Enzymes in organic synthesis. Part 3. Synthesis of enantiomerically pure prostaglandin intermediates by enzyme-catalyzed transesterification of (1SR,2RS,5SR,6RS)-bicyclo[3.3.0]octane-2,6-diol with trichloroethyl acetate in an organic solvent
Since the pancreatin-catalyzed esterification of the diol (1) with 2,2,2-trichloroethyl acetate in tetrahydrofuran is significantly slower than the esterification of the enantiomer ent-(1), the diacetate ent-(3) can be obtained from the racemic diol rac-(1) in a chemical yield of 30–35% and an enantiomeric excess (e.e.) of 97– > 99%. When the remaining enantiomerically enriched diol (1) with an e.e. in the order of 55–68% was subjected once more to the pancreatin-catalyzed esterification its e.e. could be enhanced to 90%. Then acetylation and recrystallization afforded the diacetate (3) in a chemical overall yield of 37% and an e.e. of > 99%.