Total assignment of the proton and carbon NMR spectra of the alkaloid quindoline — utilization of HMQC‐TOCSY to indirectly establish protonated carbon‐protonated carbon connectivities

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AbstractThe reisolation of the indoloquinoline alkaloid quindoline (also known as norcryptolepine) from Cryptolepis sanguinolenta is reported. The structure was unequivocally confirmed by two‐dimensional nmr methods; the proton and carbon spectra were assigned for the first time. Because of congestion in the proton spectrum HMQC‐TOCSY was used as an alternative to the more familiar COSY experiment. In addition to establishing proton‐proton connectivities, HMQC‐TOCSY affords the added benefit of providing, in an indirect sense, connectivity information between protonated carbons.