Nitrophenyl glycosides

M sodium chloride p-nitrophenyl glycosides of chitin oligosaccharides 92... 

The application of diazo coupling is somewhat limited by the availability of the p-aminophenyl glycosides, particularly of those of the oligosaccharides. Their precursors, the p-nitrophenyl glycosides, are usually obtained by the condensation of a per-O-acetylated glycosyl halide with p-nitrophenol in ethanol (Michael reaction)19,20 or by the reaction of a per-O-acetylated sugar with p-nitrophenol in the presence of a Lewis acid catalyst (Helferich reaction).21 p-Nitrobenzyl 1-thioglycosides have also been prepared by the condensation of the... 

For instance a-fucosides and a-sialosides, which are both difficult to produce by means of classical carbohydrate chemistry, have been synthesized using the corresponding nitrophenyl glycoside donors by applying pig liver a-fucosidase [59] and the sialidase from Vibrio cholerae [60], respectively. 

The Trypanosoma cruzi trani-sialidase catalyzes the reversible transfer of NeuAc from a NeuAc-a-2,3-Gal-)8-OR sequence to an acceptor hearing the Gal-)8-OR motif (Scheme 42) [54], The enzyme is a particularly useful sialidase because it has very little hydrolytic activity and tends to almost exclusively catalyze transsialylation to a galactose. However a major drawback to this method is that to drive the gly-cosylation to completion, there is a need for large quantities of complex a-2,3-linked sialyl donors, which are generally difficult to obtain from natural sources. Other natural donors with a-2,6- or a-2,8-linked sialic acids have been examined but were discovered to be poor sialyl donors for a-2,3-sialylations catalyzed by T. cruzi trans-sialidase [55]. Simple aryl a-sialosides, such as the 4-nitrophenyl glycoside 122 and methylumbelliferone glycoside 130 (Scheme 43), have been found to be excellent... 

For further data, see Refs. 367, 483, and 631. 6 Ref. 435 states syrup, [a]D —88° (E) evidently, an impure sample. c Ref. 775 states syrup, [a]D -33.1° (E), for a product of the alkaline treatment of the p-nitrophenyl glycoside its structure is probably quite different. d Ref. 632 states crystalline, hydroscopic compound, without, however, any m.p. value. e In the original paper,746 the opposite sign (printer s error) appeared (see also, the acetate479,746). r Obtained by sublimation of the lower-melting modification at 85—100°. [a]D —9° was given by mistake. 

Scheme 5.3 Hydrolysis and transglycosylation of a retaining glycosidase. LG = leaving group, to emphasise that activated donors such as nitrophenyl glycosides or fluorides are often used.

The existence of a linear free energy relationship between two enzymes acting on the same library of substrates can give an indication of common mechanism. Thus, a plot of log(kcat/Ani) for hydrolysis of a series of p-nitrophenyl glycosides and aryl glucosides by the GH 1 enzyme from the mesophile Agrobacterium... 

Snyder and Link had investigated the acid hydrolysis of some o- and p-nitrophenyl glycosides (see Table XXVII), and found that the ease of hydrolysis is in the same order as has been found for alkyl glycopyranosides ... 

M. Appam, M. Blanc-Muesser, J. Defaye, and H. Driguez, Stereoselective syntheses of O- and S-nitrophenyl glycosides. Part III. Syntheses in the ct-D-galactopyranose and ct-maltose series, Can. J. Chem., 59 (1981) 314-320. 

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