A 100-L reaction vessel was charged with 50 mM Tris buffer (Tris HCl (77.4 g) and Tris Base (196.7 g) in deionized water (42.3 L)), 12.0 L of subtilisin (PURAFECT® 4000 L, available from Genencor International), acetonitrile (5.7 L), and (±)-5-methoxycarbonyl-6-(3,4-difluorophenyl)-4-methoxymethyl-1,2,3,6-tetrahydro-2-oxopyrimidine, (2), (120 g, 0.38 mol) and the mixture was allowed to react at 37° C., pH 8.3 for 9 days. The reaction mixture was extracted with toluene (10 L). The aqueous layer was separated and washed with toluene (5 L). The combined organic extracts were washed with brine (10 L). The organic layer was concentrated by rotary evaporation, filtered, then adjusted to 400 mL volume with toluene. The (+)-2 was crystallized by adding heptane (80 mL), followed by seeding. The mixture was stirred for 1 hr, then heptane (520 mL) was added over 8 hrs. The crystals were filtered, washed with 3:2 heptane-toluene (150 mL), then dried under high vacuum to yield (+)-(6S)-5-methoxycarbonyl-6-(3,4-difluorophenyl)-4-methoxymethyl-1,2,3,6-tetrahydro-2-oxopyrimidine, ((+)-2) as a white solid.
