Total Synthesis of the Repeating Units of Proteus penneri 26 and Proteus vulgaris TG155 via a Common Disaccharide

Abstract

Herein, we report the first total synthesis of the trisaccharide and tetrasaccharide repeating units of P. penneri 26 and P. vulgaris TG155, respectively, having a common disaccharide unit, 3-α-l-QuipNAc-(1 → 3)-α-d-GlcpNAc-(1 →. Striking features of the targets are the presence of rare sugar units, l-quinovosamine and l-rhamnosamine, all joined through α-glycosidic linkages. Major challenges in the formation of 1,2-cis glycosidic linkages in the case of d-glucosamine, l-quinovosamine, and d-galactosamine have been addressed.

Total Synthesis of the Conjugation-Ready Tetrasaccharide Repeating Unit of Shewanella japonica Type Strain KMM 3299T

“…Similarly, the use of pyridine and thioacetic acid conditions also did not improve the yield of the reaction, whereas the same reaction using SnCl 2 . 2H 2 O/PhSH/Et 3 N , as the reducing agent in a mixture of CH 3 CN:CH 2 Cl 2 :CH 3 OH for 1 h followed by N -acetylation with acetic anhydride cleanly generated the corresponding acetamide. Hydrogenolysis of crude compound using H 2 , 20 wt % Pd­(OH) 2 /C in EtOH, followed by acetate deprotection using 1 N NaOH furnished target molecule 1 in 69% yield over three steps on purification by Sephadex G-25 gel.…”

Total Synthesis of a Structurally Complex Tetrasaccharide Repeating Unit of Vibrio cholerae O43

“…cholerae O43 exhibits a highly dense arrangement of diverse functional groups with five nitrogen atoms, three consecutive 1,2- cis α-linkages, and one 1,2- trans β-linkage, which makes it a fascinating synthetic target. Our laboratory has developed an expedient protocol for the synthesis of rare bacterial deoxy d -amino monosaccharide building blocks via one-pot S N 2 displacement of 2,4-bis-triflates starting from easily available d -mannose. , This protocol has been extended to rare l -counterparts and also applied to synthesize structurally diverse bacterial glycoconjugates by us and other groups. , Owing to our interest in structurally complex rare-sugar-containing bacterial oligosaccharides, we embarked upon the synthesis of the tetrasaccharide repeating unit of V . cholerae O43.…”

Total Synthesis of a Linear Tetrasaccharide Repeating Unit of Vibrio vulnificus MO6-24

“…A sequential (2+1+1) glycosylation strategy was adopted to procure tetrasaccharide 2 starting with 1,2- cis selective coupling of a reactive trifluoroacetimidate donor 3 with less nucleophilic trisaccharide C4-OH acceptor 4 . We anticipated that this 1,2- cis stereoselective coupling is going to be particularly challenging owing to the glucose type glycosyl donor ( l -quinovosamine) and poorly nucleophilic C4-OH d -galactosamine acceptor involved in it. Trisaccharide acceptor 4 in turn can be synthesized through α-stereoselective glycosylation of benzylidene-protected d -galactosamine thioglycoside donor 5 with disaccharide acceptor 6 followed by benzylidene hydrolysis and regioselective benzoylation.…”

“…The yield of the reaction was improved to 84% by performing the reaction at a lower temperature of −10 °C, by minimizing the cleavage of the glycosidic bonds. Coupling of acceptor 6 with d -galactosamine thioglycoside donor 5 using NIS/TfOH as the promoter in a CH 2 Cl 2 /Et 2 O (1:1) solvent system at −60 °C with gradual heating to −40 °C furnished fully protected trisaccharide 16 with exclusive α-stereoselectivity in 70% yield. Subsequently, the benzylidine ring in trisaccharide 16 was hydrolyzed with p -TSA, and consecutive regioselective C6 benzoyl protection of the 4,6-diol using a stoichiometric amount of BzCl gave trisaccharide C4-OH acceptor 4 in 71% yield.…”