THE STRUCTURE AND STEREOISOMERISM OF THREE MITRAGYNA ALKALOIDS

Abstract

Isorhyncophylline, the isomer into which rhyncophylline is convertible, has been found to occur in nature. Both bases are interconvertible. Isorhyncophylline on hydrolysis with dilute hydrochloric acid is converted to an aldehyde reducible to isorhyncophyllol. When the aldehyde is reduced in the Wolff–Kishner reaction, it is also isomerized and the product is isorhyncophyllane. This reduction product is oxidized by mercuric acetate to a neutral dilactam which still contains the oxindole carbonyl and further contains a new lactam carbonyl present in a six-membered ring. Reduction of the dilactam with lithium aluminum hydride gave a product having the spectroscopic properties of an indole. This confirms the assumption previously made that in rhyncophylline, ring C is five-membered. The isomerization of rhyncophylline, mitraphylline, and formosanine is described. Formosanine has been shown to be identical with uncarine-B and thus uncarine-A is the iso base derivable from formosanine.