Current Medicinal Chemistry - Volume 10, Issue 13, 2003

The specific Kunitz Bauhinia ungulata factor Xa inhibitor (BuXI) and the Bauhinia variegata trypsin inhibitor (BvTI) blocked the activity of trypsin, chymotrypsin, plasmin, plasma kallikrein and factor XIIa, and factor Xa inhibition was achieved only by BuXI (Ki 14 nM).BuXI and BvTI are highly homologous (70%). The major differences are the methionine residues at BuXI reactive site, which are involved in the inhibition, since the oxidized protein no longer inhibits factor Xa but maintains the trypsin inhibition.Quenched fluorescent substrates based on the reactive site sequence of the inhibitors were synthesized and the kinetic parameters of the hydrolysis were determined using factor Xa and trypsin. The catalytic efficiency kcat / Km 4.3 x 10-7 M-1sec-1 for Abz-VMIAALPRTMFIQ-EDDnp (lead peptide) hydrolysis by factor Xa was 10-4 - fold higher than that of Boc-Ile-Glu-Gly-Arg-AMC, widely used as factor Xa substrate.Lengthening of the substrate changed its susceptibility to factor Xa hydrolysis. Both methionine residues in the substrate influence the binding to factor Xa. Serine replacement of threonine (P1') decreases the catalytic efficiency by four orders of magnitude. Factor Xa did not hydrolyze the substrate containing the reactive site sequence of BvTI, that inhibits trypsin inhibitor but not factor Xa. Abz-VMIAALPRTMFIQ-EDDnp prolonged both the prothrombin time and the activated partial thromboplastin time, and the other modified substrates used in this experiment altered blood-clotting assays.

This review presents an overview of Choline Kinase (ChoK) inhibitors with antiproliferative activity. The consideration of ChoK as a novel target for the development of new anticancer drugs is justified. The synthesis of several derivatives based on structural modifications of hemicholinium-3 (HC-3) is not accompanied by potentiation of the neurological toxicity of HC-3. The increment of both ChoK inhibitory and antiproliferative activities was successfully obtained by the two following changes: a) substitution of the oxazonium moiety of HC-3 by several aromatic heterocycles, and b) using the 1,2-ethylene(bisbenzyl) moiety instead of the 4,4'-biphenyl fragment. In an attempt to understand the ChoK inhibitory activity, a quantitative structure-activity relationship was developed. The QSAR equations have described the forces involved in quantitative terms. The electron characteristic of the substituent at position 4 of the heterocycle and the lipophilic character of the whole molecule were found to significantly affect the antitumour activity in compounds 17-95. Trispyridinium compounds 91-95 are more potent than the bispyridinium ones 87-89 as ChoK inhibitors. Nevertheless, 91-95 are less active than 87-89 as antiproliferative agents because the latter show better lipophilicities to cross the cytosolic membranes. Inhibition of the growth of human tumours in nude mice has been demonstrated: Antitumour activity of compound 64 against human HT-29 produced a decrease of up to 70% in the size of the tumour in nude mice. These results indicate that ChoK can be used as a general target for anticancer drug design against Ras-dependent tumourigenesis.

Chemistry and biology of marine natural products from the indole and annelated indole series have become an attractive research field for development of new pharmacological lead substances. In the past years some of the isolated natural organic compounds were synthesized by chemists and evaluated with great enthusiasm to find new lead natural compounds against different diseases. In this review the latest results for new compounds including isolation, biological evaluation, synthetic pathways and some retrosynthetic analyses are summarized.

Hard drugs have been defined as drugs that are biologically active and non-metabolizable in vivo. Soft drugs are defined as drugs, which are characterized by predictable and controllable in vivo destruction (i.e. metabolism) to form non-toxic products after they have achieved their therapeutic role. Quaternary ammonium compounds, such as benzalkonium chloride, are hard antibacterial agents. Their toxicity limits their usage in humans and animals, and their chemical stability limits their usage for general environmental sanitation. Furthermore, due to their stability they are prone to induce selective antimicrobial pressure and bacterial resistance. Soft analogs of the currently available hard antibacterial agents are less toxic. However, although the soft analogs have been shown to possess antibacterial activity in in vitro studies, it is likely that their in vivo activity will be hampered by their chemical instability.

Antimalarial chemotherapy has become more complex and challenging because of multidrug resistant strains of Plasmodium falciparum. Due to resistance of malarial parasite against well known drugs, the chemotherapy of malaria has become complicated. In this review we have discussed brief introduction followed by life cycle of malaria parasite. The list of commercially available antimalarial drugs along with there action on different stages of parasite have been discussed. A brief description of their mechanism of action and advantages and disadvantages were reported. The natural products as antimalarial have been discussed in the review. On the basis of chemical classes the natural products were divided in the following categories; Quinoline alkaloids, Iso-quinoline alkaloids, Indoloquinoline alkaloids, Carbolines, Bisisoquinoline, 4-Quinazole derivatives, Trioxanes, Terpenes, Naphthoquinone, Anthraquinones, Chalcones, Hydroxy flavanones, Coumarins and phenolic glycoside. The combination chemotherapy has been highlighted in the review. The Biochemical and Immunological changes in malarial infection are discussed along with complications of malarial chemotherapy due to resistance. In the conclusion section, the future strategies for the chemotherapy of malaria have been discussed.

Glutathione peroxidase (GPX) is a well-known selenoenzyme that functions as an antioxidant and catalyzes the reduction of harmful peroxide by glutathione and protects cells against oxidative damage. Because many diseases are related to oxidative stress, GPX is an ancient foe of many diseases. Antioxidants are very useful for biological bodies, and considerable effort has been spent to find compounds that could imitate the properties of GPX. This paper reviews GPX mimics developed so far and describes a new, more effective strategy for fabricating them.Although many GPX mimics have been made, they possess serious disadvantages: low activity, low solubility in water, and, in some cases, toxicity. In order to overcome these drawbacks, we have proposed a new strategy of imitating GPX. First, a receptor with a substrate binding site is generated. Next, a catalytic group is incorporated into the receptor near the substrate binding site, allowing the catalytic group access to the functional group of the substrate. Finally, a highly efficient enzyme mimic is obtained. Using this strategy, we successfully fabricated GPX mimics that use antibodies, cyclodextrins, some enzymes and proteins as receptors and chemical modification to incorporate the catalytic group, selenocysteine (Sec). The general principle of combining a functional group involved in catalysis with a specific binding site for the substrate is an approach that could be applied to the generation of other efficient semisynthetic biocatalysts. We describe the antioxidant activities of these GPX mimics and the reasons of their being promising candidates for medicinal applications.