INDUSTRIAL-PRODUCTION OF OPTICALLY-ACTIVE INTERMEDIATE IN THE SYNTHESIS OF DILTIAZEM WITH LIPASE

An optically active (-)-(2R,3S)-3-(4-methoxyphenyl)glycidic acid methy l ester [(-)-MPGM] is a key intermediate in the synthesis of diltiazem , which is used as a typical calcium channel blocker in more than 100 countries. This chiral compound is produced industrially in a hollow-f iber ultrafiltration membrane bioreactor using a mass-produced extrace llular lipase. Serratia marcescens Sr41 8000 lipase hydrolyzing (+)-(2 S,3R)-MPGM enantioselectively was selected from among various microorg anisms. For industrial production of the lipase, a mutant of S. marces cens is used. (-)-MPGM is effectively produced by this lipase in a Sep racor membrane bioreactor system, in which the lipase is immobilized o n the spongy layer of the shell side of the membrane by physical adsor ption. Asymmetric hydrolysis is carried out semi-continuously in the m embrane bioreactor, in which a toluene solution containing (+/-)-MPGM is circulated in the shell loop and an aqueous solution containing sod ium hydrogen sulfite in the lumen loop. Since the reaction and product separation occur simultaneously in this system, (-)-MPGM with an opti cal purity of 100% e.e. is easily obtained as crystals with a high yie ld through 7 repeated runs by concentrating the organic phase after ea ch reaction. Stabilization and recovery of the lipase are also achieve d. This (-)-MPGM production system was established on an industrial sc ale in 1993 using a series of 57 m(2) membrane bioreactors containing the lipase. The development of this process has enabled the total numb er of steps required for the synthesis of diltiazem to be reduced to 5 from 9, and its production costs to be lowered by one-third. Recently , the lipA and lipBCD genes encoding the lipase and its secretion devi ce were cloned from S. marcescens. The extracellular lipase activity o f the recombinant strain of S. marcescens carrying the lipA and lipBCD genes has been found to he 25-fold greater than that of the wild type . We are now investigating large-scale lipase production using this re combinant strain.