Based on modern NMR techniques, such as pulsed field gradient and selective pulse experiments, a systematic approach is introduced confirming the regular uzarigenin- and xysmalogenin-type chirality of seven Uzara cardenolides. The chiral key positions of the steroids were determined as C-3βOH ( = non-epi), 5αH (uzarigenin-type only) and 10β CH3 (= A/B-trans), 13β CH3 and 14βOH (= C/D-cis), as well as 17αH(= non-allo) for both the previously known and two newly isolated cardenolides, i.e. the 3-O-β-glucosidesof coroglaucigenin and pachygenol. Since there are problems in separating the corresponding pairs of 5αH and Δ5,6 unsaturated analogues, the latter could be specifically analysed using the selective pulses. Unequivocal structure reference came from single crystal X-ray diffraction measurement of xysmalogenin. Full interpretation of the complex 1H NMR resonances, including spectral simulation, has led to the identification of designated key signals that give insights into the relative configurations of the whole steroid framework. It should be recognized that the stereochemical constitution of all isolated 5αH and Δ5,6 Uzara cardenolides is compatible with the essential structure of inotropic steroids.
Xysmalobium; Asclepiadaceae; Uzara steroids; cardenolides; NMR selective pulses; X-ray; xysmalogenin; configuration
Publication DOI: 10.1002/(SICI)1099-1565(200003/04)11:2<79::AID-PCA492>3.0.CO;2-HJournal NLM ID: 9200492Publisher: Chichester, Sussex, UK: Wiley
Correspondence: Pauli@uni-muenster.de
Institutions: Institut für Pharmazeutische Biologie und Phytochemie, Westfälische Wilhelms-Universität, Münster, Germany, Organisch-Chemisches Institut, Westfälische Wilhelms-Universität, Münster, Germany
Methods: 13C NMR, 1H NMR, TLC, ESI-MS, HPLC, extraction, derivatization, evaporation, HR-EI-MS
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