Current Medicinal Chemistry - Volume 11, Issue 19, 2004

The discovery and development of novel drugs has been influenced over the last several decades by new techniques in medicinal chemistry. Combinatorial and parallel synthesis chemistry techniques have opened up immense opportunities in drug discovery and development efforts. These techniques, which include solid phase organic synthesis and polymer-assisted synthesis in solution, have been routinely applied to a number of therapeutic areas. Despite the flurry of activity that characterized small molecule drug discovery efforts in the early 1990s, it was only during the mid to late 1990s that combinatorial chemistry began to make an impact on antiparasite chemotherapy. This review focuses on the development and application of combinatorial and parallel synthesis methodologies to antiparasitic drug discovery from the mid 1990s to the end of 2002. Much of this work applies to small organic molecules as inhibitors of parasite targets although some of the early applications were to the synthesis of enzyme substrates.

The search for an ideal anticoagulant has spanned decades and has resulted in several approaches and the identification of novel target molecules for preventing and treating thrombosis. The first group of new anticoagulant agents acting through direct inhibition of coagulation factors were inhibitors of thrombin, but factor Xa inhibitors and, most recently, factor VIIa inhibitors have become attractive candidates. The structures of thrombin, factor Xa and factor VIIa show similarities in their active sites and, for this reason, attempts have been made to develop synthetic agents containing in a single molecule inhibitory activity against two of the enzymes of the blood coagulation cascade. Such dual inhibitors are now in preclinical studies and are, potentially, new anticoagulant drugs with improved properties. The emphasis of this review will be placed on dual inhibitors of thrombin / factor Xa and factor Xa / factor VIIa. Comparison of the active sites of these enzymes is included for better understanding of the structural demands to be met in designing effective dual inhibitors.

Purine bases and their bioisosteric analogs are widely used as building blocks in combinatorial chemistry. Recently a great number of fused pyrimidine derivatives became known as potential drug molecules against various types of proliferative diseases, caused by over-expression of protein kinases [1]. One of the most important compound families are quinazolines : e.g. the best inhibitor of EGFR tyrosine kinase is PD153035 (6,7-dimethoxy-4-(3'- bromophenyl)amino-quinazoline) [2] and IRESSA™ (gefitinib, ZD1839) [3], developed from this compound family, is presently the only one approved and granted drug by the FDA for the treatment of advanced non-small-cell lung cancer (NSCLC). KF31327 (3-ethyl-8-[2-(4-hydroxymethylpiperidino)benzylamino]-2,3-dihydro-1H-imidazo[4,5-g]- quinazoline-2-thione dihydrochloride) from this group, showed significantly higher inhibitory activity on cyclic GMP-specific phosphodiesterase compared with those of sildenafil (Viagra™) [4]. The synthetic procedures of the example compounds are based on imidoyl chloride intermediates that were prepared from the appropriate 3H-quinazoline-4-ones. Although the key intermediates, quinazoline-4-ones, have been known since more than hundred years, their synthetic procedures have been improved much only in the past ten years. In this paper we reviewed the efficient synthetic methods of quinazolin-4-ones, and presented a novel, reliable method for their synthesis. There was no considerable effect of microwave-, or traditional thermal activation on the yield and compound purity.

The permanent therapeutic importance of morphine derivatives in pain treatment has inspired continual synthetic efforts to modify the rigid pentacyclic systems in search for new selective analgesic agents. As a result, several morphinane oximes have been synthesized recently, which have the additional advantage of possessing an oxime group that can provide a method for selective determination of opiate alkaloids in biological matrices. The oximes of hydrocodone and oxycodone have stronger analgesic effect than the parent ketones and they also proved to be effective in preventing the respiratory depressant and hypotensive actions of fentanyl. In this work a review is given on the present status of oxime pharmacology, chemistry and analysis and also the oxime and O-methyl oxime formation of 6-oxo-morphinanes with therapeutic interest (codeinone, oxycodone, hydrocodone and 14-OH-codeinone). The oxime formation was monitored by reversed-phase HPLC and the chromatographic properties of oxime isomers have been characterized. The assignation of the individual isomers isolated by preparative HPLC was performed by 1H NMR spectroscopy based on the chemical shift differences of the 5-H signals. In this way the isomeric ratio in the oxime products could also be determined. It was found that in the case of Δ7-6-oxo-morphinanes, depending on the substituents, the formation of the Z-isomer highly dominates (73-96%) over that of the Eisomer. However, for the saturated 7,8-(dihydro) derivatives the E-isomer is definitely preferred (>98%). In conclusion of a survey on the theoretical background of oxime isomerism, the conformational differences between the saturated and unsaturated morphinane systems were found responsible for the different E / Z ratios. On the basis of the isomeric ratio and the on-line CD and UV spectra of the pure isomers, the molar ellipticities and absorbancies of the isomers were calculated by a parameter estimation method.

Structural diversity of carbohydrates plays a crucial role in their large variety of roles in biological systems. This paper focuses on aspects of structure and biological functions of three classes of carbohydrates, N-linked oligosaccharides, blood group oligosaccharides and glycosaminoglycans. Conformations and dynamics in solution, as well as structure of protein-carbohydrate complexes are discussed. A short overview also describes theoretical and experimental methodologies that are used in current glycobiological research, particularly high-resolution NMR spectroscopy, X-ray crystallography and methods of computational chemistry.

The classical 4'-oxonucleoside analogs exhibit interesting biological activities such as antibiotic, antiviral and antitumor, which are believed to be the result of inhibition of the viral or cellular DNA or RNA polymerase after being converted to their corresponding 5'-triphosphates. However, the activity of 4'- oxonucleosides were limited by their susceptibility to degradation by nucleoside phosphorylases or acid hydrolysis. This aspect called for the chemical modification of the carbohydrate portion. This compulsion led to two kinds of strategies; (1) replacement of the 4'-oxygen by the methylene group - carbocyclic nucleosides; (2) replacement of the 4' oxygen by sulphur-4'-thionucleosides. This group has also conferred the resistance to the nucleoside cleavage. Although, there were some pioneering work on 4'-thionucleosides in 1960s and 1970s, the interest in this group of compounds was rekindled by the antiviral activities of 2'-deoxy-4'- thionucleosides reported independently by Secrist et al. and Walker et al. Subsequent contributions by the other authors, enhanced its standing as an important class of antiviral agents. Following is a reasonably exhaustive account of this class of compounds reported after 1990.

New drugs are urgently required for Human African Trypanosomiasis (sleeping sickness), a disease which has re-emerged as a major health threat in Sub-Saharan Africa. The third enzyme of the pentose phosphate pathway, 6-phosphogluconate dehydrogenase, has been shown to be a good target for drugs. The enzyme is essential to the trypanosomes that causes sleeping sickness and structural differences when compared to its mammalian counterpart allow for selective inhibition. Three series of inhibitors have been designed, these include phosphorylated carbohydrate substrate and transition state analogues, noncarbohydrate substrate analogues and also triphenylmethane-based compounds. All have shown selective inhibition of the trypanosomal 6-phosphogluconate dehydrogenase and representatives of each have trypanocidal activity.