Multicomponent reactions for the synthesis of pyrroles Vero´nica Este´vez, Mercedes Villacampa and J. Carlos Mene´ndez* Received 26th February 2010 DOI: 10.1039/b917644f Multicomponent reactions are one of the most interesting concepts in modern synthetic chemistry and, as shown in this critical review, they provide an attractive entry into pyrrole derivatives, which are very important heterocycles from many points of view including medicinal and pharmaceutical chemistry and materials science (97 references). 1. Introduction To set the rest of the article in context, we will make in this section some general remarks about multicomponent reactions and the importance of pyrrole. 1.1 Multicomponent reactions Present-day requirements for new synthetic methods go far beyond the traditional ones of chemo-, regio- and stereo- selectivity, and can be summarized as follows: 1. Use of simple and readily available starting materials. 2. Experimental simplicity. 3. Possibility of automation. 4. Favourable economic factors, including the cost of raw materials, human resources and energy. 5. Low environmental impact: use of environmentally friendly solvents, atom economy. For this reason, the creation of molecular diversity and complexity from simple and readily available substrates is one of the major current challenges of organic synthesis, and hence the development of processes that allow the creation of several bonds in a single operation has become one of its more attractive goals. Multicomponent reactions (MCRs) 1–5 can be defined as convergent chemical processes where three or more reagents are combined in such a way that the final product retains significant portions of all starting materials. Therefore, they lead to the connection of three or more starting materials in a single synthetic operation with high atom economy and bond-forming efficiency, thereby increasing molecular diversity and complexity in a fast and often experimentally simple fashion. 6,7 For this reason, multicomponent reactions are particularly well suited for diversity-oriented synthesis, 8–10 and the exploratory power arising from their conciseness makes them also very powerful for library synthesis aimed at carrying out structure–activity relationship (SAR) studies of drug-like compounds, which are an essential part of the research performed in pharmaceutical and agrochemical companies. 11,12 For all these reasons, the development of new multicomponent reactions is rapidly becoming one of Departamento de Quı´mica Orga ´nica y Farmace ´utica, Facultad de Farmacia, Universidad Complutense, 28040 Madrid, Spain. E-mail: [email protected]; Fax: +34 91 3941822; Tel: +34 91 3941840 Vero´ nica Este´vez Vero ´nica Este´vez was born in Madrid, and studied Pharmacy at Universidad Complutense, Madrid (UCM). She has finished a two-year postgraduate course in Medicinal Chemistry and is currently working on her PhD thesis at the Department of Organic and Medicinal Chemistry at the School of Pharmacy in UCM, under the supervision of Drs Villacampa and Mene´ndez. Her research topic deals with the develop- ment of new multicomponent reactions for the synthesis of pyrroles and their application to the preparation of bioactive compounds. Mercedes Villacampa Mercedes Villacampa was born in Madrid. She studied Pharmacy at UCM and then Optics at the same University. For her PhD thesis, she worked on the synthesis of natural product-based seroto- nin analogues. After posto- doctoral studies with Professor Nicholas Bodor at the University of Florida at Gainesville, she obtained a position of Profesor Titular at the Organic and Medicinal Chemistry Department at UCM. She has also done post- doctoral work at the laboratory of Professor Kendall N. Houk at the University of California at Los Angeles (UCLA). Her research interests include computational chemistry and the development of new synthetic methodologies, including multi- component reactions, for their application to the preparation of bioactive heterocycles. 4402 | Chem. Soc. Rev., 2010, 39, 4402–4421 This journal is c The Royal Society of Chemistry 2010 CRITICAL REVIEW www.rsc.org/csr | Chemical Society Reviews Downloaded by University of Oxford on 26 October 2010 Published on 05 July 2010 on http://pubs.rsc.org | doi:10.1039/B917644F View Online
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Multicomponent reactions for the synthesis of pyrroles
Veronica Estevez, Mercedes Villacampa and J. Carlos Menendez*
Received 26th February 2010
DOI: 10.1039/b917644f
Multicomponent reactions are one of the most interesting concepts in modern synthetic chemistry
and, as shown in this critical review, they provide an attractive entry into pyrrole derivatives,
which are very important heterocycles from many points of view including medicinal and
pharmaceutical chemistry and materials science (97 references).
1. Introduction
To set the rest of the article in context, we will make in this
section some general remarks about multicomponent reactions
and the importance of pyrrole.
1.1 Multicomponent reactions
Present-day requirements for new synthetic methods go far
beyond the traditional ones of chemo-, regio- and stereo-
selectivity, and can be summarized as follows:
1. Use of simple and readily available starting materials.
2. Experimental simplicity.
3. Possibility of automation.
4. Favourable economic factors, including the cost of raw
materials, human resources and energy.
5. Low environmental impact: use of environmentally
friendly solvents, atom economy.
For this reason, the creation of molecular diversity and
complexity from simple and readily available substrates is one
of the major current challenges of organic synthesis, and hence
the development of processes that allow the creation of several
bonds in a single operation has become one of its more
attractive goals.
Multicomponent reactions (MCRs)1–5 can be defined as
convergent chemical processes where three or more reagents
are combined in such a way that the final product retains
significant portions of all starting materials. Therefore, they
lead to the connection of three or more starting materials in a
single synthetic operation with high atom economy and
diversity and complexity in a fast and often experimentally
simple fashion.6,7 For this reason, multicomponent reactions
are particularly well suited for diversity-oriented synthesis,8–10
and the exploratory power arising from their conciseness
makes them also very powerful for library synthesis aimed at
carrying out structure–activity relationship (SAR) studies of
drug-like compounds, which are an essential part of the
research performed in pharmaceutical and agrochemical
companies.11,12 For all these reasons, the development of
new multicomponent reactions is rapidly becoming one of
Departamento de Quımica Organica y Farmaceutica,Facultad de Farmacia, Universidad Complutense, 28040 Madrid,Spain. E-mail: [email protected]; Fax: +34 91 3941822;Tel: +34 91 3941840
Veronica Estevez
Veronica Estevez was bornin Madrid, and studiedPharmacy at UniversidadComplutense, Madrid (UCM).She has finished a two-yearpostgraduate course inMedicinal Chemistry and iscurrently working on herPhD thesis at the Departmentof Organic and MedicinalChemistry at the School ofPharmacy in UCM, under thesupervision of Drs Villacampaand Menendez. Her researchtopic deals with the develop-ment of new multicomponent
reactions for the synthesis of pyrroles and their application tothe preparation of bioactive compounds.
Mercedes Villacampa
Mercedes Villacampa wasborn in Madrid. She studiedPharmacy at UCM and thenOptics at the same University.For her PhD thesis, sheworked on the synthesis ofnatural product-based seroto-nin analogues. After posto-doctoral studies withProfessor Nicholas Bodor atthe University of Florida atGainesville, she obtained aposition of Profesor Titularat the Organic and MedicinalChemistry Department atUCM. She has also done post-
doctoral work at the laboratory of Professor Kendall N. Houk atthe University of California at Los Angeles (UCLA). Herresearch interests include computational chemistry and thedevelopment of new synthetic methodologies, including multi-component reactions, for their application to the preparation ofbioactive heterocycles.
4402 | Chem. Soc. Rev., 2010, 39, 4402–4421 This journal is �c The Royal Society of Chemistry 2010
CRITICAL REVIEW www.rsc.org/csr | Chemical Society Reviews
the frontiers of organic synthesis. While a large part of the
work developed in this field is focused on reactions using
isonitriles as one of the starting materials and leading to
peptide-like structures, recent years have witnessed a steady
growth in the development of MCRs that lead directly
to heterocycles,13–16 the most important single class of
compounds in the development of bioactive substances.
1.2 Importance of pyrrole
Pyrrole is one of the most important simple heterocycles,
which is found in a broad range of natural products and drug
molecules, and is also of growing relevance in materials
science. It was first isolated in 1857 from the products of bone
pyrolysis, and identified as biologically relevant when it was
recognized as a structural fragment of heme and chlorophyll.
The current importance of pyrrole can be summarized in the
points that are detailed below.
(a) The pyrrole nucleus is widespread in nature, and, as
previously mentioned, is the key structural fragment of heme
and chlorophyll, two pigments essential for life. Some
representative examples of pyrrole-containing secondary
metabolites are summarized in Fig. 1. They include some
antibacterial 3-halopyrroles such as pentabromopseudodiline
and pioluteorine, both isolated from bacterial sources. Pyrrole
moieties are particularly prominent in marine natural
products, including dimeric structures such as nakamuric
acid17 and the axially chiral marinopyrroles, which showed
good activity against metacillin-resistant Staphylococcus
aureus strains.18 We will finally mention the storniamide
family, isolated from a variety of marine organisms (mollusks,
ascidians, sponges) and containing 3,4-diarylpyrrole frag-
ments. A number of O-methylated analogues of storniamide
A have shown potent activity as inhibitors of the multidrug
resistance (MDR) phenomenon,19 which can be considered as
the main obstacle to successful anticancer chemotherapy. For
this reason, there is much current interest in the development
of new MDR modulators.20–22
(b) One interesting property of natural and unnatural
products containing polypyrrole structural fragments is that
they are often involved in coordination and molecular recog-
nition phenomena. Besides the classical example of the tetra-
pyrrole nucleus of the porphyrins and hemoglobin, we will
also mention the case of the bacterial red pigment prodigiosin,
synthesized by bacteria belonging to the Serratia genus, and
which has antibiotic properties.23 This compound has been
shown to behave as a transporter of chloride anions and
protons across phospholipid membranes thanks to the asso-
ciation of its protonated form with chloride anion, leading to a
lipophilic species (Scheme 1).24 The torsional flexibility asso-
ciated with polypyrrole systems linked by peptide bonds is also
key to molecular recognition phenomena involved in the
interaction with DNA of the prototype minor groove natural
binders netropsin and distamycin and related drugs.25
(c) Besides the above mentioned natural products, pyrrole
substructures are present in a large number of bioactive
compounds including HIV fusion inhibitors26 and antituber-
cular compounds,27,28 among many others. As examples of
pyrrole derived drugs, we will mention the non-steroidal
antiinflamatory compound tolmetin, the anticancer drug
candidate tallimustine (related to the previously mentioned
natural product distamycin) and the cholesterol-lowering agent
atorvastatin, one of the top-selling drugs worldwide (Fig. 2).
Fig. 1 Some pyrrole-containing bioactive natural products.
J. Carlos Menendez
Jose Carlos Menendez wasborn in Madrid and obtaineddegrees in Pharmacy andChemistry, followed by aPhD in Pharmacy fromUCM. After a postdoctoralstay at the group of ProfessorSteven Ley at ImperialCollege, he returned as aProfesor Titular to theOrganic and Medicinal Chem-istry Department at UCM,where he has pursued hiscareer ever since. His researchinterests deal mostly withsynthetic work related to the
development of new antitumour drugs and ligands of prionprotein. Other projects pursued in his group place emphasis onthe development of new synthetic methodology, including workon CAN as a catalyst for synthesis and on new domino andmulticomponent reactions for the preparation of biologicallyrelevant compounds.
This journal is �c The Royal Society of Chemistry 2010 Chem. Soc. Rev., 2010, 39, 4402–4421 | 4403
developments in this field will probably involve the application
of multicomponent-based strategies to target-oriented
synthesis. We hope that this review will serve to stimulate
research in this fascinating and very useful area of organic
synthesis.
Notes and references
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