Latent inhibitors. Part 4. Irreversible inhibition of dihydro-orotate dehydrogenase by hydantoins derived from amino acids
作者:Ian G. Buntain、Colin J. Suckling、Hamish C. S. Wood
DOI:10.1039/p19880003175
日期:——
Hydantoins and ureas derivedfrom α-amino acids are shown to interact with dihydro-orotatedehydrogenasefrom Clostridium(Zymobacterium)oroticum, chiefly as weak competitive inhibitors but that the hydantoinderivedfrom phenylalanine, 5-benzyl-3-(1-carboxy-2-phenylethyl)hydantoin, is a time-dependent irreversible inhibitor of the enzyme. Inhibition experiments with derivatives of this hydantoin and
883. Organic photochemistry. Part II. Some photosensitive protecting groups
作者:J. A. Barltrop、P. Schofield
DOI:10.1039/jr9650004758
日期:——
Aminolyses of 4-Nitrophenyl Phenyl Carbonate and Thionocarbonate: Effect of Modification of Electrophilic Center from CO to CS on Reactivity and Mechanism
作者:Ik-Hwan Um、Eun Young Kim、Hye-Ran Park、Sang-Eun Jeon
DOI:10.1021/jo052417z
日期:2006.3.1
[GRAPHICS]A kinetic study is reported for nucleophilic substitution reactions of 4-nitrophenyl phenyl carbonate (5) and 4-nitrophenyl phenyl thionocarbonate (6) with a series of primary amines. The thiono compound 6 is less reactive than its oxygen analogue 5 toward strongly basic amines but is more reactive toward weakly basic CF3CH2NH2. The Bronsted-type plots obtained from the aminolyses of 5 and 6 are curved downwardly. The reactions are proposed to proceed through a stepwise mechanism with a change in the RDS on the basis of the curved Bronsted-type plots. The microscopic rate constants (k(1) and k(2)/k(-1) ratio) associated with the current aminolyses are consistent with the proposed reaction mechanism. The replacement of the C=O bond in 5 by a polarizable C=S group results in a decrease in the k(1) value but an increase in the k(2)/k(-1) ratio. Besides, such a modification of the electrophilic center causes a decrease in pK(a)degrees, defined as the pK(a) at the curvature center of curved Bronsted-type plots, but does not alter the reaction mechanism. The larger k(2)/k(-1) ratio for the reactions of 6 compared to those of 5 is proposed to be responsible for the decreased pK(a)degrees value.
BUNTAIN, IAN G.;SUCKLING, COLIN J.;WOOD, HAMISH C. S., J. CHEM. SOC. PERKIN TRANS. PT 1,(1989) N2, C. 3175-3182
作者:BUNTAIN, IAN G.、SUCKLING, COLIN J.、WOOD, HAMISH C. S.