Mannopyranosyl derivatives

Radical reduction of 1-nitro-C-glycosyl compounds. In 1983, Vasella and co-workers125 reported a stereoselective method for the synthesis of a-C-mannopyranosyl compounds by reduction of 1-nitro-C-mannopyranosyl derivatives with Bu3SnH in the presence of a,a -azoisobutyronitrile (AIBN) radical initiator. These reactions involve the formation of anomeric centered radicals. Thus, in the case of d-manno configuration as in 140, the 1,2-cts-C-pyranosyl compound 145 was obtained in 84% yield. The intermediate pyranosyl radicals 143 prefer a-attack by the tin hydride. Thus for D-glucopyranosyl derivatives, the corresponding l,2-tra x-C-pyranosyl compound 144 is obtained preferentially (Scheme 47). 

Kenne and associates (57) have applied this procedure for the synthesis of a-D-mannopyranosyl derivatives linked to L-serine/L-threonine (59 and 60). Compounds 59 and 60 were obtained by coupling 2,3,4,6-tetra-<9-acetyl-D-mannopyranosyl chloride (56) with Fmoc-L-serine benzyl ester or Fmoc-L-threonine benzyl ester in the presence of silver triflate and 4-A molecular sieves, followed by deprotection (57). 

Among D-mannopyranosyl derivatives, cyclization should be possible for /3 anomers and prohibited for the a anomers, as the latter have both substituents in axial orientation in the normal (Cl) conformation, as shown in 84. Accordingly, stability toward alkali is a characteristic of the a-D-mannopyranosyl esters of nucleoside 5 -pyrophosphates.13,22 103... 

A number of mannopyranosyl derivatives with a variety of ether and ester substituents and sulfonate leaving groups failed to show any solvent-sensitivity (29) and little or no preference for either anomer on glycosidation (Table IV, no. 

Two separate syntheses have been reported for A -acetyl-lactosamine, one via a 1,6 2,3-dianhydride derivative of lactose and the other by ascent of the series from A(-benzyl-3-0- S-D-galactopyranosyl-D-arabinosylamine, and the 3-0-, 4-0- and 6-0-o -D-mannopyranosyl derivatives of A(-acetyl-glucosamine have been reported. ... 

As part of a study on cell-surface glycans, 4-0-(2-deoxy-2-fluoro-a-D-mannopyranosyl)-D-glucopyranose (612) was prepared. Condensation of 6-0-acetyl-1,2,3-tri-0-benzyl-)3-D-glucopyranose with the protected 2-deoxy-2-fluoro-tt-D-mannopyranosyl chloride 611 gave the corresponding A-0- a- and y -D-mannopyranosyl)-D-glucopyranoside derivatives (a/) =... 

Removal of the 2 -sulfonyloxy group of 859 in a basic medium, followed by reaction with metal halides (LiBr and Nal) or hydrogen halides (HCl-1,4-dioxane, HBr-acetone, or0.1% HFin l,4-dioxane-AlF3)gave, byway of the 2,2 -anhydro intermediate 861, the 2 -halo derivatives 862-865. The 2 -deoxy analog 866 and l-(6-deoxy-6-fluoro- ff-D-mannopyranosyl)thy-mine were also prepared from 864 (R = H) and 861 (R = H), respectively. l-(4-Deoxy-4-fluoro-y -D-glucopyranosyl)thymine was obtained by the condensation method. A different kind of nucleoside, 5-(5-deoxy-5-fluoro-2,3-0-isopropylidene-a-D-ribofuranosyl)-l,3-dimethyluracil has also been prepared. ... 

Di-(2,3,4,6-tetra-0-acetyl-a-D-mannopyranosyl)-l,2,5-oxadiazole 2-oxide 306 was synthesized from D-mannose 305 by a route involving dimerization of mannopyranosyl nitrile oxide as the key step. Three methods were used for the generation of the nitrile oxide isocyanate-mediated dehydration of nitromethylmannose derivatives, treatment of aldoxime with aqueous hypochlorite, and base-induced dehydrochlorination of hydroximoyl chloride (Scheme 76) <2001TL4065, 2002T8505>. 

Fig. 16.— 13C-N.m.r. Spectra of Polysaccharides (in DsO) Containing (1— 3)- and (1—>4)-Linked /3-D-Mannopyranosyl Residues, Obtained from [2H]-Labelled D-Glu-coses. (Temperature, 70° chemical shifts expressed as 8C, relative to external tetra-methylsilane the number marked with a superscript asterisk refers to the position of labelling in each D-glucose derivative.)...

Warren and associates (18) have prepared a glycosyl azide derivative (15) of a heptasaccharide. This glycosyl azide was obtained from O-a-D-manno-pyranosyl-( 1 — 6)-0-[a-D-mannopyranosyl-( 1 — 3)-(9-a-D-mannopyrano syl-(l— 6)-0-a-D - mannopyranosyl - (1 — 3)] - O-fi- d - mannopyranosyl -(1 — 4) - O - (2 - acetamido - 2 - deoxy-/ -d-glucopyranosyl) - (1 — 4) - 2 -acetamido-2-deoxy-D-glucopyranose (12) by treatment of its peracetylated derivative 13 with trimethylsilyl trifuoromethanesulfonate, followed by reaction of the intermediary oxazoline 14 with trimethylsilyl azide. Reduction of the glycosyl azide 15 in the presence of Lindlar catalyst gave the glycosyla-mine derivative 16. The condensation of 16 with 1-tert-butyl N-(9-fluoren-... 

Cuscutic resinoside A (1 tetradecanoic acid, (115)-[[6-deoxy-3-(9-(6-deoxy-a-L-mannopyranosyl)-4-0-[(2/ ,3R)-3-hydroxy-2-niethyl-l-oxobutyl]-a-L-nianno-pyranosyl]oxy]-intramol. l,2 -ester) was obtained from the ethyl acetate-soluble fraction of a methanol extract prepared from the seeds of Cuscuta chinensis Lam. The purification of this compound employed a combination of column and preparative-scale HPLC. The structure was deduced from spectroscopic evidence and acid hydrolysis 14). The degradative process gave convolvuUnolic acid, nilic acid, and L-rhamnose. The sugar components were identified by GC analysis after being converted to their thiazolidine derivatives. This disaccharide has a unique macrocyclic lactone, which is placed between C-1 and C-2 of the first rhamnose moiety. 

The D-mannose nucleotide sugars derived from 2 -deoxyguan-osine234 and inosine50,234 were prepared by using enzymes that catalyze the synthesis of guanosine 5 -(a-D-mannopyranosyl pyrophosphate). 

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