Preferential binding of cucurbit[7]uril toward 2-amino-4-chlorophenol in chlorzoxazone

Abstract

Chlorzoxazone (CLZ) is a centrally acting skeletal muscle relaxant synthesized from 2-amino-4-chlorophenol (ACP). However, due to the toxic side effects of ACP, its concentration in CLZ formulations is strictly regulated (0.5%). In this study, we investigate the preferential binding of cucurbit[7]uril (CB7) toward CLZ and ACP using 1H NMR, isothermal titration calorimetry (ITC) and molecular dynamics (MD) simulations, to explore ​possible future uses of CB7, either for purifying CLZ from its toxic impurity (ACP) or in sensing ACP in CLZ. ITC experiments confirm the formation of 1:1 complexes, with favorable enthalpic and entropic contributions and binding constants of 1.1 × 106 and 4.9 × 104M−1 for ACP and CLZ, respectively, while 1H NMR and MD simulations reveal the guests in the complexes are included within the cavity of CB7. Molecular Mechanics Poisson-Boltzmann Surface Area (MM-PBSA) results further confirmed the favorability of CB7 toward ACP. Additional MD simulations reveal that CB6 and CB8 preferentially bind CLZ and ACP, respectively, with CB6 forming inclusion and exclusion complexes with CLZ and ACP, respectively, while CB8 forms stable 1:1 and 1:2 inclusion complexes with each guest.