Protease induced novel ring contraction reaction of 1,3-oxazin-4-one derivatives

Protease induced ring contraction reaction of ethyl-4-oxo-3-phenyl-l-oxa-5-azaspiro[5,5]-undec-2-ene-2-car☐ylate (1) yielded 4-phenyl-3-hydroxy-1H-pyrrole-2,5-dione (5). This product and its derivatives have been characterized by comparing their total identity with authentic compounds. Involvement of basic amino acid residues for the initiation of the ring contraction reaction by abstracting the proton at position-3 of the oxazinone ring has been suggested. Chemical evidence for the base catalyzed reaction pathway of compound1 leading to the formation of compound5 is presented.