Mannosyl chloride

In contrast to the behavior of 275, treatment of 274 with titanium tetrachloride gave only 3,4,6-tri-0-acetyl-2-deoxy-2-(thiocyanato)-a-D-mannosyl chloride (280). Methanolysis of 280 gave a mixture of anomeric... 

It was found122 that 2,3 5,6-di-0-isopropylidene-D-mannose reacts with p-toluenesulfonyl chloride in pyridine, but the only product isolated was the corresponding mannofuranosylpyridinium p-toluenesulfonate. On the other hand, when 2 moles of the sodium salt of 2,3 5,6-di-0-iso-propylidene-D-mannose, dissolved in dry petroleum ether, were treated with one mole of p-toluenesulfonyl chloride, there apparently resulted the nonreducing-disaccharide derivative, 2,3 5,6-di-0-isopropylidene-D-mannofuranosyl 2,3 5,6-di-0-isopropylidene-D-mannofuranoside (a compound later prepared121 by condensation of 2,3 5,6-di-0-isopropylidene-D-mannosyl chloride with 2,3 5,6-di-0-isopropylidene-D-mannose). Presumably, the following reactions had taken place (Ip = isopropylidene) ... 

Di-0-isopropylidene-D-mannosyl chloride has been prepared from di-O-isopropylidene-D-mannose by the action of phosphorus penta-chloride in light petroleum in the presence of anhydrous sodium carbonate. Hepta-O-methylcellobiose and tetra-O-methyl-D-glucopyranose have been converted to the corresponding glycosyl chlorides by the same method. ... 

When a chloroform solution of hexaacetyl-4- 8-D-glucosyl-D-mannose methyl 1,2-orthoacetate was treated with hydrogen chloride, a rapid change in rotation occurred in that the initial specific rotation of —12.7 became constant in six minutes, [ajo -f29.8 . This change in rotation was similar to that observed with alcoholic solutions. On evaporation, the chloroform solution gave a dextro-rotatory heptaacetyl-4- 8-D-glu-cosyl-D-mannosyl chloride with the structure of the common type of acetylglycosyl halides. 

Nishizawa, M, Kan, Y, Shimomoto, W, Yamada, H, a-Selective thermal glycosidation of rhamnosyl and mannosyl chlorides, Tetrahedron Lett., 31, 2431-2434, 1990. 

For example, Garegg and Iversen demonstrated that Ag2C03 was effective for the activation of mannosyl chloride 8 having 2,3-4,6-di-O-cyclohexylidene protection [17]. Reaction with... 

Phase-transfer catalysis has been used to prepare toluene-p-sulphonates. When sulphonation at the anomeric position of 2,3.5,6-di-O-cyclohexylidene-D-manno-pyranose was attempted using toluene-p-sulphonyl chloride-benzene-butyl-triethylammonium chloride, the a-mannosyl chloride and the a,a-iinked manno-disaccharide were obtained in addition to the desired product. Selective sulphonation of benzyl (or methyl) 4-0-benzyl-0 -L-rhamnopyranoside with toluene-p-sulphonyl chloride-aqueous sodium hydroxide-dichloromethane gave 65% 2-O-toluene-p-sulphonate. ... 

Benzyloxycarbonylamino) 2-nitrophenol (3.39) in 1 M sodium hydroxide (17 ml) and acetone (30 ml) at 5° is treated with tetra-O-acetyl-a-D-mannopyranosyl chloride (3.7 g) dissolved in acetone (20 ml). After 12 hr at 5°, the mixture is poured into water (200 ml) and extracted five times with chloroform. XJnreacted phenol is recovered from the chloroform extracts by six extractions with IM sodium hydroxide. The chloroform layer is washed with dilute acid, dried, and evaporated to give a mixture of (V) and mannopyranosyl chloride. Elution of the mixture from neutral alumina (Woelm) with chloroform gives the unreacted mannosyl chloride. Compound (V), seen as a pale yellow band on the column, is eluted with chloroform-ethylacetate (1 1). Yield, 0.7 g (11%) m.p., 188° (from n-propanol) - -68° (C = 0.2, CHCI3). 

Hashimoto found that low-temperature activation of mannosyl chlorides with silver triflate in the presence of alcohols leads to varying ratios of a- and P-linked mannosides [45, 126, 127]. A study of the factors controlling stereoselectivity in silver triflate-mediated mannosylation has been published [128]. Activation of O-benzyl-protected mannosyl fluorides by a combination of Sn(OTf)2 and La(C104)3 has been reported by Shibasaki to afford mixtures of a- and P-mannosides [129]. The large proportions of a-mannosides formed in the homogeneous reactions outlined in this section indicate the involvement of oxocarbonium-ions enabling the anomeric effect to dictate the steric outcome. Because the stereoselectivity of these approaches is crucially dependent on the reacting partners and conditions their scope remains limited. 

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