Securinine-type Alkaloids

Seourinine, the most abundant alkaloid of this group, was first isolated by Russian workers in 1956 but its structure was fully established only in 1962. In the subsequent years a variety of alkaloids of the same skeletal type (1) but differing in stereochemistry and minor functionality were isolated and characterized. More recently, three alkaloids possessing a lower homolog structmre (2) of the seourinine type were discovered. Table I lists the known alkaloids according to these two subgroups. Several alkaloids (phyllanthidine, suffruticodine, and suffruticonine) have not been structurally elucidated but their molecular formulas and spectral properties indicate most probably a securinine-type skeleton (Section II, L). 

Securinol C, isomeric Avith both securinol A and B 57), exhibited IR, UV, and NMR spectra consistent with a hydroxylated dihydro-securinine formulation (5S). Treatment of securinol C with methanesul-fonyl chloride in pyridine gave allosecurinine (Section II, D). Thus securinol C is a 14,15-dihydroallosecurinine-type alkaloid with a hydroxyl group located at C-14 or C-15. The latter possibility (C-15-OH) was excluded by showing that securinol C was not enantiomeric with either of the two possible 14,15-dihydroviroallosecurinine alkaloids, securinol A and B. Further examination of the NMR and mass spectra of securinol C provided evidence for the assignment of structure and partial stereochemistry 163 to securinol C. 

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