4-Quinolone hybrids and their antibacterial activities.

The emergence and wide-spread of drug-resistant bacteria including multi-drug resistant and pan-drug resistant pathogens which are associated with considerable mortality, represent a significant global health threat. 4-Quinolones which are exemplified by fluoroquinolones are the second largest chemotherapy agents used in clinical practice for the treatment of various bacterial infections. However, the resistance of bacteria to 4-quinolones develops rapidly and spreads widely throughout the world due to the long-term, inappropriate use and even abuse. To overcome the resistance and improve the potency, several strategies have been developed. Amongst them, molecular hybridization, which is based on the incorporation of two or more pharmacophores into a single molecule with a flexible linker, is one of the most practical approaches. This review aims to summarize the recent advances made towards the discovery of 4-quinolone hybrids as potential antibacterial agents as well as their structure-activity relationship (SAR). The enriched SAR may pave the way for the further rational development of 4-quinolone hybrids with excellent potency against both drug-susceptible and drug-resistant bacteria.