Imines covalent

Acetaminophen-induced hepatotoxicity is mediated by cytochrome P450 metabolism to N-acetyl-p-benzoquinone imine. Following low doses of acetaminophen the metabolite is efficiently detoxified by glutathione (GSH) however, following large doses hepatic GSH is depleted and to N-acetyl-p-benzo-quinone imine covalently binds to proteins as acet-... 

The role of the phosphate is to bind the coenzyme to the corresponding apoenzyme. Lowe and Ingraham (301) and D. Arigoni of E.T.H., Zurich, proposed an attractive hypothesis (Fig. 7.9) where the phosphate and the methyl groups form an axis about which pyridoxal could pivot between enzyme-imine and substrate-imine covalent structures. 

The Schiff-base chiral imine covalent capsules 50 and 51 have been prepared in [35] using [8-I-12] condensation of chiral diamines (R,R)-1,2-cyclohexanediamine and (/ ,/ )-1,2-cyclohex-4-enediamine with aromatic trialdehyde syntone 2 by Scheme 2.21. As follows from X-ray diffraction data, their cage frameworks with a cavity... 

A [4-1-6] condensation of triptycene triamine with the corresponding salicyl dialdehydes by Scheme 2.23 afforded 12-imine covalent capsules 52-56 the pseudooctahedral cage frameworks of 52 and 53 are reported in [38] to be self-assembled through stacking interactions of their aromatic fragments. 

Many biological processes involve an associa tion between two species in a step prior to some subsequent transformation This asso ciation can take many forms It can be a weak associ ation of the attractive van der Waals type or a stronger interaction such as a hydrogen bond It can be an electrostatic attraction between a positively charged atom of one molecule and a negatively charged atom of another Covalent bond formation between two species of complementary chemical re activity represents an extreme kind of association It often occurs in biological processes in which aide hydes or ketones react with amines via imine inter mediates... 

The mechanism of the first part of transamination is shown in Figure 29.14. The process begins with reaction between the a-amino acid and pyridoxal phosphate, which is covalently bonded to the aminotransferase by an iminc linkage between the side-chain -NTI2 group of a lysine residue and the PLP aldehyde group. Deprotonation/reprotonation of the PLP-amino acid imine in steps 2 and 3 effects tautomerization of the imine C=N bond, and hydrolysis of the tautomerized imine in step 4 gives an -keto acid plus pyridoxamine... 

There are some special cases where tetrahedral intermediates are unusually stable there are three phenomena which lead to this stability enhancement. The first is an unusually reactive carbonyl (or imine) compound which is very prone to addition. An example of such a compound is trichoroacetaldehyde or chloral, for which the covalent hydrate can be isolated. A simple way to recognize such compounds is to think of the carbonyl group as a (very) stabilized carbocation, bearing an substituent. 

The preorganisation approach (b) involves formation of strong reversible covalent arrangements (boronate esters, imines, ketals) of the monomers... 

Soil A reversible equilibrium is quickly established when aniline covalently bonds with humates in soils forming imine linkages. These quinoidal structures may oxidize to give nitrogen-substituted quinoid rings. The average second-order rate constant for this reaction in a pH 7 buffer at 30 °C is 9.47 x 10 L/g-h (Parris, 1980). In sterile soil, aniline partially degraded to azobenzene, phenazine, formanilide, and acetanilide and the tentatively identified compounds nitrobenzene and jD-benzoquinone (Pillai et ah, 1982). 

Oh, K. Jeong, K.-S. Moore, J. S. m-Phenylene ethynylene sequences joined by imine linkages Dynamic covalent oligomers. J. Org. Chem. 2003, 68, 8397-8403. 

In 2004, Rayner and coworkers reported a dynamic system for stabilizing nucleic acid duplexes by covalently appending small molecules [34]. These experiments started with a system in which 2-amino-2 -deoxyuridine (U-NH ) was site-specifically incorporated into nucleic acid strands via chemical synthesis. In the first example, U-NH was incorporated at the 3 end of the self-complementary U(-NH2)GCGCA DNA. This reactive amine-functionalized uridine was then allowed to undergo imine formation with a series of aldehydes (Ra-Rc), and aldehyde appendages that stabilize the DNA preferentially formed in the dynamic system. Upon equilibration and analysis, it was found that the double-stranded DNA modified with nalidixic aldehyde Rc at both U-NH positions was amplified 34% at the expense of Ra and Rb (Fig. 3.16). The Rc-appended DNA stabilizing modification corresponded to a 33% increase in (melting temperature). Furthermore, imine reduction of the stabilized DNA complex with NaCNBH, resulted in a 57% increase in T. ... 

The reaction of an amino group with an aldehyde or ketone leads to an imine, which, as we have just seen with aldolase, provides a splendid example of how to bond a carbonyl substrate to an enzyme, and yet maintain its chemical reactivity in terms of enolate anion chemistry. Another type of covalent interaction is quite commonly encountered, and this exploits the thiol group of cysteine. Thiols are more acidic than... 

Isomer shift data obtained from Mossbauer spectral studies of Eu" and Dy " complexes of edta, salicylaldehydatoethylenedi-imine, and 8-hydroxy-quinoline have indicated that the covalent bonding in these species is small (ca. 4 % of the total) and is attributable to electron transfer from the ligands to the partly filled 4/ shell. 

Partial/complete protein denaturation Covalent alterations Hydrolysis Deamidation Imine formation Racemization Oxidation... 

The use of lithium amides to metalate the a-position of the N-substituent of imines generates 2-azaallyl anions, typically stabilized by two or three aryl groups (Scheme 11.2) (48-62), a process pioneered by Kauffmann in 1970 (49). Although these reactive anionic species may be regarded as N-lithiated azomethine ylides if the lithium metal is covalently bonded to the imine nitrogen, they have consistently been discussed as 2-azaallyl anions. Their cyclization reactions are characterized by their enhanced reactivity toward relatively unactivated alkenes such as ethene, styrenes, stilbenes, acenaphtylene, 1,3-butadienes, diphenylacetylene, and related derivatives. Accordingly, these cycloaddition reactions are called anionic [3+2] cycloadditions. Reactions with the electron-poor alkenes are rare (54,57). Such reactivity makes a striking contrast with that of N-metalated azomethine ylides, which will be discussed below (Section 11.1.4). 

Aldolases have been classified into mechanistically distinct classes according to their mode of donor activation. Class 1 aldolases achieve stereospecific deprotonation via covalent imine/enamine formation at an active-site lysine residue, while Class II aldolases utilize a divalent transition metal cation for substrate coordination as an essential Lewis acid cofactor (usually Zn ) to facilitate deprotonation... 

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