Synthesis and biological activity of 3'-hydroxy-5'-aminobenzoxazinorifamycin derivatives.

As a part of our studies on the syntheses of benzoxazinorifamycin derivatives, 3'-hydroxy-5'-aminobenzoxazinorifamycin derivatives were synthesized, and tested for their antimicrobial activities. The antimicrobial activities of these compounds against gram-positive and gram-negative bacteria were almost identical to those of rifampicin (RFP) and rifabutain (RFB), however, antimicrobial activities against Mycobacterium tuberculosis were superior to RFP, while being similar to RFB. 3'-Hydroxy-5'-(4-alkyl-1-piperazinyl)benzoxazinorifamycin derivatives also had in vitro potent activities against Mycobacterium avium complex (MAC). Their minimal inhibitory concentration values against MAC were 2-256 times greater than RFP and RFB. Their in vivo efficacies against M. tuberculosis and MAC, after oral administration to mice, were superior to RFP and RFB, except for RFB against M. tuberculosis activity in vivo. Although they were absorbed from the gastrointestinal tract, their plasma levels were lower than that of RFP. Among these 5'-(4-alkyl-1-piperazinyl) derivatives, 3'-hydroxy-5'-(4-isobutyl-1-piperazinyl)benzoxazinorifamycin, compound 19 (KRM-1648), was selected as the most promising and its preliminary pharmacokinetic characteristics in mice were investigated. Compound 19 was distributed much more in tissues, especially in spleen and lung, than in plasma and had a long elimination time from tissues.