Sulfoxides and amides were tested as inhibitors of liver alcohol dehydrogenase and ethanol metabolism in rats. With both series of compounds, increasing the hydrophobicity resulted in better inhibition, and introduction of polar groups reduced inhibition. Of the cyclic sulfoxides, tetramethylene sulfoxide was the best inhibitor as compared to the tri- and pentamethylene analogue and other compounds, and it may be a transition-state analogue. The most promising compounds, tetramethylene sulfoxide and isovaleramide, were essentially uncompetitive inhibitors of purified horse and rat liver alcohol dehydrogenases with respect to ethanol as substrate. These compounds also were uncompetitive inhibitors in vivo, which is advantageous since the inhibition is not overcome at higher concentrations of ethanol, as it is with competitive inhibitors, such as pyrazole. The uncompetitive inhibition constants for tetramethylene sulfoxide and isovaleramide for rat liver alcohol dehydrogenase were 200 and 20 microM, respectively, in vitro, whereas in vivo the values were 340 and 180 mumol/kg. The differences in the values may be due to metabolism or distribution of the compounds. Further studies will be required to determine if isovaleramide or tetramethylene sulfoxide is suitable for therapeutic purposes.

3-Substituted thiolane 1-oxides (methyl, n-butyl, n-hexyl, and phenyl) were prepared and tested as inhibitors of horse, monkey, and rat liver alcohol dehydrogenases and of ethanol metabolism in rats. These compounds inhibit alcohol oxidation in an uncompetitive manner with respect to ethanol as a varied substrate. Lengthening the alkyl substituent increased the inhibitory potency because of tighter binding in the hydrophobic substrate binding pocket of the alcohol dehydrogenases. Thus, the 3-hexyl derivative was the most potent inhibitor of the purified rat liver alcohol dehydrogenase, with a Kii value of 0.13 microM. The 3-butyl derivative was the best inhibitor of ethanol metabolism in rats, with a Kii value of 11 mumol/kg. The acute toxicity in mice of the butyl derivative was 1.4 mmol/kg. Since high concentrations of alcohol do not prevent the inhibitory effects of these compounds, they may be particularly useful for preventing poisoning by methanol or ethylene glycol.

No abstract

Horse liver alcohol dehydrogenase is inactivated with Michaelis kinetics at pH 7 and 25 degrees C by 3-bromopropionic acid. In the absence of NAD+, the Ki is 2 mM, and the pseudo bimolecular rate constant (k3/Ki) is 0.03 M-1 s-1; in the presence of 1 mM NAD+, Ki is 2.3 mM, and k3/Ki is 0.006 M-1 s-1. 3-Bromopropionic acid is a competitive inhibitor, Ki of 0.4 mM, against ethanol as a substrate. Inactivation was prevented in the ternary complexes with NAD+ X pyrazole and NADH X isobutyramide, was retarded by NAD+, NADH, or bipyridine, and was almost unaffected by imidazole and AMP. Carboxyethylated enzyme did not detectably (as observed spectrophotometrically) bind bipyridine, NAD+, or NADH. Enzyme was inactivated with radioactive 3-bromopropionic acid, aminoethylated, and digested with trypsin and chymotrypsin. Analysis of the labeled peptides showed that Cys-174 was predominantly modified. In the presence of 1 mM NAD+, the reaction was much less specific. The interaction of the carboxyl group of 3-bromopropionic acid with the guanidino group of Arg-369 probably facilitates the selective reaction with Cys-174, which is ligated to the zinc at the active site. Carboxyethylation apparently inactivates by interfering with the proper binding of the pyrophosphate of the coenzyme to the enzyme.

Heterocyclic system containing bridgehead nitrogen atom. Bart W. Received December 17, 1968The syntheses of 3-substituted-, 2,3-disubstituted-5,6-dihydro-4H-imidazo[2,1-b]thiazoles and 3-substituted-, 2,3-disubstituted-4,5,6,7-tetrahydrothiazolo[3,2-a]pyrimidines have been achieved by reacting ketones with 2-mercaptoimidazoline and 2-mercapto-3,4,5,6-tetrahydropyrimidine respectively in the presence of iodine. The condensation has also been affected by replacing iodine with bromine.Canadian Journal of Chemistry, 47,2843 (1969) In view of the broad spectrum anthelmintic interest to improve upon the methods of synactivity of dl-6-phenyl-2,3,5,6-tetrahydro-4H-thesizing condensed thiazoles. The present imidazo [2,1 -b]thiazole hydrochloride (tetra-communication reports the synthesis of two misole-HC1) (1-3), it was thought of considerable such systems.