Total assignment of the 1H and 13C NMR chemical shifts of four bufadienolides by 2D NMR spectroscopy

Four known bufadienolides, marinobufagin (1), telocinobufagin (2), bufalin (3) and resibufogenin (4), were isolated from the toad Bufo marinus. The 1H and 13C NMR spectra were completely assigned by using a combination of 13C DEPT and 2D NMR experiments (1H1H COSY, HMQC, HMBC and NOESY). The full 1H NMR data for 1–4 and 1H and 13C NMR data for 2 are reported for the first time.