Novel highly stereospecific method of 1,2--glycosylation. Synthesis of α-D-glucosyl-D-glucoses

On Orthogonal and Selective Activation of Glycosyl Thioimidates and Thioglycosides: Application to Oligosaccharide Assembly

“…In our hands, however, their activation over the STaz leaving group was somewhat inconsistent. 15 With the reinvestigation of glycosyl thiocyanates, reactive glycosyl donors introduced by Kochetkov, 26–28 we determined that their activation can be reliably achieved with Cu(OTf) 2 , reaction conditions under which STaz group reacts sluggishly. 29 Indeed, Cu(OTf) 2 -promoted activation of thiocyanate donor 50 over STaz glycosyl acceptor 12 was very efficient and the resulting disaccharide 14 was isolated in 89% yield (Scheme 3).…”

Practical Total Synthesis of (2S,3S,4R)-1-O-(α-D-Galactopyranosyl)-N-hexacosanoyl-2-amino-1,3,4-octadecanetriol, the Antitumorial and Immunostimulatoryα-Galactosylcer-amide, KRN7000

“…An analytical sample was purified by silica-gel column chromatography, using hexane-EtOAc (100: I) as the eluent. to give pure 10 (12). (i) To a solution of crude 10 (41.2 g, ca.…”

General Aspects of the Glycosidic Bond Formation

“…A new wave of methods arose in the end of the 1980s, among which were glycosyl donors such as glycosyl acyl/carbonates [36][37][38], thiocyanates [39], diazirines [40], xanthates [41], glycals [42,43], phosphites [44,45], sulfoxides [46], sulfones [47], selenium glycosides [48], alkenyl glycosides [49][50][51] and heteroaryl glycosides [52] (Figure 1.2). These developments were followed by a variety of more recent methodologies and improvements, among which are glycosyl iodides [53], phosphates [54], Te-glycosides [55], sulfonylcarbamates [56], disulfides [57], 2-(hydroxycarbonyl) benzyl glycosides [58] and novel thio- [59,60] and O-imidates [61,62] (Figure 1.2).…”

“…In this context, glycosyl donors with 1,2-cis orientation form 1,2-trans glycosides: for example glycosyl halides with insoluble catalysts (also used for b-mannosylation) [105], a-imidates in the presence of boron trifluoride etherate (BF 3 -Et 2 O) at low temperature [106] and 1,2-anhydro sugars [107]. Conversely, 1,2-trans-oriented glycosyl donors stereospecifically afford 1,2-cis glycosides, for example highly reactive b-glucosyl halides [70], glycosyl thiocyanates [39,108] and anomeric triflates formed in situ were found superior for the synthesis of b-mannosides [109,110]. …”