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  • chylomicron  (2)
  • epimerization  (2)
  • moxalactam  (2)
  • 1
    ISSN: 1573-904X
    Keywords: mepitiostane ; superlipophilicity ; lymph–blood partition ratio ; dynamic partitioning model ; chylomicron
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The partition of mepitiostane, testosterone, and some structurally related compounds between lymph and blood in rat jejunum (lymph–blood partition ratio; LBPR) was determined, and the quantitative relationship between LBPR and lipophilicity was examined. When the ΔR m values (hydrophobic parameter derived from the mobility) relative to testosterone were 〈0.2, their logLBPRs remained approximately constant in the range of −2 to −3. When the ΔR m values of the compounds were 〉0.2, a linear correlation (r = 0.986, n = 8) was observed between these values and the logLBPRs. The LBPR, but not the extent of lymphatic absorption, of lipophilic molecules was determined strictly by the superlipophilicity, and for high partitioning into the lymph (〉50% of the absorbed amount), the ΔR m value had to be 〉0.50 (5.65 as the logP value). The relationship between LBPR and superlipophilicity could be explained on the basis of the theoretical equations derived from absorption kinetics based on a dynamic partitioning model.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Pharmaceutical research 7 (1990), S. 364-369 
    ISSN: 1573-904X
    Keywords: moxalactam ; epimerization ; frozen plasma ; frozen urine ; electrolyte ; protein binding
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The epimerization of moxalactam (LMOX) in frozen urine and plasma samples was studied during long-term storage. The R/S ratio at equilibrium [(R/S)eq] at −10°C was similar in urine and in rat and human plasma ultrafiltrate but differed from that in water. The (R/S)eq values in human plasma and its ultrafiltrate differed slightly, while they were the same in rat plasma and in its ultrafiltrate. The difference for the human plasma and ultrafiltrate may result from differences in plasma protein binding between R- and S-epimers in the liquid region of the frozen plasma. The change of R/S ratio in frozen human plasma continued below the collapse temperature of LMOX aqueous solution, where the liquid region appeared still to exist as determined by NMR measurement. Consequently, the biological LMOX samples should be preserved at or below −70°C to prevent changes in the R/S ratio.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1573-904X
    Keywords: moxalactam ; epimerization ; frozen solution ; ice ; activation energy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The epimerization rate constants of R- and S-epimers of moxalactam (LMOX) in a frozen aqueous solution decreased as the temperature decreased. The reaction proceeded in the unfrozen region remaining in the frozen solution, without being affected by the ice. The reaction stopped completely below the collapse temperature of the LMOX aqueous solution. The ratio of R- and S-epimers at equilibrium, which was equal to the ratio of the epimerization rate constant, increased as the temperature decreased. This change in the ratio at equilibrium could be ascribed to the difference in the activation energy between the two epimers.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Pharmaceutical research 9 (1992), S. 1617-1621 
    ISSN: 1573-904X
    Keywords: mepitiostane ; epitiostanol ; intrinsic lymphatic partition rate ; lipophilicity ; chylomicron
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Substitution of the steroid epitiostanol (EP) at position 17 with methoxycyclopentane yields the extremely lipophilic mepitiostane (MP) with preferential partitioning into the lymph. Most of the MP in the lymph was associated with the core lipids of chylomicrons and very low-density lipoproteins (VLDL), as was also the case for EP. However, the dialysis velocity of EP and MP from lymph to plasma differed greatly; EP, but not MP, was transferred from the lymph to the plasma. This difference was attributed to differences in their unbound fraction in the lymph. Lymphatic transfer and the logP value of several tested steroids correlated well. Therefore, the oral EP prodrug, MP, partitioned into the lymph because of its superlipophilicity and resultant retention in the core lipids of chylomicrons and VLDL.
    Type of Medium: Electronic Resource
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