SYNTHESIS OF KOJITRIOSE USING SILICON-TETHERED GLYCOSIDATION

Reaction of 3,4,6-tri-O-acetyl-beta-D-glucopyranosyl chloride (1) with potassium phenylselenate gave phenyl tri-O-acetyl-1-seleno-alpha,beta -D-glucopyranoside (2) in 59% yield. Silylation of benzyl 3,4,6-tri-O- benzyl-beta-D-glucopyranoside (4) with ethyl -chlorodimethylsilyl-1-th io-beta-D-glucopyranoside gave benzyl ylsilyl)-3,4,6-tri-O-benzyl-beta -D-glucopyranoside (5) in 35% yield. Reaction of 5 with N-iodosuccinim ide in nitromethane gave benzyl ranosyl)-3,4,6-tri-O-benzyl-beta-D-glu copyranoside (6) in 45% yield. Chlorodimethylsilylation of phenyl ,4,6 -tri-O-acetyl-1-seleno-alpha-D-glucopyranoside (2 alpha) and reaction with 6 gave benzyl 1-seleno-alpha-D-glucopyranos-2-O-yldimethylsilyl) ranosyl]-3,4,6-tri-O-benzyl-beta-D-glucopyranoside (7) in 82% yield. I ntramolecular glycosidation of 7 using N-iodosuccinimide in nitrometha ne gave benzyl ranosyl]-3,4,6-tri-O-benzyl-beta-D-glucopyranoside (8) in 45% yield. Deprotection of 8 gave kojitriose (9) in quantitative yi eld. Chlorodimethylsilylation of 1,3,4,6-tetra-O-benzyl-alpha,beta-D-f ructofuranose (10) with dimethyldichlorosilane and pyridine followed b y reaction with ethyl 3,4,6-tri-O-benzyl-1-thio-beta-D-glucopyranoside (3) gave ethyl 2-O-(1,3,4,6-tetra-O-benzyl- )-3,4,6-tri-O-benzyl-1-th io-beta-D-glucopyranoside (11) in 85% yield. Chlorodimethylsilylation of 1,3,4,6-tetra-O-benzoyl-alpha-D-fructofuranose (12) with dimethyldi chlorosilane and triethylamine followed by reaction with phenyl 3,4,6- tri-O-acetyl-1-thio-alpha-D-glucopyranoside (13) gave phenyl -3,4,6-tr i-O-acetyl-1-thio-alpha-D-glucopyranoside (14) in 62% yield. Both 11 a nd 14 failed to undergo intramolecular glycosidation.