Dimethylformamide: An Unusual Glycosylation Modulator

Abstract

A simple solution: When N,N‐dimethylformamide was used to direct the stereochemical course of glycosylation reactions, 1,2‐cis glycosylation products were formed with excellent selectivity. A straightforward highly α‐stereoselective glycosylation involving preactivation (see scheme) should find broad application and be especially useful for sequential glycosylation reactions to form oligosaccharides. LG=leaving group.

Chemical Fucosylation of a Polysaccharide: A Semisynthetic Access to Fucosylated Chondroitin Sulfate

“…24 As to the sulfation pattern in residues other than Fuc, the concurrent presence in the HSQC-DEPT spectrum (Figure 3a) of signals of both sulfated (δ H/C 4.75/77.6 ppm) and nonsulfated (δ H/C 4.08−4.14/67.9−68.9 ppm) CH at position 4 as well as sulfated (δ H/C 4.21−4.32/68.2−68.7 ppm) and nonsulfated (δ H/C 3.79/62.4 ppm) CH at position 6 of GalNAc units, 13e,29 suggested an A,C sulfation pattern for the chondroitin backbone. A structure of fCS-iv and fCS-v summarizing the information inferred from 2D-NMR analysis is depicted in Figure 4.…”

A Modular Approach to a Library of Semi‐Synthetic Fucosylated Chondroitin Sulfate Polysaccharides with Different Sulfation and Fucosylation Patterns

“…[26];(c) i) TBDMSCl, imidazole, DMF,rt, 3h,6 1%;i i) BnBr,N aH, DMF,rt, 1h,9 3%;i ii)TBAF,T HF,rt, 2h,9 4%;(d) BzCl, 1:1v/v pyridine/CH 2 Cl 2 ,rt, 3h, 80 %. [29] With fucosyl donors 2-4 and polysaccharide acceptors 1 and 8 in hand, the reactionc onditions for glycosylations were set: N-iodosuccinimide (NIS)/TMSOTf was chosen as the typical thioglycoside activator system and5:3 v/v CH 2 Cl 2 /DMFa ss olvent mixture,b ecause DMF was shown to act as an a-stereodirecting modulator in glycosylations with 2-O-benzylated thioglycoside donors, [30] including the first 1,2-cis-glycosylation of apolysaccharide acceptor. The benzylidene ring of derivative 7 was then cleaved under oxidative conditions (NaBrO 3 and Na 2 S 2 O 3 in aH 2 O/ethyl acetate mixture) [21] to afford polysaccharide acceptor 8 in 63 %y ield (over two steps from 1) [28] respectively;s ee also the Supporting Information), assuming that the signals to be compared displayed similar 1 J CH coupling constants and that ad ifferenceo fa round 5-8 Hz from the experimental set value did not cause as ubstantial variation in the integratedp eak volumes.…”

A propos of glycosyl cations and the mechanism of chemical glycosylation; the current state of the art

“…64 Recent examples on the study of additives include the addition of sulfides and sulfoxides, which afford stable glycosyl sulfonium and oxysulfonium salts, 30,65–66 and of dimethylformamide and other secondary amides, and even catalytic oxindoles, 67 leading to the formation of glycosyl imidates. 68–69 The additives area has been reviewed recently and as such we will not comment further on it here, 70 but rather we will limit ourselves to counter ions.…”