The partial synthesis of heteroyohimbine alkaloids; akuammigine, 3-isorauniticine and corynanthe alkaloid; corynantheidine.

General Approach for the Synthesis of Indole Alkaloids via the Asymmetric Pictet−Spengler Reaction: First Enantiospecific Total Synthesis of (−)-Corynantheidine as Well as the Enantiospecific Total Synthesis of (−)-Corynantheidol, (−)-Geissoschizol, and (+)-Geissoschizine

“…The all cis -relationship among the hydrogen atoms at C-3, C-15, and C-20 was confirmed by nOe studies. In addition, removal of the carboxybenzyl group via catalytic debenzylation, followed by Barton−Crich decarboxylation provided previously known ester 15 whose spectroscopic properties were in agreement in all respects to those reported earlier. 3c,e Reduction of ester 15 with LiAlH 4 at 0 °C afforded (−)-corynantheidol 2 ([α] D −102°; lit. −99°,4b −93° 6 ) in 95% yield, the spectroscopic properties of which were identical in all respects to those reported in the literature .…”

“…The optical rotation ([α] D −166°, lit. −171°, −155° 3c ) and spectroscopic properties of synthetic (−)- 1 agree in all respects to those of natural (−)-corynantheidine . The route employed 12 steps with a overall yield of 18%.…”

“…Corynantheidine 1 was first isolated in 1944 by Janot et al from the African plant Pseudocinchona africana , and the structure was determined by the same group . A number of partial and total syntheses of 1 have been reported, all of which resulted in racemates . The related corynantheidol 2 was obtained from Mitragyna parvifolia (Roxb.)…”

A Platform for the Synthesis of Corynantheine-Type Corynanthe Alkaloids

“…The corynantheine alkaloids have been of interest to the synthetic community by virtue of their structural complexity, as made evident by the several previous syntheses of corynantheidol ( 1 ) and corynantheidine ( 2 ) in the literature. − However, most of the work prior to 2000 only reported racemic or partial syntheses except for Meyer’s enantioselective approach for (−)-corynantheidol ( 1 ). − It was not until 2000 that Cook and co-workers accomplished the first enantiospecific total synthesis of (−)-corynantheidine ( 2 ), employing d -tryptophan as their chiral starting material . Following this work, several more enantioselective syntheses of (−)-corynantheidol ( 1 ) and (−)-corynantheidine ( 2 ) were reported, but their applications only extended to indole alkaloids with modest structural differences. − Interestingly, few groups have investigated a unified route toward a diverse heterocyclic series of these natural products that would enable a broader exploration of their untapped medicinal potential .…”

Crystal Structure of Akuammigine Picrate Hydrate

“…Furthermore, conversion of the alkaloids isopteropodine [30] and hirsuteine [31] to akuammigine (1) established additional stereochemical relationships.…”