Regio- and stereoselectivity of the addition of O-, S-, N-, and C-nucleophiles to the beta vinyl oxirane derived from D-glucal

Ferrier/Aza-Wacker/Epoxidation/Glycosylation (FAWEG) Sequence to Access 1,2-Trans 3-Amino-3-deoxyglycosides

3-Amino-3-deoxyglycosides constitute an essential class of nitrogen-containing sugars. Among them, many important 3-amino-3-deoxyglycosides possess a 1,2-trans relationship. In view of their numerous biological applications, the synthesis of 3-amino-3-deoxyglycosyl donors giving rise to a 1,2-trans glycosidic linkage is thus an important challenge. Even though glycals are highly polyvalent donors, the synthesis and reactivity of 3-amino-3-deoxyglycals have been little studied. In this work, we describe a new sequence, involving a Ferrier rearrangement and subsequent aza-Wacker cyclization that allows the rapid synthesis of orthogonally protected 3-amino-3-deoxyglycals. Finally a 3-amino-3-deoxygalactal derivative was submitted for the first time to an epoxidation/glycosylation with high yield and great diastereoselectivity, highlighting FAWEG (Ferrier/Aza-Wacker/Epoxidation/Glycosylation) as a new approach to access 1,2-trans 3-amino-3-deoxyglycosides.

Highly α-position regioselective ring-opening of epoxides catalyzed by halohydrin dehalogenase from Ilumatobacter coccineus: a biocatalytic approach to 2-azido-2-aryl-1-ols

Halohydrin dehalogenases are usually recognized as strict β-position regioselective enzymes in the nucleophile-mediated ring-opening of epoxides. Here we found the HheG from Ilumatobacter coccineus exhibited excellent α-position regioselectivity in the azide-mediated ring-opening of styrene oxide derivatives 1a–1k, producing the corresponding 2-azido-2-aryl-1-ols 2a–2k with the yields up to 96%.

Biocatalytic synthesis of 2-azido-2-aryl-1-ols was achieved via HheG-catalyzed α-position regioselective ring-opening of styrene oxide derivatives.

Stereoselective Synthesis of Pyrans from Epoxyalkenes: Dual Catalysis with Palladium and Brønsted Acid

We describe regio- and stereoselective cycloisomerizations of alcohols tethered to epoxyalkenes, to construct alkene-substituted pyrans. These transformations are best catalyzed by Pd(PPh₃)₄ in the presence of phosphite ligands, and with diphenylphosphinic acid as an essential Brønsted acid cocatalyst for activation of the epoxyalkene.

Chemical O-Glycosylations: An Overview

The development of glycobiology relies on the sources of particular oligosaccharides in their purest forms. As the isolation of the oligosaccharide structures from natural sources is not a reliable option for providing samples with homogeneity, chemical means become pertinent. The growing demand for diverse oligosaccharide structures has prompted the advancement of chemical strategies to stitch sugar molecules with precise stereo- and regioselectivity through the formation of glycosidic bonds. This Review will focus on the key developments towards chemical O-glycosylations in the current century. Synthesis of novel glycosyl donors and acceptors and their unique activation for successful glycosylation are discussed. This Review concludes with a summary of recent developments and comments on future prospects.

(-)-Benzyl 2,3-dide-oxy-β-d-erythro-hex-2-eno-pyran-oside

In the title compound, C₁₃H₁₆O₄, the six-membered ring of the sugar moiety shows a half-chair conformation. In the crystal, mol­ecules are connected via O—H⋯O hydrogen bonds, forming columns around twofold screw axes along the b-axis direction. There is a disorder of the benz­yloxy group, which has two possible orientations with the phenyl group lying on a common plane [site-occupancy factors = 0.589 (9) and 0.411 (9)].

Stereoselective synthesis of 2,3-unsaturated 1,6-oligosaccharides by means of a glycal-derived allyl epoxide and N-nosyl aziridine

beta-D-threo- and 4-deoxy-4-amino-alpha-D-erythro-hex-2-enopyranosyl di- (n = 0) and trisaccharides (n = 1) of types A and B were synthetized by means of a reiterative, completely stereoselective glycosylation process which makes use of the D-galactal-derived allyl epoxide 1beta and D-allal-derived allyl N-nosyl aziridine 2alpha, respectively.

Stereoselective Synthesis of 2,3-Unsaturated-aza-O-glycosides via New Diastereoisomeric N-Cbz-imino Glycal-Derived Allyl Epoxides

Diastereoisomeric D,L-N-Cbz-imino glycal-derived allyl epoxides 5 and 6 have been synthesized, and their addition reactions with alcohols examined. The reactions lead to the corresponding 2,3-unsaturated-aza-O-glycosides through a new, completely regioselective 1,4-addition process which proceeds with complete substrate-dependent stereoselectivity.

Stereoselective Uncatalyzed Synthesis of 2,3-Unsaturated-4-N-substituted-β-O-glycosides by Means of a New d-Galactal-Derived N-(Mesyl)-aziridine

The reaction of the new D-galactal-derived allylic aziridine 1beta with O-nucleophiles (alcohols and monosaccharides) affords, in a high to complete beta-stereoselectivity, the corresponding 2,3-unsaturated-beta-O-glycosides bearing a beta-N-functionality at C4.

Stereoselective synthesis of 4-(N-mesylamino)-2,3-unsaturated- alpha-O-glycosides via a new glycal-derived vinyl alpha-N-(mesyl)-aziridine

[reaction: see text] N-Mesyl aziridine 7alpha, a new activated vinyl aziridine derived from d-glucal, has been synthesized by cyclization of trans-N,O-dimesylate 6 with t-BuOK in anhydrous benzene. The reaction of 7alpha with alcohols, phenol, and monosaccharides (O-nucleophiles) leads to the corresponding 4-N-(mesylamino)-2,3-unsaturated-O-glycosides and disaccharides through a completely regioselective 1,4-addition process that proceeds with high or complete alpha-stereoselectivity.