Binding of Fidarestat Stereoisomers with Aldose Reductase

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Abstract
The stereospecificity in binding to aldose reductase (ALR2) of two fidarestat {6-fluoro-2',5'-dioxospiro[chroman-4,4'-imidazolidine]-2-carboxamide} stereoisomers [(2S,4S)and (2R,4S)] has been investigated by means of molecular dynamics simulations using freeenergy integration techniques. The difference in the free energy of binding was found to be2.0 ± 1.7 kJ/mol in favour of the (2S,4S)-form, in agreement with the experimentalinhibition data. The relative mobilities of the fidarestats complexed with ALR2 indicate alarger entropic penalty for hydrophobic binding of (2R,4S)-fidarestat compared to (2S,4S)-fidarestat, partially explaining its lower binding affinity. The two stereoisomers differmainly in the orientation of the carbamoyl moiety with respect to the active site and rotationof the bond joining the carbamoyl substituent to the ring. The detailed structural andenergetic insights obtained from out simulations allow for a better understanding of thefactors determining stereospecific inhibitor-ALR2 binding in the EPF charges model.