Divergent Synthesis of 3‐Deoxy‐d‐manno‐oct‐2‐ulosonic Acid (Kdo) Glycosides Containing α‐(2→4)‐Linked Kdo‐Kdo Unit

Abstract

Ac onvenient and divergenta pproach was developed to prepare diverse bacterial 3-deoxy-d-manno-oct-2ulosonic acid (Kdo) oligosaccharides containing aK do-a-(2!4)-Kdo fragment. The orthogonal protected a-(2!4) linked Kdo-Kdo disaccharide 3,s erving as ac ommon precursor,w as divergently transformed into the corresponding 8-, 8'-, and4 '-hydroxy disaccharides 5, 7,a nd 14,r espectively.Then, these alcohols were glycosylated, respectively,w ith the 5,7-O-di-tert-butylsilylene (DTBS) protected Kdo thioglycoside donors 1 or 2 in an a-stereoselective and high-yielding manner to afford ar ange of Kdo oligosaccharides. Finally,r emoval of all protecting groupso ft he newly formed glycosides resulted in the desired freeK do oligomer.

Chemical Synthesis and Antigenic Evaluation of Inner Core Oligosaccharides from Acinetobacter baumannii Lipopolysaccharide

“…These disaccharides are orthogonally substituted. The C4, C5′/7′, and C8′ positions of 5 were protected, respectively, by an allyl (All) ether, a cyclic DTBS acetal, and a tert ‐butyldimethylsilyl (TBS) ether, [22] while the C4 and C4′ positions of 6 were substituted, respectively, by an All and a TBS group. So, the use of these orthogonal protecting groups will make it possible to install Kdo or Glc p NA moieties at C4‐, C4′‐, or C5′‐branching points in an optimal order, thus leading to the expected backbones.…”

Kdo Glycosylations and Their Application in Oligosaccharide Synthesis**

“…In 2015, Huang et al. reported that Kdo ethyl thioglycosides with C5‐OH and C7‐OH as TBS ethers were highly effective donors for the stereoselective synthesis of α‐Kdo glycosides [26,27] . Initially, the role of cyclic acetals in stereoselectivity was evaluated by different types of donors with and without a cyclic protecting group.…”

“…[18b-c,20a-b,25] In 2015, Huang et al reported that Kdo ethyl thioglycosides with C5-OH and C7-OH as TBS ethers were highly effective donors for the stereoselective synthesis of α-Kdo glycosides. [26,27] Initially, the role of cyclic acetals in stereoselectivity was evaluated by different types of donors with and without a cyclic protecting group. After the ideal conditions for αselectivity were established, a range of acceptors was used to produce α-Kdo glycosides (Scheme 3).…”

Chemical Synthesis of the Nonreducing Hexasaccharide Fragment of Axinelloside A Based on a Stepwise Glycosylation Approach

“…The α-configuration of the newly formed fucoside was unambiguously confirmed by the characteristic doublet for the anomeric signal of the α- l -Fuc p moiety (δ H1′ 5.29, d, J H1′/H2′ = 3.4 Hz). Then, the TBS group of 11 was selectively removed with 20 equiv of Et 3 N·3HF to clearly furnish the corresponding disaccharide alcohol 12 . Condensation of this compound with 4,6- O -benzylidene-protected d -thiogalactoside donor 7 under similar activation conditions as described above gave exclusively α-(1→3)-linked trisaccharide 13 in a good 73% yield.…”