Rhamnosyl chloride

L-Rhap-(1—>4)-a]6— Rhamnosyl chloride, a-methylstyrene Thiorhamnoside, PhSeOTf 51... 

Glycosylation at the C-26 hemiacetal of 38 was achieved by using the classical Koenigs-Knorr glycosylation. Treatment of 38 with rhamnosyl chloride 36 and silver tiiflate in the presence of TMU provided trisaccharide 39 in 55% yield. Hydroboration followed by PDC oxidation afforded desired ketone 4 0. A palladium (II) hydroxide catalyzed debenzylation of 40 under hydrogen atmosphere gave 2. This completes the first total synthesis of a saponin however, aqueous solutions of 2 were not sweet at all. ... 

A very simple procedure for 0-glycosidation without the need for metal salts involves heating perbenzylglycosyl chlorides and alcohols in dichloromethane in the presence of tetramethylurea. Cholesterol and tetra-O-benzyl-a-D-glucopyranosyl chloride gave 92% of the glycosides (a 0, 60 40). In the case of the a-L-rhamnosyl chloride only a-products were obtained. ... 

Tri-O-benzyl-a-L-rhamnosyl chloride, on heating, gave the first L-series cyclo-oligosaccharides. ... 

The inner disaccharide unit of the trisaccharide hapten of the M. avium serovar 8 GPL148 was assembled in a manner similar to that of the serovar 20, but with reaction of the rhamnosyl trichloroacetimidate (80b) with the benzylidene acetal (81). O-Deacetylation of the product yielded the disaccharide acceptor (84) for the next glycosylation. Incorporation of the pyruvate acetal moiety into the terminal 3-O-methyl-D-glucose residue of 85 was achieved by transacetalation with methyl pyruvate diethyl dithioacetal, with sulfuryl chloride-triflic acid as catalyst. From the mixture of products the desired diastereomer was separated and converted by successive O-debenzylation, acetylation, selective 1-O-deacetylation, and reaction with trichloroacetonitrile into the trichloroacetimidate 86. Reaction of glycosyl donor 86 with acceptor 84, with trimethylsilyl triflate as promoter, afforded fully... 

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

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