27 No. 2
Natural Products and Biodiversity
Virinder S. Parmar (editor)
Pure and Applied Chemistry
Vol. 77, No. 1, pp. 1-344 (2005)
Nature has vast hidden treasures that may benefit humanity. Bioresources have tremendous potential to lead to the development of new pharmaceuticals, nutraceuticals, and agrochemicals. An impressive number of modern drugs have been isolated from natural sources, particularly from plants. Besides plant materials, the past century has seen an increasing role played by microorganisms in the production of antibiotics and other drugs for the treatment of serious diseases. More recently, marine organisms have proved to be a rich source of novel bioactive agents.
To address these issues, the University of Delhi in collaboration with the Council of Scientific & Industrial Research (CSIR, India) organized a joint meeting of the IUPAC 4th Conference on Biodiversity and the 23rd Conference on the Chemistry of Natural Products, which was held 26-31 January 2004 in Delhi. The nearly 1000 scientists and scholars from around the world who attended enjoyed around 175 plenary and invited lectures by eminent scientists and about 450 poster presentations.
The conference themes covered a range of topics, such as biodiversity and bio-prospecting, innovative utilization of bio-resources, novel strategies in integrated pest management, bioremediation of industrial and nuclear waste, and green chemistry. A collection of papers based upon lectures presented at the conference is published in the January 2005 issue of Pure and Applied Chemistry. Following are summaries of selected papers from the issue.
Natural Products Chemistry
The curative properties of plants have unfolded gradually over many centuries and, despite the wealth of knowledge that has accumulated through traditional medicine, many species in the plant kingdom still remain to be surveyed systematically for their biologically active chemical constituents. The conference featured many presentations by leading scientists in this area. For example, C. Mahidol, B. Sener, and G.M. Cragg highlighted research intended to discover therapeutic agents in some Thai plants and Turkish marine organisms. Atta-Ur-Rahman explained how his group has identified several new classes of potent cholinesterase, urease, phosphodiesterase, glucuronidase, and prolyl endopeptidase inhibitors from natural sources. E. Dagne presented results of a phytochemical examination of Commiphora myrrha (Nees) Engl. He has isolated novel furanosesquiterpenoids from this plant source, which show significant analgesic properties.
Enzymes have been shown to have a wide variety of applications in diverse types of organic reactions, including the preparation of polymeric materials. The stereo-, regio-, and chemoselectivity of enzymes observed in small molecule reactions have also been observed in the synthesis of polymeric materials. The increasing diversity of commercially available enzymes makes possible greater control of molecular architecture.
A.C. Watterson described an extremely flexible chemo-enzymatic synthesis of several families of PEG based amphiphilic polymers with well-defined structures. The methods permit variation of molecular structure over a wide range of monomer units, essentially permitting properties to be tuned to a particular application, for example in the design of drug delivery systems. These block copolymers have been used to target drugs into cells and modify drug intracellular distribution to increase drug-specific activity.
Bioactivity of Natural Products
In recent years, many researchers have shown the detrimental effects of light, dioxygen, and radicals on humans. The consequences may be the onset of cancer, diabetes, cataract, atherosclerosis, inflammation, and possibly many other diseases. Phenols are widely employed by living organisms (as well as food industries) to limit the effects of reactive oxygen species.
M. Foti’s paper describes the mechanism of action of the antioxidant activity of phenols and discusses the effect of solvents on the antioxidant activity of compounds. In another paper, H.G. Raj shares his recent discovery of a unique membrane-bound enzyme that catalyzes the transfer of acetyl groups from polyphenolic peracetates to certain enzyme proteins, resulting in the modulation of the catalytic activity. This enzyme, called Transacetylase, was found to be ubiquitous in the tissues of several animal species and a variety of cells.
Malaria is a major killer of children in the tropical world and remains a significant scientific challenge. V.S. Chauhan’s paper highlights the importance and urgency of developing malarial vaccine programs. Since glycolysis is the primary source of ATP for malarial parasite during the intraerythrocytic stage, glycolytic enzymes present themselves as potential targets for inhibitors. P. Balaram sheds light on Plasmodium falciparum triosephosphate isomerase, a central enzyme in glycolytic pathway. K. Chibale’s paper describes the synthesis and antimalarial screening of a series of novel β-amino alcohol derivatives, which show improved antiplasmodial activity.
Among important challenges now facing synthetic organic chemists is the need to design and produce chemically well-defined molecules that are useful in medicine, agriculture, and biology. In his paper, D. Basavaiah describes how he has successfully employed the Baylis-Hillman reaction, an atom economical carbon-carbon bond forming reaction between the a-position of an activated alkene and a carbon electrophile, for the synthesis of an interesting class of heterocyclic molecules of biological importance.
In another paper, E. van der Eycken describes the Diels-Alder reactions of polymer-bound 2(1H)-pyrazinones with acetylenes, which offers an efficient solid-phase methodology for the separation of the resulting products (i.e., pyridines and pyridones) using the concept of traceless linking. Upon reaction, pyridines are released into solution phase, whereas pyridones stay on the solid support and can be cleaved from the resin, affording the final compounds in moderate to high purities. He compares the pros and cons of microwave-assisted protocol with the conventional thermal method.
H.B. Kagan’s paper focuses on the use of Me3SiCN. He describes the asymmetric reduction of ketones by trimethoxysilane in the presence of catalytic amounts of monolithium salt of (R)-BINOL. He also used this catalyst and related compounds in the trimethylsilylcyanation of various aromatic aldehydes to synthesize chiral cyanohydrins. E.J. Thomas’ paper describes the results of using allyl metal reagents for the control of remote stereocenters, with applications in the synthesis of complex natural products (e.g., epothilone B and pamamycin 607).
The papers contained in this issue of PAC offer encouraging evidence that natural products research is vigorous and rich with future promise.
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