Synthesis of 7-thio-substituted 4-oxoquinoline-3-carboxylic acids with antibacterial activity

A series of C-7 thio-substituted 1-cyclopropyl-1,4-dihydro-4-oxoquinoline-3-carboxylic acids were prepared and tested for their antibacterial activity. Structure-activity relationships associated with the C-5 and C-7 substituents were discussed. Among the C-7 substituents including alkylthio, arylthio, heteroarylthio, and cyclic aminothio groups, a 2-aminoethylthio group was the best for enhancing in vitro antibacterial activity. The C-5 variants increased activity in the order OH less than F less than H less than NH2. Of compounds prepared in this work, 5-amino-7-(2-aminoethyl)thio-1-cyclopropyl-6,8-difluoro-1,4-dihydro-4 -oxo-quinoline-3-carboxylic acid (18) was the most active.