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Communication | Regular issue | Vol 43, No. 11, 1996, pp.2347-2351
Published online, 1st January, 1970
DOI: 10.3987/COM-96-7597
Unusual Enamide Cleavage of Frangufoline under Mild Acidic Condition

Dae-Yeon Suh, Yong Chul Kim, Yong Nam Han, and Byung Hoon Han

*Natural Products Research Institute, Seoul National University, 28, Yungun, Jongro Seoul 110-460, Korea

Abstract

In mild acidic condition (2N HCl, 55 °C), frangufoline, a frangulanine type 14-membered cyclopeptide alkaloid was first converted via unusual enamide cleavage to sanjoinine-G2, which was further hydrolyzed to a linear compound, (S)-[(N’,N’)-dimethylphenylalanyl[-(2S,3S)-3-(p-formylphenoxyleucyl)-(S)-leucine. From the extensive acid hydrolysates, 4-hydroxybenzaldehyde was also isolated. Air oxidation of the vinylic double bond followed by the liberation of formaldehyde is proposed for a possible mechanism for the ring cleavage.