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Communication | Regular issue | Vol 27, No. 8, 1988, pp.1827-1836
Published online, 1st January, 1970
DOI: 10.3987/COM-88-4609
Flavine Coenzyme Mediated Photooxidation of 3’,4’-Anhydrovinblastine. Further Information on the Later Stages of Bisindole Alkaloid Biosynthesis.

James Peter Kutney,* Lewis Siu Leung Choi, Jun Nakano, and Hiroki Tsukamoto

*Department of Chemistry, The University of British Columbia, 2036 Main Mall, Vancouver, B.C., V6T 1Z1, Canada

Abstract

Flavine coenzyme mediated photooxidation of 3’,4’-anhydrovinblastine (4) has afforded an excellent route to the highly unstable dihydropyridinium intermediate 3. The role of 3 as the initially formed biointermediate in the enzyme-catalyzed coupling of catharanthine (1) and vindoline (2) can now be evaluated in terms of irs crucial role in the biosynthesis of the various bisindole alkaloids such as 4, leurosine (5). catharine (6). vinblastine (7). and vinamidine (8). Extensive studies are presented to establish the structure and chemistry of 3. Techniques such as 13C-nmr and Attached Proton Test (APT) are employed. It is also shown that in the non-enzymatic FMN conversion of 4 to 3, the process proceeds with preferential removal of the C5’-αH in the indole unit of 4 (66% removal in deuterio-labelled as substrate) while in the comparable enzymatic conversion predominant retention of this proton is maintained (65% retention of C5’-αH in deuterio-labelled 4). A similar study in the bioconversion of 4 to 3 with commercial horseradish peroxidase reveals a 50% removal of this proton. Clearly the nature of the stereoselectivicy of the enzymatic process in the generation of 3 is dependent on the nature of oxidases/peroxidases present in the enzyme mixture employed. These studies also provide mechanistic information about the one-electron promoted bioconversion of 4 to 3.