H-1 and C-13 chemical shift assignments and stereochemistry of matrine and oxymatrine

Matrine and oxymatrine were extracted from Sophora flaveseens, and their H-1 and C-13 nuclear magnetic resonances (NMR) were unambiguously assigned by a combination of different two-dimensional 2-D H-1-C-13 and H-1-H-1 correlation experiments of HMQC, HMQC-TOCSY and MAXY. The technique of using those experiments to make the assignment of the heavily overlapped spectrum is demonstrated. The coupling constants of matrine were measured by 2-D J-resolved spectrum and 1-D spectra extracted from the slices of 2-D MAXY spectrum. The stereochemistry of the titled compounds was established from the NMR spectroscopy.