Lipase-catalyzed synthesis of chiral amides. A systematic study of the variables that control the synthesis

A systematic study of the aminolysis of esters catalyzed by different lipases From different origins was carried out. A factorial analysis showed that the main variables that control the amide synthesis are: temperature, hydrophobicity of the solvent, reaction volume and amount of water added to the reactor medium. Besides, several undescribed interactions of variables are significative in the control of the process, too. The resolution of racemic esters or amines was analyzed. Lipases from Rhizopus niveus,Candida antarctica B and PPL gave the best enantioselectivities in the resolution of chiral esters while C.rugosa and P.cepacia lipases were the less interesting lipases. alpha-Chymotrypsin shows lower enantioselectivity and yield than Rhizopus niveus, C. antarctica B and PPL lipases in the resolution of racemic esters. This protease needs a large excess of acyl donor in respect to the amine and works at a lower temperature than lipases due to its low thermostability. All the tested lipases showed R-enantiopreference in the aminolysis of esters using (R,S) 1-phenyl-ethylamine. In this reaction, the lipase A from C. antarctica, (SP526) and Rhizopus niveus lipase are good catalysts for the synthesis. On the other, PS and PPL are less interesting biocatalysts. Therefore, the optimum biocatalyst is different if we want to resolve (R,S) esters or (R,S) amines. The aminolysis is interesting for the resolution of racemic amines but not for the resolution of racemic esters. The immobilization does not alter the enantiopreference of the lipases. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.