Effective and chemoselective glycosylations using 2,3-unsaturated sugars

Abstract

Glycosyl donors containing a double bond between C2 and C3 were designed by mimicking the reaction mechanism of lysozyme-initiated hydrolysis of mucopolysaccharides. It was found that, under various glycosylation conditions, the reactivities of 2,3-unsaturated glycosyl acetates were significantly higher, while those of the corresponding 2,3-unsaturated-4-keto glycosyl acetates were much lower than those of the corresponding 2,3-dideoxy (2,3-saturated) glycosyl acetates. Based on these results, chemoselective glycosylations were effectively realized via combinatorial techniques in short-steps using three types of glycosyl donors to construct several types of deoxyoligosaccharides. Furthermore, the highly reactive 2,3-unsaturated glycosyl acetates were found to be useful in the synthesis of the O-glycosides of low reactive tertiary alcohols.

Design of chemical glycosyl donors: does changing ring conformation influence selectivity/reactivity?

“…49 Inspired by the mechanism of lysozyme hydrolysis, Toshima et al designed conformationally distorted glycosyl donors with 2,3-double bonds into a half-chair conformation to enhance the reactivity of pyranoside donors (Scheme 16). 50 Consistent with the expectation that the double bonds effectively stabilize the cation generated at the anomeric center, the competitive reaction between 77 and 78 in the presence of acceptor 79 gave glycoside 80 as a major product.…”

A Survey of Recent Synthetic Applications of 2,3-Dideoxy-Hex-2-enopyranosides

“…Toshima and co-workers reported on the chemoselective assembly of differently substituted 2,3-unsaturated pyranoses [161,162]. Thus, 2,3-unsaturated-4-keto glycosyl acetates, e.g., 193 , were found to display lower reactivity than 2,3-unsaturated-4-hydroxy glycosyl acetates, e.g., 192 , in the presence of Lewis acids, and could therefore be used as glycosyl acceptors with the latter acting as glycosyl donors.…”

C-Aryl Glycosylation: Palladium-Catalyzed Aryl–Allyl Coupling of Achmatowicz Rearrangement Products with Arylboronic Acids

“…Column eluents: hexane/EtOAc (20/ 1), R f = 0.45 (hexane/EtOAc = 6/1). 1 H NMR (400 MHz, CDCl 3 ) δ 7.30 (t, J = 7.5 Hz, 1H), 7.22−7.15 (m, 3H), 7.12 (dd, J = 10.4, 2.3 Hz, 1H), 6.27 (dd, J = 10.4, 2.3 Hz, 1H), 5.35 (d, J = 2.1 Hz, 1H), 4.33 (d,J = 16.3 Hz,1H),4.23 (d,J = 16.4 Hz,1H),2.38 (s,3H).…”