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  • 1
    ISSN: 1573-904X
    Keywords: chiral stationary phases ; human serum albumin ; protein binding ; binding sites ; high-performance liquid chromatography ; immobilized proteins ; chemical modification
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The in situ modification of an immobilized human serum albumin (HSA) high-performance liquid chromatographic chiral stationary phase by p-nitrophenyl acetate is reported. This procedure, which is thought to affect primarily a single reactive tyrosine residue within the protein structure, influenced the chromatographic retention and enantioselectivity factors of a wide range of solutes. For certain solutes, increases in both capacity factor and chiral resolution were observed. Ultrafiltration studies on representative test solutes using free HSA, treated in a similar manner to the immobilized protein, gave similar results as the chromatographic observations, indicating that the latter effects are not artifactual results of immobilization. The effect of the modification of HSA on the binding behavior of drugs reportedly sharing the site predominantly affected by the derivatization, namely, the indole–benzodiazepine binding site, varied greatly. This observation suggests that the affected binding area is not a single, tightly structurally defined site.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 4 (1992), S. 273-273 
    ISSN: 0899-0042
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 0899-0042
    Keywords: stereoselective excretion ; enantioselective ; chromatography ; assay validation ; hydroxychloroquine metabolism ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A sequential achiral-chiral high-performance liquid chromatographic system has been developed for the quantitation in urine of the enantiomers of hydroxychloroquine (HCQ), and of its 3 major metabolites, desethylhydroxychloroquine (DHCQ), desethylchloroquine (DCQ), and bisdesethylchloroquine (BDCQ). HCQ and its metabolites were separated and quantified on a cyano-bonded phase, and the enantiomeric ratios were determined using a Chiral-AGP chiral stationary phase. The assay validation and application of this method to a preliminary study in a human volunteer are presented. In this subject, the initial 0-4 h urine contained the 2 HCQ enantiomers in a ratio of (+)-HCQ:(-)-HCQ of 3:2; by the 2,064 h of the study, this ratio had reversed to (+)-HCQ:(-)-HCQ of 3:7. © 1993 Wiley-Liss, Inc.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 5 (1993), S. 84-90 
    ISSN: 0899-0042
    Keywords: in vitro dissolution ; enantioselective ; enantiomers ; bioequivalency ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The stereoselectivity of the in vitro dissolution of two commercially available sustained release formulations of rac-verapamil (rac-VER) has been investigated. The studies were carried out using a single-tablet continuous-flow apparatus and the concentrations of R- and S-VER released from the formulations were measured using enantioselective chromatography on a high performance liquid chromatography (HPLC) chiral stationary phase containing immobilized α1-acid glycoprotein (Chiral AGP-column). The data from this study demonstrates that the two formulations have different dissolution profiles and that the amount of drug dissolved was highly dependent on pH. In addition, between pH 3 and 8, the total cumulative amount of R-VER released was greater than the amount of S-VER and a statistically significant difference (P 〈 0.01) was detected at pH 6. The results of this study indicate that bioavailability and bioequivalency studies should consider the possibility of enantioselective dissolution when racemic compounds are present in the formulations. © 1993 Wiley-Liss, Inc.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 0899-0042
    Keywords: hydroxychloroquine ; enantiomers ; stereoselectivity ; distribution ; interconversion ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Hydroxychloroquine (HCQ) stereoselective distribution was investigated in rabbits after 20 mg/kg po of racemic-HCQ (rac-HCQ) and 20 mg/kg po of each enantiomer, 97% pure (-)-(R)-HCQ and 99% pure (+)-(S)-HCQ. Concentrations were 4 to 6 times higher in whole blood than in plasma. Melanin did not affect plasma and whole blood levels since concentrations did not differ between pigmented and nonpigmented animals. After single and multiple doses of the separate enantiomers, only 5-10% of the antipode could be measured, in blood or plasma. Therefore, there was no significant interconversion from one enantiomer into the other. Following rac-HCQ, plasma (+)-(S)-levels always surpassed (-)-(R)-ones while in whole blood, (-)-(R)-HCQ concentrations were always the highest. When the enantiomers were administered separately, blood concentrations achieved after (-)-(R)-HCQ were higher, especially after multiple doses. These observations suggest that (-)-(R)-HCQ is preferentially concentrated by cellular components of blood. This enantioselective distribution of HCQ could be secondary to a stereoselective protein binding to plasma proteins, although a more specific binding of (-)-(R)-HCQ to blood cells cannot be ruled out. Since in whole blood (-)-(R)-HCQ is retained in cellular components, metabolism would favour the more available (+)-(S)-enantiomer. © 1994 Wiley-Liss, Inc.
    Additional Material: 7 Ill.
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  • 6
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 6 (1994), S. 47-50 
    ISSN: 0899-0042
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 0899-0042
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An enantioselective assay has been developed for the determination of the enantiomers of ketorolac and its metabolite p-hydroxyketorolac in plasma and urine. The analytical method utilizes a coupled achiral-chiral HPLC system where the initial separation of ketorolac from p-hydroxyketorolac and matrix interferences was achieved on a C18-stationary phase and the enantioselective separations of the two target solutes were accomplished on a human serum albumin-based chiral stationary phase. The two columns were attached in sequence and the assay was carried out without the necessity of column-switching techniques. The method has been validated for use in pharmacokinetic and metabolic studies and represents the initial report of the determination of ketorolac and p-hydroxyketorolac enantiomers in urine. The results of the study indicate that after the administration of racemic ketorolac there was an enantioselective distribution of ketorolac enantiomers in plasma [(R)-ketorolac: (S)-ketorolac = 3.89 ± 0.93 (n = 6) and urine (R)-ketorolac: (S)-ketorolac = 1.26 ± 0.09 (n = 7)]. The mean ratio of the p-hydroxyketorolac enantiomers was 1.77 ± 0.46 (n = 7). Both ketorolac and p-hydroxyketorolac are glucuronized in the acyl carboxyl moiety and the results of this study indicate that this process is not enantiospecific. © 1994 Wiley-Liss, Inc.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 0899-0042
    Keywords: enantioselective tissue sequestration ; hydroxychloroquine stereoisomers ; cornea ; iris ; retina ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The disposition of the enantiomers of hydroxychloroquine (HCQ) and its major metabolites in ocular tissues of rabbits has been studied. Both albino, New Zealand White (NZW), and pigmented animals were administered daily oral doses of rac-HCQ, (S)-HCQ or (R)-HCQ (20 mg/kg) over 1, 6, or 8 day periods or for 8 days followed by a 7-day washout period. At the end of the study periods, plasma and whole blood samples were collected and the rabbits were sacrificed. The eyes were collected, the aqueous humor removed with a syringe, and the eyes separated into the cornea, lens, vitreous body, iris, choroid-retina, sclera, and conjunctiva. The concentrations of (R)-HCQ, (S)-HCQ, and their respective metabolites were determined using a validated enantioselective liquid chromatographic assay. The data from these studies indicate that HCQ accumulated in both pigmented and nonpigmented ocular tissues. In the pigmented tissues, HCQ and its metabolites were bound to melanin and the binding was not enantiospecific. In the nonpigmented tissues and in the iris and retina-choroid of the NZW rabbits, the accumulation appeared to be the result of a reversible and enantioselective binding of HCQ and its metabolites to an unidentified biopolymer present in these ocular tissues. © 1994 Wiley-liss, Inc.
    Additional Material: 2 Ill.
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  • 9
    ISSN: 0899-0042
    Keywords: (S)-naphthylurea chiral stationary phase ; subcritical fluid chromatography ; supercritical fluid chromatography ; antimalarial agents ; enantiomeric separations ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The behavior of mefloquine, halofantrine, enpiroline, quinine, quinidine, chloroquine and primaquine is studied by subcritical fluid chromatography on a (S)-naphthylurea column (250 mm × 4.6 mm ID) with a subcritical mobile phase composed of carbon dioxide, methanol and triethylamine (flow rate of 3 ml/min). Except for primaquine and chloroquine, each enantiomer was separated at a temperature between 40 and 60°C, and at a pressure below 15 MPa. A 98/2, v/v CO2/methanol 0.1% triethylamine mixture allowed the separation of halofantrine enantiomers while the enantiomers of the more polar metabolite (N-desbutylhalofantrine) were separated with a 80-20 v/v mixture as used for mefloquine, enpiroline, quinine and quinidine. The influence of temperature, pressure and of the nature of the mobile phase is discussed. © 1993 Wiley-Liss, Inc.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
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  • 10
    ISSN: 0899-0042
    Keywords: chiral stationary phase ; mobile phase modifier ; digoxin ; warfarin ; medium chain fatty acid ; bilirubin ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Specific ligand markers for the various binding sites of human serum albumin (HSA) have been described in the literature. Some of these markers (medium chain fatty acids, warfarin, digoxin, and bilirubin) were used as mobile phase modifiers. Using a high performance liquid chromatographic (HPLC) column containing HSA as stationary phase, their influence was investigated on the separation in this phase of the enantiomers of three benzodiazepines (temazepam, oxazepam, and lorazepam). Displacement effects were observed with medium chain fatty acids. This influence was proportional to the chain length and to the concentration of acid. Allosteric cooperative effects were noted with digoxin for the three benzodiazepines. Both displacement and cooperative effects were observed with warfarin. Stereoselectivity was decreased for temazepam and oxazepam and increased for lorazepam. © 1993 Wiley-Liss, Inc.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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