Synthesis of gem-difluorinated nucleoside analogues of the liposidomycins and evaluation as MraY inhibitors

Two gem-difluoromethylenated nucleoside moieties of liposidomycins, 3 and 4, were designed and synthesized. Compound 3 was assembled from lactol 5 and gem-difluoromethylenated nucleoside 6. In the synthesis of target molecule 4, the coupling of the trichloroacetimidate derivative of gem-difluoromethylenated furanose 7 with nucleoside 8 in the presence of TMSOTf gave the unexpected compound 16 when CH3CN was used as solvent. This results from acetonitrile acting as a nucleophile and participating in the glycosylation reaction. This unusual process may be correlated with the presence of the electron-withdrawing gem-difluoro substituents at the C-2 position of furanose. Compound 3 demonstrated 29% inhibition of MraY at 11.4 mM.