Synthesis and structure−activity relationship of 8-substituted protoberberine derivatives as a novel class of antitubercular agents

The emergence of multi-drug resistant tuberculosis (MDR-TB) has heightened the need for new chemical classes and innovative strategies to tackle TB infections. It is urgent to discover new classes of molecules without cross-resistance with currently used antimycobacterial drugs. Eighteen new 8-substituted protoberberine derivatives were synthesized and evaluated for their anti-mycobacterial activities against Mycobacterium tuberculosis (M. tuberculosis) strain H37Rv. Among them, compound 7g was the most effective antitubercular agent with minimum inhibitory concentration (MIC) of 0.5 μg/mL. Moreover, it also afforded a potent antitubercular effect against clinically isolated MDR strains of M. tuberculosis with MICs ranging from 0.25 to 1.0 μg/mL, suggesting a novel mode of action. The structure−activity relationship (SAR) analysis revealed that introduction of a substituent at the 8-position in pseudoprotoberberine, especially an n-decyl, could significantly enhance the anti-TB activity. We consider 8-n-decylberberines to be a novel family of anti-tubercular agents with an advantage of inhibiting MDR strains of M. tuberculosis.