Volume 77, Issue 1

The gradual transition from the long-standing use of monodrug therapy in classical medicine to the new concept of a multidrug and multitarget therapy has great implications for the research strategies of natural products chemistry and phytomedicine. The rationalization of the new strategies, however, requires great efforts in: standardization of mono- and multiphytopreparations using all available high-tech methods; screening of extracts and their constituents by integration of modern molecular biological bioassays; and controlled, clinical studies, inclusive of pharmacokinetic and bioavailability investigations, aimed at evidence-based phytotherapy. The first results obtained in recent years are explained using several examples of phytopharmacological and clinical studies. These show the therapeutic superiority of many plant extracts over single isolated constituents, as well as the bioequivalence of many phytopharmaceuticals with synthetic chemotherapeutics.

Nature has been a source of medicinal agents for thousands of years and continues to be an abundant source of novel chemotypes and pharmacophores. With only 5 to 15 % of the approximately 250 000 species of higher plants systematically investigated, and the potential of the marine environment barely tapped, these areas will remain a rich source of novel bioactive compounds. Less than 1 % of bacterial and 5 % of fungal species are currently known, and the potential of novel microbial sources, particularly those found in extreme environments, seems unbounded. To these natural sources can be added the potential to investigate the rational design of novel structure types within certain classes of microbial metabolites through genetic engineering. It is apparent that Nature can provide the novel chemical scaffolds for elaboration by combinatorial approaches (chemical and biochemical), thus leading to agents that have been optimized on the basis of their pharmacological activities. The proven natural product drug discovery track record, coupled with the continuing threat to biodiversity through the destruction of terrestrial and marine ecosystems and the current low number of new chemical entities in pharmaceutical industry pipelines, provides a compelling argument in favor of expanded multidisciplinary and international collaboration in the exploration of Nature as a source of novel leads for the development of drugs and other valuable bioactive agents.

Extensive phytochemical investigations on 30 Piper species growing in India and other medicinal plants have revealed the presence of a large number of novel compounds belonging to different classes. The antiviral activity of several lignans and neolignans belonging to different structural types has been evaluated against six different viral strains. Further, the effects of ethanol, chloroform, and hexane extracts of Piper longum and Piper galiatum on TNF-α induced expression of intercellular adhesion molecule-1 (ICAM-1) on human umbilical vein endothelial cells have been studied, a novel aromatic ester was isolated from the most active extract of P. longum . A potential antifungal compound having implications in treating aspergillosis was isolated from an important Indian medicinal plant, Datura metel .

The Mauritian population has a long tradition in the use of ethno-medicine, and the practice is still strong, especially in the treatment of minor ailments. Such interest stems from an existing culture, and many “tisanes” are still prepared from plant materials and sold in several markets around the island. This paper will focus on the various chemical/biological screening techniques currently being used to evaluate the biological properties of medicinal plant extracts. Particular emphasis will be put on extraction and various screening for biological/pharmacological properties. Due consideration will be given to the pharmacological approaches that utilize different animal models for the in vitro and in vivo screening of medicinal plant extracts.

Discovery for the advancement of medicine and understanding of life sciences constitutes one of the most powerful ways in which biodiversity can contribute to human society. Bioresources have tremendous potential in providing bioactive compounds for the development of new lead candidates for pharmaceuticals, nutraceuticals, and agrochemicals. Therefore, natural products continue to be an important source of modern drugs in clinical use as an active ingredient, starting material to produce semi-synthetic drugs as well as templates for totally synthetic drugs. The key to success for discovering therapeutic agents from bioresources is based on bioassay-directed isolation techniques. High-throughput screening tests and mechanism-based screening protocols as well as information of folkloric utilization of plants have led to the discovery of lead compounds as drug candidates. Given the current research and development performance associated with the understanding of disease process, there is still a great need for novel compounds with unique mechanisms of action to treat diseases such as cancer, Alzheimer’s disease, arthritis, diabetes, etc. The lecture will highlight bioactive compounds arising from the screening of some Turkish plant extracts. Due to human population growth and economic pressure, the loss of the earth’s biodiversity is one of the most pressing environmental and development issues today. IUPAC-approved recommendations for global cooperation on sustainable utilization and conservation of biodiversity will also be presented as the dissemination effort of the recommendation.

The development of anti-invasive and anti-metastatic drugs is a major challenge in current cancer research. A model to study invasion in vitro consisted of organotypic confronting cultures of human MCF-7/6 mammary cancer cells with embryonic chicken heart fragments. Untreated cultures show occupation and destruction of the normal heart fragments within eight days. Inhibition of invasion was observed after addition of the following alkaloids and (poly)phenolics to the culture medium: (+)-catechin, tangeretin, xanthohumol, 3,7-dimethoxyflavone, prenylated chalcones, a pyrazole derivative, an isoxazolylcoumarin, and a prenylated desoxybenzoin. The action targets have been found both in the cancer cells and the surrounding host tissue. We hope that the further characterization of these targets will eventually lead to the development of clinically applicable anti-invasive drugs.

Several classes of natural products with significant inhibitory activity against target enzymes involved in several diseases have been identified. Spectrophotometer and high-throughput assays were used to assess the inhibition of prolyl endopeptidase (PEP), which led us to some novel inhibitors having potential as anticancer agents. Inhibition of cholinesterase enzymes has led to the discovery of new inhibitors with potential for use in Alzheimer’s disease and other neurological disorders. We have also discovered several potent antioxidant agents from natural sources by using a battery of antioxidant assays. Anti-inflammatory activity of a number of natural products was assayed through a cell-based in vitro bioassay. This article also contains a section on a slightly different topic of chemical basis of memory as presented during the lecture. The theory of the chemical basis of memory based on hydrogen bonding in the brain is further elaborated.

A detailed mechanism for the spontaneous transformation of 2-chloro-1-hydroxyoctoda-3(8),5-dien-4-one, a metabolite of Portieria hornemanni , into 4,5-dimethylbenzo[ b ]furan was presented. Five new terpenoids have been isolated from the red alga Laurencia luzonensis . Five species of sponges yielded various metabolites: furanosesterterpenes from Ircinia sp., scalarane derivatives from Phyllospongia sp., polyketides from Theonella cf. swinhoei , a polyacetylene from Callyspongia sp., and cyclic depsipeptides from Suberites japonicus . Other new metabolites were sponge-derived secomanoalide derivative and imidazole alkaloids from nudibranchs, briarane class diterpenes from octocorals, and cyclofarnesylated hydroquinones, floresolides A-C, from an ascidian, Aplidium sp. Many of these compounds showed cytotoxicity.

A wide variety of polyphenolic compounds (i.e., 4-methylcoumarins, xanthones, pyrazoles, and pyrazolylacrylonitriles) have been examined for their antioxidant effect on NADPH-catalyzed liver-microsomal lipid peroxidation with a view to establishing their structure–activity relationship. Dihydroxy-/diacetoxy-4-methylcoumarin derivatives have been shown to be radical scavengers. The effect of nine different xanthones has been examined on the modulation of cytokine-induced expression of intercellular adhesion molecule-1 (ICAM-1) in human endothelial cells. 1,4-Dihydroxyxanthone showed enhanced antioxidant activity as well as ICAM-1 inhibitory activity.

Total syntheses of epothilone B and pamamycin 607, which feature reactions between functionalized allylstannanes and aldehydes to introduce a ( Z )-trisubstituted double-bond and remote stereocenters stereoselectively, are discussed. Recent work concerned with carrying out this chemistry without the use of allylstannanes as starting materials and progress toward a total synthesis of bryostatins are also presented.

3,3,4,4-Tetraethoxy-1-butyne, available in high yield in four simple steps from ethyl vinyl ether, is a highly functionalized alkyne, which appears to be a versatile starting material for the synthesis of a range of alkylated, more-or-less deoxygenated carbohydrate mimics. However, many of the reactions used to achieve extension and subsequent structural modification of the carbon chain as well as removal of the protecting groups turn out to be rather sensitive to the substituents’ steric and electronic influence. As a result, the reactivity pattern that emerges is somewhat complex.

Starting from inexpensive furan and furfuryl alcohol, a noniterative approach to the synthesis of pentadeca-1,3,5,7,9,11,13,15-octols and their derivatives has been developed. The method relies upon the double [4+3]-cycloaddition of 1,1,3-trichloro-2-oxylallyl cation with 2,2'-methylenedifuran and conversion of the adducts into meso and (±)- threo -1,1'-methylenebis ( cis - and trans -4,6-dihydroxycyclohept-1-ene) derivatives. The latter undergo oxidative cleavage of their alkene moieties, generating 5-hydroxy-7-oxoaldehydes that are reduced diastereoselectively into either syn or anti -5,7-diols. Asymmetry is realized using either chiral desymmetrization with Sharpless asymmetric dihydroxylation or by kinetic resolution of polyols using lipase-catalyzed acetylations. All of the possible stereomeric pentadeca-1,3,5,7,9,11,13,15-octols and derivatives can be obtained with high stereoselectivity applying simple operations, thus demonstrating the high stereodiversity of this new, noniterative approach to the asymmetric synthesis of long-chain polyketides.

Synthetic approaches to the total synthesis of plakortone B, as well as diastereoselective nucleophilic additions to furyl aldehyde and furyl sulfonylimine employing chiral 3-boronates as auxiliary are presented.

An efficient one pot synthesis of thio and selenolevoglucosans from 1,6-diactivated carbohydrate derivatives has been achieved using benzyltriethylammonium tetrathiomolybdate, [BnNEt 3 ] 2 MoS 4 , as a sulfur transfer reagent and tetraethylammonium tetraselenotungstate, [Et 4 N] 2 WSe 4 , as a selenium transfer reagent, respectively. The methodology has also been extended to the synthesis of 1,5-epithio and 1,5-episeleno pentoses.

The demand for diverse compound libraries for screening in drug discovery and materials science is the driving force behind the development of new technologies for rapid parallel and combinatorial synthesis. The focus of this article will be on the scaffold decoration of biologically active dihydropyrimidines (DHPMs) of the Biginelli type, exploring the diversity on all six positions around the scaffold. This opens up the generation of a very large number of analogs given the commercial availability of the building blocks that are used in the functionalization process.

Due to the growing interest in small molecules that could help in understanding protein–protein interactions based on signal transduction, the demand for the generation of small-molecule libraries that are inspired by bioactive natural products has grown significantly. Many of these pathways are highly complex and present tremendous challenges with the use of classical tools. A rapid access to natural product-like small molecules having structural complexity and diversity is crucial for systematically dissecting the functions of complex protein networking and understanding cell signaling pathways. The complex nature, the three-dimensional architecture, and the number of protein binding functional groups presented in three-dimensional arrays are some of the attractive features to incorporate in small-molecule chemical probes to be used as modulators of protein function.

Several substituted α-alkoxy phenyl propionic acids were synthesized, and their hypotriglyceridemic properties were evaluated in Swiss albino mice. Some of the compounds showed excellent triglyceride- and cholesterol-lowering properties even at a dose of 1 mg/kg. 2,5-Substituted pyrrole-containing heterocycles were among the most potent alkoxy propionic acid class of compounds. These compounds also showed excellent antidiabetic activities in animal models.

A new strategy has been developed for the synthesis of naturally occurring 6-alkenyl phenolic acids and 3-alkylpyridine alkaloids of biological importance. This strategy makes use of the proper substituted aryl or pyridyl sulfone as the potent intermediate. A carbanion was generated from the sulfone by treating it with NaH in dimethylformamide (DMF) at –5 °C and was used for alkylation reaction with alkyl/alkenyl bromide in DMF at 0 °C to give product, which, on reduction with sodium-amalgam, yielded the desired natural product. Using this methodology, we have synthesized 11 natural 6-alkyl/alkenyl salicylic acids, which were known to possess strong antimicrobial activities against many pathogens and had also shown molluscicidal activity against the snail Biomphalaria glabrata . This methodology was also extended to synthesize two natural 3-alkylpyridine alkaloids that were known to possess strong cytotoxic activity against P-388 murine leukemia cells with IC 50 values of 1–2.3 μg/ml. Taking leads from these natural products, we have also synthesized a number of related compounds in order to find a potential drug candidate for the future. This paper presents the highlights of the work done on the synthesis of these two classes of compounds.

A set of substituted piperazinyloxazolidinone derivatives has been studied for their antibacterial activity in a few gram-positive bacteria. The structural modifications have provided a superior compound than linezolid, the only drug of this class in the market at present.

Biocatalytic polymerization reactions on a variety of substrates leading to value-added polymers have been summarized. The main focus of this review is on the control of molecular architecture during enzymatic polymerization reactions. Combined with chemical reactions, several extremely flexible chemo-enzymatic synthetic procedures are described to produce families of new polymeric materials with novel properties. The properties of the synthesized polymers and their applications in various fields, such as drug delivery and flame retardant materials, have also been studied and discussed.

The synthetic potential of enzymes related to organic synthesis has been applied profusely, especially since the introduction of their use in organic solvents. Enzymes offer the opportunity to carry out highly chemo-, regio-, and enantioselective transformations. The use of enzymes in the synthetic sequence provides unique advantages of efficiency and environmental friendliness. Owing to their low cost and applicability to a broad range of substrates, lipases have become the most versatile class of biocatalysts in organic synthesis. We have screened a battery of lipases to carry out highly selective reactions for the synthesis of a wide range of organic compounds and polymeric materials.

Chemo-enzymatic methods constitute a promising approach to obtain various biologically active compounds, including enantiomerically pure substances. Entrapment in gels is one of the most convenient methods to stabilize enzymes for their application in water/organic media. Proteases and lipases are widely used for enantioselective transformations of various organic compounds in water-poor media. In this study, chymotrypsin was entrapped into a composite poly( N -vinyl caprolactam)-calcium alginate (PVCL-CaAlg) and covalently attached to poly(vinyl alcohol) (PVA) cryogel beads. Lipase was immobilized by covalently attaching to aldehyde-bearing PVA cryogel beads. The activities of the entrapped biocatalysts were studied. Both entrapped α-chymotrypsin and lipase retained high activity in acetonitrile/water medium (water content 0.5–20 %) and displayed high storage stability for several months. The high operational stability of immobilized α-chymotrypsin and lipase in a cyclic process (up to 912 h in total) was also demonstrated. Gel-immobilized enzymes were successfully used to obtain optically pure L-phenylalanine (ee 98.6 and 83 % in the case of α-chymotrypsin and lipase, respectively) by enantioselective hydrolysis of Schiff’s base of amino acid ethyl ester in an acetonitrile/water system.

Different (±)-4-(3/4-acetoxyaryl)-5-ethoxycarbonyl-6-methyl-3,4-dihydropyrimidin-2-ones have been synthesized and subjected to enantioselective deacetylation reactions mediated by different lipases in organic media. Novozyme 435 in tetrahydrofuran:diisopropyl ether was found to be the catalyst of choice for efficient enantioselective deacetylation of dihydropyrimidinones under study. Further, we discovered that lipase isolated from Pseudomonas aeruginosa can be used for selective acylation of secondary hydroxyl groups in nucleosides. This observation can be very useful for selective manipulation of different hydroxyl groups in nucleosides.

The acetylation of proteins in biological systems is largely catalyzed by specific acetyl transferases utilizing acetyl CoA as the acetyl donor. The enzymatic acetylation of proteins independent of acetyl CoA was unknown until we discovered a unique membrane-bound enzyme in mammalian cells catalyzing the transfer of acetyl groups from polyphenolic peracetates (PAs) to certain enzyme proteins, resulting in the modulation of their catalytic activities. Since for the enzyme, acetyl derivatives of several classes of polyphenols such as coumarins, flavones, chromones, and xanthones were found to be acetyl donors, the enzyme was termed as acetoxy drug: protein transacetylase (TAase). TAase was found to be ubiquitously present in tissues of several animal species and a variety of animal cells. Liver microsomal cytochrome P-450 (CYP), NADPH-cytochrome c reductase and cytosolic glutathione S -transferase (GST) were found to be the targets for TAase-catalyzed acetylation by the model acetoxy drug 7,8-diacetoxy-4-methylcoumarin (DAMC). Accordingly, the catalytic activities of CYP-linked, mixed function oxidases (MFOs) and GST were irreversibly inhibited while the reductase was remarkably activated. In this report, we have reviewed the details concerning purification and characterization of TAase and the protein acetylation by DAMC. Quantitative structure–activity relationship (QSAR) studies concerning the specificities of various PAs to liver microsomal TAase and TAase-related biological effects have also been reviewed.

A low-temperature, alkaline, and detergent-compatible lipase from Fusarium globulosum (FGL) has been produced using an inexpensive source, viz. neem oil. Maximum lipase production of 12 300 U/L was achieved in 96 h on optimizing various physicochemical parameters. The lipase exhibited remarkable stability in the presence of commercial detergents, bleaching agents, and proteases. The lipase showed a novel property of marked activation on prolonged incubation at alkaline pH. Wash performance analysis of the commercial detergent for removal of fatty stains improved upon addition of this lipase.

A new class of ruthenium complex-based macrodye and a dinuclear complex were synthesized via a biocatalytic route employing hematin as an efficient biocatalyst. The photovoltaic overall efficiency of the dinuclear complex was found to be 2.1 % and higher than the polymeric complex (0.33 %). Furthermore, we have developed an environmentally benign methodology for the synthesis of novel pegylated polyphenolics. The reaction conditions used do not require any organic solvents, and all the reactions were performed in aqueous media. The synthesized polymers were soluble in both organic and aqueous media, and provide further opportunity to tailor the properties. Finally, a novel biomimetic method for the synthesis of a conducting molecular complex of polypyrrole and of thiophene substitute in the presence of a polyelectrolyte, such as polystyrene sulfonate (SPS), is presented. A synthetic enzyme based on hematin was used to catalyze the polymerization of pyrrole (PYR) and 3,4-ethylenedioxythiophene (EDOT) in the presence of SPS. Copolymers of EDOT and PYR have also been synthesized, and these novel materials have been shown to exhibit high electrical conductivity.

The preparation of flavors and fragrances has to be done with great care. When these compounds are meant for consumption, no toxic chemicals are allowed during their preparation. For use in non-food additives, a high purity is required. Both constraints can be easily fulfilled when enzymes are used as catalyst during the production of these compounds. This paper summarizes the work that we have done regarding the preparation of branched-chain fatty acids (sheep flavors) using lipases, the production of glucosides (controlled-release flavors) using glucosidases, the formation of terpene alcohols and grapefruit flavor using enzymes from chicory, and the formation of phenolic antioxidants using lipases.

Triosephosphate isomerase (TIM), a central enzyme in the glycolytic pathway, has been the subject of extensive structural and mechanistic investigations over the past 30 years. The TIM barrel is the prototype of the (β/α) 8 barrel fold, which is one of the most extensively used structural motifs in enzymes. Mechanistic studies on TIM from a variety of sources have emphasized the importance of loop 6 dynamics for enzyme activity. Several conserved residues in TIM have been investigated by extensive site-directed mutagenesis of the enzyme from yeast, chicken, and trypanosoma. The cloning and sequencing of the TIM gene from the malarial parasite Plasmodium falciparum in 1993 revealed the unexpected mutation of a hitherto conserved residue serine (S96) to phenylalanine (F96). Subsequent results from the genome sequencing programs of Plasmodium falciparum , Plasmodium vivax , and Plasmodium yoelii confirmed the presence of the S96F mutation in malarial parasites. The crystal structure of PfTIM and several inhibitor complexes, including a high-resolution (1.1 Å) structure of the PfTIM 2-phosphoglycerate complex, revealed that loop 6 had a propensity to remain open, even in several ligand bound structures. Furthermore, both open and closed forms could be characterized for the same complex. Since glycolysis is the primary source of ATP for the malarial parasite during the intraerythrocytic stage, glycolytic enzymes present themselves as potential targets for inhibitors. Two distinct approaches have been explored. The use of dimer interface peptides, which interfere with assembly, has proved promising. Inactivation of the enzyme by modification of a cysteine (C13) residue, which lies close to the active site residue, lysine (K12) is another potential strategy. The differential reactivity, of the four-cysteine residues, at positions 13, 126, 196, and 217 in each subunit has been established using electrospray ionization mass spectrometry. Studies of single tryptophan mutants (W11F and W168F) of PfTIM provide a probe to study folding, stability, and inhibitor interactions.

The generation of a single anionic or cationic center at an alkaline or acidic pH in a given molecule presents a unique opportunity to examine the electrostatic make-up of these molecules both at the neutral or ionic state. The generation of a single cationic center in the phenyl-nicotinamide system provided new straightforward evidence showing that the charge density of the electron-deficient pyridinium was actually enhanced by the donation of the charge from the electron-rich phenyl group (i.e., the pyridinyl became more basic by ca. 0.5 p K a unit compared to an analogous system where phenyl was absent) owing to the electrostatic interactions between these two moieties. On the other hand, the generation of the 5'-guanylate ion in the hexameric single-strand (ss) RNA [5'-GAAAAC-3'], in comparison with the constituent trimeric, tetrameric, and pentameric-ssRNAs, has unequivocally shown how far the electrostatic cross-talk (as an interplay of Coulombic attractive or repulsive forces) in this electronically coupled system propagates through the intervening p A p nucleotide steps until the terminal p C -3' residue in comparison with the neutral counterpart. The footprint of the propagation of this electrostatic cross-talk among the neighboring nucleobases is evident by measurement of p K a s from the marker protons of ionization point (i.e., of G ) as well as from the neighboring marker protons (i.e., of A or C ) in the vicinity, as well as from the change of the chemical environment (i.e., chemical shifts) around their aromatic marker protons (δH2, δH8, δH5, and δH6) owing to a change of the stacking-destacking equilibrium as a function of pH.

MicroRNAs (miRNAs) are phylogenetically widespread, small noncoding RNAs of 18–25 nucleotides in length, and are expressed in animals and plants. These small RNAs can regulate gene expression at the translational level through interactions with their target messenger RNAs, and have a role in the development of Caenorhabditis elegans , plants, and mammals. Although more than 200 miRNAs have been found in mammals, it is not easy to identify their targets. We investigated the target genes of miRNAs and analyzed the function of these miRNAs during retinoic acid (RA)-induced neuronal differentiation.

We report herein our results for locked nucleic acid (LNA)-type oligonucleotides containing pyrene residues. Pyrene has a large hydrophobic and planar surface area and is therefore a potential intercalating unit; furthermore, it is interesting as a fluorescent tag when covalently bound to DNA. Synthesis and hybridization of conformationally locked universal base surrogates are described together with efficient interstrand communication as shown by the formation of pyrene excimer bands for duplexes containing 2'- N -(pyren-1-yl)methyl-2'-amino-LNA monomers positioned in a zipper-like manner within a DNA duplex.

Aromatic and heteroaromatic groups that are forced to intercalate at specific positions in DNA are versatile probes of DNA–DNA and DNA–protein recognition. Fluorescent nucleobases are of value since they are able to report on localized alterations of DNA duplex structure. However, the fluorescence of the vast majority of base surrogates becomes quenched upon intercalation in DNA. Peptide nucleic acid (PNA)-based probes are presented in which the intercalator dye thiazole orange (TO) serves as a fluorescent base surrogate. In these probes, fluorescence increases (5–60-fold) upon hybridization. PNA-bearing TO as fluorescent base surrogate could hence prove useful in real-time polymerase chain reaction (PCR) applications and in live cell analysis. Forced intercalation of aromatic polycycles can help to explore the binding mechanism of DNA-modifying enzymes. We discuss studies of DNA-methyltransferases (MTases) which commence methylation of nucleobases in DNA by flipping the target nucleotide completely out of the helix. A method for probing the base-flipping mechanism is suggested. It draws upon the observation that large hydrophobic base surrogates in the face of the swung-out base can enhance the DNA-enzyme binding affinity possibly by disrupting target base-stacking and stabilizing the apparent abasic site.

A biocatalytic approach has been developed to synthesize conducting polyaniline (PANI) nanoparticles. The method involves the formation of nanocomposites of PANI and poly(acrylic acid) (PAA) by polymerizing aniline (AN)-camphorsulfonic acid (CSA) macromonomer (AN/CSA) using a biocatalyst in the presence of template PAA. The second step involves the separation of PANI polymers from PAA and CSA in the nanocomposites. The formation of PANI nanoparticles by this two-step approach is studied by transmission electron microscopy (TEM). High-resolution solution 13 C NMR and UV/visible spectroscopic techniques have been used to characterize the formation of conducting PANI chains by the enzymatic method.