Cyclodextrin derivatives in GC separation of racemates with different volatilities. Part XIX: Thermodynamic aspects of enantioselective GC separation of some volatiles with γ‐cyclodextrins 2,3‐substituted with methyl and acetyl groups

Abstract

Cyclodextrin derivatives in GC separation of racemates with different volatilities. Part XIX: Thermodynamic aspects of enantioselective GC separation of some volatiles with c-cyclodextrins 2,3-substituted with methyl and acetyl groupsThe thermodynamic parameters involved in the enantiomer separation of two homologous series of c-lactones (C 6 -C 8 and C 10 -C 12 ) and a group of structurally related monoterpenoids with a p-menthane skeleton (menthol, i-menthol, neo-menthol, neo-imenthol, menthone, i-menthone, and 3-oxo-1,8-cineole) are determined to investigate how inverted substitution in positions 2 and 3 of the cyclodextrin ring with methyl and acetyl groups influences the enantioselectivity of 2-O-methyl-3-O-acetyl-6-O-thexyldimethylsilyl-c-cyclodextrin and 2-O-acetyl-3-O-methyl-6-O-t-hexyl-dimethylsilyl-c-cyclodextrin. The thermodynamic results show that the methyl and acyl groups, in positions 2 and 3 respectively, act complementarily to increase enantioselectivity and that the relative configuration of the stereogenic centres in the selectands influences enantiomer separation.

Cyclodextrin derivatives in enantiomer GC separation of volatiles. Part XXI: Complexation of some terpenoids with 2‐O‐acetyl‐3‐O‐methyl‐ and 2‐O‐methyl‐3‐O‐acetyl‐6‐O‐t‐hexyldimethylsilyl‐γ‐cyclodextrins: Molecular Mechanics and Molecular Dynamics

“…These results generally agree with the thermodynamic data calculated from the enantioselective GC separation [36] and further confirm some of the likely hypotheses that could concern the differences in enantioselectivity of the two CD derivatives investigated when applied to chiral recognition of menthol analogues.…”

“…The 2-ME-3-AC-derivative separated a high number of racemates well, while the 2-AC-3-MEderivative had lower enantioselectivity, and in general gave lower resolution. More recently [36] the thermodynamic parameters involved in the enantioselection of a group of monoterpenoids with a p-menthane skeleton (menthol, i-menthol, neo-menthol, neo-i-menthol, menthone, i-menthone, and 3-oxo-1,8-cineole) were measured using 2-ME-3-AC-and 2-AC-3-ME-6-THDMSc-CDs as stationary phases. With some exceptions, both CD derivatives showed good enantioselectivity for all menthol analogues under investigation.…”

“…The aim was to predict, if possible, how chromatographic separation with the two modified CD derivatives was affected by the configuration of substituents in positions 1, 3, and 4 in the guest racemates (in particular of hydroxyl or oxo groups in position 3 of the p-menthane skeleton) as well as by the 1,8-epoxy bridge in 3-oxo-p-menthane. Our overall goal is to calculate the differences in host/guest interaction energies between the two substituted CD derivatives and the terpenoid analogues; they are presumably responsible for the different enantioselectivity, in particular if they are in agreement with the differences in thermodynamic parameters calculated elsewhere through enantiomer GC separation [36]. For this purpose, particular attention was paid to interactions between relevant CD substituents (AC, ME, and THDMS) and the substituents at positions 1, 3, and 4 of the ligands (and 7 for the cineoles).…”

Substituent effects on chiral resolutions of derivatized 1‐phenylalkylamines by heptakis(2,3‐di‐O‐methyl‐6‐O‐tert‐butyldimethylsilyl)‐β‐cyclodextrin GC stationary phase

“…Various β‐CD derivatives with bulky 6‐ O ‐ tert ‐butyldimethylsilyl substituents are among the most useful chiral selectors, providing good enantioselectivity for diverse groups of chiral analytes as well as high column efficiency even at low temperatures . Even though a number of new CD derivatives have been developed and proven to be versatile, the understanding of the influence of analyte structure on chiral separation for each CD derivative by GC is thus far insufficient and limited to a certain groups of analytes and CD derivatives . Consequently, the selection of appropriate CD derivative for the separation of new chiral analytes is still challenging.…”

“…[6][7][8][9] Even though a number of new CD derivatives have been developed and proven to be versatile, the understanding of the influence of analyte structure on chiral separation for each CD derivative by GC is thus far insufficient and limited to a certain groups of analytes and CD derivatives. [10][11][12][13][14][15] Consequently, the selection of appropriate CD derivative for the separation of new chiral analytes is still challenging. Therefore, more studies on the relationship of analyte structures and enantioselectivity offered by existing CD derivatives are still essential and might be beneficial for the enantioseparation of new compounds.…”