Non-aqueous capillary electrophoretic enantioseparation of N-derivatized amino acids using cinchona alkaloids and derivatives as chiral counter-ions

Abstract

A non-aqueous capillary electrophoretic method developed with quinine and tert.-butyl carbamoylated quinine as chiral selectors for the enantioseparation of N-protected amino acids was applied to the investigation of other quinine derivatives as chiral additives. The optimum composition of the background electrolyte was found to be 12.5 mM ammonia, 100 mM octanoic acid and 10 mM chiral selector in an ethanol-methanol (60:40, v / v) mixture. Under these conditions, a series of chiral acids, as various benzoyl, 3,5-dinitrobenzoyl and 3,5-dinitrobenzyloxycarbonyl amino acid derivatives were investigated with regards to selectand-selector relationships and enantioselectivity employing quinine, quinidine, cinchonine, cinchonidine, tert.-butyl carbamoylated quinine, tert.-butyl carbamoylated quinidine, dinitrophenyl carbamoylated quinine and cyclohexyl carbamoylated quinine as chiral selector.

Sensitive chiral analysis by capillary electrophoresis

“…The main chiral selectors used in NACE for chiral separations are CDs and their derivatives (see Table 1) [56]. Ion-pairing compounds, such as camphorsulfonate enantiomers [57] and quinine derivatives, have also been employed [58][59][60][61][62].…”

Effects of organic solvents on sample pretreatment and separation performances in capillary electrophoresis

“…The advantages of employing nonaqueous CE for chiral separations were cited in a series of recent papers [154][155][156][157][158][159][160]. For example, (i) Piette et al [154,155] reported the use of quinine and quinidine derivatives as chiral selectors for the CE separation of N-derivatized amino acids, with the separation medium containing a mixture of ethanol-methanol (60:40); (ii) Busby et al [156] reported the chiral separation of 34 pharmaceutical weak-base analytes using nonaqueous CE in which the acidic methanol background electrolytes contained the sodium salt of a new, single-isomer chiral selector, octakis(2,3-Odimethyl-6-6-O-sulfo)-g-CD; (iii) nonaqueous ion-pair CE was employed by Czerwenka et al [157] for the chiral separation of N-protected alanine peptide enantiomers using tert-butylcarbamoylquine as the chiral counterion; (iv) the synergistic effects of ion-pairing in the chiral separation of basic pharmaceuticals was investigated in nonaqueous CE by Servais et al [158] using an ion-pairing reagent (alkanesulfonates or (1)-S-camphorsulfonate) in combination with CDs; (v) a chiral nonaqueous CE system, using the partial-filling technique with MS detection, was reported by Rudaz et al [159] and Lodén et al [160] for the determination of chiral drugs, such as methadone and pronethalol, respectively.…”

Chiral separations by capillary electrophoresis: Recent developments and applications

“…Quinine [83], tert-butyl carbamoylated quinine and other cinchona alkaloids and derivatives were also investigated for the chiral separation of N-protected amino acids [84][85][86][87]. Higher enantioselectivity was observed using the cinchona alkaloid derivatives, especially those with a carbamate function [85]. Moreover, the presence of a bulky substituent on the carbamoylated derivatives or the use of dimeric forms of carbamoylated quinine and quinidine derivatives had a favorable effect on the enantioselectivity [86,87].…”