Enzymatic transformation of a prostaglandin (bimatoprost) intermediate

A process for the selective conversion of the (R)-epimer substrate in a mixture comprising either:

• (a) (S)-I, (1S,5R,6R,7R)-6-[(3S)-3-hydroxy-5-phenyl-1-pentenyl]-7-[(4-benzoyl)oxy]-2-oxabicyclo[3,3,0]octan-3-one and (R)-I, (1S,5R,6R,7R)-6-[(3R)-3-hydroxy-5-phenyl-1-pentenyl]-7-[(4-benzoyl)oxy]-2-oxabicyclo[3,3,0]octan-3-one, or
• (b) (S)-III, (1S,5R,6R,7R)-6-[(3R)-3-acetoxy-5-phenyl-1-pentenyl]-7-[(4-benzoyl)oxy]-2-oxabicyclo[3,3,0]octan-3-one and (R)-III, (1S,5R,6R,7R)-6-[(3R)-3-acetoxy-5-phenyl-1-pentenyl]-7-[(4-benzoyl)oxy]-2-oxabicyclo[3,3,0]octan-3-one,
• wherein, for (a), the mixture is combined with an acetylating agent in the presence of a lipase to form an acetylation reaction mixture, wherein the (R)-I substrate is selectively converted to (R)-III, and, for (b), the mixture is combined with a C1-6 alcohol in the presence of a lipase to form an alcoholysis reaction mixture, wherein the (R)-III substrate is selectively converted to (R)-I;
• and recovering the (S)-I substrate from 1(a) or recovering the (S)-III substrate from 1(b).