Thermodynamics, simulation and chiral recognition mechanism of two asymmetric center quinolone

Abstract

A novel antibacterial quinolone was prepared with two chiral centers. For medicinal safety purposes, the four stereoisomers of the molecule are separated by HPLC using a Chiral (+)-Crownpack column (25 cm × 0.46 cm, 5.0 μm) with an eluent of 50 mM H₂SO₄. The values of the retention, separation, and resolution factors of RR-, SS-, RS-, and SR-stereoisomers were in the range of 1.15-7.55, 1.18 to 2.34, and 1.05 to 2.38 at 15, 20, 25, 30 and 35 °C temperatures. The values of the linearity, limits of detection, and limits of quantitation were in the range of 55.6-125, 1.5 to 4.0, and 14.0-37.6 μg mL^-1. Chiral HPLC separation was validated properly. The thermodynamics parameters were in the range of 1.96-10.72 kJ mol^-1 (ΔΔH), 0.013-0.041 kJ mol^-1K^-1 (ΔΔS) and -0.52 to -1.99 kJ mol^-1K^-1 (ΔG₂₉₈). These values confirmed chiral separation as spontaneous and thermodynamically stable. The simulation study was used to understand the mechanism of the chiral separation at the supramolecular level. The binding affinities of the stereoisomers with the chiral stationary phase were in the range of -3.0 to -3.5 kcal mol^-1. The hydrogen bonding was found responsible for the chiral separation. The reported HPLC conditions are inexpensive and may be used to separate the four stereoisomers successfully in any sample.

Keywords: Chiral resolution; Quinolone; Simulation; Thermodynamics.