New rifamycins modified at positions 3 and 4. Synthesis, structure and biological evaluation.

A number of semisynthetic rifamycin derivatives modified at positions 3 and/or 4, belonging to general structures 3, 5, and 6 (see Scheme 1), have been prepared. The synthesis, structure and antimicrobial evaluation of the new compounds are described. All the derivatives have "in vitro" antibacterial activities well comparable with that of rifampicin.