Synthesis of the benzo-β-carboline isoneocryptolepine: the missing indoloquinoline isomer in the alkaloid series cryptolepine, neocryptolepine and isocryptolepine

Abstract

7 H-Indolo[2,3- c]quinoline has been synthesized in two steps via a new approach starting from commercially available 3-bromoquinoline and 2-bromoaniline. The new methodology consists of two consecutive palladium-catalyzed reactions: a selective Buchwald/Hartwig amination followed by an intramolecular Heck-type reaction. Alternatively, the same skeleton has also been prepared via the combination of a Suzuki arylation with an intramolecular nitrene insertion starting from 4-chloroquinoline and {2-[(2,2-dimethylpropanoyl)amino]phenyl}boronic acid. Selective methylation of 7 H-indolo[2,3- c]quinoline yielded 5-methyl-5 H-indolo[2,3- c]quinoline (Isoneocryptolepine) which is an interesting new lead compound in the search for new antiplasmodial drugs.