Imidazole, phosphorylation

Phosphorylation of phenolate anions with dimethyl phosphorochloridothionate in water-dichloromethane systems normally gives large amounts of dithiopyrophos-phate because of extensive hydrolysis of the phosphorus chloride, but in the presence of tetrabutylammonium salts and 1 % imidazole, phosphorylation of the phenolate anion is complete. The explanation lies in an evident combination of activation of acylating agent (by imidazole) and of nucleophile (by phase-transfer catalysis).71... 

An alternative method involves reaction of an a-acylaminoketone (12) with a primary amine and subsequent ring closure of the resultant Schiff s base (13) with phosphoryl chloride. This enables the introduction of a 1-substituent as in (14) to be carried out efficiently, and if the amine were replaced with a monosubstituted hydrazine, the imidazole derivative (IS) resulted (78LA1916). 

From this observation of the inhibition by adenosine, and other observations, Newell and Tucker suspected the existence of a common synthetic pathway for adenosine and thiamine, and proved (with the help of a collection of mutants) that the bifurcation occurred after the 5-amino- l-(P-D-ribofura-nosyl)imidazole 5 -phosphate (46) step (Scheme 23). Finally, they found that 5-amino-l-(0-D-ribofuranosyl)imidazole (47), labeled with l4C in the imidazole ring, was incorporated into pyramine without significant loss of molar radioactivity by a mutant that is able to use this nucleoside (presumably after phosphorylation).53,54... 

Ferric ion was immobilized on a Chelating Sepharose Fast Flow column preparatory to the separation of seven enkephalin-related phosphopep-tides.17 Non-phosphorylated peptides flowed through the column, and the bound fraction contained the product. The capacity of the column was found to be 23 pmol/mL by frontal elution analysis. Cupric ion was immobilized on Chelating Superose for the isolation of bovine serum albumin.18 Cupric ion was immobilized on a Pharmacia HiTrap column for the separation of Protein C from prothrombin, a separation that was used to model the subsequent apparently successful separation of Factor IX from prothrombin Factor IX activity of the eluate was, however, not checked.19 Imidazole was used as the displacement agent to recover p-galactosidase from unclarified homogenates injected onto a nickel-loaded IMAC column.20 Pretreatment with nucleases and cleaning in place between injections were required procedures. A sixfold purification factor was observed. 

The phosphorylation of alcohols by CEP-imidazole (41 X=N) with CEP-ring retention is already well-established. Following from the observation that CEP-pyrrole (41 X=CH) phosphorylates alcohols with CEP-ring opening, an explanation has been advanced based upon the differences in apicophilicities of the pyrrole and imidazole moieties in pentaco-ordinate intermediates (Scheme 10). A scale of relative reactivities based upon the reactions in the equations... 

A mixed anhydride probably is formed as an intermediate which is cleaved inter-molecularily by the imidazole set free in the first step. For example, reaction with the compound in which R1 =thymyl and R2 = C6H5 yielded quantitatively O-thymylphos-phoric imidazolide and benzoylimidazole.[25 Phosphoryldiimidazoles are also used as condensing agents for the synthesis of amides and peptides, as well as for phosphorylations (see Chapters 4, 5 and 12). 

With neutral phosphoric monoimidazolides, which are more reactive than the ionic species the reaction time for phosphorylation of an alcohol is reduced. A one-flask synthesis of unsymmetrical phosphoric diesters from N-( 1,2-dimethylethylenedioxy-phosphoryl)imidazole, prepared from di(l,2-dimethylethylene)pyrophosphate and imidazole, is presented below [103,[11]... 

Lali, F. V., Hunt, A. E., Turner, S. J., and Foxwell, B. M. (2000). The pyridinyl imidazole inhibitor SB203580 blocks phosphoinositide-dependent protein kinase activity, protein kinase B phosphorylation, and retinoblastoma hyperphosphorylation in interleukin-2-stimulated T cells independendy ofp38 mitogen-activated protein kinase. J. Biol. Chem. 275, 7395-7402. 

Determination of electrochemical oxidation potentials and electrochemical reduction of 13 p-phosphorylated acyclic nitrones shows that phosphorylated compounds have a clear anodic shift of potentials of both, oxidation (Ep 1.40 to 2.00 V versus SCE in CH3CN) and reduction (Ep—0.94 to —2.06 V). This is caused by a strong electron-acceptor influence of the diethoxyphosphoryl group (430). In contrast, a reversible one-electron oxidation of azulene nitrones (233) (Scheme 2.80) occurs 0.6 V below the Ep potential of PBN, that is at the value one observes the oxidation of AH -imidazole-1,3-dioxides (219) (428, 429). In other words, the corresponding RC (234) is 14 kcal more stable than the RC of PBN. Although the EPR spectrum of RC (234) was not recorded, RC (236) from dinitrone (235) turned out to be rather stable and gave an EPR spectrum (170). 

Imidazolones, particularly 2-imidazolones, give the corresponding chloro derivatives when heated with phosphoryl chloride, especially with copper(I) chloride as catalyst [76MI1 80AJC1545 90EGP3828208]. The same reagents convert imidazole N-oxides into 2-chloroimidazoles [75JCS(P1)275]. 

Analogues of (751) react with derivatives of phosphorus-containing acids to form 1-phosphoryl-imidazoles (90CHE599). The same compound also silylates ketones to give enol silyl ethers and/or siloxyalkylimidazoles (Scheme 107) (87JC271). 

In its active form CheA undergoes autophosphorylation, that is, the phosphorylation of a histidine imidazole group in one of its subunits by the protein kinase active site of an adjacent subunit. The phospho group is then transferred from phospho-CheA to another protein, CheY. Phospho-CheY interacts with the flagellar motor proteins (Chapter 19) periodically causing a reversal of direction of the bacterial flagella. As a result the bacteria tumble and then usually move... 

These polyphosphates can then phosphorylate nucleosides rather efficiently.48 If amino acids are present then AMP-amino acids are synthesized (see under peptide synthesis), but if imidazole is present then im-... 

It should be recalled here that the alcoholic hydroxyl of serine does not possess a dissociation constant within the pH range, accessible to enzymic reactions. Therefore, this amino acid cannot influence the pH-activity curve. On the other hand, it is well known that DFP inhibition is initially reversible and becomes only slowly irreversible. This has been demonstrated for true ChE from electric eel by Nachmansohn and associates (46) and for plasma ChE by Mackworth and Webb (47). Similarly, a stepwise reaction with inhibitors, containing the diethyl phosphoryl moiety, has been made probable by Hobbiger (34)- Therefore, it appears possible that phosphates are first attacked by the imidazol moiety of the esteratic site, in conformity with the catalytic influence of free imidazol on phosphate hydrolysis (48). This step is followed by transfer to serine. The final product is a trialkyl phosphate XV, which is not split by imidazol (scheme F). 

The question naturally arises why the final form XV of the phosphoryl-ated enzyme, in which the imidazol ring is free, should be unable to catalyze further hydrolytic reactions. 

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