Ready chemistry with a rare sugar: Altrobioside synthesis and analysis of conformational characteristics

• Published in: Carbohydrate research 2024-10, Vol.544, p.109228, Article 109228
• Main Authors: Lütjohann, Clemens, Näther, Christian, Lindhorst, Thisbe K.
• Format: Article
• Language: English
• Subjects: Altrobiosides; Altrose; Carbohydrate Conformation; Chemistry Techniques, Synthetic; Conformational analysis; Glycosylation; Molecular Conformation; Stereoisomerism; VCD spectroscopy
• ISSN: 0008-6215; 1873-426X; 1873-426X
• DOI: 10.1016/j.carres.2024.109228

We describe the synthesis of the full set of the so far unknown methyl altrobiosides and the initial analysis of the conformational dynamic which occurs in some of the synthesized compounds. d-Altrose chemistry has largely been neglected as it is a rare sugar and has first to be synthesized from glucose or mannose, respectively. Nevertheless, d-altrose is particularly interesting as the energy barrier between the complementary chair conformations is rather low and therefore dynamic mixtures of conformers might occur. We describe the ready synthesis of the selectively protected altrosyl acceptors for the glycosidation from d-mannose and the altrosyl-trichloroacetimidate as useful glycosyl donor to achieve the (1 → 2), (1 → 3), (1 → 4), and (1 → 6)-α-linked altrobiosides. The diastereomeric α- and β-O-(d-altropyranosyl)-trichloroacetimidates adopt different ring conformations as analyzed by NMR and VCD spectroscopy. Also, the pyranose ring conformations of the obtained altrobiosides apparently differ from a regular 4C1 chair according to NMR analysis and are influenced by the regiochemistry of the interglycosidic linkage. [Display omitted] •The first synthesis of all four regioisomeric methyl altrobiosides is shown.•The altrosides employed as glycosyl acceptors were derived from methyl α-d-mannoside.•The Lattrell-Dax reaction was used for epimerization.•The two anomeric O-(altropyranosyl)trichloroacetimidates adopt different conformations.•VCD spectroscopy was employed for conformational analysis.