From a Single Benzene Substrate

Such syntheses are subdivided according to whether the Nl,C8a, N1,C2, or C2,C3 bond is formed during the procedure to afford a quinoxaline. 

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B3LYP/6-31+G level calculations on the reaction between a-bromoacetophenones and hydroxide ion in the gas phase suggest that two products (from substitution of the or-bromine and addition to the carbonyl carbon) form from a single transition state where the OH nucleophile is associated with both the C and the carbonyl carbon. Trajectory calculations have shown that substrates with a more electron-withdrawing substituent than meta-C on the benzene ring react at the carbonyl group, while those with more electron-donating substituents react at bromine. 

Aliphatic nitriles react slowly with phenols and phenyl ethers in the presence of trifluoromethanesulphonic acid to give ketones after hydrolysis, in a variation of the Houben-Hoesch reaction. The crystalline complex of copper(i) triflate and benzene induces the acylation of aromatic substrates with selenol esters, affording a transition-metal mediated version of the Friedel-Crafts reaction. Aromatic carboxylic acids can be converted into symmetrical diaryl ketones in good yield by treatment of their 5-(2-pyridyl)thioesters with bis-(l,5-cyclo-octadiene)nickel [equation (15)]. In contrast to other methods for preparing symmetrical aromatic ketones, this method allows their preparation from a single starting material. 

Fiqtire 3.5 (a) Competitive inhibition inhibitor and substrate compete for the same binding site. For example, indole, phenol, and benzene bind in the binding pocket of chymotrypsin and inhibit the hydrolysis of derivatives of tryptophan, tyrosine, and / phenylalanine, (b) Noncompetitive inhibition inhibitor and substrate bind simultaneously to the enzyme. An example is the inhibition of fructose 1,6-diphosphatase by AMP. This type of inhibition is very common with multisubstrate enzymes. A rare example of / uncompetitive inhibition of a single-substrate enzyme is the inhibition of alkaline phosphatase by L-phenylalanine. This enzyme is composed of two identical subunitjs, so presumably the phenylalanine binds at one site and the substrate at the other. [From N. K. Ghosh and W. H. Fishman, J. Biol. Chem. 241, 2516 (1966) see also M. Caswell and M. Caplow, Biochemistry 19, 2907 (1980). 

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