Beaver indolizidine

The previous review on Nuphar (water-lily) alkaloids in this treatise appeared in Volume 35, and covered the period 1974-1987 (7). It overlapped in part with the treatment of simple bicyclic Nuphar metabolites in Volume 28 (7). Nuphar alkaloids include sesquiterpenoid monomeric (C15) piperidine and quinolizidine alkaloids as well as more complex dimeric (C30) sulfur-containing metabolites. Related metabolites isolated from the scent glands of the Canadian beaver, Castor fiber, also include a unique indolizidine alkaloid 944 606). Only the indolizidine and simple quinolizidine alkaloids are relevant to the present review. Compounds mentioned in the ensuing discussion are illustrated in Fig. 18. 

The chemistry shown in Eq. (21) uses a / -amino selenide as a radical precursor. /S-Amido radical cyclizations in which y -amido selenides served as the radical precursors have also been reported. One example has been described within the context of an approach to the ABC-ring system of manzamine A [47]. Another appears in an efficient synthesis of indolizidine 72, a component of castoreum derived from the Canadian beaver scent gland (Eq. 22) [48]. It is notable that allylic strain plays a role in the latter free-radical cyclization, as the furyl residue undoubtedly occupies an axial site on the incipient tetrahydropiperidone ring. 

Related C15 quinolizidines and one indolizidine alkaloid have also been found in the exudate from the scent glands of the Canadian beaver Castor fiber) (castoreum, previously used as a fixative in perfumery). For convenience, these animal alkaloids wiU be included in the present discussion. 

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