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In vitro metabolism of the novel antiinflammatory agent 6-(4'-fluorophenyl)-5-(4'-pyridyl)-2,3-dihydroimidazo-[2,1-b]-thiazole.

6-(4'-Fluorophenyl)-5-(4'-pyridyl)-2,3-dihydroimidazo-[2,1-b]-thia zole (SK&F 86002) is a dual inhibitor of arachidonic acid metabolism which has therapeutic potential for the treatment of inflammatory diseases. Previous studies in rats, in vivo, demonstrated that SK&F 86002 metabolism proceeds by sequential steps of sulfur and nitrogen oxidation. Therefore, these studies were designed to 1) identify the enzymes (flavin vs. cytochrome P-450-dependent monooxygenases) which were responsible for SK&F 86002 metabolism in vitro in hepatic microsomal suspensions from Sprague-Dawley rats, 2) characterize sex-dependent differences, and 3) quantitate the effect of pretreatment with SK&F 86002. All three steps in the sequential metabolism of SK&F 86002 to the N-oxide sulfone metabolite were quantitated individually. The three oxidation steps appeared to be catalyzed primarily by cytochrome P-450; heat inactivation (used to destroy flavin monooxygenase) had little effect on the metabolism of each compound. Further,N-octylamine failed to stimulate the metabolism of any compound and the cytochrome P-450 inhibitors (SK&F 525-A, metyrapone, and alpha-naphthoflavone) resulted in a marked inhibition of the metabolism of all three substrates. Maximal velocities for metabolism of all three substrates (SK&F 86002, sulfoxide, and sulfone) in microsomes isolated from male rats, were 3- to 5-fold greater than observed in female rats. Furthermore, pretreatment of male rats with SK&F 86002 (60 mg/kg/day for 3 days) resulted in a change in the in vitro metabolism of all three substrates generally characterized by an increase in Vmax and/or a fall in km.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

[Inactivation of yeast apopyruvate decarboxylase by lipophilic n-alkyl-substituted thiazole salts].

Yeast apopyruvate decarboxylase is irreversibly inactivated by 3-dodecyl-4-methylthiazolium bromide (I), 3-dodecyl-4-methyl-5-beta-hydroxyethylthiazolium bromide (II), 3-hexadecyl-4-methyltiazolium bromide (III), 3-hexadecyl-4-methyl-5-beta-hydroxyethyliazolium bromide (IV). 3-Octyl-4-methylthiazolium bromide (V) possesses insignificant inactivating properties. The relationship between residual enzymatic activity and concentration of thiazolium salts (II, IV) which are more similar structural analogs of thiamine is of the S-like pattern. In the case of thiazolium salts (I, III) this relationship is almost linear. The measure of inactivation of apopyruvate decarboxylase in the presence of substances (I-IV) increases with the hydrocarbon chain length of n-alkyl substituent of the quaternary nitrogen atom of the thiazolium salt. The calculated second-order-rate constants are 5.43.10(2) (I) 1.52.10(3) (II). 2.83.10(4) (III). 4.85.10(4) M-1 min-1 (IV). The UV spectroscopic method has shown that a hypsochromic shift of longwave absorbtion maxima and a decrease of their extinction occur under interaction of thiazolium salts (I-V) with tryptophan. This fact evidence for possible complexing of compounds (I-V) with indole residues of protein. The hydrophobic interactions are supposed to be a crucial factor in the inactivation mechanism of yeast apopyruvate decarboxylase.

Isoenzymes↗

Drugs derived from thiazole and imidazole or with nitrogen-carbon-sulphur or tertiary amino groups. Prediction of secondary antithyroid activity by UV/visible spectroscopy.

The chemical structure of various drugs suggests their potential interference with thyroid metabolism by complexing molecular iodine in the thyroid gland. Spectroscopic analysis shows that such compounds form charge-transfer complexes with iodine in a 1:1 stoichiometry. The values of formation constant Kc indicate strong donor-acceptor interactions. Biochemical and histological studies carried out on the rat demonstrated that a correlation exists between the Kc values and the antithyroid activity. A mechanism of action of these molecules on thyroid function is proposed. The potential antithyroid activity of such compounds can therefore be predicted from the Kc values.

Animals↗