The main metabolic pathway of oracin, a new potential cytostatic drug, in human liver microsomes and cytosol: Stereoselectivity of reoxidation of theprincipal metabolite 11-dihydrooracin to oracin

Chirality is a prominent feature of most biological processes. The intrinsi c asymmetry of receptors, enzymes, and other endogenous macromolecules repr esents the basis for biological discrimination between the stereoisomeric f orms of all foreign compounds in organism. Stereoselectivity and stereospec ificity, two principal chiral attributes of enzyme activity, play important role in biotransformation process of drugs and other xenobiotics. The ster eospecificity of enzymes leads to the preferential formation of certain ena ntiomer, the stereoselectivity of enzymes, on the other hand, expresses the preference of one stereoisomer form of substrate for subsequent biotransfo rmation. An approach to the study of different conditions for the formation of the two enantiomers of principal metabolite of potential cytostatic dru g oracin in Man in vitro is described. The futile cycle, in which the princ ipal metabolite is converted to the parent drug, is also discussed. The res ults emphasise the fact that the stereospecificity of enzymes in Man is oft en distinct from other laboratory species studied.