Enantioselective Preparation and Enzymatic Cleavage of Spiroisoxazoline Amides

Several enantiopure spiroisoxazoline amides were prepared from tert-butylester 22, which is obtained via an enantiotopic groups differentiating high pressure Diels–Alder cycloaddition. Treatment of these amides with an isoxazoline-splitting enzyme, which is involved in an injury induced defense reaction of the sponge Aplysina cauliformis, proves the bromoatoms in the cyclohexenone moiety to be important for enzyme binding, while the presence of the N–H bond of a monoalkylamide turned out to be mandatory for ring fission. The pertinence of these results to the ring splitting mechanism is discussed.