Regioselectivity in inhibition of peptide deformylase from Haemophilus influenzae by 4- vs 5-azaindole hydroxamic acid derivatives: Biochemical, structural and antimicrobial studies.

Ribosome assisted protein synthesis in all prokaryotes begins with a formylated methionine. Deformylation and demethionylation of these newly synthesized proteins are critical co-translational events carried out by peptide deformylase (PDF) and methionine aminopeptidase (MetAP) in all living cells. Since the mechanism of N-terminal modification is common between the infectious microbes and the host human cells, it is a challenge to identify selective inhibitors. Given that both MetAP and PDF are metalloenzymes, and have strong affinity for hydroxamic acids, we reasoned that the azaindole-based hydroxamic acids could inhibit the PDF enzymes. In the present study we describe the screening of a 17-compound library with 4- and 5- substituted azaindole hydroxamic acid derivatives against PDF enzyme from H. influenzae (HiPDF), M. tuberculosis (MtPDF) and human PDF (HsPDF). Several of these molecules showed nanomolar inhibition against HiPDF enzyme, best at 21 nM (15). On the other hand, none of these compounds inhibited the human enzyme while only two molecules showed moderate inhibition against Mtb enzyme. Surprisingly only 5-substituted azaindole derivatives inhibited the PDF enzymes. Some of the 5-substituted azaindole compounds inhibited the growth of different microbes indicating their potential application in antimicrobial therapy. Crystallographic and modeling studies provided the mechanistic view of regioselective inhibition.