A-methyl glycoside

Disregarding nonoxygen functional groups (amino, dimethylamino, and so on) only the 2,3,6-trideoxyhexoses were isolated from natural products. However, some of the isomeric trideoxyhexoses were chemically synthesized. Thus, the methyl a-glycosides of 3,4,6 - tr i de o xy - d - erj> f/ ro - he x o p y r a n o s e, 3,4,6-tri-deoxy-D-t/zreo-hexopyranose and 2,4,6-trideoxy-D-eryt/iro-hexopyranose were synthesized from methyl 4,6-dideoxy-a-D-xy/o-hexopyranoside via selective sub-... 

Catalytic oxidation of methyl a-D-fructofuranoside over Pt C led to the uronic acid 96, which is the methyl-a glycoside of D-/yxo-5-hexulosonic acid.155... 

The methyl a-glycoside methyl ester of this sugar was prepared by the methylation of methyl (methyl 2,5-di-0-methyl-a-D-glucosid)uronate with dimethyl sulfate and sodium hydroxide, followed by esterification with diazomethane. The constitution follows from the method of synthesis. 

SCHEME 2.31 One-pot tritylation-silylation-acylation of (a) methyl a-glycosides and (b) p-thioglycosides. 

J7. Jeanloz, R. W., and Flowers, H. M., The isolation and synthesis of the methyl ester methyl a-glycoside of 3-O-P-D-glucuronosyl-W-acetyI-D-glucosamine (hyalobiu-ronic acid). J. Am. Chem. Soc. 84, 3030 (1962). 

The configuration about C 1 is the same in the methyl a-glycosides of all the D-aldohexose. Evidence they all yield the same compound upon oxidation by HIO4. 

Problem 34.24 The products of HIO4 oxidation of the methyl a-glycosides of the D-aldohexoses are shown in Sec. 34.17. What products would have been obtained if these glycosides had contained hve-membered rings ... 

Upon oxidation by HIO4 the methyl glycoside Q yields the same product (shown on p. 1099) as that obtained from methyl a-glycosides of the D-aldohexoses however, it consumes only one mole of HIO4 and yields no formic acid. 

The methyl a-glycoside (82) of the disaccharide fragment, which appears to be thermodynamically the more stable, was formed preponderantly on... 

Af-Acetyl-9-azido-9-deoxy-neuraminic acid (methyl a-glycoside)... 

Af-Acetyl-9-thio-neuraminic acid 5-N-Acetyl-4,9-di-0-acetyl-neuraminic acid 5-N-Acetyl-2,7-dideoxy-2-H-neuraminic acid 5-iV-Acetyl-2,8-dideoxy-2-He,-neuraminic acid 5-A -Acetyl-4,7-dideoxy-neuraminic acid 5-A -Acetyl-7,9-dideoxy-neuraminic acid 5-/V-Acetyl-7,8-diepi-neuraminic acid (methyl a-glycoside) 5-A -Acetyl-7,7-dimethoxy- 3-neuraminic acid methyl glycoside 5-A -Acetyl-8,8-dimethoxy-neuraminic acid methyl a- and 3-glycoside 5-A -Acetyl-7,8,9-tri-0-acetyl-neuraminic acid 5-N-Acety 1-4,7,9-trideoxy-neuraminic acid... 

This conception works out as shown in Scheme 10 CTP 23 formed by the above described sequence is directly consumed by -acetyl neuraminic acid 26 under the catalytic influence of cytidine-5 -monophosphosialate synthase (E.C. 2.7.7.43). This enzyme is isolated from calf brain by ammonium sulfate precipitation (2 5) and subsequent affinity chromatography. The stationary phase consists of CNBr-activated Sepharose 4B reacted with p-[3-(2-amino ethylthio)propyl]-iV-acetyl neuraminic acid 27, which is synthesized by radiating a mixture of the allyl glycoside and cysteamine to achieve radical C-S bond formation (24), The behavior of methyl p-N-acetyl-neuraminic acid as an inhibitor is in accordance with Zbiral s findings (25), where the methyl a-glycoside has been shown to compete with the native substrate for the enzyme, and thus 27 is recommended to be an ideally suited ligand (Scheme 9). A typical analytical run is shown in Scheme 9. Due to elution of the protein fraction by a salt gradient, the transfer to a preparative scale is rather difEcult denaturation occurs and thus a drop in activity down to 6% is observed. 

Jeanloz RW, Flowtas HM (1962) Isolation and synthesis of methyl ester-methyl a-glycoside of 3-P-D-glucurraiosyl-N-acetyl-D-glucosamine (hyalobiuronic acid). J Am Chem Soc 84 3030... 

---