Syntheses of T(N) building blocks Nalpha-(9-fluorenylmethoxycarbonyl)-O-(3,4,6-tri-O-acetyl-2-azido-2-deoxy-alpha-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.
Liu
Mian
M
Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, Minneapolis, MN 55455, USA.
Young
Victor G
VG
Lohani
Sachin
S
Live
David
D
Barany
George
G
D015295:Antigens, Tumor-Associated, Carbohydrate / Q000737:chemistry*; D001671:Biochemistry / Q000379:methods; D002240:Carbohydrate Sequence; D018360:Crystallography, X-Ray; D006020:Glycopeptides / Q000138:chemical synthesis* / Q000737:chemistry; D006031:Glycosylation; D008094:Lithium / Q000737:chemistry; D008969:Molecular Sequence Data; D015394:Molecular Structure; D012964:Sodium / Q000737:chemistry
D015295:Antigens, Tumor-Associated, Carbohydrate; D006020:Glycopeptides; C504159:N(alpha)-(9-fluorenylmethoxycarbonyl)-O-(3,4,6-tri-O-acetyl-2-azido-2-deoxygalactopyranosyl)serine pentafluorphenyl ester; C504161:N(alpha)-(9-fluorenylmethoxycarbonyl)-O-(3,4,6-tri-O-acetyl-2-azido-2-deoxygalactopyranosyl)threonine pentafluorphenyl ester; C040286:Tn antigen; D008094:Lithium; D012964:Sodium