Indor and 1H-NMR. Studies of the Ansa Conformation of Hexahydrorifamycin S

The study of 16, 17, 18, 19, 28, 29-hexahydrorifamycin S by ¹H-NMR. spectroscopy using INDOR at 100 MHz and homodecoupling at 270 MHz has shown that the conformation of the ansa fragment C(20)-C(27) and the position of this fragment relative to the naphthoquinone chromophore are practically the same as those of rifamycin S. This finding rules out the hypothesis that the lower activity of the hydrogenated rifamycins could be due to a different conformation.