Penicillamine enantiomer separation

Kovacs-Hadady and Kiss [27] studied the chromatographic characteristics of thia-zolidinecarboxylic acid derivatives, formed by reaction of (i>) and (L)-penicillamine with various substituted benzaldehydes and heterocyclic aldehydes in order to evaluate the aldehydes as derivatizing agents for separation of the penicillamine enantiomers. The TLC method of Martens et al. [28] was used. Transformation to thiazolidine carboxylic acids with benzaldehyde and substituted benzaldehydes was not complete, so formaldehyde is still the preferred reagent for separation of the enantiomers. 

Merino-Merino et al. [32] used the OPA reagent (o-phthaldehyde condensed with 2-mercaptoethanol) to separate penicillamine enantiomers after their derivatization. Racemic and (/q-penicillamine were dissolved in aqueous 0.5 M NaOH, and treated with the derivatizing solution (methanolic o-phthaldehyde and 2-mercaptoethanol in 0.4 M potassium borate buffer solution of pH 10). The reaction mixture was set aside for 2 min at room temperture, whereupon a portion of solution was analyzed by HPLC. The method used a Cyclobond column (25 cm x 4.6 mm) maintained at 5 °C, a mobile phase of ethanol/1% triethylammonium acetate (1 1 pH 4.5) eluted at... 

Cellulose was the first sorbent for which the resolution of racemic amino acids was demonstrated [23]. From this beginning, derivatives such as microcrystalline triacetylcellulose and /3-cyclodextrin bonded to silica were developed. The most popular sorbent for the control of optical purity is a reversed-phase silica gel impregnated with a chiral selector (a proline derivative) and copper (II) ions. Separations are possible if the analytes of interest form chelate complexes with the copper ions such as D,L-Dopa and D.L-penicillamine [24], Silica gel has also been impregnated with (-) brucine for resolving enantiomeric mixtures of amino acids [25] and a number of amino alcohol adrenergic blockers were resolved with another chiral selector [26]. A worthwhile review on enantiomer separations by TLC has been published [27],... 

Kovacs-Hadady, K. and Kiss, I.T., Attempts for the chromatographic separation of D- and L-penicillamine enantiomers, Chromatographia, 24, 677,1987. 

Gotti et al. [42] reported an analytical study of penicillamine in pharmaceuticals by capillary zone electrophoresis. Dispersions of the drug (0.4 mg/mL for the determination of (/q-penicillaminc in water containing 0.03% of the internal standard, S -met hy I - r-cystei ne, were injected at 5 kPa for 10 seconds into the capillary (48.5 cm x 50 pm i.d., 40 cm to detector). Electrophoresis was carried out at 15 °C and 30 kV, with a pH 2.5 buffer of 50 mM potassium phosphate and detection at 200 rnn. Calibration graphs were linear for 0.2-0.6 pg/mL (detection limit = 90 pM). For a more sensitive determination of penicillamine, or for the separation of its enantiomers, a derivative was prepared. Solutions (0.5 mL, final concentration 20 pg/mL) in 10 mM phosphate buffer (pH 8) were mixed with 1 mL of methanolic 0.015% 1,1 -[ethylidenebis-(sulfonyl)]bis-benzene and, after 2 min, with 0.5 mL of pH 2.5 phosphate buffer. An internal standard (0.03% tryptophan, 0.15 mL) was added and aliquots were injected. With the same pH 2.5 buffer and detection at 220 nm, calibration graphs were linear for 9.3-37.2 pg/mL, with a detection limit of 2.5 pM. For the determination of small amounts of (L)-penicillamine impurity, the final analyte concentration was 75 pg/mL, the pH 2.5 buffer contained 5 mM beta-cyclodextrin and 30 mM (+)-camphor-10-sulfonic acid, with a voltage of 20 kV, and detection at 220 nm. Calibration graphs were linear for 0.5-2% of the toxic (L)-enantiomer, with a detection limit of 0.3%. 

Abou-Basha and Aboul-Enein [22] presented an isocratic and simple HPLC method for the direct resolution of the clenbuterol enantiomers. The method involved the use of a urea-type CSP made of hS )-indoline-2-carboxylic acid and (R)-1 -(naphthyl) ethylamine known as the Chirex 3022 column. The separation factor (a) obtained was 1.27 and the resolution factor (Rs) was 4.2 when using a mobile phase composed of hexane-1,2-dichloroethane-ethanol (80 10 10, v/v/v). The (+)-enantiomer eluted first with a capacity factor (k) of 2.67 followed by a (—)-enantiomer with a k of 3.38. Biesel et al. [23] resolved 1-benzylcyclohexane-1,2-diamine hydrochloride on a Chirex D-penicillamine column. Gasparrini et al. [24] synthesized a series of the chiral selectors based on /ra s -1,2 - d i a m i n o eye I o hexane. The developed CSPs were used for the chiral resolution of arylacetic acids, alcohols, sulfoxides, selenoxides, phosphinates, tertiary phosphine oxides, and benzodiazepines. In another study, the same authors [25] described the chiral resolution of /i-aminocstcrs enantiomers on synthetic CSPs based on a re-acidic derivatives of trans- 1,2-diaminocyclohexane... 

Using chiral thiols for derivative formation, isoindoles are formed from amino acids and amino alcohols. BOC-L-cysteine, N-acetyl-L-cysteine, Af-acetyl-D-penicillamine [340] and l-thio-jS-D-glucose [341] have been shown to be suitable reagents which allow the separation of most amino acid enantiomers using reversed phase column chromatography. Thus, OPA/N-acetyl-L-cysteine has been used among others for the separation of enantiomers of aspartate [342], baclofen [343], norepinephrine, dopa [344] and lombricine [345]. 

---