Atropisomerism of a Podophyllotoxin Derivative: Experimental and Computational Study:

Diphyllin-7′-O-β-D-glucoside, a podophyllotoxin derivative, was isolated from the roots of Dysosma versipellis. The 1H and 13C NMR spectra acquired at 300 K exhibited doubling of signals, suggesting the existence of two rotamers in solution. Variable-temperature 1H NMR experiments indicated a dynamic exchange process between the two rotamers. DFT calculations verified nearly equal energies for the two rotamers about the single bond C7′-O7.