Amides transfer reactions

The results of these [ N]N2 labeling experiments thus show that isolated heterocysts are capable of reducing N2 to and that the NH4 was assimilated into glutamine. That is, activity of glutamine synthetase is coupled to nitrogenase in these cells. It is possible that a faction of the [ N] glutamine was catabolized in heterocysts, but due to the relatively low amount of total assimilated we were unable to detect the products. We have consistently observed in cyanobacteria that approximately 10 -fold hi er levels of incorporation of can be attained with NU4 than with [ N]N2 as substrate. Therefore, to study metabolism of NH4 and glutamine further, we incubated isolated heterocysts with NH4 and other substrates of amidation and amide transfer reactions. 

Table 5-III lists the glutamine amide transfer reactions of purine and pyrimidine biosynthesis de novo, and of purine and pyrimidine ribonucleotide interconversion, and several more that occur in other areas of metabolism. All have features in common 1, 3).

The possible function of this enzyme in the regulation of the pathway is discussed below. It is listed with glutamine amide transfer reactions in Table 5-III and with other phosphoiibo ltransferases in Table 5-IV. 

As would be expected for a glutamine amide transfer reaction (Chapter 5), the animal enzyme prefers glutamine as amino group donor, but can use ammonia to a lesser extent. 

The amide transfer reactions can be distinguished from the transamidation reactions studied by Fruton et al. as follows. The enzyme is not a peptidase or protease. The amide (or hydroxylamine) transfer is restricted to the /3-carboxyl of aspartic acid or the y-carboxyl of glutamic acid the transfer is not associated with hydrolysis of the amide it does depend on ATP or ADP, arsenate or phosphate, and Mn++, but this dependence notwithstanding, it shares with the peptidase-protease type of transamidation its independence of energy or phosphate transfer. 

When one compares the inhibitor picture of amino acid transfer by peptidases and of 7-glutamyl and glycine transpeptidases on the one hand, with that of amino acid incorporation on the other, one sees at a glance that they are quite different (Table VIII). Additional examples of contrast not shown in the table are HCN, which activates the transferase activity as it does the hydrolytic action of papain and inhibits amino acid incorporation the amide transfer reactions are activated by arsenate the synthesis of serum albumin is inhibited. 

Palladium complexes also catalyze the carbonylation of halides. Aryl (see 13-13), vinylic, benzylic, and allylic halides (especially iodides) can be converted to carboxylic esters with CO, an alcohol or alkoxide, and a palladium complex. Similar reactivity was reported with vinyl triflates. Use of an amine instead of the alcohol or alkoxide leads to an amide. Reaction with an amine, AJBN, CO, and a tetraalkyltin catalyst also leads to an amide. Similar reaction with an alcohol, under Xe irradiation, leads to the ester. Benzylic and allylic halides were converted to carboxylic acids electrocatalytically, with CO and a cobalt imine complex. Vinylic halides were similarly converted with CO and nickel cyanide, under phase-transfer conditions. ... 

OS 10] [R 10] [P 9] The specific interfadal area was varied for a phase-transfer reaction for four amide formations from two amines and two acid chlorides [23[. This was done by filling the solutions in normal test-tubes of varying diameter (1-5 X cm ) and using a micro reactor which had the largest specific interface (45 X cm ). The yields of all foiu reactions are highly and similarly dependent on... 

Figure 4 Dynamic dilution of sample for HPLC analysis of amidation/cyclization reaction. Transfer solvent methoxyethanol flow rate 1 ml/min. Detection refractive index.

Thus, the family of azolides represents a versatile system of reagents with graduated reactivity, as will be shown in the following section by a comparison of kinetic data. Subsequent chapters will then demonstrate that this reactivity gradation is found as well for alcoholysis to esters, aminolysis to amides and peptides, hydrazinolysis, and a great variety of other azolide reactions. The preparative value of azolides is not limited to these acyl-transfer reactions, however. For example, azolides offer new synthetic routes to aldehydes and ketones via carboxylic acid azolides. In all these reactions it is of special value that the transformation of carboxylic acids to their azolides is achieved very easily in most cases the azolides need not even be isolated (Chapter 2). 

For imidazole-transfer reactions leading to imidoylimidazoles by conversion of secondary amides or thioamides with sulfinyldiimidazole, see reference [14a]. For imidazole-transfer reactions with nucleobases see Section 12.11. 

Proton transfer reactions are often the first step in many reactions that alcohols, ethers, aldehydes, ketones, esters, amides, and carboxylic acids undergo. 

Considerable interest remains in catalyzed hydrogen-transfer reactions using as donor solvents alcohols, glycols, aldehydes, amides, acids, ethers, cyclic amines, and even aromatic hydrocarbons such as alkylben-... 

Acyl-transfer reactions are some of the most important conversions in organic chemistry and biochemistry. Recent work has shown that adjacent cationic groups can also activate amides in acyl-transfer reactions. Friedel-Crafts acylations are known to proceed well with carboxylic acids, acid chlorides (and other halides), and acid anhydrides, but there are virtually no examples of acylations with simple amides.19 During studies related to unsaturated amides, we observed a cyclization reaction that is essentially an intramolecular acyl-transfer reaction involving an amide (eq 15). The indanone product is formed by a cyclization involving the dicationic species (40). To examine this further, the related amides 41 and 42 were studied in superacid promoted conversions (eqs 16-17). It was found that amide 42 leads to the indanone product while 41... 

Besides the intramolecular acyl-transfer reactions, electrophilic activation is shown to occur with intermolecular Friedel-Craft-type reactions.18 When the simple amides (45a,b) are reacted in the presence of superacid, the monoprotonated species (46a,b) is unreactive towards benzene (eq 18). Although in the case of 45b a trace amount of benzophenone is detected as a product, more than 95% of the starting amides 45a,b are isolated upon workup. In contrast, amides 47 and 48 give the acyl-transfer products in good yields (eqs 19-20). It was proposed that dications 49-50 are formed in the superacidic solution. The results indicate that protonated amino-groups can activate the adjacent (protonated) amide-groups in acyl-transfer reactions. 

Bromides are less reactive than the corresponding iodides in atom transfer processes. However, activated bromides such as diethyl bromomalonate [36] and bromomalonitrile [53] react with olefins under Et3B/02 initiation. Kha-rasch type reactions of bromotrichloromethane with alkenes are also initiated by Et3B/02 [41]. On the other hand, a remarkable Lewis acid effect was reported by Porter. Atom-transfer reactions of an a-bromooxazolidinone amide with alkenes are strongly favored in the presence of Lewis acids such as Sc(0Tf)3 or Yb(0Tf)3, this reaction was successively applied to the... 

For the primary and secondary a-alkoxy radicals 24 and 29, the rate constants for reaction with Bu3SnH are about an order of magnitude smaller than those for reactions of the tin hydride with alkyl radicals, whereas for the secondary a-ester radical 30 and a-amide radicals 28 and 31, the tin hydride reaction rate constants are similar to those of alkyl radicals. Because the reductions in C-H BDE due to alkoxy, ester, and amide groups are comparable, the exothermicities of the H-atom transfer reactions will be similar for these types of radicals and cannot be the major factor resulting in the difference in rates. Alternatively, some polarization in the transition states for the H-atom transfer reactions would explain the kinetic results. The electron-rich tin hydride reacts more rapidly with the electron-deficient a-ester and a-amide radicals than with the electron-rich a-alkoxy radicals. 

Since formation of EGBs from amides, in all cases, is the result of direct reduction and H2 formation (and has to be done ex situ), the monomeric as well as the polymeric EGBs are recovered as the PB. Their reactions as bases have to be driven either by a thermodynamically favored proton transfer reaction or by a fast follow-up reaction of the depro-tonated substrate, which - particularly for (33) -is difficult, since (33) is a good nucleophile. 

Oxaziranes are in a real sense active oxygen compounds and exhibit many reactions grossly analogous to those of organic peroxides. Thus they undergo one electron transfer reaction with ferrous salts and on pyrolysis they are converted to amides. Oxaziranes are also useful synthetic intermediates since in appropriate cases they may be isomerized to aromatic nitrones which are a convenient source of N-alkylhydroxylamines. The reaction of oxaziranes with peracids also provides a source of nitrosoal-kanes and is in many instances the method of choice for preparation of these compounds. ... 

Many examples of catalytic nucleic acids obtained by in vitro selection demonstrate that reactions catalyzed by ribozymes are not restricted to phosphodiester chemistry. Some of these ribozymes have activities that are highly relevant for theories of the origin of life. Hager et al. have outlined five roles for RNA to be verified experimentally to show that this transition could have occurred during evolution [127]. Four of these RNA functionalities have already been proven Its ability to specifically complex amino acids [128-132], its ability to catalyze RNA aminoacylation [106, 123, 133], acyl-transfer reactions [76, 86], amide-bond formation [76,77], and peptidyl transfer [65,66]. The remaining reaction, amino acid activation has not been demonstrated so far. 

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