Conformational Study on Securinega Alkaloids

3 X-Ray Crystal Structure of Securinine/Virosecurinine Free Base 

15-Dihydrosecurinine (5) was isolated from the mother Hquor of the extract of Securinega suffruticosa (PaU.) Rehder. This compound shared the 

Although its structure remained previously unclear, phyUanthidine (6) was suspected to be the N-oxide derivative of aUosecurinine (3) because 

The absolute configuration of phyUanthidine (6) was proposed on the basis of the stereochemical outcome of the oxidation reaction of allosecur-inine. This transformation passes through a [2,3]-Meisenheimer/[l,3]-sigmatropic rearrangement sequence, and the geometry of the end product 

Interestingly, margaritarine (9) represents the sole natural representative of tryptamine-substituted Securinega alkaloids. AUomargaritarine 269, prepared by semisynthesis from securinine (1), has been reported and will be discussed in Section 8.1. However, the small abundance of margaritarine (9) in the plant renders its study difficult and presence of others stereoisomers in related species should be considered. Phytochemical studies in the future might confirm or discard this speculation. 

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