Concise Synthesis of Lactococcus garvieae Lipoteichoic Acids Through an Additive-Modulated Preactivation Protocol and the Immunological Studies

Reaction Rate and Stereoselectivity Enhancement in Glycosidations with O-Glycosyl Trihaloacetimidate Donors due to Catalysis by a Lewis Acid–Nitrile Cooperative Effect

“…When glycerol was employed as a glycosyl acceptor, either with O-tert-butyldiphenylsilyl (TBDPS) protection (E) or Obenzoyl (Bz) protection (F), the glycosidation proceeded smoothly to give the β-linked products that are, for instance, key constituents of lipoteichoic acids. 62 Although thioglycosides were found to be activated by gold(III) salts, 36 interestingly, even thioglycosides were well tolerated in this catalysis system as glycosyl acceptors, affording the desired glycosidation products with apparently no loss of yield or stereoselectivity (for instance, 2Hβ, 2Iβ, 4Gβ, and 14Gβ). The observations and results obtained so far have to be rationalized by a novel reaction mechanism (vide inf ra).…”

“…With per- O -benzyl O -glucopyranosyl and O -galactopyranosyl donors, such as 1 and 3 , generally excellent β-selectivities were obtained, with the formation of 1,2-, 1,3- 1,4-, and 1,6-linkages, respectively ( 2Aβ – 2Dβ , 4Aβ – 4Cβ ). When glycerol was employed as a glycosyl acceptor, either with O - tert- butyldiphenylsilyl (TBDPS) protection ( E ) or O -benzoyl (Bz) protection ( F ), the glycosidation proceeded smoothly to give the β-linked products that are, for instance, key constituents of lipoteichoic acids . Although thioglycosides were found to be activated by gold­(III) salts, interestingly, even thioglycosides were well tolerated in this catalysis system as glycosyl acceptors, affording the desired glycosidation products with apparently no loss of yield or stereoselectivity (for instance, 2Hβ , 2Iβ , 4Gβ , and 14Gβ ).…”

Synthesis of Core M3 Matriglycan Constituents via an Additive-Controlled 1,2-cis-Xylopyranosylation with O-Xylosyl Imidates as Donors

“…Owing to such advantages, the precise stereocontrolled construction of five distinctive gluco-and galactopyranosidic linkages were successfully accomplished in multigram scale, thus leading to the first total synthesis of a series of Lactococcus garvieae lipoteichoic acid (LTA) molecules. 33 Despite these achievements, an efficient 1,2-cis-xylopyranosylation strategy is still lacking. Hence, it follows whether, after activation of the xylosyl donor, the modulation of the reaction course by an additive will work as well in this case.…”

“…Moreover, since the glycosidation outcome is not directed by the initial anomeric configuration of the glycosyl donor under the preactivation conditions, it provides an extra synthetic convenience, especially for the large scale synthesis of complex molecules. Owing to such advantages, the precise stereocontrolled construction of five distinctive gluco- and galactopyranosidic linkages were successfully accomplished in multigram scale, thus leading to the first total synthesis of a series of Lactococcus garvieae lipoteichoic acid (LTA) molecules …”

“…In order to achieve our synthetic goals, a concise and practical strategy for 1,2- cis -xylopyranosylation was required. To this aim, an additive-modulated glycosidation strategy, adjusting the desired stereoselectivity by additives during the reaction and minimizing time costly protecting group manipulations, was envisioned. − , Recently, we established an O -glycosyl trichloroacetimidate-based additive-modulated strategy to construct 1,2- cis -gluco-/galactosidic bonds. This method utilizes common and inexpensive reagents as promoters and additives and does not require participating protecting groups; it is independent of the donor anomeric configuration and affords excellent yields and stereoselectivities with O -glycosyl imidate donors.…”