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The first total synthesis of the branched oligosaccharide OSE-1 of Mycobacterium gordonae (strain 990) is reported. An intramolecular aglycon delivery approach was used for constructing the desymmetrized 1,1'-α,α-linked trehalose moiety. A [3+2] glycosylation of the trisaccharide donor and trehalose acceptor furnished the right hand side pentasaccharide. Regioselective O3 glycosylation of L-rhamnosyl 2,3-diol allowed expedient synthesis of the left hand side tetrasaccharide. The nonasaccharide was assembled in a highly convergent fashion through a [4+5] glycosylation.

Making ends meet: The L-gulopyranosyl trichloroacetimidate and 1,6-anhydro-2,3-di-O-benzyl-beta-L-gulopyranose, efficiently derived from L-ascorbic acid, were individually used as a starting unit and an elongation unit to prepare L-guluronic acid linked alginate oligosaccharides in excellent alpha selectivity and in good yields.

The D-glucosamine derivative (III) is efficiently transformed into oxazolidinone of D-xylosamine (IV), D-allosamine and D-ribosamine.

A novel and convenient route for the synthesis of biologically potent and rare L-hexose derivatives from D-glucose is described. Conversion of diacetone-alpha-D-glucose (14) into 1,2:3,5-di-O-isopropylidene-beta-L-idofuranose (19) was efficiently carried out in two steps. Orthogonal isopropylidene rearrangement of compound 19 led to 1,2:5,6-di-O-isopropylidene-beta-L-idofuranose (27), which underwent regioselective epimerization at the C3 position to give the L-talo- and 3-functionalized L-idofuranosyl derivatives. Hydrolysis of compound 19 under acidic conditions furnished 1,6-anhydro-beta-L-idopyranose (35) in excellent yield, which was successfully transformed into the corresponding L-allo, L-altro, L-gulo, and L-ido derivatives via regioselective benzylation, benzoylation, triflation and nucleophilic substitution as the key steps. Applications of these 1,6-anhydro-beta-L-hexopyranoses as valuable building blocks to the syntheses of 4-methylcoumarin-7-yl-alpha-L-iduronic acid and the disaccharide moieties of bleomycin A(2) as well as heparan sulfate are highlighted.

The total synthesis of the title trisaccharide involves the transformation of D-mannose into an orthogonally protected acetamido-amino sugar building block, two stereoselective glycosylations, selective attachment of a glutaric acid linker, and an amide bond formation.

Covering: 1964 to 2013 Bacteria have unusual glycans on their surfaces which distinguish them from the host cells. These unique structures offer avenues for targeting bacteria with specific therapeutics and vaccine. However, these rare sugars are not accessible in acceptable purity and amounts by isolation from natural sources. Thus, procurement of orthogonally protected rare sugar building blocks through efficient chemical synthesis is regarded as a crucial step towards the development of glycoconjugate vaccines. This Highlight focuses on recent advances in the synthesis of the bacterial deoxy amino hexopyranoside building blocks and their application in constructing various biologically important bacterial O-glycans.

Carbohydrates and glycoconjugates play important roles in complex life processes. Development of carbohydrate-based therapeutics is a major focus of our laboratory requiring the synthesis of glycolipid antigens for biological evaluation. Stereoselective formation of O- and C-glycosides is one of the central challenges in carbohydrate synthesis. In this pursuit, we employ glycosyl iodides as unique glycosyl donors to construct functionally enriched appendages on the anomeric center of the sugar moiety in a highly efficient and stereoselective manner. These constructs can be used to rapidly synthesize a panoply of glycoside analogs for biological studies. In this minireview, glycosyl iodide mediated syntheses of α-linked O-glycolipids such as KRN 7000 and BbGL2 as well C-glycolipid analogs are described.

Making ends meet: The L-gulopyranosyl trichloroacetimidate and 1,6-anhydro-2,3-di-O-benzyl-beta-L-gulopyranose, efficiently derived from L-ascorbic acid, were individually used as a starting unit and an elongation unit to prepare L-guluronic acid linked alginate oligosaccharides in excellent alpha selectivity and in good yields.

Solvent-free per-O-acetylation of hexoses with a stoichiometric amount of acetic anhydride employing 0.03 mol % Cu(OTf)2 proceeded in high yields (90-99%) at room temperature to give exclusively pyranosyl products as an anomeric mixture, the alpha/beta ratio of which was dependent on the temperature and amount of catalyst used. Sequential anomeric substitution with p-thiocresol in the presence of BF3.etherate gave the thioglycosides, isolated exclusively or predominantly as one anomer in 66-75% yields.

A triethylsilane-reductive etherification of the trimethylsilyl ethers with a variety of carbonyl compounds in good yields at room temperature employing 0.5 mol% Cu(OTf) 2 as an extremely efficient catalyst is described here.