Deamination absence

We have also shown ( 8) that other bases stronger than CH-CX) (pK. 4.75) catalyse the decomposition of N -nitroso-2-pyrrolidone at o C. With the exception of imidazole, these reactions follow uncomplicated second order kinetics (Rate = kp[Substrate][Base]) and only products of deamination (hydrolysisT are obtained. Generally, values increase with the base strength of the catalyst and fit tne Br/e(nsted relationship withes 0.66. However, the absence of significant catalysis by sterically hindered bases 2,6-lutidine), the strong catalysis by imidazole relative to HPOi (k2(Imidazole)/k2(HP0J ) = 83) and by hydroxide ion relative to... 

Formation of a lactam as a late metabolite is also possible, as documented by the identification of an important and novel lactam metabolite of the antimalarial drug primaquine (11.148) [161]. When 11.148 was incubated with hamster liver fractions for periods of up to 1 d in the absence of added cofactors, oxidative deamination at both amino groups was the primary metabolic reaction. The metabolite resulting from loss of the primary amino group was further oxidized to the carboxylic acid, which was recovered partly as such and partly as the lactam 11.149. 

The formation of a ruthenium vinylidene is proposed as the key intermediate in the regioselective addition of hydrazine to terminal alkynes [55]. This reaction, which proceeds via addition of the primary amino group of a 1,1-disubstituted hydrazine followed by deamination, provides an unprecedented access to a variety of aromatic and aliphatic nitriles. The tris(pyrazolyl)borate complex RuCl(Tp)(PPh3)2 gave the best catalytic activity in the absence of any chloride abstractor (Scheme 10.17). 

Diphenylacetylene has also been reacted with iodouracil 431 having a formamidine moiety under similar conditions to afford the dehydrogenated product 432 and the deaminated product 433 via intermediates 435 and 436, respectively. The selectivity increased in the presence of lithium chloride, whereby 93% of 432 with a trace amount of 433 were obtained. The lithium cation prevents the insertion of palladium into intermediate 434 to form intermediate 436, which is necessary to form 433. The reaction of 431 with asymmetric acetylenes in the presence of lithium chloride afforded the dehydrogenated pyridopyrimidines 437 and 439. However, reaction of 422 with acetylenic compounds in the absence of lithium chloride afforded the deaminated pyridopyrimidines 438 and 440 (Equation 37) <2000TL5899>. 

We don t observe oxidative deamination in the absence of oxidants. We may boil ethylenediamine with copper indefinitely without any chemical changes taking place. This observation is in addition to the lack of chloride-induced deamination, which conflicts with the hydride transfer mechanism. Moreover, if this mechanism did occur, it would imply a copper-induced exchange of hydrogen between the methylene group and water. 

Dr. Anbar In other words, in the absence of an oxidizing agent, you would expect an induced exchange between the methylene group and water—an exchange with a half-life of less than a minute, since it has to proceed faster than the deamination. 

Deamination appears to proceed equally rapidly both in the presence and absence of oxygen. Stein and Weiss (S18) examined this phenomenon and deduced that deamination can be accompanied by both oxidation and reduction. In the absence of oxygen the H atom, rather than the HO radical is the effective agent. This mechanism is satisfactory for the simple amino acids (glycine, alanine, and serine) studied by these workers. With the more complex amino acids yields of ammonia become less and side chains may be preferentially broken. 

The occurrence of some substitution in the deamination of 2-amino-2-deoxy-/3-D-mannopyranosides131 152 (72), and its absence in the reaction of the a-D-pyranoside150 69, must be due to the steric effect of the axial anomeric substituent which (in the a-D-pyran-oside) hinders the approach of the nucleophile (water) to either the C-2 carbonium ion or to C-2 of the diazonium ion. The glucose and glucitol tentatively detected as minor products in the deamination of 72 (R = D-glucose residue and R = D-glucitol residue) presumably arose by way of a hydride shift of H-l to C-2. 2-Deoxy-D-glucono-1,5-lactone (75) was not detected, as it would probably have. o,... 

Biodegradation. Nitrosubstituted compounds are subject to a variety of degradative processes. Under anaerobic conditions TNT is readily reduced to the corresponding aromatic amines and subsequently deaminated to toluene. As shown in the section on hydrocarbons, Llie latter can be mineralized under anaerobic conditions, leading to the potentially complete mineralization of TNT in the absence of oxygen. 

The absence of neighboring-group participation in deamination reactions seems to be a fairly general phenomenon in the chemistry of these hot ions, although when the neighboring group is as reactive as p-methoxyphenyl some participation may occur.41... 

It would be of interest to attempt this reduction under Bomewhat modified conditions deamination might be achieved by treating the diazonium chloride with hypophosphorous acid at 0° to +5° in the absence of copper. 

Studies with various subcellular fractions are useful to ascertain which enzyme systems are involved in the metabolism of a chug candidate. In the absence of added cofactors, oxidative reactions such as oxidative deamination that are supported by mitochondria or by Ever microsomes contaminated with mitochondria membranes (as is the case with microsomes prepared from frozen liver samples) are likely catalyzed by monoamine oxidase (MAO), whereas oxidative reactions supported by cytosol are likely catalyzed by aldehyde oxidase and/or xanthine oxidase (a possible role for these enzymes in the metabolism of... 

Fig. 1. a-Oxidation of amino acids. Hydroxyl radical (or other reactive radical) abstracts hydrogen atom from the a-carbon. The C-centered free radical formed may react with other amino acid residues or dimerize in the absence of oxygen, which leads to protein aggregation. In die presence of oxygen the carbon-centered radical forms peroxyl radical. Reduction of peroxyl radical leads to protein hydroperoxide. Decomposition of hydroperoxide leads to formation of carbonyl compounds via either oxidative deamination or oxidative decarboxylation. Oxidation of the new carbonyl group forms a carboxyl group. 

Another very simple approach to 18,20-oxygenated steroids is nitrous acid deamination of pyrrolines of the type CCXXXVI. In this manner, Buzetti et al. 165) prepared 18-hydroxyprogesterone CCXXXII. The pyrrolines (CCXXXVI) are readily accessible from the demethyl-conanine type (CCXXXIV) by the Ruschig method. The position of the double bond was established 98) in a model pyrroline from the absence... 

In deaminative reactions, the cyclopropyl cations 14 seem to be more developed than in thermolysis or solvolysis. The reason may be that the nitrogen molecule, the best known leaving group, is not dependent on the anchimeric assistance of the C2-C3 bond when it leaves the cyclopropyl ring. Numerous examples of deaminations are known, even those, where in the absence of a stabilizing substituent R,. j at the reaction center, cyclopropanes 15 are observed in addition to allylic products 13. " ... 

The first attempts at gene therapy were directed at trying to correct severe combined immunodeficiency (SCID) which is caused, in some cases, by a deficiency of adenosine deaminase (ADA), that is expressed in all tissues. ADA deaminates both adenosine and deoxyadenosine and, in the absence of ADA, deoxyadenosine accumulates in cells. Deoxyadenosine can be phosphorylated by the enzyme deoxcytidine kinase to produce deoxyadenosine... 

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