RESUMEN
A highly enantio- and diastereoselective strategy to access any member of the sarpagine/macroline family of oxindole alkaloids via internal asymmetric induction was developed from readily available d-(+)-tryptophan. At the center of this approach was the diastereospecific generation of the spiro[pyrrolidine-3,3'-oxindole] moiety at an early stage via a tert-butyl hypochlorite-promoted oxidative rearrangement of a chiral tetrahydro-ß-carboline derivative. This key branching point determined the spatial configuration at the C-7 spiro center to be entirely 7R or 7S. Other key stereospecific processes were the asymmetric Pictet-Spengler reaction and Dieckmann cyclization, which were scalable to the 600 and 150â gram levels, respectively. Execution of this approach resulted in first enantiospecific total synthesis of (+)-isoalstonisine and (-)-macrogentine from the chitosenine series (7R), as well as (+)-alstonisine, (+)-alstofoline, (-)-alstonoxineâ A and (+)-Na -demethylalstonisine from the alstonisine series (7S).
Asunto(s)
Alcaloides/síntesis química , Indoles/síntesis química , Alcaloides/química , Cristalografía por Rayos X , Ciclización , Indoles/química , Conformación Molecular , Oxindoles , Compuestos de Espiro , EstereoisomerismoRESUMEN
To gain access to 3-propoxy-ß-carboline hydrochloride (3-PBC·HCl) (1·HCl) and ß-carboline-3-carboxylate-tert-butyl ester (ßCCt) (2), potential clinical agents active against alcohol self-administration, a two-step route was developed. This process involves a palladium-catalyzed Buchwald-Hartwig coupling and an intramolecular Heck reaction. This two-step route provides rapid access to multigram quantities of 3-PBC (1) and ßCCt (2), as well as analogues for studies of alcohol self-administration. The overall yield of 3-PBC (1) was improved from 8% to 50% by this route.