Active glycolaldehyde

D-erythro-Pentulose 5-phosphate (XLIV) has been formed by the action of transketolase on hydroxypyruvate (XLII) and D-glycerose 3-phosphate, the hydroxypyruvate being decarboxylated196 to active glycolaldehyde which then reacts with the triose phosphate by an acyloin reaction.28 The active glycolaldehyde is also formed from L-glycero-tetrulose, d-altro-heptulose 7-phosphate, D-fructose 6-phosphate, and D-i/ireo-pentulose 5-phosphate and it reacts with various aldehydes (acceptors) to give ketoses.198, 200 Thus, substitution of L-gfh/cero-tetrulose for hydroxypyruvate in the above experiment also resulted in formation of D-en/i/iro-pentulose... 

The tetrose phosphate (LVI) acts as an acceptor for active glycolaldehyde derived from n-i/ireo-pentulose 5-phosphate (LII), and thus, in the presence of transketolase, yields D-fructose 6-phosphate (LV) and D-glyc-erose 3-phosphate. The reverse of this reaction has been observed.200 The... 

The oxidation of glycolaldehyde by tetrachloroaurate was carried out in acetic acid-sodium acetate buffer and found to be first order in [Au(III)] and [glycolaldehyde]. H+ and Cr both retarded the reaction. A compatible mechanism was proposed, which involves a one-step, rate-determining, two-electron transfer and the involvement of three gold species, AuCH, AuClsCOHa), and AuClsCOH), the last being the most active. 

This thiamin pyrophosphate-dependent enzyme [EC 2.2.1.1], also known as glycolaldehyde transferase, catalyzes the reversible reaction of sedoheptulose 7-phos-phate with D-glyceraldehyde 3-phosphate to produce D-ribose 5-phosphate and o-xylulose 5-phosphate. The enzyme exhibits a wide specificity for both reactants. It also can catalyze the reaction of hydroxypyruvate with R—CHO to produce carbon dioxide and R—CH(OH)—C(=0)—CH2OH. Transketolase isolated from Alkaligenes faecalis shows high activity with D-erythrose as the acceptor substrate. 

Scheme 2.2.2.1 Principal reactions of transketolase. Ketose donor substrates include xylulose 5-phosphate (upper left) or hydroxypyruvate (lower left). Acceptor substrates are a-hydroxyaldehydes. A C2 unit ( activated glycolaldehyde ) is transferred to the acceptor substrate via a ThDP-bound a, 3-dihydroxyethyl group thereby forming a novel ketose of 3S,4R...

It was shown that both a N,N -dialkylpyrazinium salt and a mixture of glycolaldehyde with an amino compound are highly active in free radical formation as well as in browning. 

The triazol-5-ylidene 12 was found to be a powerful catalyst for the conversion of formaldehyde to glycolaldehyde in a formoin reaction [25.] The concept of triazolium salt catalysis appeared to show promise, and consequently our research group undertook the synthesis of a variety of chiral triazolium salts for the asymmetric benzoin reaction [26]. However, the ce-values and catalytic activities shifted widely with slight structural changes in the substitution pattern of the triazolium system. The most active catalyst 15 (Fig. 9.4) afforded benzoin (6, Ar = Ph) in its (R -configuration with 75% ee and a satisfactory yield of 66%. 

By selecting (he proper reaction conditions, ccdialt and rhodium catalysts prove active for the direct hydrogenation of the intermediate di dehyde (0 ethylene glycol [44). Glycolaldehyde is also formed with a zeolite/NaOH catalyst [451, Monsanto has patented a route to ethylene ycol, which starts with methanol (Equation (21)) [46]. 

Recent work by Teles et al. [32] has shown that triazolium salts are highly active catalysts for the condensation of formaldehyde affording glycolaldehyde (for-moin reaction). In terms of activity, these catalysts proved considerably superior to the thiazolium salts previously used for this transformation. Investigations into the mechanism have shown that the catalytic cycle corresponds to the mechanism proposed by Breslow [32]. 

The first stage, involving the transfer of active glycolaldehyde, can be accomplished in the laboratory by use of spinach or rat-liver transketolase, and the products isolated and characterized as the barium salt and 2,7-anhydride, respectively. The second stage is catalyzed by liver or yeast transaldolase and is believed to involve the enzymic transfer of a 1,3-di-hydroxy-2-propanone residue sedoheptulose 7-phosphate and D-fructose... 

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