Asymmetric Total Synthesis of an Iboga-Type Indole Alkaloid, Voacangalactone, Newly Isolated from Voacanga africana

Abstract

A new hexacyclic iboga-type indole alkaloid, voacangalactone (1), was isolated from Voacanga africana , and its structure including the absolute configuration was established by asymmetric total synthesis involving such key steps as the asymmetric Diels-Alder reaction using an aminodiene and the construction of an isoquinuclidine ring and an indole skeleton.

Simple indole alkaloids and those with a nonrearranged monoterpenoid unit

“…72 The welwitindolinone, possessing a bicyclo[4.3.1]decane ring system, is a unique family of oxyindole-containing alkaloids, isolated from a series of marine and terrestrial cyanobacteria. Syntheses of N-methylwelwitindolinone C isothiocyanate (146), C3-hydroxy-N-methylwelwitindolinone C isothiocyanate (147), N-methylwelwitindolinone C isonitrile (148), C3-hydroxy-N-methylwelwitindolinone C isonitrile (149), and N-methylwelwitindolinone D isonitrile (150) were reported by three groups.…”

“…Further transformation of 419 via the construction of the isoquinuclidine ring and indole ring led to (À)-418 (Scheme 86). 147 Syntheses of ibogamine (420) and epiibogamine (421) were reported. The reductive Heck-type annulation was employed to construct the iboga scaffold in the nal step (Scheme 87).…”

Compounds with Anti-Onchocercal Activity from Voacanga africana Stapf (Apocynaceae): Identification and Molecular Modeling

“…The crude methanol extract of V. africana was subjected to silica gel normal phase open column chromatography and elution with a gradient of ethyl acetate in hexane. Repeated column chromatography through Sephadex LH-20, preparative thin-layer chromatography (TLC) yielded a new bisindole alkaloid derivative named voacamine A (1) along with eight known compounds, voacangine (2), voacristine (3),coronaridine (4), tabernanthine (5), iboxygaine (6), voacamine (7), voacorine (8), and conoduramine (9) [16][17][18][19][20][21][22][23][24][25] (Figure 1). The structures of the compounds were established based on NMR ( Figures S3-S25) analyses as well as by comparison with published data.…”

Gold‐Catalyzed Indole Ring Synthesis

“…Like copper, palladium, and rhodium, gold effects the cyclization of o-alkynylanilines to indoles with ease. This basic electrophilic cyclization was improved upon by Marinelli [6,7], was adapted to the synthesis of indole libraries [8,9], was used with supported gold nanoparticles and o-alkynylnitroarenes under hydrogenation conditions in a one-pot indole synthesis [10], and was employed in total syntheses of the alkaloids (-)-mersicarpine [11] and voacangalactone [12]. There have been an abundance of extensions to the Au-catalyzed cyclization of o-alkynylanilines to afford 2,3-disubstituted indoles.…”