title: 3-methylcyclohexanone thiosemicarbazone: determination of E/Z isomerization barrier by dynamic high-performance liquid chromatography, configuration assignment and theoretical study of the mechanisms involved by the spontaneous, acid and base catalyzed processes.
abstract: Here, we report on the simultaneous direct HPLC diastereo- and enantioseparation of 3-methylcyclohexanone thiosemicarbazone (3-MCET) on a polysaccharide-based chiral stationary phase under normal-phase conditions. The optimized chromatographic system was employed in dynamic HPLC experiments (DHPLC), as well as detection technique in a batch wise approach to determine the rate constants and the corresponding free energy activation barriers of the spontaneous, base- and acid-promoted E/Z diastereomerization of 3-MCET. The stereochemical characterization of four stereoisomers of 3-MCET was fully accomplished by integrating the results obtained by chemical correlation method with those derived by theoretical calculations and experimental investigations of circular dichroism (CD). As a final goal, a deepened analysis of the perturbing effect exercised by the stationary phase on rate constant values measured through DHPLC determinations as a function of the chromatographic separation factor α of the interconverting species was successfully accomplished. This revealed quite small deviations from the equivalent kinetic values obtained by off-column batch wise procedure, and suggested a possible effective correction of rate constants measured by DHPLC approach.
authors.affiliation: Dipartimento di Chimica e Tecnologie del Farmaco, "Sapienza" Università di Roma, P.le A. Moro 5, 00185 Rome, Italy.
authors.forename: Simone
authors.initials: S
authors.lastname: Carradori
authors.forename: Roberto
authors.initials: R
authors.lastname: Cirilli
authors.forename: Simona
authors.initials: S
authors.lastname: Dei Cicchi
authors.forename: Rosella
authors.initials: R
authors.lastname: Ferretti
authors.forename: Sergio
authors.initials: S
authors.lastname: Menta
authors.forename: Marco
authors.initials: M
authors.lastname: Pierini
authors.forename: Daniela
authors.initials: D
authors.lastname: Secci
mesh_terms: D000143:Acids / Q000737:chemistry*; D000468:Alkalies / Q000737:chemistry*; D002384:Catalysis; D002851:Chromatography, High Pressure Liquid / Q000379:methods*; D007536:Isomerism; D008958:Models, Molecular; D008962:Models, Theoretical; D013056:Spectrophotometry, Ultraviolet; D013237:Stereoisomerism; D013882:Thiosemicarbazones / Q000737:chemistry*
chemical_list: C578597:3-methylcyclohexanone thiosemicarbazone; D000143:Acids; D000468:Alkalies; D013882:Thiosemicarbazones