443(7)

(3) 5-Amino-1-(3-phenylpropyl)-1H-imidazole-4-carboxamide(1d) Mp 1981∘C Yield 76 1H NMR (600MHz DMSO-d6) 120575 717ndash730 (m 5H ArH) 711 (s 1H CH) 661 676

(pair of s 2H CONH2) 580 (s 2H NH

2) 382 (t CH

2

119869 = 72Hz) 250ndash258 (m 2H CH2) 191ndash199 (m 2H CH

2)

EI-MSmz (relative intensity) 2442 (M 44) 2103 (26) 1401(61) 1231 (82) 1171 (42) 109 (33) 911 (100) 770 (18) 650(25) 442 (14)

(4) 5-Amino-1-(4-phenylbutyl)-1H-imidazole-4-carboxamide(1i)Mp 222∘CYield 72 1HNMR(600MHzDMSO-d

6)

120575 714ndash727 (m 5H ArH) 707 (s 1H CH) 657 670 (pair ofs 2H CONH

2) 576 (s 2H NH

2) 380 (t CH

2 119869 = 9Hz)

258 (t CH2 119869 = 78Hz) 162ndash166 (m 2H CH

2) 149ndash154

(m 2H CH2) EI-MSmz (relative intensity) 2585 (M+ 51)

2242 (22) 2138 (9) 1541 (13) 1499 (22) 1372 (12) 1261 (17)1089 (28) 911 (100) 769 (14) 650 (26)

(5) 5-Amino-1-[1-(1-hydroxyethyl)-2-phenylethyl]-1H-imida-zole-4-carboxamide (1n)Mp 2314∘C Yield 67 1H NMR(600MHz DMSO-d

6) 120575 712ndash723 (m 6H ArH) 656 669

(pair of s 2H CONH2) 560 (s 2H NH

2) 531 (d 1H OH

119869 = 6Hz) 418ndash422 (m 1H CH) 390ndash393 (m 1H CH)312ndash326 (m 2H CH

2) 105 (d 3H CH

3 119869 = 3Hz) EI-MS

mz (relative intensity) 2742 (M+ 5) 166 (2) 126 (17) 109(15) 912 (100) 770 (17) 650 (27) 512 (12) 453 (60)

(6) 5-Amino-1-[1-(1-hydroxyethyl)-4-phenylbutyl]-1H-imida-zole-4-carboxamide (1p) 1H NMR (600MHz DMSO-d

6)

120575 712ndash726 (m 6H ArH+1H) 675 660 (pair of s 2HCONH

2) 574 (s 2H NH

2) 513 (d 1H OH 119869 = 18Hz)

382ndash383 (m 2H CH+CH) 253ndash261 (m 2H CH2) 180ndash

191 (m 2H CH2) 132ndash141 (m 2H CH

2) 095 (d 3H CH

3

119869 = 3Hz) EI-MS mz (relative intensity) 3036 (M+1 13)3022 (M+ 73) 2681 (25) 2404 (8) 2569 (168) 1529 (208)126 (100) 1089 (71) 911 (83) 770 (13) 651 (14) 552 (14)431 (25)

412 General Procedure for the Preparation of Purin-6-OneDerivatives (2andash2q) 14mmol of 5-amino-1-substituted-4-carboxamide-1H-imidazole (1) was dissolved in 10mL ofabsolute methanol Then 56mmol of the appropriate ester isadded into this solution This mixture was added in 10mL ofmethoxide-methanol solution prepared from sodium (015 g63mmol) and 10mL of absolute methanol The mixturewas refluxed for 15ndash20 h After cooling the solvent wasevaporated off and the residue was taken into ethyl acetateThe organic phase was dried over Na

2SO4and evaporated

And the residue was purified via silica gel chromatography(eluent the mixture of ethyl acetate and methanol) to obtainthe pure product (2andash2q)

(1) 9-(2-Hydroxy-ethyl)-2-(3-methoxy-benzyl)-19-dihydro-purin-6-one (2a) The data of 1HNMR IR EI-MS elementalanalysis and X-ray crystal was reported in our previousstudy [23]

(2) 2-(34-Dimethoxy-benzyl)-9-(2-hydroxy-ethyl)-19-dihy-dro-purin-6-one (2b) Mp 2236∘C Yield 76 1H NMR(400MHz DMSO-d

6) 120575 1227 (s NH 1H) 795 (s CH

1H) 702 (s ArH 1H) 686ndash693 (m ArH 2H) 497 (tOH 1H 119869 = 28Hz) 415 (t CH

2 2H 119869 = 52Hz) 386 (s

CH2 2H) 374ndash371 (8H OCH

3+CH2) 13C NMR (100MHz

DMSO-d6) 120575 1578 1573 1494 1491 1483 1411 1294 1224

1212 1131 1123 5985 5603 5595 559 465 EI-MS mz(relative intensity) 3300 (M+ 100) 2991 (39) 2851 (15)2710 (33) 2390 (17) 1511 (24) 1351 (23) 1091 (19) 911 (12)771 (16) 652 (18) 512 (7) 452 (13) IR (cmminus1) 3327 (N-H)3079 2939 1711 (C=O) 1583 1516 1439 1408 1262 1237 11621067 1058 1020 647 Anal calcd for C

16H18N4O4 C 5817

H 549 N 1696 Found C 5815 H 582 N 1663

(3) 9-Benzyl-2-(2-methyl-benzyl)-19-dihydro-purin-6-one(2c) The data of 1H NMR 13C NMR IR EI-MS andelemental analysis was reported in our previous study [25]

(4) 2-(34-Dimethoxy-phenyl)-9-(3-phenyl-propyl)-19-dihy-dro-purin-6-one (2d) Mp 2353∘C Yield 45 1H NMR(600MHz DMSO-d

6) 120575 1233 (br s 1H NH) 811 (s 1H

CH) 775 (s 1H ArH) 780 (d 1H ArH 119869 = 42Hz) 718ndash729(m 5H ArH) 711 (d 1H ArH 119869 = 45Hz) 421 (t 2H CH

2

Journal of Chemistry 7

119869 = 72Hz) 386 (s 3H OCH3) 385 (s 3H OCH

3) 263

(t 2H CH2 119869 = 78Hz) 217ndash222 (m 2H CH

2) 13C NMR

(100MHz DMSO-d6) 120575 1580 1530 15192 15986 1494

1490 1489 1413 1410 1288 1264 1249 1216 1120 1113562 561 433 326 315 EI-MS mz (relative intensity)3902 (M+ 75) 3635 (19) 2850 (100) 2691 (10) 1989 (17)1642 (12) 148 (8) 1172 (13) 1042 (10) 911 (67) 772 (13)650 (21) 513 (7) IR (cmminus1) 3431 (N-H) 3093 3012 29331685 (C=O) 1559 1539 1514 1304 1269 1223 1178 1024 876754 702 Anal calcd for C

22H22N4O3 C 6768 H 568 N

1435 Found C 6805 H 538 N 1418

(5) 2-Benzyl-9-(3-phenyl-propyl)-19-dihydro-purin-6-one(2e) Mp 2251∘C Yield 62 1H NMR (600MHz DMSO-d6) 120575 1238 (s 1H NH) 804 (s 1H CH) 715ndash736 (m 10H

ArH) 412 (t 2H CH2 119869 = 72) 396 (s 2H CH

2) 254 (t

2H CH2 119869 = 78Hz) 208ndash213 (m 2H CH

2) 13C NMR

(100MHz DMSO-d6) 120575 1578 1570 1493 1413 1406 1372

1292 1289 1288 1287 1273 1264 1226 434 394 325314 EI-MSmz (relative intensity) 3443 (M+ 2) 2392 (22)1831 (6) 1172 (10) 911 (100) 772 (22) 652 (24) 512 (15)442 (29) IR (cmminus1) 3442 (N-H) 3097 2940 2864 1724(C=O) 1581 1494 1453 1410 1361 1128 718 698 654 Analcalcd for C

21H20N4O C 7323 H 585 N 1627 Found C

7359 H 610 N 1662

(6) 2-(2-Methyl-benzyl)-9-(3-phenyl-propyl)-19-dihydro-pur-in-6-one (2f ) Mp 2142∘C Yield 57 1HNMR (600MHzDMSO-d

6) 120575 1233 (s 1H NH) 803 (s 1H CH) 711ndash726

(m 9H ArH) 406 (t 2H CH2 119869 = 72Hz) 397 (s 2H

CH2) 250 (t 2H CH

2 119869 = 108Hz) 234 (s 3H CH

3)

204ndash207 (m 2H CH2) 13C NMR (100MHz DMSO-d

6) 120575

1578 1569 1493 1412 14059 14057 1370 1357 1305 12951288 1286 1273 1264 1226 435 382 325 313 199 EI-MS mz (relative intensity) 3583 (M+ 35) 3432 (20) 2533(100) 2544 (40) 2403 (16) 2283 (16) 1053 (15) 912 (52) IR(cmminus1) 3433 (N-H) 3069 3026 2948 2867 1718 (C=O) 15821493 1454 1410 1364 1157 1125 756 695 651 Anal calcd forC22H22N4O C 7372 H 619 N 1563 Found C 7409 H

625 N 1598

(7) 2-(4-Chloro-phenyl)-9-(3-phenyl-propyl)-19-dihydro-pur-in-6-one (2g) Mp 2484∘C Yield 42 1HNMR (600MHzDMSO-d

6) 120575 1253 (s 1H NH) 816 (s 1H CH) 813 (d 2H

119869 = 42Hz) 762 (d 2H 119869 = 39Hz) 718ndash729 (m 5H ArH)422 (t 2H CH

2 119869 = 72Hz) 262 (t 2H CH

2 119869 = 72Hz)

217ndash220 (m 2H CH2) EI-MS mz (relative intensity) 364

(M+ 23) 3435 (15) 2775 (17) 2590 (100) 2405 (16) 2255(20) 1994 (12) 1186 (26) 1035 (18) 910 (43) 771 (12) 651(13) 443 (21) IR (cmminus1) 3433 (N-H) 3097 2940 2860 1705(C=O) 1549 1493 1452 1411 1364 1128 1090 1008 846 787755 698 682 Anal calcd for C

20H17ClN4OC 6584 H 470

N 1536 Found C 6617 H 504 N 1503

(8) 2-(24-Dichloro-phenoxymethyl)-9-(3-phenyl-propyl)-19-dihydro-purin-6-one (2h)Mp 1882∘C Yield 66 1HNMR(600MHz DMSO-d

6) 120575 1251 (s 1H NH) 811 (s 1H CH)

758 (s 1H ArH) 713ndash734 (m 7H ArH) 514 (s 2H CH2)

411 (t 2H CH2 119869 = 66Hz) 250 (t 2H CH

2 119869 = 126Hz)

203ndash205 (m 2H CH2) EI-MSmz (relative intensity) 4304

(M+1 7) 4295 (M+ 7) 4280 (18) 3931 (10) 3445 (6) 2773(18) 2685 (33) 2669 (70) 2402 (17) 1986 (8) 1829 (8) 1642(72) 1618 (100) 1259 (12) 980 (15) 911 (28) 626 (21) IR(cmminus1) 3441 (N-H) 3098 3027 2939 2811 1718 (C=O) 16001532 1482 1456 1412 1301 818 753 699 504 Anal calcd forC21H18Cl2N4O2 C 5875 H 423 N 1305 Found C 5839

H 411 N 1312

(9) 2-Benzyl-9-(4-phenyl-butyl)-19-dihydro-purin-6-one (2i)Mp 1973∘C Yield 73 1HNMR (600MHz DMSO-d

6) 120575

1238 (s 1H NH) 804 (s 1H CH) 713ndash733 (m 10H ArH)412 (t 2H CH

2 119869 = 66Hz) 394 (s 2H CH

2) 256 (t 2H

CH2 119869 = 78Hz) 176ndash181 (m 2H CH

2) 146ndash151 (m 2H

CH2) EI-MS mz (relative intensity) 3581 (M+ 5551) 3301

(2866) 2672 (826) 2531 (2071) 2391 (2638) 2253 (4565)213 (966) 1090 (1593) 911 (10000) 770 (1093) 650 (1775)552 (737) 452 (1401) IR (cmminus1) 3427 (N-H) 3103 30612936 2860 1723 (C=O) 1578 1454 1412 1373 1357 1127 944748 698 658 Anal calcd for C

22H22N4O C 7372 H 619

N 1563 Found C 7379 H 614 N 1593

(10) 2-(3-Methoxy-benzyl)-9-(4-phenyl-butyl)-19-dihydro-purin-6-one (2j) Mp 1773∘C Yield 41 1H NMR(600MHz DMSO-d

6) 120575 1234 (s 1H NH) 803 (s 1H CH)

712ndash726 (m 6H ArH) 695 (s 1H ArH) 688 (d 1H ArH119869 = 36Hz) 681 (d 1H ArH 119869 = 39Hz) 413 (t 2H CH

2

119869 = 66Hz) 391 (s 2H CH2) 371 (s 3H OCH

3) 256 (t

2H CH2 119869 = 72Hz) 178ndash180 (m 2H CH

2) 148ndash151 (m

2H CH2) 13C NMR (100MHz DMSO-d

6) 120575 1597 1578

1569 1493 1422 1406 1385 1300 1287 1287 1262 12251213 1151 1126 554 433 407 348 295 283 EI-MSmz (relative intensity) 3882 (M+ 59) 3429 (22) 2839(32) 2690 (35) 2552 (74) 2395 (23) 2258 (60) 2124 (23)1828 (33) 1608 (28) 1473 (29) 1312 (37) 1090 (38) 1028(39) 906 (100) 766 (28) 443 (27) IR (cmminus1) 3433 (N-H)3085 2938 1673 (C=O) 1582 1453 1379 1257 1146 1049 747700 Anal calcd for C

23H24N4O2 C 7111 H 623 N 1442

Found C 7139 H 620 N 1478

(11) 2-(2-Methyl-benzyl)-9-(4-phenyl-butyl)-19-dihydro-pur-in-6-one (2k) Mp 2194∘C Yield 62 1HNMR (600MHzDMSO-d

6) 120575 1231 (s 1H NH) 802 (s 1H CH) 710ndash

725 (m 9H ArH) 406 (t 2H CH2 119869 = 66Hz) 396

(s 2H CH2) 232 (s 3H CH

3) 173ndash175 (m 2H CH

2)

142ndash145 (m 2H CH2) EI-MSmz (relative intensity) 3723

(M+ 1241) 3443 (1998) 2533 (1456) 2403 (10000) 2243(1422) 912 (2945) 764 (732) IR (cmminus1) 3440 (N-H) 31023026 2942 2860 1723 (C=O) 1582 1559 1493 1452 14101364 1159 1123 759 696 652 Anal calcd for C

23H24N4O

C 7417 H 649 N 1504 Found C 7421 H 645 N1534

(12) 2-(24-Dichloro-phenoxymethyl)-9-(4-phenyl-butyl)-19-dihydro-purin-6-one (2l) Mp 2086∘C Yield 72 1HNMR (600MHz DMSO-d

6) 120575 1251 (s 1H NH) 809 (s

1H CH) 760 (s 1H ArH) 736 (d 1H ArH 119869 = 45Hz)712ndash725 (m 6H ArH) 514 (s 2H CH

2) 410 (t 2H CH

2

119869 = 6Hz) 250ndash253 (2H CH2) 169ndash172 (m 2H CH

2)

8 Journal of Chemistry

140ndash144 (m 2H CH2) EI-MSmz (relative intensity) 4436

(M+ 71) 4423 (51) 3724 (29) 3692 (40) 3564 (99) 3288(54) 2962 (28) 2561 (100) 2390 (44) 2118 (70) 1608 (39)1032 (72) 912 (37) 773 (59) 762 (74) 513 (24) 432 (36)IR (cmminus1) 3437 (N-H) 3098 3028 2932 2862 1718 (C=O)1602 1481 1456 1411 1234 820 720 699 651 506 Analcalcd for C

22H20Cl2N4O2 C 5960 H 455 N 1264 Found

C 5931 H 423 N 1231

(13) 2-(4-Chloro-phenyl)-9-(4-phenyl-butyl)-19-dihydro-pur-in-6-one (2m)Mp 2281∘C Yield 30 1HNMR (600MHzDMSO-d

6) 120575 1252 (s 1H NH) 814 (s 1H CH) 811 (d 2H

119869 = 42Hz) 761 (d 2H 119869 = 42Hz) 714ndash724 (m 5H ArH)423 (t 2H CH

2 119869 = 66Hz) 262 (t 2H CH

2 119869 = 72Hz)

185ndash187 (m 2H CH2) 154ndash157 (m 2H CH

2) EI-MS mz

(relative intensity) 3793 (M+1 24) 3781 (M+ 49) 3379 (30)2749 (14) 2593 (38) 2243 (3) 1643 (13)1093 (17) 911 (100)IR (cmminus1) 3435 (N-H) 3103 3026 2937 2859 1688 (C=O)1600 1549 1494 1454 1411 1367 1090 1011 842 787 732 699498 472 Anal calcd for C

21H19ClN4O C 6658 H 505 N

1479 Found C 6628 H 488 N 1446

(14) 2-Benzyl-9-(1-benzyl-2-hydroxy-propyl)-19-dihydro-pur-in-6-one (2n) Mp 2252∘C Yield 66 1HNMR (600MHzCDCl

3) 120575 1249 (s 1H NH) 683ndash742 (m 11H ArH) 438ndash

440 (m 2H CH2) 413 (s 2H CH

2) 321ndash331 (m 2H CH

2)

139 (d 3H CH3 119869 = 3Hz) EI-MS mz (relative intensity)

3744 (M+ 22) 3304 (27) 3292 (24) 2833 (7) 2263 (83)2250 (57) 1028 (21) 911 (100) 770 (17) 650 (22) 453 (18)IR (cmminus1) 3214 1677 (C=O) 1591 1455 1374 716 691 Analcalcd for C

22H22N4O2 C 7057 H 592 N 1496 Found C

7039 H 584 N 1477

(15) 9-(1-Benzyl-2-hydroxy-propyl)-2-(2-methyl-benzyl)-19-dihydro-purin-6-one (2o) Mp 866∘C Yield 88 1HNMR (600MHz DMSO-d

6) 120575 1224 (s 1H NH) 799 (s

1H CH) 688ndash721 (m 10H ArH) 442ndash445 (m 1H CH)393ndash404 (m 1H CH) 391 (s 2H CH

2) 321ndash323 (m

1H CH) 232 (s 3H CH3) 091 (d 3H CH

3 119869 = 3Hz)

13C NMR (100MHz DMSO-d6) 120575 1577 1565 1493 1401

1384 13699 1357 1305 1294 1289 1285 1273 1265 12631223 684 631 381 356 207 199 EI-MS mz (relativeintensity) 3883 (M+ 99) 3426 (25) 2403 (100) 2234 (26)2123 (21) 1313 (35) 911 (17) 768 (16) 429 (17) IR (cmminus1)3389 (N-H) 3087 2970 1680 (C=O) 1586 1495 1456 14081372 1154 1124 746 701 650 Anal calcd for C

23H24N4O2

C 7111 H 623 N 1442 Found C 7109 H 650 N1407

(16) 2-Benzyl-9-[1-(1-hydroxy-ethyl)-4-phenyl-butyl]-19-dihy-dro-purin-6-one (2p) Mp 1804∘C Yield 78 1H NMR(600MHz DMSO-d

6) 120575 1238 (s 1H NH) 805 (s 1H CH)

702ndash733 (m 10H ArH) 514 (d 1H OH 119869 = 54Hz) 422ndash426 (m 1H CH) 394 (3H CH

2+CH) 241ndash245 (m 2H

CH2) 200ndash206 (m 2H CH

2) 121ndash129 (m 2H CH

2) 087

(d 3H CH3 119869 = 6Hz) IR (cmminus1) 3397 (N-H) 3085 3026

2934 1666 (C=O) 1581 1402 1372 749 699 Anal calcd forC24H26N4O2 C 7162 H 651 N 1392 Found C 7139 H

658 N 1404

(17) 2-(4-Chloro-phenyl)-9-[1-(1-hydroxy-ethyl)-4-phenyl-bu-tyl]-19-dihydro-purin-6-one (2q) The Mixture of Isomers(1 1) Mp 2634∘C Yield 39 1HNMR (600MHz DMSO-d6) 120575 1254 (s 1H NH) 816 (s 1H CH) 811ndash813 (m 3H

ArH) 807 (s 1H ArH) 761 (d 4H ArH) 515 (dd 1H OH119869 = 6Hz) 435ndash445 (m 1H CH) 404ndash410 (m 1H CH)251ndash263 (m 2H CH

2) 187ndash211 (m 2H CH

2) 129ndash141 (m

2H CH2) 095 (d 3H CH

3 119869 = 6Hz) EI-MS mz (relative

intensity) 4230 (M+ 4) 2469 (3) 1381 (7) 1042 (7) 911(100) 772 (10) 650 (17) 512 (6) 451 (37) IR (cmminus1) 3436(N-H) 3084 2930 1687 (C=O) 1599 1548 1492 1367 1089840 699 549 Anal calcd for C

23H23ClN4O2 C 6532 H

548 N 1325 Found C 6566 H 659 N 1358

413 General Procedures of Synthesis of 2r and 2s

(1) 2-Benzyl-9-(1-benzyl-2-oxo-propyl)-19-dihydro-purin-6-one (2r) 15mL of absolute dichloromethane and triethyl-amine (522 g 639mmol) was added to 2n (058 g155mmol) and the mixture was cooled to 0∘C using anice-bath 15mL of DMSO and 326 g of pyridinesulphurtrioxide complex were added and the mixture was thenunder an atmosphere of nitrogen stirred in ice bath for 1 hand heated at 60∘C for further 6 h 20mL of water was addedto the solution and the mixture was extracted three timeswith in each case 25mL of dichloromethane The organicphases were washed with water and then dried over sodiumsulfate and concentrated using a rotary evaporatorThe crudeproduct was purified by chromatography to give 043 g oftitle compound

Mp 60∘C Yield 747 1H NMR (600MHz CDCl3)

120575 1284 (br 1H NH) 775 (s 1H CH) 696ndash738 (m 10HArH) 540 (dd 1H CH 119869 = 54Hz 119869 = 102Hz) 407 (s2H CH

2) 357 (dd 1H CH 119869 = 54Hz 119869 = 144Hz) 329

(dd 1H CH 119869 = 102Hz 119869 = 138Hz) 218 (s 3H CH3)

13C NMR (100MHz CDCl3) 120575 20247 15949 14946 1575

14962 1391 1355 1353 1293 1289 1287 1274 1273 1221643 413 369 280 EI-MS mz (relative intensity) 3720(M+ 16) 3292 (100) 2249 (38) 2127 (8) 1028 (33) 911 (79)769 (19) 650 (21) 512 (7) 432 (43) IR (cmminus1) 3440 (N-H)3087 3029 2922 1684 (C=O) 1580 1455 1410 717 699 Analcalcd for C

22H20N4O2 C 7095 H 541 N 1504 Found C

7076 H 573 N 1456

(2) 9-(1-Benzyl-2-oxo-propyl)-2-(2-methyl-benzyl)-19-dihy-dro-purin-6-one (2s) 2s was prepared by oxidating 2o usingsimilar method to that of compound 2r

Mp 2090∘C Yield 72 1H NMR (600MHz CDCl3)

120575 1212 (s 1H NH) 772 (s 1H CH) 694ndash728 (m 9H ArH)530 (dd 1H CH

2 119869 = 54Hz 119869 = 9Hz) 352 (dd 1H CH

2

119869 = 54Hz 119869 = 144Hz) 324 (dd 1H CH2 119869 = 138Hz

119869 = 102Hz) 231 (s 3H CH3) 210 (s 3H CH

3CO) EI-MS

mz (relative intensity) 3864 (M+ 8) 3428 (17) 2985 (13)2253 (30) 1995 (9) 1713 (12) 1432 (19) 1033 (35) 910 (100)772 (10) 652 (12) 436 (8) 13C NMR (101MHz DMSO-d6) 120575 2036 1576 1571 1492 1405 1370 1356 1305 1294

1290 1287 1273 1270 1263 1223 649 381 351 275 199IR (cmminus1) 3440 (N-H) 3081 3025 2905 1731 (C=O) 16601587 1458 1408 1354 1234 1174 748 732 655 Anal calcd for

Journal of Chemistry 9

C23H22N4O2 C 7148 H 574 N 1450 Found C 7131 H

609 N 1448

414 The Procedure for Synthesis of 2c-1 and 2c-2 [26] Amixture of 2c (022 g) and NaH (70 004 g) in 6mL of dryDMF was stirred at room temperature for 05 h then allybromide (015 g) was added to this solution and stirred for45 h at the same temperature And ice-water (100mL) wasadded to the solution with stirring the solid deposited wasfiltered andwashedwithwaterThe two regioisomers croppedwere separated by column chromatography on silica gel usingthe mixture of petroleum ether and EtOAc as eluting solventto afford the corresponding 2c-1 (008 g) and 2c-2 (013 g) asthe first and second fractions respectively

(1) 1-Allyl-9-benzyl-2-(2-methyl-benzyl)-19-dihydro-purin-6-one 2c-1 Mp 82∘C Yield 33 1HNMR (600MHz DMSO-d6) 120575 821 (s 1H CH) 702ndash730 (m 9H ArH) 599ndash600 (m

1H CH2) 509 (dd 2H CH

2 119869 = 522Hz 119869 = 624Hz) 508

(s 2H CH2) 475ndash498 (m 2H CH

2) 420 (s 3H CH

3) 214

(s 3H CH3) EI-MS mz (relative intensity) 3701 (M+ 16)

3550 (10) 2789 (6) 2653 (8) 2382 (6) 1711 (19) 1050 (21)913 (100) 768 (8) 650 (22) 442 (6) IR (cmminus1) 3442 30852945 1689 (C=O) 1553 1515 1354 1186 750 718 Anal calcdfor C

23H22N4O C 7457 H 599 N 1512 Found C 7391

H 579 N 1539

(2) 6-Allyloxy-9-benzyl-2-(2-methyl-benzyl)-9H-purine 2c-2Mp 1335∘C Yield 53 1H NMR (600MHz DMSO-d

6)

120575 844 (s 1H CH) 711ndash731 (m 9H ArH) 602ndash609 (m 1HCH) 539 (s 2H CH

2) 536 (d 1H CH 119869 = 12Hz) 524 (d

1H CH 119869 = 102Hz) 499 (d 1H CH2) 417 (s 2H CH

2)

232 (s 3H CH3) EI-MS mz (relative intensity) 3702 (M+

3) 1288 (5) 1051 (12) 911 (100) 893 (10) 651 (25) 552 (8)441 (18) IR (cmminus1) 3417 3077 2944 1597 1574 1445 14101375 1245 1065 935 741 643 Anal calcd for Anal calcd forC23H22N4O C 7457 H 599 N 1512 Found C 7439 H

553 N 1498

42 Enzymatic Activities of Recombinant Human PDE2 Usingan In Vitro Enzymatic Assay The enzyme inhibitory activ-ities of the synthesized compounds were evaluated againstPDE2 using recombinant human PDE2 by BPS BioscienceInc (San Diego California USA) using fluorescence polar-ization method Tested compounds were dissolved in DMSOand diluted in assay buffer (final DMSO concentration 1final inhibitor concentration 10120583M) PDE activity assayswere performed in duplicate at each concentration Thereaction was conducted at room temperature for 60 minutesin a 50 120583L mixture containing reaction buffer 100 nM FAM-cAMP as substrate 1 120583M cGMP recombinant human PDE2(075 ngreaction) and a tested compound Fluorescenceintensity was measured at an excitation of 485 nm and anemission of 528 nm using BioTek Synergytrade 2 microplatereader (San Diego California USA)

Fluorescence intensity was converted to fluorescencepolarization using the Gen5 softwareThe fluorescence polar-ization data were analyzed using the computer softwareGraphPad Prism (GraphPad Software Inc San Diego CA)

The value of fluorescence polarization (FP119905) from the reac-

tions without the compound was defined as 100 activityIn the absence of PDE2 and the compound the value offluorescent polarization (FP

119887) was defined as 0 activity

The percent activity in the presence of the compound wascalculated according to the following equation activity =(FP minus FP

119887)(FP119905minus FP119887) times 100 In the equation FP is the

fluorescence polarization in the presence of the compound

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

The research was supported in part by National Institutesof Health (Grant RC1MH088480) National Natural ScienceFoundation of China (Grant 21273089) and the Special Fundfor Basic Scientific Research of Central Colleges South-Central University for Nationalities (CZY14004)

References

[1] M J Speakman ldquoPDE5 inhibitors in the treatment of LUTSrdquoCurrent Pharmaceutical Design vol 15 no 30 pp 3502ndash35052009

[2] Y-J Wang Y-L Jiang H-F Tang C-Z Zhao and J-Q ChenldquoZl-n-91 a selective phosphodiesterase 4 inhibitor suppressesinflammatory response in a COPD-like rat modelrdquo Interna-tional Immunopharmacology vol 10 no 2 pp 252ndash258 2010

[3] A T Bender and J A Beavo ldquoCyclic nucleotide phosphodi-esterases molecular regulation to clinical userdquo PharmacologicalReviews vol 58 no 3 pp 488ndash520 2006

[4] C Lugnier ldquoCyclic nucleotide phosphodiesterase (PDE) super-family a new target for the development of specific therapeuticagentsrdquo Pharmacology amp Therapeutics vol 109 no 3 pp 366ndash398 2006

[5] K Omori and J Kotera ldquoOverview of PDEs and their regula-tionrdquo Circulation Research vol 100 no 3 pp 309ndash327 2007

[6] H L Trong N Beier W K Sonnenburg et al ldquoAmino acidsequence of the cyclic GMP stimulated cyclic nucleotide phos-phodiesterase from bovine heartrdquo Biochemistry vol 29 no 44pp 10280ndash10288 1990

[7] E Reyes-Irisarri M Markerink-Van Ittersum G Mengod andJ De Vente ldquoExpression of the cGMP-specific phosphodi-esterases 2 and 9 in normal and Alzheimerrsquos disease humanbrainsrdquoThe European Journal of Neuroscience vol 25 no 11 pp3332ndash3338 2007

[8] F G Boess M Hendrix F-J van der Staay et al ldquoInhibitionof phosphodiesterase 2 increases neuronal cGMP synapticplasticity and memory performancerdquo Neuropharmacology vol47 no 7 pp 1081ndash1092 2004

[9] K Domek-Łopacinska and J B Strosznajder ldquoThe effect ofselective inhibition of cyclic GMP hydrolyzing phosphodi-esterases 2 and 5 on learning and memory processes and nitricoxide synthase activity in brain during agingrdquo Brain Researchvol 1216 pp 68ndash77 2008

[10] A Masood Y Huang H Hajjhussein et al ldquoAnxiolytic effectsof phosphodiesterase-2 inhibitors associated with increased

10 Journal of Chemistry

cGMP signalingrdquo Journal of Pharmacology and ExperimentalTherapeutics vol 331 no 2 pp 690ndash699 2009

[11] A S R Sierksma K Rutten S Sydlik et al ldquoChronic phospho-diesterase type 2 inhibition improves memory in the APPswePS1dE9mouse model of Alzheimerrsquos diseaserdquoNeuropharmacol-ogy vol 64 pp 124ndash136 2013

[12] T Podzuweit P Nennstiel and A Muller ldquoIsozyme selectiveinhibition of cGMP-stimulated cyclic nucleotide phosphodi-esterases by erythro-9-(2-hydroxy-3-nonyl) adeninerdquo CellularSignalling vol 7 no 7 pp 733ndash738 1995

[13] J Seybold D Thomas M Witzenrath et al ldquoTumor necrosisfactor-120572-dependent expression of phosphodiesterase 2 role inendothelial hyperpermeabilityrdquo Blood vol 105 no 9 pp 3569ndash3576 2005

[14] M Abarghaz S Biondi J Duranton E Limanton C Mon-dadori and P Wagner ldquoPreparation of benzo[14]diazepin-2-one derivatives as phosphodiesterase PDE2 inhibitorsrdquoNeuro3D Fr Application EP 1548011 p 46 2005

[15] O A H Reneerkens K Rutten E Bollen et al ldquoInhibitionof phoshodiesterase type 2 or type 10 reverses object memorydeficits induced by scopolamine or MK-801rdquo Behavioural BrainResearch vol 236 no 1 pp 16ndash22 2013

[16] J Pandit M D Forman K F Fennell K S Dillman andF S Menniti ldquoMechanism for the allosteric regulation ofphosphodiesterase 2A deduced from the X-ray structure of anear full-length constructrdquo Proceedings of the National Academyof Sciences of the United States of America vol 106 no 43 pp18225ndash18230 2009

[17] M S Plummer J Cornicelli H Roark et al ldquoDiscovery ofpotent selective bioavailable phosphodiesterase 2 (PDE2)inhibitors active in an osteoarthritis pain model Part I Trans-formation of selective pyrazolodiazepinone phosphodiesterase4 (PDE4) inhibitors into selective PDE2 inhibitorsrdquo Bioorganicamp Medicinal Chemistry Letters vol 23 no 11 pp 3438ndash34422013

[18] J Zhu P Rehse and M He PDE2 Catalytic DomainPDE2-Specific Inhibitor Composite Crystal and its Growth MethodAmerican Chemical Society (ACS) Shanghai MedicilonShanghai China 2014

[19] T Banerjee S Chaudhuri M Moore S Ray P S Chatterjeeand P Roychowdhury ldquoSynthesis and crystal structures of5-amino-1-(2-hydroxyethyl)imidazole-4-carboxamide and 5-amino-1-(2-chloroethyl)-4-cyanoimidazolerdquo Journal of Chemi-cal Crystallography vol 29 no 12 pp 1281ndash1286 1999

[20] B Alhede F P Clausen J Juhl-Christensen K K McCluskeyand H F Preikschat ldquoA simple and efficient synthesis of9-substituted guanines Cyclodesulfurization of 1-substituted5-[(thiocarbamoyl)amino]imidazole-4-carboxamides underaqueous basic conditionsrdquo Journal of Organic Chemistry vol56 no 6 pp 2139ndash2143 1991

[21] E Shaw ldquoObservations on the cyclization of a substituted120572-formamidoamidine to aminoimidazolecarboxamide deriva-tivesrdquo Journal of Organic Chemistry vol 30 no 10 pp 3371ndash3373 1965

[22] U Niewoehner E Bischoff J Huetter E Perzborn and HSchuetz ldquoPreparation of Purin-6-one derivatives for treatmentof cardiovascular and urogenital diseasesrdquo EP 771799 BayerAG Leverkusen Germany pp50 1997

[23] X Y Zhao X Chen G-F Yang and C-G Zhan ldquoStructuralassignment of 6-oxy purine derivatives through computational

modeling synthesis X-ray diffraction and spectroscopic anal-ysisrdquo Journal of Physical Chemistry B vol 114 no 20 pp 6968ndash6972 2010

[24] J Beltman D E Becker E Butt et al ldquoCharacterization ofcyclic nucleotide phosphodiesterases with cyclic GMP analogstopology of the catalytic domainsrdquo Molecular Pharmacologyvol 47 no 2 pp 330ndash339 1995

[25] X-j Zhao X Chen G-f Yang and C-g Zhan ldquoSynthesisof 9-benzyl-2-substituted-purin-6-one derivatives and theirbioactivity and molecular docking as potential human phos-phodiesterase-2 inhibitorsrdquo Zhongguo Yaowu Huaxue Zazhivol 23 pp 277ndash285 2013

[26] R Islam N Ashida and T Nagamatsu ldquoSynthesis and regio-selective N- and O-alkylation of 3-alkyl-5-phenyl-3H-[123]triazolo[45-d]pyrimidin-7(6H)-ones and 2-phenyl-9-propyl-9H-purin-6(1H)-one with evaluation of antiviral and antitumoractivitiesrdquo Tetrahedron vol 64 no 42 pp 9885ndash9894 2008

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