13 IBOGA ALKALOIDSの合成研究 : dl-Ibogamine,dl-Epiibogamine dl-Ibogaine,dl-Epiibogaine,dl-Tabernanthine,dl-Epitabernanthineの全合成

抄録

Ibogamine(Ia) and ibogaine(IIa), the representative menbers of these alkaloids, were already synthesized by Buchi, Nagata, Kutney, and Sallay, independently. We also reported the synthesis of dl-epiibogamine. We have now extended our method to the syntheses of dl-ibogamine, dl-ibogaine, dl-epiibogaine, dl-tabernanthine(IIIa), and dl-epitabernanthine(IIIb), which involves separation of the stereoisomers of the penultimate Products(XVI). The Ziegler cyclization of (V) gave a complicated mixture of products, which was separated by chromatography to give two enamines: (VIIIa) mp163-4°and its epimer (VIIIb) mp240-6°. Both enamines were hydrolysed with C-HCl, and the product was esterified with diazomethane to afford the (XIIa) mp70°, and (XIIb) mp66-8°as a mixture. The ketal-ester(XIII) obtained from the (XIIa) was converted by Corey's method to the acetyl derivative(XIV). The Huang-Minlon reduction and subsequent deketalization gave the ketone(XVI) which gave two spots on tlc. Chromatography of (XVI) afforded (XVIa) pic., mp178-180°and (XVIb) pic., mp184-6°. (XVIa) and (XVIb) were obtained by the same treatment of (XIIb) as (XIIa). The Fischer indole cyclization of (XVIa) with phenylhydrazine by anhydrous formic acid gave dl-ibogamine, mp132-4°. On treatment of (XVIb) in a similar way, dl-epiibogamine, mp194-6°, was obtained. This result makes clear the configuration of ethyl group, namely, (XVIa) is exo-ethyl derivative and (XVIb) is endo-ethyl derivative. We also synthesized dl-ibogaine; mp111-5°, dl-epiibogaine; mp179-180°, dl-tabernanthine; mp181-5°and dl-epitabernanthine; mp216-21°, stereospecifically, by use of methoxy substituted phenylhydrazine in stead of phenylhydrazine.