Glyoxal hemiacetal

A variation involves the reaction of benzylamines with glyoxal hemiacetal (168). Cyclization of the intermediate (35) with sulfuric acid produces the same isoquinoline as that obtained from the Schiff base derived from an aromatic aldehyde and aminoacetal. This method has proved especially useful for the synthesis of 1-substituted isoquinolines. 

Other work with the lower-carbon sugars and related compounds during the years in Basle included the oxidative cleavage of 3,4-0-isopropylidene-D-mannitol with lead tetraacetate, to produce an acetonated tartaric dialdehyde (with H. Appel), the application of the Strecker synthesis to this dialdehyde and to 2,3-0-isopropylidene-D-glyceraldehyde (with L. Feldman), and studies based on glyoxal hemiacetal and nn-tartronaldehydic acid (with E. Baer and H. Nidecker). 

From prior attempts at FruA-catalyzed DHAP additions to glyoxal or glutaric dialdehyde no product had been isolated, probably because the dialdehydes can cause cross-linking of the protein and thereby irreversibly destroy its enzymatic activity. On the other hand, hydroxylated aldehydes were assumed to form stable intramolecular hemiacetals in aqueous solution, which may mask the reactivity of free dialdehydes. Using the branched-chain glutaric dialdehyde 38 as a potential precursor to carbon-linked disaccharide mimetics (Scheme 2.2.5.14), we... 

What you have learned in Section 9.1.1 about electronic substituent effects explains why intermolecular hemiacetal formation from the electron-deficient carbonyl compounds methyl glyoxalate (A) and ninhydrin (B) take place quantitatively ... 

When considered solely as the dialdehyde form, oxystarch is a polyacetal of D-erythrose and glyoxal (98), although it will actually contain hemiacetal and other linkages, mentioned in the introduction. After hydrolysis of oxystarch, the optical rotation was near that for the equilibrium value of d-... 

The solution frequently becomes warm,12 and its refractive index,1 viscosity,2 freezing point-composition curve,3 and ultraviolet absorption spectrum 36 are not those which would be expected if no reaction took place. Usually hydrates or hemiacetals of simple aldehydes are too unstable to be isolated, but a number of them are actually known and their physical properties have been determined.4 When the carbonyl group is attached to an electron-attracting group (making the carbonyl carbon atom abnormally positive), stable hydrates are frequently formed. Glyoxal, chloral, and ketomalonic acid are common examples. 

An enzymatic oxidation reaction, presumably to form the hemiacetal at the a-position, which is followed by hydrolysis to release glyoxalic acid and decrease the sire of the PEG molecule by one unit ... 

It is the relative ease of hydrolysis of hemiacetals I and II from a polysaccharide that is so attractive in effecting dispersibility. Glyoxal-treated xanthan gum and other gums are very dispersible because of their relative insolubility but as the acetals are hydrolyzed, the gums begin to hydrate at a rate that allows each gum particle to remain separated to form lump-free solutions. 

The reaction of the (aminophenyl)pyrrolylamine (59) with ethyl glyoxalate ethoxy hemiacetal in ethanol afforded the pyrrolo-l,2,5-benzotriazepine (60) (77% yield) via a Pictet-Spengler type condensation. Treatment of (60) with chloroacetyl chloride, followed by cyclization with methyl-amine, gave the diketopiperazine derivative (61), which was reduced with lithium aluminum hydride to yield the pyrazino[2,l-i/]pyrrolo[l,2-Z>]-l,2,5-benzotriazepine (62) (80% yield) (Scheme 10)... 

To determine the effect of deuterium substitution on formation of 51a. another method was employed to generate glyoxal. 2,3,-Dihydroxy-1.4-dioxane 59, a hemiacetal derivative of glyoxal, is a very useful precursor that does not require the 40% aqueous solution (Ref, 121). A mixture of 59 and benzylamine-A. Mr/j CD3CN/D2O with formic add-d2 as catalyst produced 51a containing no deuterium. The yield of 51a was only 30% after 22 hours, compared to 61% when the reaction was conducted in the same manner and the same concentrations with benzylamine/CHjCN/... 

The reaction of ascorbic acid with aldehydes in aqueous solutions yields the corresponding hemiacetals. The reaction with methyl-glyoxal (a typical product of carbohydrate degradation) gives rise to two cyclic hemiacetals (5-125). Similar products are produced with acrolein, the degradation product of glycerol. 

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