ALBERT

All Library Books, journals and Electronic Records Telegrafenberg

feed icon rss

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
  • 1
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 9 (1997), S. 307-312 
    ISSN: 0899-0042
    Keywords: stereoselective release ; stereoselective dissolution ; propranolol ; enantiomers ; cellulose derivatives ; tablet matrices ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The dissolution characteristics of propranolol enantiomers from tablet formulations containing cellulose, or one of eight cellulose derivatives, were determined under a range of conditions. The derivatives examined were: cellulose tris(phenylcarbamate) (1), cellulose tris(2,3-dichlorophenylcarbamate) (2), cellulose tris 2,4-dichlorophenylcarbamate (3), cellulose tris(2,6-dichlorophenylcarbamate) (4), cellulose tris(2,3-dimethylphenylcarbamate) (5), cellulose tris(3,4-dichlorophenylcarbamate) (6), cellulose tris (3,5-dichlorophenylcarbamate) (7), cellulose tris(3,5-dimethylphenylcarbamate) (8). In water at 25°C, the release rates of (-)R-propranolol were generally greater than those of (-)-S-propranolol, although these differences were not always statistically significant; only compounds 5 and 8 demonstrated significant enantioselectivity. Using compound 8 in further experiments, statistically significant stereoselective dissolution of propranolol HCl was observed in buffer pH 7.4 at 25°C (intrinsic dissolution rates: 0.41 ± 0.01 mgcm2min-1 for R-propranolol and 0.30 ± 0.02 mgcm2min-1 for S-propranolol; P = 0.003). The cumulative amounts of enantiomers released at every time point were also found to be statistically significant (mean ratio R:S 1.25 ± 0.05). The observed low stereoselectivity of 8 with propranolol base was probably attributable to low solubility in pH 7.4 buffer, although stereoselective release did increase with time. This suggested that there is a relationship between stereoselectivity and contact time in an aqueous environment. Results also suggested that increased temperature may affect the release process as well as stereoselective interactions of 8 with individual enantiomers. To conclude, differential release of rac-propranolol from cellulose derivative matrices has been demonstrated, which supports the principle of stereoselective retardation as a potential means of stereoselective drug delivery for solid dosage forms. Chirality 9:307-312, 1997. © 1997 Wiley-Liss, Inc.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 2
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 7 (1995), S. 305-309 
    ISSN: 0899-0042
    Keywords: percutaneous penetration ; skin ; keratin ; ceramide ; monolayer ; modelling ; stereoselectivity ; protein binding ; interaction ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The stratum corneum, the rate-limiting barrier to percutaneous penetration, is made up of several components, principally keratin and ceramides. These are potential sources of chiral discrimination that could result in differential diffusion rates, dependent upon the stereochemistry of the solute. Although binding to keratin can occur it is not a stereoselective process [percent binding to solubilised epidermal keratin: (R)-propranolol 7.9 ± 1.7, (S)-propranolol 8.3 ± 2.0]. On the other hand, studies with ceramide monolayers produced qualitative evidence of dose-dependent stereoselective interaction when the pure diastereomers of ephedrine were present in the aqueous subphase which suggested that differences in diffusion rates might occur in skin. However, the differences in permeation rates in vitro for these diastereomers through human skin were not statistically different [(+)-(1S, 2R)-ephedrine 119.1 ± 2.6 μg/cm2, (-)-(1R,2S)-ephedrine 107.0 ± 3.9 μg/cm2, 12 h]. Time averaging, involving contributions from binding to all lipid headgroups present in the intercellular channels, may obscure specific differential interactions. Further, any stereospecific interaction may be subtle and readily overwhelmed if diffusant concentration is greater than the capacity of the skin to differentiate between stereoisomers. Evidence for intrinsic stereoselectivity in skin permeation has therefore yet to be obtained. © 1995 Wiley-Liss, Inc.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 3
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 9 (1997), S. 139-144 
    ISSN: 0899-0042
    Keywords: thin-layer chromatography ; propranolol ; bupranolol ; enantiomers ; cellulose derivatives ; chiral stationary phase ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Cellulose triphenylcarbamate derivatives have been used as stationary phases for resolution of the enantiomers of the β-blockers propranolol and bupranolol by TLC. The derivatives examined were: cellulose trisphenylacarbamate (1), cellulose tris(2,3-dichlorophenyl carbamate) (2), cellulose tris(2,4-dichlorophenyl carbamate) (3), cellulose tris(2,6-dichlorophenyl carbamate) (4), cellulose tris (2,3-dimethylphenyl carbamate) (5), cellulose tris(3,4-dichlorophenyl carbamate) (6), cellulose tris(3,5-dichlorophenyl carbamate) (7), and cellulose tris(3,5-dimethylphenyl carbamate) (8). A variety of mobile phases were used to achieve useful separations and the effects of solvent polarity are also discussed. The best resolution of rac-propranolol was obtained on CSP 8 (RfR = 0.26, RfS = 0.06, α = 4.33) in mobile phase hexane:propan-2-ol (80:20 v/v). The best resolution of rac-bupranolol was obtained on CSP 5 (RfR = 0.29, RfS = 0.09, α = 3.22) in mobile phase hexane:propan-2-ol (80:20 v/v). These results demonstrated the potential of cellulose triphenylcarbamates as chiral stationary phases in TLC and indicate that this is potentially a useful method for the direct, simple, and rapid (within 30 min) resolution of racemates in the analytical control of enantiomeric purity. Physical aspects such as problems in cracking of the CSP, adhesion to plate, and interference of spot detection due to triphenylcarbamate chromphores are also discussed, along with the method employed to overcome them. Chirality 9:139-144, 1997. © 1997 Wiley-Liss, Inc.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...