Hydrolysis preferential

Acid or alkaline hydrolysis preferentially breaks the 5 -bond, which is in contrast to the action of phosphodiesterase which attacks only the 3 -bond. 

This reaction occurs (in competition with hydrolysis) preferentially in compounds in which a relatively acidic proton is located at a carbon atom adjacent to the carbon atom carrying the leaving group (i.e., the halogen). These criteria are optimally met in 1,1,2,2-tetrachloroethane, where the four electron-withdrawing chlorine atoms render the hydrogens more acidic and, simultaneously, hinder nucleophilic attack. In aqueous solution, 1,1,2,2-tetrachloroethane ii converted more or less quantitatively to trichloroethylene (Haag and Mill, 1987) by a so-called E2 (elimination, bimolccular) mechanism that is, the elimination takes place in a concerted reaction with OH ... 

Treatment of ceUulose with acids results in preferential hydrolysis in the more accessible amorphous regions and produces a product known as microcrystalline ceUulose (MCC). MCC is used to prepare fat-free or reduced-fat food products, to strengthen and stabilize food foams, as a tableting aid, and as a noncalotic bulking agent for dietetic foods. It has GRAS status. 

Reduction of the sodium salt of equilenin 17-ethylene ketal with lithium, sodium or potassium in ammonia at —70° occurs predominantly in the B-ring, affording, after acid hydrolysis, equilin (29) in up to 76% yield (55% isolated). The preferential reduction of the B-ring reflects the relative, but not absolute, resistance to reduction conferred on the A-ring by the naphthoxide ion. Some A-ring reduction does compete kinetically with B-ring reduction, since the epimeric 3-hydroxyestra-5,7,9-trien-17-ones are the major reaction by-products. Simple phenoxide ions usually reduce slowly... 

Reaction with the electrophilic peroxodisulfate occurs preferentially at the para position, leading to formation of a cyclohexadienone derivative 5, which loses a proton to give the aromatic compound 6. Subsequent hydrolysis of the sulfate 6 yields 1,4-dihydroxybenzene 3 ... 

In a similar vein, acylation of the corticoid 50 with furoyl chloride gives the diacyl derivative 51. Reduction with sodium borohydride serves to convert the 11-ketone to the alcohol 52. Hydrolysis under mild acid conditions preferentially removes the acyl group at the less hindered 21 position. The hydroxyl group in that derivative (53) is then converted to the mesylate 54. Replacement by chlorine affords mometasone (55) [12]. 

The nonphosphorylated compounds may be readily obtained by chemical or, preferentially, by mild phosphatase hydrolysis of the 1-phosphates. Reactor design17 and enzyme immobilization techniques18 have been evaluated for efficient practical syntheses. Owing to the narrow specificity... 

The method is very useful for the synthesis of physiologically interesting a-mcthylamino acids, e.g., methyl dopa from the 3,4-dimethoxybenzyl derivative. The excellent stereoselection achieved in the process, however, is caused by the preferential crystallization of one pure diastereomerfrom the equilibrium mixture formed in the reversible Strecker reaction. Thus, the pure diastcrcomers with benzyl substituents, dissolved in chloroform or acetonitrile, give equilibrium mixtures of both diastereomers in a ratio of about 7 347. This effect has also been found for other s-methylamino nitriles of quite different structure49. If the amino nitrile (R1 = Bn) is synthesized in acetonitrile solution, the diastereomers do not crystallize while immediate hydrolysis indicates a ratio of the diastereomeric amino nitriles (S)I(R) of 86 1447. 

Effector Gq/11 Preferentially increases Pi hydrolysis and elevates [Ca2+]j Gq/n Preferentially increases Pi hydrolysis and elevates [Ca2+]j (in recombinant systems) Gq/nPreferentially increases Pi hydrolysis and elevates [Ca2+], Intrinsic ligandgated ion channel GsPreferentially increases cAMP formation. 

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