New aminoacyl-tRNA synthetase inhibitors as antibacterial agents

Increasing rates of bacterial resistance to known classes of antibiotics present a severe global challenge. As a consequence, the search for new chemical entities that address novel bacterial targets remains ongoing. Aminoacyl-tRNA synthetases (aa-RS) are essential enzymes for protein biosynthesis and emerged as an interesting target class in antibacterial research. These enzymes are present in all living organisms, and they are indispensable for the highly specific translation of the messenger-RNA (mRNA) template into protein via specific transfer-RNAs (tRNAs) as adapter molecules. When one aa-RS is inhibited, the corresponding tRNA is not charged and is therefore unavailable for translation. This leads to protein synthesis inhibition, which, in turn, causes cell growth arrest. Consequently, each compound that inhibits any of the aa-RS is a potential antibacterial agent. The clinical utility of this principle is proven by the natural product Ile-RS inhibitor pseudomonic acid, which is currently marketed as an antibacterial agent for topical application. Various chemical structures that inhibit aa-RS have been identified. These inhibitors have either been isolated from natural sources or have been generated synthetically. The synthetic inhibitors are modifications of natural inhibitors, derivatives of the natural synthetase substrates and reaction intermediates, or have been identified by screening of compound libraries. The recent progress achieved with these different classes of aa-RS inhibitors and their antibacterial potential in vitro and in vivo is discussed in this review.