N-Acetyl imidazole

Feeney, R. E., and St. K. Komatsu Role of Tyrosines in Metal-Complexing Properties of Transferrins. (To be presented at the 152nd meeting of the American Chemical Society, September 12-18, 1966, New York, N. Y.) The role of hydroxyls (tyrosyls) in the binding of metals by human serum transferrin and chicken ovotransferrin has been shown by chemical means. Acetylation of the transferrins with N-acetyl imidazole inactivated the metal-binding activity. Deacetylation of the acetylated transferrins with hydroxylamine reactivated the transferrins. 

Capping, acylation of the unreacted amino groups in SPPS using acetic anhydride, N-acetyl imidazole, or other acylating agents in order to avoid further chain elongation of the mismatch sequence at a later stage. These capped core sequences can usually easily be separated from the desired final peptide. 

Recent calculations which take into account the corrected value of 0.320 for the Ei value of the DPN-DPNH couplet show that the AFJ for the hydrolysis of the pyrophosphate bond in ATP is —8,640 calories (Anfinsen and Kielley, personal communication). If this value is correct, the AFo for the hydrolysis of thiolesters, acetyl-P and N-acetyl imidazole will be about —8,600, —11,200 and —14,000 calories respectively instead of the higher values which are reported in this paper. 

For the intramolecular catalysis in the aminolysis of N-acetyl-imidazole by diamines [68, 69] the catalytic group is in the same molecule as the nucleophile, and the problem of distinguishing between nucleophilic and general base catalysis does not arise. The rate law for the aminolysis of N-acetylimidazole by monoamines has both terms of first and of second order in amine, but in the aminolysis by ethylene diamine the term which is first order in amine is relatively more important. The rate constant for this reaction is 186 times greater than that for a monoamine of comparable basicity and a similar rate enhancement is found for the reaction with 1,3-diaminopropane. Rather smaller rate enhancements are found with 1,4-diaminobutane and 1,5-diaminopentane (see Table 4). Intramolecular catalysis is also found in the aminolysis of methyl formate... 

There also appears to be a slight rate enhancement in the reaction of the monoprotonated form of 1,3-diaminopropane with N-acetyl-imidazole. This may arise from an intramolecularly acid catalysed breakdown of the tetrahedral intermediate 45. 

Imidazoles.—Dipole-moment measurements suggest that N-acetyl-imidazole, -benzimidazole, and -indole exist as equilibrium mixtures of (Z)- and ( )-conformers. ... 

Histamine is rapidly degraded by oxidative de-samination by the diaminooxidase histaminase, acetylation of the NH2-group, methylation of the ring and oxidation of the methylhistamines by the mono-aminoxidase. The main metabolites are the N-methyl-imidazole acetic acid and the imidazole acetic acid. Histamine interacts with at least four different specific receptors Hi to H4 (see Table 1). 

The cleavage of 4-nitrophenyl acetate by [Co(NH3)5OH]2+ and [Co(NH3)5Im]2+ (Im = N-deprotonated imidazole) has been studied in water and DMSO solvents.192 All the reactions are exclusively nucleophilic as demonstrated by the detection of the acetylated products [(NH3)sCo02CMe]2+ and [(NH3)5CoImCoMe]3+. Typical kinetic data are summarized in Table 18. The large difference in the reactivity of the two complexes towards 4-nitrophenyl acetate is closely paralleled by their differences in basicity. In Me2SO the complexes have a similar reactivity towards the ester (fcMIm = 30M 1 s 1, k OH = 0.72 M"1 s-1 at 25 °C), and this increase is largely due to the marked increase in the basicity of [Co(NH3)5OH]2+ relative to that of [Co(NH3)5Im]2+ in the dipolar aprotic solvent. 

Some selected examples of 7c-barriers are given in Table XII. Conformational states of N-acetyl derivatives of pyrazole, imidazole, 1,2,3-triazole, 1,2,4-triazole, indole, benzimidazole, benzotriazole, indazole, and tetrazole have been studied by 13C NMR (78JCS(P2)99). In some cases, the occurrence of only one isomer precludes the determination of the barrier, as for 1-acetylpyrazole (74BSF1137) and 1-acetylindoles (750MR445). 

TMS derivatives of biogenic amines are used in combination with acyl derivatives for electron-capture detection. Horning et al. [97] presented retention data of TMS-N-acetyl and TMS-N-HFB derivatives of a number of these substances on SE-30, OV-1 and OV-17. The derivatives were prepared by the following procedure. A 1-mg amount of the amine or amino hydrochloride was dissolved in 0.1 ml of acetonitrile and 0.2 ml of TMS-imida-zole was added. After heating for 3 h at 60°C, 5 mg of N-acetylimidazole (or 0.1 ml of HFB-imidazole) were added and the solution was heated at 80°C for 3 h (30 min at 60°C). The solution was used directly for the GC analysis. 

Included in Table II are the stability constants for gly-gly-L-his and its N-acetyl derivative. In acidic solutions both ligands use the imidazole... 

The same type of calculations have been performed using experimental X-ray structure factors on crystalline phosphoric acid, 7V-acetyl-a,P-dehydrophenyl-alamine methylamide, and N-acetyl-1 -tryptophan methylamide by Souhassou [60] on urea, 9-methyladenosine, and imidazole by Stewart [32] and on 1-alanine [61] and annulene derivatives [62] by Destro and co-workers. The latter authors collected their X-ray data at 16 K [63]. Stewart [32] showed that the positions of the (3, -1) critical points from the promolecule are very close to those of the multipole electron density, but that large differences appear in comparing the density, the Laplacian maps, and the ellipticities at the critical points. Destro et al. [67] showed that the results obtained may be slightly dependent on the refinement model. 

One of the major difficulties in obtaining NMR spectra of imidazoles is a consequence of their low solubility in most suitable solvents except for water. This may often lead to incomplete, or ill-defined, spectra, particularly where there are a number of exchangeable hydrogen atoms, e.g., in polyhydroxyalkyl-substituted imidazoles. Some imidazoles, for instance, 1-methyl- and 2-acetyl-4-methylimida-zole are readily soluble in deuteriochloroform, while deuteriated pyridine, acetone, or dimethyl sulfoxide may prove useful in other cases. Reddy et ai.220 have suggested conversion of imidazoles into their N-acetyl derivatives which are soluble either in deuteriochloroform or in a mixture of deuteriochloroform and dimethyl sulfoxide. Although, as mentioned above, in neutral organic solvents the 4- and... 

A totally different approach to bis-carbene ligands on a cyclic scaffold comes from Burgess and coworkers [351], They start from AA -dimethyl-l,2-diaminocyclohexane and acetylate this compound with chloroacetic acid chloride. Addition of an N-substituted imidazole yields the chiral bis-imidazolium salt (see Figure 3.110). Reaction with silver(I) oxide and carbene transfer to palladium(II) completes the reaction sequence. 

E5, 525 (COOR COOH) N-Acetoacetyl- XV/1, 181 N-Acetyl-a-methyl- E21a, 836 5-Alk —5-CH3 —3-[CH(CH3) —Ar]—4-oxo—4,5-H2 — 3H-imidazol/ Hydrolyse + Ac20 a-subst. E16d, 410 (Hydrolyse) E21a, 828 [l-Acyl-3-alk(3,5-dialk)—2-tert.-butyl — 4-imidazoldin — 2-on/Hydroly-se]... 

The parent perhydro-imidazol[l,5-a]pyridine (130) and the two ro-tamers of the corresponding N-acetyl derivatives (131 and 132) all favor... 

The reaction of acylimidazoles with imidazole is subject to both imidazole and imidazolium ion catalysis (Fife, 1965). The latter reaction is no doubt due to the imidazole-catalyzed hydration of acetylimidazolium ion, as in 18, and fully analogous to the N-methylimidazole-catalyzed hydrolysis of N-acetyl,N -methylimidazolium ion. The mechanism of the former reaction is undefined at the present time, since no 0 exchange studies have been performed with acylimidazoles in more alkaline solution where imidazole catalysis occurs. The leaving group, the imidazole anion, is quite basic (piC = 14-5) therefore it is possible that general base-catalyzed decomposition of the neutral tetrahedral intermediate (24) or general acid-assisted decomposition of the anionic tetrahedral intermediate (25) may occur. The general base-catalyzed alkaline hydrolysis of amides most probably occurs by the... 

---