Glycosyl Alkoxythioimidates as Complementary Building Blocks for Chemical Glycosylation

Abstract

It is reported that S-glycosyl O-methyl phenylcarbamothioates (SNea carbamothioates) have a fully orthogonal character in comparison to S-benzoxazolyl (SBox) glycosides. This complete orthogonality was revealed by performing competitive glycosylation experiments in the presence of various promoters. The results obtained indicate that SNea carbamothioates have a very similar reactivity profile to that of glycosyl thiocyanates, yet are significantly more stable and tolerate selected protecting group manipulations. These features make the SNea carbamothioates new promising building blocks for further utilization in oligosaccharide synthesis.

Regenerative Glycosylation

“…33 A series of reactions between perbenzylated bromides with glycosyl acceptor 4 34 was performed as depicted in Table 1 (entries 1–3). First, a reaction of bromide 2 with acceptor 4 was performed in the presence of TMSOTf (0.08 equiv) as the activator and Ag 2 O (3.0 equiv) as the HBr scavenger.…”

“…Thus, glycosidation of donor 14 with 2-OH acceptor 20 34 to form disaccharide 21 was enhanced from 27% (no HOFox) to 85% (25 mol % HOFox, entry 2). Both reactions were stopped after 3 h. Glycosidation of donor 14 with 3-OH acceptor 22 34 to form disaccharide 23 41 was enhanced from 13% (6 h, no HOFox) to 98% (2 h, 25 mol % HOFox, entry 3). Glycosidation of donor 14 with 4-OH acceptor 24 34 to form disaccharide 25 18 was enhanced from 14% (3 h, no HOFox) to 86% (3 h, 25 mol % HOFox, entry 4).…”

“…Both reactions were stopped after 3 h. Glycosidation of donor 14 with 3-OH acceptor 22 34 to form disaccharide 23 41 was enhanced from 13% (6 h, no HOFox) to 98% (2 h, 25 mol % HOFox, entry 3). Glycosidation of donor 14 with 4-OH acceptor 24 34 to form disaccharide 25 18 was enhanced from 14% (3 h, no HOFox) to 86% (3 h, 25 mol % HOFox, entry 4). After this initial success, we investigated benzoylated acceptors that are generally less reactive than their benzylated counterparts, which often translates into reduced yields.…”

Organocatalytic, difluorocarbene-based S-difluoromethylation of thiocarbonyl compounds

“…Thioamides 1b-g and thiocarbamates 9a,b were prepared by the reported procedures, using commercially available 2,4-bis(4-methoxyphenyl)-1,3,2,4-dithiadiphosphetane-2,4-disulfide (Lawesson's reagent) for 1b-g [29] and commercially available isothiocyanates for 9a,b [32].…”

OFox imidates as versatile glycosyl donors for chemical glycosylation

“…Hence, our initial focus has been centered on examining the effect of this activator on OFox glycosides. Unfortunately, the reaction of per-acetylated OFox donor 5 with glycosyl acceptor 14 25 in the presence of TMSOTf gave low yields for the formation of the corresponding disaccharide (<50% yield).…”