Galacto, Gluco, Manno, and Disaccharide-Based C-Glycosides of 2-Amino-2-deoxy Sugars

Abstract

[reaction: see text] Starting from readily available precursors, selenoglycosides derived from GalNAc, GlcNAc, and ManNAc were prepared by either a one- or a two-step process. The anomeric selenides underwent facile C-Se homolysis to provide the corresponding anomeric radicals, which were trapped with alkenes to give C-glycosides. This provides a general entry to alpha-C-glycosides based on 2-amino-2-deoxy sugars that is also applicable to disaccharide variants.

Radicals and Carbohydrates

“…In the addition of l-fucos-1-yl radical to α,β-unsaturated ester 14, two 1,3-distant stereocenters are created with high diastereoselectivity: the first one results from a totally selective α-C-glycosylation under stereoelectronic control and the second by a hydrogen-atom transfer (HAT) reaction which proceeded preferentially to the 2,3-syn isomer 15. 34 Some limitations associated with the use of glycosyl bromides of 2-amido sugar as radical precursors, which in some cases led only to the corresponding oxazoline, prompted Gallagher 35,36 to examine alternative radical precursors in these compounds. The anomeric selenides derived from d-GlcNAc, d-ManNAc, and d-GalNAc 16 underwent smooth C-Se homolysis and the resulting radicals were trapped with electron-deficient olefins to give C-glycosides 17.…”

Experimental and computational studies of nJ(77Se,1H) selenium–proton couplings in selenoglycosides

“…n J( 77 Se, 1 H) Coupling Constants Over the years, the heteronuclear single quantum multiple bond correlation (HSQMBC) [19,20] experiment has found widespread application for the measurement of heteronuclear long-range coupling constants involving 13 C-1 H, 15 N-1 H, 31 P-1 H and more recently, the 77 Se-1 H pair of nuclei. [21] The experiment offers good sensitivity and straightforward implementation on most spectrometers and coupling constants can be directly measured from the antiphase splitting of the HSQMBC multiplets along the 1 H dimension.…”

“…Selenosugars and, specifically, selenoglycosides play an important role in synthetic carbohydrate chemistry as stable glycosyl donors11, 12 which can be selectively activated13 in oligosaccharide syntheses for the preparation of C‐glycosides and various glycoconjugates 14–16. They are also useful in structural and biochemical investigations of glycosidase enzymes as hydrolytically stable glycoside surrogates 17, 18.…”

On-water synthesis of glycosyl selenocyanate derivatives and their application in the metal free organocatalytic preparation of nonglycosidic selenium linked pseudodisaccharide derivatives

“… 11–15 Organoselenium chemistry has become an important topic of research due to the unique chemical behaviour of Se-containing compounds and their pharmacological potential. 16–20 Although, selenium has been incorporated in different classes of molecules to improve their therapeutic index, 21 the introduction of selenium within the carbohydrate framework has received less attention except for a few reports which include the synthesis of anomeric selenoglycosides 22–27 and their application in the preparation of oligosaccharides, 28–30 glycal derivatives, 31 glycosyl fluorides, 32 C-glycosides 33 and medicinally useful compounds. 34 The synthesis of some cyclic sugar intermediates containing selenium in the ring has also been pursued.…”