Ein neuer Abbau des Indolalkaloids Kopsin; chemische Korrelierung der Alkaloide vom Kopsin‐ und Pleiocarpin‐Typ mit Minovincin

Abstract

A new chemical degradation of (–)‐kopsine is described which completely confirms the structure of this alkaloid. Correlation of (–)‐aspidofractinine, (–)‐pleiocarpine and (–)‐kopsine with (–)‐minovincine establishes the absolute stereochemistry of these bases. It appears that, in contrast to the aspidospermine group, all alkaloids containing the aspidofractinine skeleton possess the same absolute stereochemistry.

Stereoselective Synthesis of (+)-Aspidofractinine

“…Aspidofractinine is a complex alkaloid isolated from the leaves of Pleiocarpa tubicana and Aspidosperma refractum, and its structure was elucidated in 1963 by Schmid and co-workers (Figure ) . It has since been isolated from Aspidosperma pyrifolium and other Apocynaceae species .…”

Electrochemical oxidation of aspidofractinine-type alkaloids: Formation of kopsine, kopsidine, kopsinitarine and bisindole derivatives

“…The extract was washed, dried (Na 2 SO 4 ), and the solvent was then removed under reduced pressure. The resulting product was chromatographed over SiO 2 (1% MeOH-CHCl 3 ) to afford pure kopsidine C 24 (15 mg, 15% from kopsingine 2) as a light yellow oil, [α] (35), 427 (20), 425 (50), 413 (12), 355 (11), 337 (100) and 107 (18).…”

Alkaloids

“…Olivacine (341) was synthesized by several groups [336]. Uleine (342), apparicine (343), and vallesamine (344) also do not bear a tryptamine unit as a distinguishable feature in their fundamental structure, but they are normally grouped under the Aspidosperma family since they occur in Aspidosperma species. Synthesis of uleine (342) was achieved stereoselectively by Büchi [337], whereas Kametani [338] published the efficient synthesis of several members of the dasycarpidone-uleine series.…”

“…In fact, minovincine (353) was chemically converted into aspidofractinine (352) by treatment with hydrochloric acid and subsequent reduction [377]. The degradation of kopsine (351) to aspidofractinine (352) indicated its absolute configuration, [343]. …”