title: Combined approach using capillary electrophoresis, NMR and molecular modeling for ambrisentan related substances analysis: Investigation of intermolecular affinities, complexation and separation mechanism.
abstract: A comprehensive investigation on the CE separation mechanisms and on the inclusion complexation with CyDs of the chiral drug S-ambrisentan (S-AMB), its R-enantiomer and other impurities was performed by different techniques. A CE method was previously set up allowing the simultaneous determination of the enantiomeric purity and of impurities of S-AMB, based on the addition of SDS micelles and γ-cyclodextrin (γCyD) to borate buffer. In this study, the electrophoretic behavior of the analytes in terms of selectivity and mobility with respect to the addition of different CyDs was first investigated, evidencing the presence of interactions for all the CyDs, but the unique ability of γCyD for obtaining the separation of all the compounds. By molecular modeling, aggregates between SDS micelles and analytes, and inclusion complexes between CyDs, SDS and/or analytes of different stoichiometries were simulated. The potential and the gain energy of complexes were calculated on the minimized conformations, showing the great tendency of γCyD of forming mixed complexes with one or two SDS molecules and with the analyte, even if with different affinities among the analytes. For 1:1:1 mixed complexes with different CyDs, the highest difference of potential energy between the enantiomers' complexes was observed for γCyD. Two-dimensional NOE spectroscopy experiments were performed for S-AMB and I1and pointed out the interactions of the aromatic moiety of the analytes and of SDS aliphatic chain with γCyD protons, confirming the existence of γCyD mixed complexes. The high affinity of SDS for the γCyD cavity was suggested to justify the fundamental role of SDS in modulating and achieving the CE separation, due to its influence both on the stability and on the type of complexes between γCyD and the analytes.
authors.affiliation: Department of Chemistry "U. Schiff", University of Florence, Via U. Schiff 6, 50019 Sesto Fiorentino, Florence, Italy.
authors.forename: Benedetta
authors.initials: B
authors.lastname: Pasquini
authors.affiliation: Department of Neuroscience, Psychology, Drug Research and Child Health, Section of Pharmaceutical and Nutraceutical Sciences, University of Florence, Via U. Schiff 6, 50019 Sesto Fiorentino, Florence, Italy.
authors.forename: Fabrizio
authors.initials: F
authors.lastname: Melani
authors.affiliation: Department of Chemistry "U. Schiff", University of Florence, Via U. Schiff 6, 50019 Sesto Fiorentino, Florence, Italy.
authors.forename: Claudia
authors.initials: C
authors.lastname: Caprini
authors.affiliation: Department of Chemistry "U. Schiff", University of Florence, Via della Lastruccia 3-13, 50019 Sesto Fiorentino, Florence, Italy.
authors.forename: Massimo
authors.initials: M
authors.lastname: Del Bubba
authors.affiliation: Department of Chemistry "U. Schiff", University of Florence, Via U. Schiff 6, 50019 Sesto Fiorentino, Florence, Italy.
authors.forename: Sergio
authors.initials: S
authors.lastname: Pinzauti
authors.affiliation: Department of Chemistry "U. Schiff", University of Florence, Via U. Schiff 6, 50019 Sesto Fiorentino, Florence, Italy. Electronic address: serena.orlandini@unifi.it.
authors.forename: Serena
authors.initials: S
authors.lastname: Orlandini
authors.affiliation: Department of Chemistry "U. Schiff", University of Florence, Via U. Schiff 6, 50019 Sesto Fiorentino, Florence, Italy. Electronic address: sandra.furlanetto@unifi.it.
authors.forename: Sandra
authors.initials: S
authors.lastname: Furlanetto
mesh_terms: D003505:Cyclodextrins; D019075:Electrophoresis, Capillary; D009682:Magnetic Resonance Spectroscopy; D010666:Phenylpropionates; D011724:Pyridazines; D013237:Stereoisomerism
chemical_list: D003505:Cyclodextrins; D010666:Phenylpropionates; D011724:Pyridazines; C467894:ambrisentan
keywords: Ambrisentan; Capillary electrophoresis; Enantioseparation; Inclusion complex; Molecular modeling; NMR