Amides, also

Much of protein engineering concerns attempts to explore the relationship between protein stmcture and function. Proteins are polymers of amino acids (qv), which have general stmcture +H3N—CHR—COO , where R, the amino acid side chain, determines the unique identity and hence the stmcture and reactivity of the amino acid (Fig. 1, Table 1). Formation of a polypeptide or protein from the constituent amino acids involves the condensation of the amino-nitrogen of one residue to the carboxylate-carbon of another residue to form an amide, also called peptide, bond and water. The linear order in which amino acids are linked in the protein is called the primary stmcture of the protein or, more commonly, the amino acid sequence. Only 20 amino acid stmctures are used commonly in the cellular biosynthesis of proteins (qv). 

In addition to copolymerisation, polyethylenes terrninated as ketones, alcohols, and carboxyHc acids with molecular weights as high as 700 daltons are now available. The products offer the same chemical functionaHty as common fatty alcohols and acids, but are higher melting and harder. Similar to the fatty alcohols and acids, derivatives such as ethoxylates, esters, and amides also are available as higher melting versions of the fatty derivatives. 

Benzyl chloride is manufactured by the thermal or photochemical chlorination of toluene at 65—100°C (37). At lower temperatures the amount of ring-chlorinated by-products is increased. The chlorination is usually carried to no more than about 50% toluene conversion in order to minimize the amount of benzal chloride formed. Overall yield based on toluene is more than 90%. Various materials, including phosphoms pentachloride, have been reported to catalyze the side-chain chlorination. These compounds and others such as amides also reduce ring chlorination by complexing metallic impurities (38). 

Secondary amides also undergo the McLafferty rearrangement ... 

There are amines such as A-methylnitroamine, that are too weakly nucleophilic to be able to form covalent adducts with arenediazonium ions. The products of the latter appear to be those of salts ArNJ N(N02)CH3, as found by Baranchik et al. (1957). Amides also appear not to be sufficiently nucleophilic, but thioamides are, as is shown by the reaction of A-phenylthiourea in the presence of NaOH (Scheme 13-12 Nesynov et al., 1970). First a (probably homolytic) phenylation-de-diazoniation takes place, followed by A-coupling. Selenourea also reacts a mixture of products is formed, which indicates a reaction of the same type as with thiourea (Nesynov and Aldokhina, 1976). 

The function of the NBS is therefore to provide a source of Brj in a low, steady-state concentration and to use up the HBr liberated in step 1. " The main evidence for this mechanism is that NBS and Br2 show similar selectivity " and that the various N-bromo amides also show similar selectivity, " which is consistent with the hypothesis that the same species is abstracting in each case. " ... 

Aminotroponiminato)yttrium amides also catalyze the regioselective IH of primary aminoalkynes of Eq. (4.79), but the catalytic activity is lower (TOE < 1 h ) [300]. 

Enolates of phenylglycinol amides also exhibit good diastereoselectivity.97 A chelating interaction with the deprotonated hydroxy group is probably involved here as well. 

This is a strong directing effect that can exert stereochemical control even when steric effects are opposed. Entries 4 and 5 in Scheme 12.11 illustrate the hydroxy-directing effect. Other substituents capable of hydrogen bonding, in particular amides, also can exert a. vyn-directing effect.79... 

Exposure of ammoniacal silver chloride solutions to air or heat produces a black crystalline deposit of fulminating silver , mainly silver nitride, with silver diimide and silver amide also possibly present [1], Attention is drawn [2] to the possible explosion hazard in a method of recovering silver from the chloride by passing an ammoniacal solution of the chloride through an ion exchange column to separate the Ag(NH3)+ ion, prior to elution as the nitrate [3], It is essential to avoid letting the ammoniacal solution stand for several hours, either alone or on the column [2], See Silver nitride... 

The use of a nitrogen nucleophile in the side chain (as an amide) also leads to an intramolecular 1,4-addition under the standard conditions for the palladium-catalyzed 1,4-oxidation reactions52. Nitrogen nucleophiles employed for this reaction comprise tosy-lamides, carboxamides, carbamates and ureas. The reactions are run in acetone-acetic acid with p-benzoquinone (BQ) as the oxidant. In most cases highly stereo- and regioselective reactions were obtained and some examples are given in Table 3. 

Aldehydes and ketones are readily reduced back to primary and secondary alcohols, respectively. In the case of ketones, although the reduction is reversible, ketoreductase utilizes NADPH, the concentration of which is higher than NADP+, and this drives the reaction toward the secondary alcohol. A good example is warfarin as shown in Figure 5.3 (19). However, aldehydes are further oxidized to carboxylic acids and carboxylic acids are not reduced back to aldehydes thus eliminating the aldehyde. Reductive metabolism of esters and amides also does not generally occur. 

Hydrogen bonding Because primary amides have two N-H bonds, they have even stronger hydrogen bonds than carboxylic acids. Secondary amides also experience hydrogen bonding. 

Base hydrolysis of amides also requires quite vigorous conditions, but mechanistically it is exactly equivalent to base hydrolysis of esters. After nucleophilic attack of hydroxide on to the carbonyl, the tetrahedral anionic intermediate is able to lose either an amide anion (care with nomenclature here, the amide anion is quite different from the amide molecule) or hydroxide. Although loss of hydroxide is preferred, since the amide anion is a stronger base than hydroxide, this would merely reverse the reaction. 

Direct oxidation of amides also can lead to Hofmann-type rearrangement with formation of amines or carbamates. One reagent that is used is Pb(02CCH3)4. 

Reaction with sodium amide also yields the same compound with liberation of ammonia ... 

Meyers and Shimano further expanded the scope of this methodology to include lithium amides as the nucleophile. The authors meticulously optimized the reaction conditions and determined the scope of the amide addition. Selected examples are listed in Table 8.32 (Scheme 8.163). The best results were obtained when THF was used as the solvent together with a stoichiometric amount of HMPA, relative to the lithium amide. The reaction was quite sensitive to the steric demand of the amide. Thus, lithium diethylamide give no product whereas lithium methyl n-pentylamide and lithium piperidide gave efficient reaction. Primary amides also failed to react. 

Further experiments disproved Wohl s theories1-3 4 as to a direct condensation mechanism. By degradation of 2,3,4,5-tetra-O-acetyl-L-arabinononitrile82 (5) in the presence of propionamide or benzamide, l,l-bis(acetamido)-l-deoxy-L-erythritol (6) was obtained in yields comparable to those obtained when the reaction was conducted in the absence of these extraneous amides. Also, an excess of acetamide in the medium did not increase the formation of nitrogenated carbohydrate derivatives. 

Amides and Imides, Inorganic. An inorganic amide, also called ammonobase, is a compd in which one hydrogen in ammonia is replaced by a metal, as for instance sodamide, NaNHj. An inorganic imide is a compd in which two hydrogens are replaced by metals, eg, lead imide, PbNH... 

Furthermore, amphoteric behavior resulting from complex formation with excess amide also parallels that in water ... 

Magnesium amides also add to unsymmetrical ir-allylpalladium complexes on the less substituted terminus (equation 275).199... 

The needle-like crystals have no colour or smell, but have a strong acidic taste. They are not readily dissolved by water, they are not hygroscopic, and are fairly stable. The compound is at once decomposed by water at 0° into amidosulphonie acid and sulphuryl amide HN(S02.NH2)2+H20=S02(NH2)2+NH2.HS03. The mol. wt. determinations of the salt in aq. soln., and the electrical conductivity confirm this reaction. The electrical conductivity of aq. soln. gives values corresponding with those for amidosulphonie acid, since the sulphuryl amide also produced is not an electrolyte. The compound is insoluble in benzene, and chloroform ... 

Hydroxytriazolines generally yield triazoles by loss of water (Section IV,A,3,b). However, the fused-ring triazolines 110 and 111 when heated lead to amides 112 and 113.260 Formation ofl 13 involves the cleavage of the C-4/C-5 bond of the triazoline ring both amides also result by the action of acid on the respective triazolines. 

One area of application is the analysis of flavours in foods in order to ascertain, for example, the ripeness of fruit or the maturity of cheeses [42]. For this purpose dendrimers were used which can distinguish certain carbonyl compounds such as ketones, aldehydes, esters, and amides, also in mixtures. For example, measurement of the concentration of 2-heptanal is of importance specifically for determination of the degree of ripeness of apples. The concentration of this compound increases significantly with increasing ripeness [43]. This technique can also serve as an electronic nose for quality control of high-value products such as saffron, which in powder form may contain undesired contaminants (adulterants) such as curcuma, safflower, or marigold. 

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