Amides, conjugated

Acylating Amine Tetrahedral Amide Conjugate acid... 

An investigation of acylaziridines was carried out by comparison of IR, NMR and MS data and included some 1,2-dibenzoylaziridines as well as 2-p-nitrobenzoyl-3-phenyl-oxaziridine (68IZV1530). Amide conjugation in acylated nitrogen-containing three-membered rings is weaker than in open chain acid amides. 

Shtamburg and coworkers have reported that A,A -dialkoxy-A,A -dicarboalkoxyhydra-zines (219) have lower barriers to amide isomerization and weaker anomeric interactions . They measured a barrier to amide isomerization of only 9.8 kcalmoD. Furthermore, benzylic methylenes in A-benzyloxy systems were isochronous down to at least —90°C. These results are in line with observations for the A,A -diacyl-A,A -dialkoxyhydrazines since, in the carboalkoxy systems, the nitrogen lone pairs are lowered in energy by the additional electron demand, thereby reducing both amide conjugation and anomeric overlap. 

The carbonyl band at 1785 cm-1 for N-substituted 4,4-diphenyl-l,2-oxazetidin-3-ones is higher than that of /3-lactams. Here, as with l,2-diazetidin-3-ones, the additional heteroatom reduces amide conjugation (68JOC3619). 

The rotational barriers of A-nitroso-, A-formyl and A-(A,A-dimethylcarbamoyl)-azetidines, compared with those of analogous acyclic amides, suggest that amide conjugation is weaker when the nitrogen is part of an azetidine ring (87KGS912). 

The basic skeleton of the protein zig-zags up and down in the usual way the amide bonds (shown in black) are rigid because of the amide conjugation and are held in the shape shown. Each amino acid may have a different substituent (R1, R2, R3, etc.) or some may be the same. 

Foreign carboxylic acids and amines undergo biological acylation to form amide conjugates. Acylation reactions are of two types. The first involves an activated conjugating intermediate, acetyl CoA, and the xenobiotic. The reaction is referred to as acetylation. 

Michael additions to conjugated carbonyls can be catalyzed by gold species. Among them, arene additions are the most studied area but other nucleophiles can attack the gold-coordinated enones as well. In fact, the intermolecular aza-Michael additions of carbamates to enones was reported in 2002 with both Au(I) and Au(III) salts, and in 2007 an intramolecular aUcoxide and amide conjugate addition has been developed and applied to the synthesis of (+)-andrachcinidine (equation 132). In the latter case, the enones are formed as intermediates in a previous gold-catalyzed step that is the hydration of an alkyne and methanol loss. Then the cyclization takes place to give piperidines. 

Considerable theoretical work has been done to explain equatorial alkylations such as the one illustrated in equation (S). The simplest model of a dipole-stabilized anion is V-methylformamide anion, HCONHCH2 . The geometric requirements for this system are strict the lone pair on carbon is 16-18 kcal mol more stable when oriented in the nodal plane of the amide ir-system than when rotated 90 into conjugation. To explain the removal of an equatorial hydrogen, it has been suggested that the electronic effects of extended amide conjugation should be felt relatively early along the reaction coordinate for proton removal . Thus equatorial protons are removed for stereoelectronic reasons, and... 

Results of X-ray diffraction analysis of SP2335 confirm the effect of the electronic state of the N atom on the length ofthe Cspiro-Obond. In SP23, due to the amide conjugation of the N-atom LEP with the it-electron system of the carbonyl group, the activity of the LEP and the efficiency of the n-a interaction must be lower than in SP5. Therefore, the C8piro-N bond (1.47 A) is not shortened while the Cspiro-0 bond (1.44 A) is much less elongated than in SP5. 

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