Asymmetric Synthesis of Drug Intermediates using Microorganisms

Abstract

There has been an increasing awareness of the enormous potential of microorganisms and enzymes to transform synthetic chemicals, in a highly chemo, regio and enantioselective manner. In the present work, an attempt was made to evaluate the potential of some selected fungi species to effect reduction of selected ketones and oxidation of selected sulphides. Saccharomyces cerevisae was selected for evaluating the effect of various physicochemical parameters on the (microbial induced) biotransformation, as it showed considerable reduction of the substrate, 3-[5-[(4-flurophenyl)-1, 5, dioxopentol]- yl] –4- (S) phenyl oxazolidin-2-one. The experimental results showed that maximum reduction occurred at pH of 7.6, temperature of 30° C, incubation period of 48 hours and biomass concentration of 6 g. High concentration of substrate had a negative effect on the rate of bioconversion. It was found that the organic solvents adversely affected the enzymatic reaction, while use of surfactant had a favorable effect on bioconversion. The interaction of various culture condition variables on reductase activity was also studied using S. cerevisiae. Central composite design and Response surface methodology were used in the design of the experiments and analysis of the results. The model could be successfully used for accurately predicting enzyme activity based on a new set of independent variables. Rhizopus stolonifer was found to be effective in carrying out sulphoxidation of omeprazole intermediate and the various factors affecting the reaction were studied. The ideal reaction time for the conversion was found to be 48 hours. A substrate concentration of 0.04% was found to be well-tolerated by the microbial cell. The pH and temperature of the reaction mixture in the range selected, did not affect the enzyme activity significantly. Biosulphoxidation in water miscible solvents was significantly low while the reaction did not proceed in water immiscible solvents. Use of β-cyclodextrin and surfactants in the reaction did not increase the product yield. The study on variation in the culture conditions revealed that glucose as the carbon source was most suitable for sulphoxidation. The addition of organic nitrogen and divalent metal ion salts did not haveany significant effect on the ability of the organism in bringing about sulphoxidation. Change in initial media pH and temperature did not significantly affect bioconversion.