Antibacterial profile against drug-resistant Staphylococcus epidermidis clinical strain and structure-activity relationship studies of 1H-pyrazolo[3,4-b]pyridine and thieno[2,3-b]pyridine derivatives.

Antibacterial resistance is a complex problem that contributes to health and economic losses worldwide. The Staphylococcus epidermidis is an important nosocomial pathogen that affects immunocompromised patients or those with indwelling devices. Currently, there are several resistant strains including S. epidermidis that became an important medical issue mainly in hospital environment. In this work, we report the biological and theoretical evaluations of a 4-(arylamino)-1-phenyl-1H-pyrazolo[3,4-b]pyridine-5-carboxylic acids series (1, 1a-m) and the comparison with a new isosteric ring nucleus series, 4-(arylamino)thieno[2,3-b]pyridine-5-carboxylic acids derivatives (2, 2a-m). Our results revealed the 1H-pyrazolo[3,4-b]pyridine derivatives significant antibacterial activity against a drug-resistant S. epidermidis clinical strain in contrast to the thieno[2,3-b]pyridine series. The minimal inhibitory concentration (MIC) of the most active derivatives (1a, 1c, 1e, and 1f) against S. epidermidis was similar to that of oxacillin and twofold better than chloramphenicol. Interestingly, the position of the functional groups has a great impact on the activity as observed in our structure-activity relationship (SAR) study. The SAR of 1H-pyrazolo[3,4-b]pyridine derivatives shows that the highest inhibitory activity is observed when the meta position is occupied by electronegative substituents. The molecular modeling analysis of frontier molecular orbitals revealed that the LUMO density is less intense in meta than in ortho and para positions for both series (1 and 2), whereas HOMO density is overconcentrated in 1H-pyrazolo[3,4-b]pyridine ring nucleus compared to the thieno[2,3-b]pyridine system. The most active derivatives of series 1 were submitted to in silico ADMET screening, which confirmed these compounds as potential antibacterial candidates.