Structure-activity relationships in 4-deoxypyrido[1',2'-1,2]imidazo[5,4-c]rifamycin SV derivatives

New 4-deoxyhalogenopyrido[1',2'-1,2]imidazo[5,4-c]rifamycin SV derivatives (V-VIII) have been prepared as an extention of a program which led to the synthesis of analogous pyrido- and alkylpyrido compounds (I-IV) displaying a low level of g.i. absorption. The new compounds give comparatively much lower ED50 p.o./s.c. ratios showing a recovery in the extent of oral absorption. XPS, N.M.R., and HPLC data rationalize this activity in hydrophilicity due to the electron-withdrawing inductive effect of the halogen atoms bound to the pyridoimidazo system. This effect is exerted in particular on the negatively charged N(2'), and is the opposite as that exerted by the alkyl groups present in (I-III).