H-1 and C-13 NMR study of quaternary benzo[c]phenanthridine alkaloids

H-1, C-13 and in some cases also N-15 chemical shifts of quaternary benzo[c ]phenanthridine alkaloids (fagaronine, chelerythrine, chelilutine, chelirub ine, nitidine, sanguilutine, sanguinarine, and sanguirubine) were systemati cally studied by NMR spectroscopy and ab initio calculations. The assignmen t of signals in the H-1 and C-13 NMR spectra was obtained from 2D NOE and g radient-enhanced single-quantum multiple bond correlation (GSQMBC) experime nts. The ab initio geometry optimization using Gaussian 94 at the RHF/6-31 G** level, followed by the calculation of chemical shielding using the deMo n/NMR code at the IGLO II level, were carried out in order to rationalize t he assignment of individual experimentally determined resonances. Copyright (C) 1999 John Wiley & Sons, Ltd.