Fig. 2: Retro-synthetic analysis of hasubanan alkaloids: a unified synthetic route.

a Pathway a: formation of C5-N bond for the synthesis of sinoracutine (9) of sub-group D; b Pathway b: formation of C14-N bond for the synthesis of (-)-cepharamine (4) of sub-group B; c Pathway c: formation of C6-N bond for the synthesis of (-)-cepharatines A (5) and C (6) of sub-group C.