Chemoenzymatic synthesis of a tachykinin NK-2 antagonist

A non-peptide tachykinin antagonist has been synthesized in a short and efficient four step sequence starting from a chiral enol acetate, which was obtained in enantiomerically pure form by resolution using a lipase catalysed transesterification reaction. The biotransformation was optimized in terms of solvent, temperature and immobilization method used. Oxidative cleavage of the (+)-enol acetate to give the key aldehyde ester intermediate could be achieved indirectly by oxidative rearrangement to an enone followed by Baeyer–Villiger oxidation and ring opening, or by epoxidation, rearrangement and oxidative cleavage or most directly by ozonolysis. X-Ray crystallographic analysis of a camphanic ester derivative of an ester alcohol confirmed that the absolute configuration of the enol acetate was (S).