Acyl sugar

Glycosyl fluorides have also been prepared by treatment of per-O-acyl or partially 0-acylated sugars with hydrogen fluoride [liquid HF (for example, see Refs. 38 and 39) or HF in acetic acid or dichloromethane], as exemplified by 2,3,4-tri-O-benzyl-a-D-xylopyranosyl (18), a-D-glucopyranosyl (19), tetra-O-pivaloyl-a-D-glucopyranosyl (20), and 2,3,5-tri-O-acetyl-D-xylofur-anosyl fluorides (21) (see Table 1). Frequently, HF treatment - leads to... 

Table Z14 Variation in selected acyl sugar concentrations as a function of latitude in Lycopersicon pennelli (from Shapiro et al., 1994)...

Glycosyl halides, a very important group of carbohydrate derivatives, are commonly prepared14 from per-O-acylated sugars by reaction with hydrogen halides or halides of aluminum or titanium. The selection of the method depends mainly on the anomeric configuration of the substrate, the kind of its O-acyl groups, and the stability of the product to be prepared. 

From these experiments it would appear that the presence of a free aldehyde group is a necessary but not a sufficient condition for the formation of diamides in the above reactions. Once formed, the aldehyde group must be stabilized long enough to allow it to react with one or more amide molecules, the latter arising from the ammonolysis of the ester groups present in the acylated sugar. 

It appears that Fischer and Bergmann, were the first workers to apply the well-known catalytic effect of the sodium alkoxides to the hydrolysis of acylated sugars in alcoholic solution. 

Red-purple colors in the flowers of orchids have been shown to be derived from altogether 15 cyanidin and peonidin glycosides, with aromatic acylated sugars attached at both the 7- and 3 -positions (Table Intramolecular associations between these... 

K. Jansson, S. Ahlforts, T. Frejd, J. Kihlberg, G. Magnusson, J. Dahmdn, G. Noori, and K. Stenvall, 2-(TrimethyIsiIyl)ethyI glycosides. Synthesis, anomeric deblocking, and transformation into 1,2-trans 1-O-acyl sugars, J. Org. Chem. 53 5629 (1988). 

In the foregoing Sections, we have frequently mentioned the acetates and other esters, such as the pentaacetates of the hexoses and octaacetates of the disaccharides. It is appropriate to summarize here Fischer s work on the partially acylated sugars and alditols. He encountered some of these compounds accidentally but, when their relation to natural compounds became apparent, he prepared them by intent, using constantly improved methods. 

Table II (which contains a comparison not only of the relative stabilities of the O-acetylglycosyl halides but also of O-benzoylglycosyl halides, O-acylated sugars, and O-acylated glycosides). However, it is apparent that the theory oversimplifies the situation. For example, Hassel and Ottar84 have pointed out that the formation of 1,5-m-O-acetylglycosyl halide may be achieved in S vl reaction mechanisms or in cases where the natures of the old and new substituents are sufficiently different. Tetra-0-acetyl-/3-D-glucopyranosyl chloride is such a substance, and would exist in the Cl conformation (L) since, according to the theory, the 1C conformation LI would be highly unstable. However, for replacement of...

Deprotection of 1-O-acyl sugars. Ethanolamine can selectively cleave the gly-cosyl ester bond of even peracylated aldoses.1... 

The Fujii group has also applied their strategy to the regio- and stereoselective deprotection of acylated sugars.34 They designed the phosphonylated glucose derivative 22 in which the two 4-(A -acetylamino)phenylacetyl groups at C-3 and... 

Scheme 2.17 Transformation of 2-(trimethyIsilyl)ethyl (TMSEt) glycosides into 1-O-acyl sugars.

Glycosyl bromides are most commonly prepared by treatment of a per-0-acylated sugar derivative with a solution of HBr in acetic acid (Scheme 4.2b). The more stable a-anomer is usually obtained in high yield. In this reaction, the anomeric acetyl moiety is converted into a good leaving... 

Bitter taste is elicited by structurally diverse compounds, including phenols, ions, amino acids and peptides, alkaloids, acylated sugars, glycosides, nitrogenous compounds, and thiocarbamates. Taste receptor cells are primarily associated with papillae on the tongue. The signal transduction mechanisms by which taste perception occurs are well not understood, but are the focus of intensive research as reviewed recently (6). 

The alternative fusion method for nucleoside synthesis involves the reaction of a purine with an acylated sugar in the presence of a suitable acid such as p-toluenesulfonic acid or a compound such as tin(IV) chloride or antimony chloride. One of many examples includes the preparation (48% yield) of 2,6-dibromo-9-(j8-D-ribofuranosyl)purine by fusion at 130 °C over 30 minutes of l,2,3,5-tetra-0-acetyl-j8-D-ribose with 2,6-dibromopurine in the presence of p-toluenesulfonic acid (B-68Mi4090i, p. 180). 

Lichtenthaler FW, Voss P, Heerd A. Stannic chloride catalysed glycosidations of silylated purines with fully acylated sugars. Tetrahedron Lett. 1974 15 2141-2144. 

Magnesol, a hydrated magnesium acid silicate produced by the Food Machinery and Chemical Corporation, Westvaco Chemical Division, South Charleston, W. Virginia. This adsorbent has been useful in the chromatography of several types of acyl sugar derivative. 

Ronchetti and Toma [71] have shown that lipases from Pseudomonas fluorescens (PFL) and from Candida cylindracea are able to acylate sugars of the o-series in a different position than their enantiomeric L-sugars. For instance, using PFL, methyl a-o-fucopyranoside was butyrylated at the C-2 position in 88% overall yield and 96 % regioselectivity, and methyl a-L-fucopyranoside gave butyrylation at C-4 in 45% overall yield and 97% regioselectivity. 

---