l-Carnitine Esters as “Soft”, Broad-Spectrum Antimicrobial Amphiphiles

A new class of antimicrobial, “soft”, quaternary ammonium l-carnitine esters, of the type (CH3)3N+-CH2-CHOCO(R1)-CH2-COO(R2) Cl-, has been designed, with R1 and R2 being in general long-chain alkyl substituents. The series shows good activity against a wide range of bacteria, yeasts, and fungi. Lipophilicity has been measured by RP-HPLC method to give the logarithm of the experimental capacity factor (log k‘), and a quantitative relationship has been determined between log k‘ and the theoretical partition coefficient (CLOGP); also, bond−dipole descriptors have been introduced into calculations by accounting for polar moieties present within the apolar cores of the molecules, giving a more refined calculated capacity factor (log k‘calcd). Finally the latter has been related to the antimicrobial activity (MIC values). The proposed models are predictive for the best broad-spectrum antimicrobial compound within the series.