Synthesis and Antimicrobial Activity of the Hybrid Molecules between Sulfonamides and Active Antimicrobial Pleuromutilin Derivative

A series of novel hybrid molecules between sulfonamides and active antimicrobial 14-o-(3-carboxy-phenylsulfide)-mutilin were synthesized, and their in vitro antibacterial activities were evaluated by the broth microdilution. Results indicated that these compounds displayed potent antimicrobial activities in vitro against various drug-susceptible and drug-resistant Gram-positive bacteria such as Staphylococci and streptococci, including methicillin-resistant Staphylococcus aureus, and mycoplasma. In particular, sulfapyridine analog (6c) exhibited more potent inhibitory activity against Gram-positive bacteria and mycoplasma, including Staphylococcus aureus (MIC = 0.016-0.063 mu g/mL), methicillin-resistant Staphylococcus aureus (MIC = 0.016 mu g/mL), Streptococcus pneumoniae (MIC = 0.032-0.063 mu g/mL), Mycoplasma gallisepticum (MIC = 0.004 mu g/mL), with respect to other synthesized compounds and reference drugs sulfonamide (MIC = 8-128 mu g/mL) and valnemulin (MIC = 0.004-0.5 mu g/mL). Furthermore, comparison between MIC values of pleuromutilin-sulfonamide hybrids 6a-f with pleuromutilin parent compound 3 revealed that these modifications at 14 position side chain of the pleuromutilin with benzene sulfonamide could greatly improve the antibacterial activity especially against Gram-positives.