摘要:
                                Introduction of an anisotropic substituent to the C-6 position of 2', 3'-O-isopropylideneuridine altered the differences in the chemical shift between the methyl signals (Δδ Me) of the isopropylidene group. Thus, exceptions to Imbach's criterion for β-D-ribofuranosyl nucleosides have now been observed for the first time.