Mechanism based QSAR studies of N-phenylbenzamides as antimicrobial agents.

N-Phenyl benzamides are potent antibacterial agents. They are active against both Gram-positive and Gram-negative bacteria. The Gram-positive bacteria have strong and thick cell wall while the Gram-negative bacterial have thin and permeable cell wall. The DFT based QSAR reveals that molecular weight and total energy significantly contribute to activity against both kinds of target. The electrophilicity index involved in QSAR models derived with anti-Gram-positive activity indicates the dominance of electrostatic interaction. The molar refractivity and logP is involved in QSAR model derived with anti-Gram-negative activity shows steric and hydrophobic interaction. The CoMFA and CoMSIA results also indicate that anti-Gram-positive bacterial activity is a function of electrostatic field effect but the anti-Gram-negative activity depends on hydrophobicity and steric field effect. The CoMFA and CoMSIA contour maps give an indication, the electropositive group around benzene "X" and an electronegative group around carbonyl oxygen is desirable for better anti-Gram-positive bacterial activity. A hydrophobic group around meta position of ring "X" with bulky group at ortho position and a small group at para position are desirable for better activity against Gram-negative target. The findings are reasonable and the mechanism might be different due to difference in composition of cell wall. The cell wall of Gram-positive target does not allow the permeability and only external electrostatic interaction is possible while the cell wall of Gram-negative target allows the permeability of molecules inside the cell for possible hydrophobic and steric bulk interaction.