STUDIES OF VITAMIN-D (CALCIFEROL) AND ITS ANALOGS .49. SELECTIVE ACYLATION OF A-RING PRECURSORS OF VITAMIN-D USING ENZYMES IN ORGANIC-SOLVENTS

Whereas Chromobacterium viscosum lipase (CVL) catalyzes selectively the acylation of the C-5 hydroxyl of the three stereoisomeric vitamin D A-ring precursors 2a, 3a and 3b, only the C-3 hydroxyl of the fourth stereoisomer 2b is acylated under the same conditions in organic solvent. In a convenient application, the racemic vitamin D A-ring precursor 4, possessing only the C-5 hydroxyl, was resolved using suitable conditions identified from the studies of 2 and 3.