Enantiomeric resolution of cyclobutanones and related derivatives by enzyme-catalyzed acylation and hydrolysis

A method for the regio- and enantioselective protection and deprotection of a number of cyclobutanone derivatives employing the isolated enzyme porcine pancreatic lipase (PPL) has been developed. PPL catalyzes the regioselective acylation or deacylation of the C-3 substituent in (2S,3R)-(+)-bis[hydroxymethyl]-1,1-dimethoxycyclobutanone and its enantiomer. Photochemical ring expansion of the corresponding cyclobutanones in methanol gave anomeric mixtures of the methyl furanosides with stereochemical retention of the ring substituents. The PPL-catalyzed hydrolysis of the acetal derived from (2S,3R)-bis[acetoxymethyl]cyclobutanone resulted in a regioselective reaction of the C-3 acetoxymethyl group. PPL exhibits no hydrolysis activity toward the acetal derived from the enantiomeric cyclobutanone diacetate.

Racemic 2-acetoxymethyl-3,3-dimethylcyclobutanone was converted to its enantiomerically enriched (S)-alcohol by PPL-catalyzed hydrolysis. The corresponding methyl furanoside obtained from the photochemical ring expansion of racemic 2-acetoxymethyl-3,3-dimethylcyclobutanone in methanol is not an effective substrate for PPL mediated hydrolysis.