Rhamnosyl trichloroacetimidate

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... 

A convergent synthesis of the pentasaccharide derivative 33 of the triterpeniod saponin obtained from the plant Spergularia ramosa was achieved as outlined in Scheme 6 68 The entire assembly relied on use of the trichloroacetimidate protocol and was accomplished in a three plus two fashion. The assembly of the trisaccharide was initiated by the glycosidation of glucosyl trichloroacetimidate donor 22 with rhamnosyl diol acceptor 23 to provide disaccharide 24 in 63% yield. The latter could be used directly as the glycosyl acceptor for the reaction with xylosyl donor 25, leading... 

The macrolactone calonyctin A, a plant growth regulator, has been synthesized (Scheme 42) [184, 185], The quinovose acceptor was glycosylated subsequently with the suitably protected quinovosyl, rhamnosyl, and quinovosyl trichloroacetimidates all steps could be performed stereospecifically. Transformation of the tetra-saccharide into the trichloroacetimidate and glycosylation of the racemic hydroxy acid derivative gave two epimeric compounds. Separation and lactonization gave calonyctin A. 

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