Attempted Synthesis of Vinca Alkaloids Condensed with Three-Membered Rings.

András Keglevich,Csaba Szántay,Péter Keglevich,Zsuzsanna Sánta,Réka Pápai,Áron Szigetvári,Miklós Dékány,Szabolcs Mayer,László Hazai

doi:10.3390/molecules23102574

Abstract

Our successful work for the synthesis of cyclopropanated vinblastine and its derivatives by the Simmons–Smith reaction was followed to build up further three-membered rings into the 14,15-position of the vindoline part of the dimer alkaloid. Halogenated 14,15-cyclopropanovindoline was prepared by reactions with iodoform and bromoform, respectively, in the presence of diethylzinc. Reactions of dichlorocarbene with vindoline resulted in the 10-formyl derivative. Unexpectedly, in the case of the dimer alkaloids vinblastine and vincristine, the rearranged products containing an oxirane ring in the catharanthine part were isolated from the reactions. The attempted epoxidation of vindoline and catharanthine also led to anomalous rearranged products. In the epoxidation reaction of vindoline, an o-quinonoid derivative was obtained, in the course of the epoxidation of catharanthine, a hydroxyindolenine type product and a spiro derivative formed by ring contraction reaction, were isolated. The coupling reaction of vindoline and the spiro derivative obtained in the epoxidation of catharanthine did not result in a bisindole alkaloid. Instead, two surprising vindoline trimers were discovered and characterized by NMR spectroscopy and mass spectrometry.

Highlights

The “dimer alkaloids” vinblastine and vincristine (VCR, 2) (Figure 1), isolated from the Madagascar periwinkle Catharanthus roseus, belong to the family of the so-called “bisindole” alkaloids [1,2,3,4,5]
Our first purpose was to build up the halogencyclopropane ring in place of the C(14)=C(15)
The residue was purified by preparative TLC and catharanthine (3) was obtained (111 mg, 39%)

Summary

Introduction

The “dimer alkaloids” vinblastine (vincaleukoblastine, VLB, 1) and vincristine (VCR, 2) (Figure 1), isolated from the Madagascar periwinkle Catharanthus roseus, belong to the family of the so-called “bisindole” alkaloids [1,2,3,4,5]. Their structure comprises two indole-related “monomers”: derivatives of catharanthine (3) and vindoline (4).

Objectives

Methods

Results

Conclusion