UNUSUAL ENAMIDE CLEAVAGE OF FRANGUFOLINE UNDER MILD ACIDIC CONDITION

In mild acidic condition (2N HCl, 55 degrees C), frangufoline, a frang ulanine type 14-membered cyclopeptide alkaloid was first converted via unusual enamide cleavage to sanjoinine-G2, which was further hydrolyz ed to a linear compound, (S)-[(N',N')-dimethylphenylalanyl]-(2S,3S)-3- (p-formylphenoxyleucyl)-(S)-leucine. From the extensive acid hydrolys ates, 4-hydroxybenzaldehyde was also isolated. Air oxidation of the vi nylic double bond followed by the liberation of formaldehyde is propos ed for a possible mechanism for the ring cleavage.