The objective of this project is to develop new technology of fundamental importance in the use of enzymes as catalysts in organic synthesis and to apply this technology to the synthesis of compounds important in pharmaceutical production and development.
The specific aims are to develop a general reversible linkage strategy for the use of Coenzyme A (CoA) ester utilizing enzymes as catalysts in organic synthesis and to develop a general method for the quantitative enzymatic conversion of racemic carboxylic acids possessing asymmetry at the alpha-carbon into one enantiomer in high optical purity. The CoA portion of the project will involve separation of the CoA ester into the reactive (thioester) and the larger recognition portions to be connected in situ by a reversible imine or hemithioacetal linkage. This linked CoA ester analog will be employed as a substrate for CoA ester utilizing enzymes so that simple thioesters will be used in synthetic transformations with only a catalytic amount of the larger recognition moiety. This technology will be used in acyl transfer reactions including the chloramphenicol acetyltransferase catalyzed synthesis of acyl chloramphenicols useful as a palitable form of the drug. Also, the asymmetric hydration of alpha,beta-unsaturated thioesters will be carried out to form chiral synthons useful in the preparation of numerous useful drugs and beta-hydroxy, alpha-amino acids which serve as components of natural antibiotics. The second part of the project will involve the use of dithioesters and possibly thionoesters as substrates for hydrolytic enzymes in kinetic resolution reactions. The alpha-protons of dithioesters are quite acidic so that dithioesters of acids having an asymmetric center and one proton on the alpha-carbon will continuously racemize in solution. Selective enzymatic hydrolysis of one enantiomer will allow quantitative conversion to one product in high optical purity. This technology will be employed in the synthesis of several alpha-arylpropionates useful as analgesic and antiinflammatory agents, amino acids found in natural antibiotics, and several other classes of pharmaceutically useful compounds. The technology developed is expected to have important immediate synthetic applications and general implications far beyond the specific applications addressed in this grant period.
