Cyclic imide structures

The above is an example of the Guareschi reaction. It is applicable to most dialkyl ketones and to alicyclic ketones (e.g., cyclohexanone, cyc/opentanone, etc.). The condensation product (I) is probably formed by a simple Knoe-venagel reaction of the ketone and ethyl cyanoacetate to yield ethyl a-cyano-pp dimethylacrylate (CH3)2C=C(CN)COOCjHj, followed by a Michael ad tion of a second molecule of ethyl cyanoacetate finally, the carbethoxyl groups are converted to the cyclic imide structure by the action of ammonia. 

Acidic hydrolysis of the amide group at pH 4.5 is a very slow reaction. Strong acidic conditions leads to a progressive insolubilization of the reaction product because of formation of cyclic imide structures ... 

Deamidation. The side chain of amide linkage in a Gin or Asn residue is hydrolysed to form a free carboxylic acid that gives mixtures of peptides in which the polypeptide backbone is attached via an alpha-carboxyl linkage (Asp/Glu) or is attached via beta carboxyl linkage (iso-Asp/Glu) [4]. The key step in the reaction is the formation of a five- or six-membered cyclic imide structure [5], and this degradative reaction most often occurs at a higher rate at the sequence Asn-Gly. 

Highly crosslinked cellular materials, having predominately cyclic imide structures in the main chain, may be prepared from a cyclic anhydride reaction with polyisocyanates. For example, mixtures of MA, diisocyanates, surfactant, and water may be molded, with loss of CO2, into fine-celled structural materials. 

The discovery of cyclic imides of the heavier chalcogens is a relatively recent development. The ring systems that have been structurally characterized all have bulky substituents attached to the nitrogen atoms, viz., Se3(NR)2 (74, R= Bu, Ad),30,152 Se3(N Bu)3 (75),160 Se Bu (76)208 and Se9(N Bu)6 (77).208 The only known cyclic tellurium imide is Te3(NtBu)3.150... 

The influence of secondary structure on reactions of deamidation has been confirmed in a number of studies. Thus, deamidation was inversely proportional to the extent of a-helicity in model peptides [120], Similarly, a-hel-ices and /3-turns were found to stabilize asparagine residues against deamidation, whereas the effect of /3-sheets was unclear [114], The tertiary structure of proteins is also a major determinant of chemical stability, in particular against deamidation [121], on the basis of several factors such as the stabilization of elements of secondary structure and restrictions to local flexibility, as also discussed for the reactivity of aspartic acid residues (Sect. 6.3.3). Furthermore, deamidation is markedly decreased in regions of low polarity in the interior of proteins because the formation of cyclic imides (Fig. 6.29, Pathway e) is favored by deprotonation of the nucleophilic backbone N-atom, which is markedly reduced in solvents of low polarity [100][112],... 

Several blue tetra- and octanuclear Pt complexes, prepared upon reaction of cis-[Pt(NH3)2(H20)2]2+ with open and cyclic amides, as well as cyclic imides and a uracil nu-cleobase, and comprised of binuclear building blocks interacting through Pt-Pt bond formation, have been isolated and structurally characterized in recent years. Without exception, the average Pt oxidation state in these compounds is 2.25. Nevertheless, the structure and mode of action as antitumor agents of the Platinum Pyrimidine Blues , as prepared by Rosenberg in the early 70 s, remain elusive. This account represents a summary of our present knowledge on cationic Platinum Blues , with a focus on those blues obtained from cis-[Pt(NH3)2(H20)2]2+ and pyrimidine nucleobases, and presents speculations on reasonable alternative structures. 

Until 1960 the structures of certain 1,2,4-dithiazole derivatives were formulated as (59) by analogy with cyclic imides, but as a result of the X-ray work of Hordvik and others (Table 1) and the IR studies of Emeleus and coworkers (63JCS3165), molecules having R1 = H are known to have the structures (1 R1 = R2 = H) in the solid state. Whether an equilibrium exists between the two forms in solution, however, has yet to be determined, and no tautomeric studies appear to have been carried out for examples in which R15 H. 

The coupling reaction of allylindium reagents with cyclic imides gives diverse products depending on the structure of both the substrates and the reagents (Scheme 49).206... 

Zhang et al. [36] combine DFT-based conformation analysis with quantitative structure-activity relationship (QSAR) analysis. They looked at bioactive conformations for 25 cyclic imide derivatives as proto-porphyrinogen oxidase (PPO) inhibitors. PPO is the last common enzyme in the biosynthetic... 

Most hydrogen-bond-containing crystal structures are homomolecular, i.e. both the hydrogen-bond accepting and donating functionality exist in the same molecule. Examples of such co-crystals are urea and thiourea derivatives as well as non-cyclic imides . 

El-Kabbani, O., Darmanin, C., Schneider, T. R., Hazemann, 1., Ruiz, E., Oka, M., Joachimiak, A., Schulze-Briese, C., Tomizaki, T, Mitschler, A., Podjarny, A. Ultrahigh resolution drug design II atomic resolution structures of human aldose reductase holoenzyme com-plexed with Eidarestat and Minalrestat implications for the binding of cyclic imide inhibitors. Proteins Struct. Fund. Bioinf. 2004, 55, 805-813. 

The Imides are nitrogen containing analogs of the Anhydrides. They contain the -C(=0)-NH-C(=0)-Iinkage and are usually cyclic in structure. As with the other carbonyl containing compounds, the protons of aliphatic groups alpha to the C(=0) group are weakly deshielded. The Imide NH proton resonates at low field (8-12 ppm) and is usually a very broad absorption band. 

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