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Structural revision of stemoburkilline from an E-alkene to a Z-alkene
Kwankamol Sastraruji1, Stephen G Pyne, Alison T Ung
1School of Chemistry, University of Wollongong, Wollongong, New South Wales 2522, Australia.
Abstract:
Semisynthesis studies starting from (11Z)-1',2'-didehydrostemofoline (4) indicated that the known Stemona alkaloid stemoburkilline is the Z-isomer and not the E-isomer as initially reported. The semisynthesis involved conversion of (11Z)-1',2'-didehydrostemofoline (4) to 11(S),12(S)-dihydrostemofoline (3) followed by a stereoselective base-catalyzed ring-opening reaction to give (Z)-stemoburkilline (8). The same product was obtained using a similar synthetic protocol starting from isostemofoline (6) via a based-catalyzed ring-opening reaction of 11(S),12(R)-dihydrostemofoline (1). A re-examination of the crude root extracts of Stemona burkillii Prain and further NOE studies established stemoburkilline as the Z-isomer (8).
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