Stereochemical Assignment of Pseudoindoxyl Alkaloids

Abstract

The stereochemistries of the C2 and C3 positions in three pseudoindoxyl alkaloids, i.e., mitragynine pseudoindoxyl, yohimbine pseudoindoxyl, and P-yohimbine pseudoindoxyl, were elucidated by spectroscopic analyses.The CD spectra of these compounds and that of fluorocarpamine showed the antipodal-like curves in the long wavelength region.The leaves of Mitragyna speciosa Korth.have been known as an opium substitute in traditional use by Thai and Malay natives.A number of pharmacological studies of this plant have been carried out, but the principle as well as.the mechanism of the biological activities of this folk medicine have not been completely elucidated up to n0w.lThe major alkaloidal constituent in the leaves is an indole alkaloid, mitragynine (I), and several minor components have been isolated.2In 1974, Zarembo er al. reported that mitragynine pseudoindoxyl, which was obtained by the microbial transformation of mitragynine (1) by the fungus Helminthosporum sp., displayed analgesic activity in the D'Amour-Smith test almost ten-fold stronger than mitragynine (1) i t s e ~f .~ During the investigation of medicinally useful compounds from Mitragyna plants, we have had chemical and pharmacological interest in mitragynine pseudoindoxyl.Thus far many natural and semisynthetic pseudo-