Identification of isomeric tropane alkaloids from Schizanthus grohamii by HPLC-NMR with loop storage and HPLC-UV-MS/SPE-NIVlR using a cryogenic flow probe

Two fully automated HPLC-NMR methods are reported and compared for the structure elucidation of four isomeric tropane alkaloids from the stem-bark of an endemic Chilean plant, Schizanthus grahamii Gill. (Solanaceae). The first approach interfaced a conventional HPLC column to NMR by means of a loop storage unit. After elution with a mobile phase consisting of deuterated water and standard protonated organic solvents, the separated analytes were momentarily stored in a loop cassette and then transferred one-at-a-time to the NMR flow probe for measurements. The second strategy combined HPLC with parallel ion-trap MS detection and NMR spectroscopy using an integrated solid-phase extraction (SPE) unit for post-column analyte trapping. The SPE cartridges were dried under a gentle stream of nitrogen and analytes were sequentially eluted and directed to a cryogenically cooled flow-probe with an NMR-friendly solvent. The structures of the four isomeric alkaloids, 3 alpha-senecioyloxy-7 beta-hydroxytropane, 3 alpha-hydroxy-7 beta-angeloyloxytropane, 3 alpha-hydroxy-7 beta-tigloyloxytropane and 3 alpha-hydroxy-7 beta-senecioyloxytropane, were unambiguously determined by combining NMR assignments with MS data. Copyright (C) 2005 John Wiley & Sons, Ltd.