Vobasine

The absolute configuration of koumine has also been confirmed by a biomimetic synthesis of koumine from vobasine (50) (43). The configuration was correlated with L(—)-tryptophan, since vobasine was reduced to drega-mine (51) and the latter had been synthesized from L(—)-tryptophan with conservation of the (S) configuration of the amino acid, which corresponds to C-5 of koumine (44). 

The configurations of the stereo centers for ervatamine alkaloids were established by chemical correlations (189, 190) with the vobasine series and supported further by an X-ray diffraction study of 44 (191). 

Laboratory transformations took advantage of fragmentation of dregamine (30), tabemaemontanine (31), and vobasine (32) as N4 oxide induced by treatment with trifluoroacetic anhydride (Polonovski-Potier reaction) (192) and reductive capture of the intermediate iminium ion (Scheme 1). 

Although there is no in vivo correlation, the cooccurrence of 51 and 54 in T. mocquerysii suggests 278 as a reasonable common intermediate formed by vobasine (32) (Scheme 4) through its N4-oxide or other biological equivalents). 

Vincamine (91) is the major alkaloid of V. minor, a plant used against headache and vertigo. It exerts a sedative CNS action and produces a fall in blood pressure. The principal activity is a moderate cerebral vasodilation. Clinical studies have demonstrated that i.v. administration of 91 to humans reduces the arterial blood pressure and increases cerebral blood flow and oxygen consumption. The improved cerebral hemodynamic conditions significantly and positively affect the state of patients with advanced arteriosclerosis with beneficial effects on memory, concentration, and behavior. It has thereafter been introduced under several trade names as a pharmaceutical in many European countries (232). Vobasine (32) has been widely studied it exhibits a weak CNS depressive, analgesic, and antipyretic action (21). 

---