Stereoselective Synthesis of 2-Azido-2-deoxy-β-d-mannosides via Cs₂CO₃-Mediated Anomeric O-Alkylation with Primary Triflates: Synthesis of a Tetrasaccharide Fragment of Micrococcus luteus Teichuronic Acid

Abstract

Cesium carbonate-mediated anomeric O-alkylation of various protected 2-azido-2-deoxy-D-mannoses with primary triflate electrophiles afforded corresponding 2-azido-2-deoxy-βmannosides in good yields and excellent anomeric selectivity. In addition, 1,3-dibromo-5,5-dimethylhydantoin was found to be the optimal oxidant for preparation of those 2-azido-2-deoxy-Dmannoses from their corresponding thioglycosides. The utilization of this method was demonstrated in the synthesis of a tetrasaccharide fragment of Micrococcus luteus teichuronic acid containing N-acetyl-β-D-mannosaminuronic acid (ManNAcA).

Recent Advances in Stereocontrolled Mannosylation: Focus on Glycans Comprising Acidic and/or Amino Sugars

“…[118] Cesium carbonate mediated anomeric O-alkylation of 2azido-2-deoxy mannosides to yield β-mannosides were explored with sugar derived primary triflates and was capitalized in the synthesis of tetrasaccharide fragment of Micrococcus luteus teichuronic acid (Scheme 16). [119] 2-Azido hemiacetal 62 was glycosylated with 6-O-triflate containing D-glucosyl derivative 63 with cesium carbonate to obtain β-mannoside 64, which was subjected to a series of transformations to obtain trichloroacetimidate disaccharide donor 66. TMSOTf mediated glycosylation of 66 with 4-OH disaccharide acceptor 67 resulted in a fully protected α-(1!4)-linked tetrasaccharide 68.…”

2,3-Carbamate mannosamine glycosyl donors in glycosylation reactions of diacetone-d-glucose. An experimental and theoretical study

“…There is evidence that lower selectivities are observed in glycosylation of 2-azidomannosyl donors under Crich conditions, despite the presence of the benzylidene protecting group [19][20]. Advances in β-mannosylation cannot be generalized to mannosamine, and further studies are required to find new protocols [21][22][23].…”

Synthesis of 2-Amino-2-deoxy-β-d-mannosides via Stereoselective Anomeric O-Alkylation of 2N,3O-Oxazolidinone-Protected d-Mannosamine: Synthesis of the Trisaccharide Repeating Unit of Streptococcus pneumoniae 19F Polysaccharide

“… In addition, a similar strategy was successfully applied to the construction of β-(1 → 6)-linked 2-azido-2-deoxy-mannosides 8 involving 2-azido-2-deoxy-mannose 6 and primary triflates (b, Scheme ). However, less reactive sugar-derived secondary electrophiles were found not suitable for anomeric O -alkylation of 2-azido-2-deoxy-mannose 6. For instance, only a trace amount of 2-azido-2-deoxy- d -mannoside 14 was obtained employing 2-azido-2-deoxy- d -mannose 6 and d -galactose-derived C4-triflate 13 under optimal conditions (entry 1, Table ).…”