A CHEMO-ENZYMATIC ELABORATION OF A QUARTERNARY CHIRAL CENTER : AN ALTERNATIVE APPROACH TO THE SIDE CHAIN OF FURAQUINOCIN D

A new approach to ethyl (2R, 3R)-2-t-butyldimethylsilyloxymethyl-3-hydroxy-2-methylbutanoate, a compound which is related to a synthetic intermediate of the side chain of furaquinocin D, is described. The characteristic feature of this compound is a quarternary chiral center and an adjacent secondary alcohol, both of which are in a stereochemically defined state, and the setup of these functionalities was achieved by a combination of stereoselective chemical and enzymatic reactions. The reduction of ethyl 2-hydroxymethyl-2-methyl-3-oxobutanoate with excess NaBH4 afforded (2R∗, 3R∗)-(±)-hydroxy ester with a high diastereomeric excess. After protecting the primary hydroxy group as TBDMS ether, the optical resolution was achieved by lipase-catalyzed hydrolysis of the corresponding chloroacetate in a highly enantioselective manner.