Solution and solid-state structure of N-acetamido-3,4,6-tri-O-acetyl-2-azido-2-deoxy-α-d-galactopyranosylamine

“Armed and disarmed” theory in the addition of an azide radical to glucals

“Armed” glucals were prone to undergo kinetic process. The torsional strains govern the selectivity. Meanwhile, “disarmed” glucals preferred thermodynamic radical addition. A sialic acid containing trisaccharide was also synthesized by the method.

Comparative structural analysis of 5,6,7,9-tetra-O-acetyl-4,8-anhydro-1,3-dideoxy-d-glycero-l-gluco-nonulose and its 1-O-acetylated analog, 1,2,3,4,6-penta-O-acetyl-β-d-galactopyranose using X-ray crystallography

Comparative X-ray diffraction analysis of 5,6,7,9-tetra-O-acetyl-4,8-anhydro-1,3-dideoxy-D-glycero-L-gluco-nonulose (1) and a structurally related analog, 1,2,3,4,6-penta-O-acetyl-beta-D-galactopyranose (2), are reported. Both crystals have one molecule in the unit cell and the pyranose rings in both exist in the 4C1 conformation.

Syntheses of TN building blocks Nα-(9-fluorenylmethoxycarbonyl)-O-(3,4,6-tri-O-acetyl-2-azido-2-deoxy-α-d-galactopyranosyl)-l-serine/l-threonine pentafluorophenyl esters: comparison of protocols and elucidation of side reactions

T(N) antigen building blocks Nalpha-(9-fluorenylmethoxycarbonyl)-O-(3,4,6-tri-O-acetyl-2-azido-2-deoxy-alpha-D-galactopyranosyl)-L-serine/L-threonine pentafluorophenyl ester [Fmoc-L-Ser/L-Thr(Ac3-alpha-D-GalN3)-OPfp, 13/14] have been synthesized by two different routes, which have been compared. Overall isolated yields [three or four chemical steps, and minimal intermediary purification steps] of enantiopure 13 and 14 were 5-18% and 6-10%, respectively, based on 3,4,6-tri-O-acetyl-D-galactal (1). A byproduct of the initial azidonitration reaction of the synthetic sequence, that is, N-acetyl-3,4,6-tri-O-acetyl-2-azido-2-deoxy-alpha-D-galactopyranosylamine (5), has been characterized by X-ray crystallography, and shown by 1H NMR spectroscopy to form complexes with lithium bromide, lithium iodide, or sodium iodide in acetonitrile-d3. Intermediates 3,4,6-tri-O-acetyl-2-azido-2-deoxy-alpha-D-galactopyranosyl bromide (6) and 3,4,6-tri-O-acetyl-2-azido-2-deoxy-beta-D-galactopyranosyl chloride (7) were used to glycosylate Nalpha-(9-fluorenylmethoxycarbonyl)-L-serine/L-threonine pentafluorophenyl esters [Fmoc-L-Ser/L-Thr-OPfp, 11/12]. Previously undescribed low-level dehydration side reactions were observed at this stage; the unwanted byproducts were easily removed by column chromatography.