The Hydroxylated, Tetracyclic Bisquinolizidine Alkaloids Baptifoline and Epibaptifoline: Enantioselective Synthesis and Unambiguous Assignment of their Configuration at C-13

The epimeric bisquinolizidines baptifoline and epibaptifoline are C-13 hydroxylated derivatives of the well-known lupine alkaloid anagyrine. We synthesized both compounds from 11-allylcytisine and determined their uncertain configuration at the C-13 stereocenter by NMR, chemical transformation, and X-ray. The alcohol function was found to be in endo (alpha) position in baptifoline (configuration: 7R, 9R, 11R, 13R) and in exo (beta) position in epibaptifoline (configuration: 7R, 9R, 11R, 13S).