Acetylated nitro sugar

Acetylated nitro sugar, Diels-Alder reactions, 7... 

As far as intermolecular, substrate-controlled additions are concerned, unsaturated nitro sugars can serve as acceptors. For example, when 3-0-acetyl-5,6-dideoxy-l,2-O-isopropylidene-6-nitro-a-D-. v7o-hexofuranos-5-ene (8) was treated with methanolic sodium hydroxide, 3-0-acetyl-6-deoxy-l,2-O-isopropylidene-5-0-methyl-6-nitro-D-glucofuranose (9) and L-/cfo-furanose (10) were formed in a ratio of ca. 4 1 (estimated by TLC, no isolated yields reported)59. Upon prolonged reaction, additional deacetylation was observed. 

In order to minimize such possible side-reactions as anomerization of glycosides and acetolysis of acetal structures, alternative techniques of acetylation have been studied. Whereas basic catalysis leads to severe complications in certain nitro sugar derivatives (see Section IV,2a and c pp. 124, 129), boron trifluoride etherate has proved to be an excellent agent for satisfactory acetylation of glycosides, O-benzyl-idenated glycosides, and disaccharides that contain a deoxynitro function.148,149... 

Although, for 185 and 187, aromatization provides an increased driving-force for the elimination process, there is a general tendency, with nitro sugars, for unsaturation and ensuing complications148 to be induced by pyridine-acetic anhydride, so that this system could be employed for acetylation in only a few favorable cases.84,148,152,154,169... 

From nitro-sugars. - iV-Acetyl-lactosamine 30 and N-acetyl-cpt-lactosamine 31 were obtained as a manno-nch epimeric mixture on ozonolysis of the 2-acetamido-l-nitro-derivatives 29, obtained from 3-0-(p-D-galactosyl)-D-arabinose 28 (Scheme 8). The / a /io-isomer 32 could be obtained in 15% yield from 28), by direct crystallization. Treatment of the product mixture with aqueous ammonia gave a g/uco-rich mixture from which the g/oco-isomer 30 could be crystallized (32% yield from 28). Similar procedures applied to L-arabinose led to 2-acetamido-2-deoxy-L-mannose and - glucose... 

The c.i.(CH and i-C4H )-m.s. of acetylated glyco-furanosyl and -pyranosyl fluorides has been investigated and the influence of configuration reported.other reported c.i.-m.s. studies have been on nitro-sugars (in which negative ion analysis gave [M+NOa] peaks), methyl hexopyranoside nitrates, and the xanthate and S roethylthiocarbonate derivatives of l,2 5,6-di-Q-isopropylidene-3- -methyl-c(-D-allofuranose. 

Treatment of methyl 2,3,4-tri-0-acetyl-6-deoxy-6-iodo-a-D-glucopyranoside with sodium nitrite and phloroglucinol gave the 6-deoxy-6-nitro-sugar, which was converted, via the a-bromide, into the corresponding adenin-9-yl nucleoside. ... 

The two nitro-sugars (Al) and (42) were obtained in a 4 1 ratio, and were readily converted to the corresponding 4-amino-4-deoxy-keto-pyranosides by hydrogenation. The peracetate of (41) gave the dlaminonitro-sugar (43) as the major product upon treatment with methanollc ammonia and subsequent N-acetylation. Similar products were obtained from 1,2-0 -isopropylidene-a-D-fructopyranose, which... 

The first probable values for the molecular size of the native pectins from apple and sugar beet were obtained by Schneider and co-workers.71 These workers prepared the nitro- and acetyl-derivatives in order to avoid the anomalous behavior due to charge effects which occurred using the unsubstituted polysaccharides. From osmotic and viscometric measurements on the nitrate, values for the molecular weight of 30,000-100,000 were found, the constant Km in Staudinger s equation being 6(10)-4. Viscometric measurements indicated that there was little difference in size between the two derivatives. 

The nitroalcohols are esterified by the usual acylating agents in the presence of acidic catalysts. With the nitroglycols of the sugar series, acetic anhydride containing a trace of sulfuric acid gives rapid and complete acetylation. Basic acetylation catalysts, such as pyridine or sodium acetate, are not satisfactory, presumably due to interaction with the nitro group. 

---