Current Medicinal Chemistry - Volume 9, Issue 5, 2002

Schizophrenia is a debilitating mental disease affecting approximately 1% of the population worldwide. Since the discovery of the first modern treatment for schizophrenia, chlorpromazine, in 1952 there have been many new structures investigated, only a small fraction of which have resulted in clinically useful drugs. Of these, haloperidol may be regarded as the drug for first line treatment. Since then, clozapine has emerged as the benchmark therapeutic ameliorating positive and negative symptoms and devoid of movement disorders, with its greatest feature being improvement of treatment-resistant patients. However, a major, potential lethal side-effect of clozapine is the induction of agranulocytosis, a blood disorder with unknown mechanism that results in lowered white-blood cell counts and consequent susceptibility to infections.In the 50 years of antipsychotic drug development, several novel theories have evolved that focus on receptor sub-types (serotonin 5-HT2A, dopamine D2 and D4) and the degree to which they need to be selectively attenuated by the drugs. Also of significance is the location of these receptors in the brain in relation to the disease state, the myriad of side-effects associated with antipsychotics and physicochemical properties of antipsychotic molecules relative to models of the drugs and the GPCR receptors involved.The techniques for investigation have shown increasing sophistication and refinement over this period, involving cloned receptors and PET scanning for determination of receptor location, density and binding, and rate constants at receptors. Knowledge of receptor structure, although in its infancy since no membrane bound CNS-receptor has yet been crystallized, is likely to benefit substantially with advances in computer-aided modelling.Overall, these new techniques have resulted in a number of novel antipsychotics such as risperidone, sertindole, olanzapine, seroquel, zotepine and ziprasidone, whose design, synthesis and testing has benefited enormously from the accumulated knowledge base of the past 50 years.In this review, we will provide a comprehensive update of the theories of action and clinical profiles of the latest drugs listed. The following appraisal of the literature will provide the practising medicinal chemist interested in this critical area of research with sufficient insight and understanding, to embark on productive investigations into the design and development of new therapeutic agents devoid of clinically limiting side-effects.

In thirteen years since the appearance of Endothelin (ET) on the international scene, possibility of its involvement in a variety of diseases has attracted the attention of medicinal chemists in search of novel therapeutics for various cardiovascular diseases (CVDs). Discovery of pharmaceutical agents which either block the generation of ET from its precursor or antagonize its binding to cellular receptor, should not only provide means to assess the physiological role of ET, but lead to useful therapy for conditions associated with altered production or responsiveness to ET. In this review article, we have attempted to present in a classified format, the kaleidoscope of ET receptor antagonists that have emerged through structure activity relationship studies using the parent peptide as well as from screening of various compound libraries. By all indications, the variety and range of small molecules that are currently under investigation continues to open up newer opportunities and lures fresh groups of scientists into this research arena. Presently a number of these compounds are in the clinics, being evaluated for their beneficial effects in a range of human pathologies such as essential hypertension and chronic heart failure.

Platelet aggregation plays a key role in the pathogenesis of thromboembolic diseases such as myocardial infarction, stroke, unstable angina and peripheral artery disease. Until recently, aspirin was the only antiplatelet agent available to prevent or treat these events. Over the past several years, there has been a substantial expansion in the antiplatelet armamentarium as well as in the understanding of the clinical importance of antiplatelet therapy in limiting the complications of thrombosis. Aspirin was one of the first agents to be adopted and it remains as the standard therapy with the higher amount of available clinical information. Following aspirin, ADP receptor antagonists like ticlopidine and clopidogrel as well as phosphodiesterase inhibitors dipyridamole and cilostazol have been introduced. Glycoprotein (GP) IIb / IIIa receptor antagonists like eptifibatide, tirofiban and abciximab are the newer antiplatelet agents which act at the end of the common pathway of platelet aggregation. Although results of clinical studies with the first oral GPIIb / IIIa antagonists were disappointing, agents of the new generation might expand the potential application of GPIIb / IIIa targeted therapy. This review will highlight recent advances in the development of aspirin, phosphodiesterase inhibitors, ADP receptor antagonists and the platelet glycoprotein IIb / IIIa inhibitors. The emphasis of this paper has been placed on the chemical aspects of these agents.

Retinoids, all-trans-retinoic acid (1a) and its analogs, act as specific modulators of cellular differentiation and proliferation, through binding to and activating specific nuclear receptors, retinoic acid receptors (RARs) and retinoid X receptors (RXRs). Retinoids have chemotherapeutic roles in dermatology and oncology, but their usefulness is restricted by the high toxicity of retinoic acid and its hydrophobic analogs. We have developed various retinoidal benzoic acid derivatives, and named them retinobenzoic acids. Among them, aromatic amides such as Am80 (7) and Am580 (8) have superior pharmacological characteristics, including RAR subtype selectivity. Structural modification based on the ligand superfamily concept afforded several types of RAR antagonists, benzimidazole derivatives, BIPh (41) and BIBn (42), and dibenzodiazepine derivatives, LE135 (46) and LE540 (47). LE135 (46) is a unique antagonist with RARβ-selectivity. During investigations on the structureactivity relationships of retinobenzoic acids, several retinoid synergists (RXRs agonists), such as HX600 (49), DA113 (55h) and TZ335 (57), have been found. These compounds are expected to modulate other nuclear receptors which form heterodimers with RXRs, besides retinoids. Further, we found some RXRs antagonists, HX531 (60) and HX603 (61), which inhibit the activation of both RXR homodimers and RXR·RAR heterodimers. In this review, we describe our investigations on these structurally and biologically unique retinoids and retinoid-regulatory compounds.

Due to the many technological advancements in biology and development of new fields such as biotechnology and bioinformatics, our knowledge of cellular functions has been growing rapidly and Biology has entered the Information Age. Along with the technological advancements has come a rapid increase in identification of biomolecular targets involved in diseases. Recently, structure-based drug design studies have emphasized integration of the clinical, cellular, biochemical, structural, and biophysical knowledge of the target. Due to advances in sequencing the human genome, in chemical synthesis and structure determination of biological targets using X-ray and NMR techniques, and in high-performance computing, many scientists from both experimental and theoretical fields focus on structure-based drug design. As scientists in such wide-ranging disciplines, we must understand the data from and educate one another about the strengths and weaknesses of our various disciplines. Since 1990, we have been using computers to visually evaluate ligand binding. In this review, the author will focus on computational methods that not only visualize but also quantify the nature and strength of ligand-macromolecule contacts. Such quantification can be very useful both for medicinal chemists to design ligands and for molecular biologists to design rational protein design experiments to study the effect of amino acid changes on ligand binding.