Preparation, crystal structure and antibacterial activity of condensation products of usnic acid and acyl hydrazides

Three condensation products of usnic acid with the hydrazides of α-naphthoic, caprylic, and oxamic acids, respectively, have been prepared and characterized by spectrometric methods. A reassignment of the ¹³C-NMR spectral data of usnic acid has been done. The crystal structure of usnic acid 11-[(1-naphthoyl)hydrazone] ethanol solvate (1:1) has been determined. This substance crystallizes in the monoclinic crystal system, the space group P2₁, with the unit cell dimensiones a = 7.7365(7) Å, b = 19.632(2) Å, c = 9.4150(15) Å, β = 108.830(11)° V = 1405.0(4) ų, and Z = 2. At the end of the structure analysis R = 0.055, R_w = 0.052 and S = 0.89. The antibacterial activities of the compounds have been evaluated. The greatest activity against Staphylococcus aureus was found for usnic acid, somewhat lower for the derivatives with hydrazides of α-naphthoic and caprylic acid, and much lower for the derivative with semioxamazide. The activities of these compounds probably depend on their lipophilicity.