Microwave-assisted one-pot synthesis of 1,6-anhydrosugars and orthogonally protected thioglycosides.

Living organisms employ glycans as recognition elements because of their large structural information density. Well-defined sugar structures are needed to fully understand and take advantage of glycan functions, but sufficient quantities of these compounds cannot be readily obtained from natural sources and have to be synthesized. Among the bottlenecks in the chemical synthesis of complex glycans is the preparation of suitably protected monosaccharide building blocks. Thus, easy, rapid, and efficient methods for building-block acquisition are desirable. Herein, we describe routes directly starting from the free sugars toward notable monosaccharide derivatives through microwave-assisted one-pot synthesis. The procedure followed the in situ generation of per-O-trimethylsilylated monosaccharide intermediates, which provided 1,6-anhydrosugars or thioglycosides upon treatment with either trimethylsilyl trifluoromethanesulfonate or trimethyl(4-methylphenylthio)silane and ZnI2, respectively, under microwave irradiation. We successfully extended the methodology to regioselective protecting group installation and manipulation toward a number of thioglucosides and the glycosylation of persilylated derivatives, all of which were conducted in a single vessel. These developed approaches open the possibility for generating arrays of suitably protected building blocks for oligosaccharide assembly in a short period with minimal number of purification stages.

One-pot synthesis of N-acetyl- and N-glycolylneuraminic acid capped trisaccharides and evaluation of their influenza A(H1 N1) inhibition.

Human lung epithelial cells natively offer terminal N-acetylneuraminic acid (Neu5Ac) α(2→6)-linked to galactose (Gal) as binding sites for influenza virus hemagglutinin. N-Glycolylneuraminic acid (Neu5Gc) in place of Neu5Ac is known to affect hemagglutinin binding in other species. Not normally generated by humans, Neu5Gc may find its way to human cells from dietary sources. To compare their influence in influenza virus infection, six trisaccharides with Neu5Ac or Neu5Gc α(2→6) linked to Gal and with different reducing end sugar units were prepared using one-pot assembly and divergent transformation. The sugar assembly made use of an N-phthaloyl-protected sialyl imidate for chemoselective activation and α-stereoselective coupling with a thiogalactoside. Assessment of cytopathic effect showed that the Neu5Gc-capped trisaccharides inhibited the viral infection better than their Neu5Ac counterparts.

Synthesis of the heparin-based anticoagulant drug fondaparinux.

Fondaparinux, a synthetic pentasaccharide based on the heparin antithrombin-binding domain, is an approved clinical anticoagulant. Although it is a better and safer alternative to pharmaceutical heparins in many cases, its high cost, which results from the difficult and tedious synthesis, is a deterrent for its widespread use. The chemical synthesis of fondaparinux was achieved in an efficient and concise manner from commercially available D-glucosamine, diacetone α-D-glucose, and penta-O-acetyl-D-glucose. The method involves suitably functionalized building blocks that are readily accessible and employs shared intermediates and a series of one-pot reactions that considerably reduce the synthetic effort and improve the yield.

Total synthesis of tetraacylated phosphatidylinositol hexamannoside and evaluation of its immunomodulatory activity.

Tuberculosis, aggravated by drug-resistant strains and HIV co-infection of the causative agent Mycobacterium tuberculosis, is a global problem that affects millions of people. With essential immunoregulatory roles, phosphatidylinositol mannosides are among the cell-envelope components critical to the pathogenesis and survival of M. tuberculosis inside its host. Here we report the first synthesis of the highly complex tetraacylated phosphatidylinositol hexamannoside (Ac2PIM6), having stearic and tuberculostearic acids as lipid components. Our effort makes use of stereoelectronic and steric effects to control the regioselective and stereoselective outcomes and minimize the synthetic steps, particularly in the key desymmetrization and functionalization of myo-inositol. A short synthesis of tuberculostearic acid in six steps from the Roche ester is also described. Mice exposed to the synthesized Ac2PIM6 exhibit increased production of interleukin-4 and interferon-γ, and the corresponding adjuvant effect is shown by the induction of ovalbumin- and tetanus toxoid-specific antibodies.