Novel steroidal β-carboline derivatives as promising antibacterial candidates against methicillin-resistant Staphylococcus aureus.

A novel series of steroidal β-carboline quaternary ammonium derivatives (SCQADs) derived from natural cholic acid and its derivatives was designed, synthesized and biologically evaluated against four Gram-positive bacteria for the first time. Most of these derivatives exhibited promising antibacterial activity against the tested strains, particularly, compound 21g displayed strong antibacterial activity against MRSA (MIC = 0.5-1 μg/mL) with low cytotoxicity. Meanwhile, derivative 21g was able to quickly kill Gram-positive bacteria within 0.5 h without inducing bacterial resistance. Preliminary mechanistic explorations indicated that compound 21g destroyed bacterial cell membranes to exert its antibacterial effects. Moreover, 21g exhibited high in vivo efficacy and high survival protection in a mouse skin abscess model. These findings suggested that compound 21g has great potential to develop as an antibacterial agent.