Methylglyoxal reactions

The rate data for the OH-methylglyoxal reaction by Kleindienst et al. (1982) and of Plum et al. (1983) differ by over a factor of 2. The more recent measurements of Tyndall et al. (1995) by discharge flow and by Baeza-Romero et al. (2007) by pulsed photolysis lie between the earlier determinations and agree well with one another see table IV-D-2 and figure IV-D-2. The mean of these two measurements at 298 K is 1.30 x 10 cm molecule" s", which lies close to the mean of the earlier measurements. The temperature dependent measurements of Tyndall et al. and of Baeza Romero et al. agree well... 

As the reaction sequence of Scheme 12-38 can be stopped at the stage of the oo-methylglyoxal phenylhydrazone (12.78), it is possible to synthesize asymmetrically substituted formazanes (12.80, Ar = Ar ) by reacting acetone with one equivalent of a diazonium ion ArNJ under acidic conditions and then coupling the co-methyl-glyoxal phenylhydrazone with Ar NJ in alkaline solution. 

Clostridium bifermentans reduced 2,4,6-trinitrotoluene to 2,4,6-triaminotoluene, and a metabolite was formed by reaction of one of the amino groups with methylglyoxal (Lewis et al. 1996). 

A cross-coupling reaction of aldehydes with a-diketones proceeded in the presence of water to give the corresponding adducts in moderate to good yield. It is possible to use the substrates such as phenyl-glyoxal monohydrate, aqueous methylglyoxal, formalin, and aqueous a-chloroacetaldehyde for this reaction.330... 

Reaction of 6-aminopyrimidines with 2 mol of a-ketoaldehyde in aqueous medium gave rise to the zwitterionic a-iminocarboxylic acids thus, 214 with methylglyoxal gave the pyrimido[l,6- ]pyrimidin-2-carboxylic acid 215 (Equation 26) <2005W02005/039589>. 

The extent of oxidation, when determined by the reaction of the product with phenylhydrazine, is 85%. Hydrolysis of the oxidized xylan should produce approximately equimolar quantities of D-glyceraldehyde and glyoxal. Experimental determination of glyceraldehyde indicates 67 % of the theoretical when the oxidized xylan is distilled with sulfuric acid and the evolved methylglyoxal measured as the phenylosazone. Glyoxal is isolated in 63% yield, when separated as the phenylosazone or as the dioxime. Aldehyde groups in the oxidized xylan may be further... 

Photolytic. Glyoxal, methylglyoxal, and biacetyl were produced from the photooxidation of 1,2,3-trimethylbenzene by OH radicals in air at 25 °C (Tuazon et al., 1986a). The rate constant for the reaction of 1,2,3-trimethylbenzene and OH radicals at room temperature was 1.53 x 10 " cmVmolecule-sec (Hansen et al., 1975). A rate constant of 1.49 x 10 L/molecule-sec was reported for the reaction of 1,2,3-trimethylbenzene with OH radicals in the gas phase (Darnall et al., 1976). Similarly, a room temperature rate constant of 3.16 x 10 " cm /molecule-sec was reported for the vapor-phase reaction of 1,2,3-trimethylbenzene with OH radicals (Atkinson, 1985). At 25 °C, a rate constant of 2.69 x lO " cm /molecule-sec was reported for the same reaction (Ohta and Ohyama, 1985). 2,3-Butanedione was the only products identified from the OH radical-initiated reaction of 1,2,4-trimethylbenzene in the presence of nitrogen dioxide. The amount of 2,3-butanedione formed decreased with increased concentration of nitrogen dioxide (Bethel et al., 2000). 

D,L-Lactaldehyde, CHs-CHOH-CHO, is reduced by fermenting yeast to 1,2-propylene glycol. In this reaction 1,2-propylene glycol containing excess of the dextrorotatory component was obtained by Neuberg and Vercellone by means of top yeast. On the other hand, acetol (see p. 84) and methylglyoxal (see p. 85) yield a levorotatory 1,2-propylene... 

The other important type of reaction leading to the formation of two bonds between a metal and four-atom fragment is addition of carbenoids, i.e. germylenes and stannylenes, to a-dicarbonyl and related compounds. The process can be classified as redox (4 + 1) cycloaddition since the dicarbonyl fragment is reduced while the carbenoid is oxidized. Formally the simplest example of such reactions is the interaction of methylglyoxal with activated tin metal to give a cyclic stannylene, Sn(II) enediolate (see Scheme 34) <83CL1825>. 

The direct alkylation of aminopyrazines is usually unsatisfactory as a synthetic method because it mainly takes place at the most basic ring nitrogen. However, 3,6-diamino-2,5-dicyanopyrazines are successfully alkylated by treatment with alkyl iodide or bromide in protic solvent in the presence of alkali such as NaOH in dimethylacetamide (DMA) to form bis(dialkylamino)pyrazines <1998DP(39)49>. Reaction of 2,6-diamino-3,5-diarylpyrazine with methylglyoxal in aqueous HCl-ethanol led to -alkylation but no formation of the expected bicyclic imidazolo[l,2- z]pyrazine <2001S768>. 

Although enzymes tend to be extremely specific they are not always completely able to avoid side reactions. Triose phosphate isomerase releases small amounts of methylglyoxal (Eq. 13-28), presumably as... 

The rather toxic methylglyoxal is formed in many organisms and within human tissues.174 It arises in part as a side reaction of triose phosphate isomerase (Eq. 13-28) and also from oxidation of acetone (Eq. 17-7) or aminoacetone, a metabolite of threonine (Chapter 24).175 In addition, yeast and some bacteria, including E. coli, have a methylglyoxal synthase that converts dihydroxyacetone to methylglyoxal, apparently using a mechanism similar to that of triose phosphate isomerase. It presumably forms enediolate 2 of Eq. 13-26, which eliminates inorganic phosphate to yield methyl-... 

On the basis of analogous reaction systems, it would be expected a priori that decomposition of this alkoxy radical to methylglyoxal CH3C(0)CHO would predominate [27],... 

The pH-rate profile for unbuffered hydrolysis of glyceraldehyde-3-phosphate (6-3-P) has been attributed to hydrolysis of the monoanion of the phosphate monoester at pH < 4, spontaneous formation of glyceraldehyde from the phosphate dianion at pH 7-8, and, at higher pH, hydroxide-catalysed methylglyoxal formation. Reaction of the dianion is not subject to a solvent isotope effect and is believed to occur by the irreversible ElcB mechanism whereby an enediolate intermediate, formed on rate-determining C(2) deprotonation, subsequently expels phosphate trianion by C—0 bond breaking. The diethylacetal and 2-methyl-G-3-P do not hydrolyse under the same conditions.5... 

Two dehydration reactions, one preceding the first electron uptake and the other interposed between the first and second electron uptake, are also involved in polarographic reduction of aliphatic a-dicarbonyl compounds 86), such as diacetyl (R = CHs) or methylglyoxal (R = H). 

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