title: Diastereo- and enantioseparation of a N(α)-Boc amino acid with a zwitterionic quinine-based stationary phase: focus on the stereorecognition mechanism.
abstract: A chiral chromatography method enabling the simultaneous diastereo- and enantioseparation of N(α)-Boc-N(4)-(hydroorotyl)-4-aminophenylalanine [Boc-Aph(Hor)-OH, 1] was optimized with a quinine-based zwitterionic stationary phase. The polar-ionic eluent system consisting of ACN:MeOH:water-49.7:49.7:0.6 (v/v/v) with formic acid (4.0mM) and diethylamine (2.5mM), allowed the successful separation of the four acid stereoisomers: αd,d-/d,l-1=1.08; αd,l-/l,d-1=1.08; αl,d-/l,l-1=1.40. According to the in-house developed synthetic procedure and the recorded electronic circular dichroism spectra, the following stereoisomeric elution order was readily established in the optimal chromatographic conditions: d,d-1<d,l-1<l,d-1<l,l-1. With the aim of better understanding the molecular basis of the retention behaviour of the four stereoisomers in the employed chromatographic system and conditions, a computational protocol consisting in molecular dynamics simulations was applied. The use of the three descriptors INTER (in kcalmol(-1), encoding for the interaction energy between the selector SO unit and the whole system), INTER_SA (in kcalmol(-1), encoding for the interaction energy between SO and the sole selectand SA), and SELF (in kcalmol(-1), encoding for the conformational energy of SA relative to its minimum energy registered by the collected snapshots) revealed the active role of achiral sub-structural elements of the chiral stationary phase and eluent components in the overall stereorecognition mechanism.
authors.affiliation: Department of Pharmaceutical Sciences, University of Perugia, Via Fabretti 48, 06123 Perugia, Italy.
authors.forename: Federica
authors.initials: F
authors.lastname: Ianni
authors.affiliation: Department of Pharmaceutical Sciences, University of Perugia, Via Fabretti 48, 06123 Perugia, Italy.
authors.forename: Andrea
authors.initials: A
authors.lastname: Carotti
authors.affiliation: Department of Pharmaceutical Sciences, University of Perugia, Via Fabretti 48, 06123 Perugia, Italy.
authors.forename: Maura
authors.initials: M
authors.lastname: Marinozzi
authors.affiliation: Department of Pharmaceutical Sciences, University of Perugia, Via Fabretti 48, 06123 Perugia, Italy.
authors.forename: Gloria
authors.initials: G
authors.lastname: Marcelli
authors.affiliation: Department of Physics and Geology, University of Perugia, Via Pascoli 1, 06123 Perugia, Italy.
authors.forename: Alessandro
authors.initials: A
authors.lastname: Di Michele
authors.affiliation: Department of Pharmaceutical Sciences, University of Perugia, Via Fabretti 48, 06123 Perugia, Italy. Electronic address: roccaldo.sardella@unipg.it.
authors.forename: Roccaldo
authors.initials: R
authors.lastname: Sardella
authors.affiliation: Department of Analytical Chemistry, University of Vienna, Währinger Strasse 38, 1090 Vienna, Austria.
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Lindner
authors.affiliation: Department of Pharmaceutical Sciences, University of Perugia, Via Fabretti 48, 06123 Perugia, Italy.
authors.forename: Benedetto
authors.initials: B
authors.lastname: Natalini
mesh_terms: D000596:Amino Acids / Q000737:chemistry / Q000302:isolation & purification*; D002851:Chromatography, High Pressure Liquid; D002852:Chromatography, Ion Exchange; D002929:Cinchona / Q000737:chemistry; D004048:Diethylamines / Q000737:chemistry; D005561:Formates / Q000737:chemistry; D056004:Molecular Dynamics Simulation; D010649:Phenylalanine / Q000031:analogs & derivatives* / Q000737:chemistry / Q000302:isolation & purification; D011803:Quinine / Q000737:chemistry*; D013237:Stereoisomerism
chemical_list: D000596:Amino Acids; D004048:Diethylamines; D005561:Formates; C030544:formic acid; C009722:4-aminophenylalanine; D010649:Phenylalanine; D011803:Quinine; C034281:diethylamine
keywords: Chiral recognition mechanism; Cinchona alkaloid-derived zwitterionic chiral stationary phases; Diastereo- and enantioseparation; Electronic circular dichroism; Pharmaceutically relevant N(α)-Boc amino acid; Polar-ionic mode