A highly stereoselective construction of 1,2-trans-β-glycosidic linkages capitalizing on 2-azido-2-deoxy-d-glycosyl diphenyl phosphates as glycosyl donors

New Principles for Glycoside‐Bond Formation

“…The solvent effect of propionitrile was exploited to further enhance the b selectivity of the glycosylation with 2-azido-2-deoxyglycosyl phosphates. [192] Thus, in the construction of 1,2-trans and 1,2-cis glycosidic linkages, results with other glycosylation methods, such as the trichloroacetimidate method, could be transferred to the glycosylation with O-glycosyl phosphates. [193] Scheme 15.…”

Protecting Group-Free Glycoligation by the Desulfurative Rearrangement of Allylic Disulfides as a Means of Assembly of Oligosaccharide Mimetics

“…As exemplified in Schemes 7 and 8, and as is described fully in the experimental section (Schemes 9–14), these units were assembled by the combination of standard coupling methods with variations on the themes set out in Schemes 2–5 for the introduction of the allylic disulfide and thiol moieties. These syntheses were generally uneventful and featured, inter alia, the use of acetonitrile to direct glycosylations to the β-stereochemistry in the 2-azido-2-deoxyglucose series, 34 the use of the sulfoxide glycosylation 35 method and the activation of glycosyl sulfoxides in the presence of thioglycosides as described originally by the van Boom group, 35b,36 the application of the Ley-type bisacetal protecting group for the 3- and 4-positions in the glucosamine series, 37 and the employment of both diisopropylidene glucofuranose and a 4,6- O -benzylidene protected glucopyranosyl 3-ol 3,38 as acceptors in the synthesis of laminaribiose derivatives. As in the monosaccharide series thiols were, with the exception of the laminaribiosyl thiol 65 , generated and handled as thioacetates which were cleaved immediately prior to use typically with concomitant removal of any residual acetate esters.…”

A stereocontrolled construction of 2-azido-2-deoxy-1,2-cis-α-galactosidic linkages utilizing 2-azido-4,6-O-benzylidene-2-deoxygalactopyranosyl diphenyl phosphates: stereoselective synthesis of mucin core 5 and core 7 structures

“…At the outset of this work, the glycosidation of 3-O-acetyl-2-azido-4,6-O-benzylidene-2-deoxy--D-galactopyranosyl diphenyl phosphate (1a) 27 was explored using Fmoc-protected serine derivative 2 (1.1 equiv) as an acceptor alcohol. The reaction using TMSOTf (1.1 equiv) as a promoter and 5-Å molecular sieves (MS) in Et 2 O proceeded at 0 °C to completion within 0.1 h, giving glycoside 3a in 83% yield (Table 1, entry 1).…”

“…31 The use of -phosphate 1a gave virtually the same product yield and -selectivity as those obtained with -phosphate 1a (entries 8 vs 13), because thermodynamically less-stable -phosphates anomerize to the corresponding -phosphates in the presence of acids. 27,32 Therefore, stereoselective preparation of -or -phosphates is not a requirement for this method. From comparison of the/ ratios obtained with 2-azido-3,4,6-tri-O-benzyl-2-deoxy--D-galactosyl diphenyl phosphate and 3,4,6-tri-O-acetyl-protected diphenyl phosphate 19 (vide infra), 33 the presence of a 4,6-O-benzylidene acetal group proved to be crucial for high levels of -selectivity.…”