Affinity and enantioselectivity of Rifamycin SV towards low molecular weight compounds

Association of amino acids and some other low molecular weight compounds with rifamycin SV in water has been studied by ¹H NMR titrations. Rifamycin binds aromatic amino acids with pronounced enantioselectivity in favor of l-enantiomers and forms complexes with heterocyclic compounds but does not interact with simple benzene derivatives. Binding constants correlate with LUMO energies and hydrophobicities (expressed as log P values) of guest molecules indicating contributions to the binding free energy from aromatic stacking interactions with the naphthohydroquinone fragment of rifamycin SV and from hydrophobic interactions. Proposed mode of binding is supported by semiempirical calculations of structures of host-guest complexes.