Synthesis of Oligosaccharides Related to a Biodynamic Saponin from Calamus Insignis as Their Propargyl Glycosides

Abstract

The total synthesis of the carbohydrate portion (pentaand tetrasaccharides) of steroidal saponins, isolated from Calamus insignis, is reported. A simple route is followed, starting from commercially available D-glucose and L-rhamnose, through high-yielding protecting group manipulation strategies. Sulfuric acid immobilized on silica (H 2 SO 4 /silica)

A Convergent Synthesis of 6‐O‐Branched β‐Glucan Oligosaccharides

“…[16] To a solution of 10 (10.00 g, 20.09 mmol), TEA (17.9 mL, 127.27 mmol) and catalytic amount of DMAP in anhydrous CH 2 Cl 2 (160 mL) was added benzoyl chloride (3.7 mL, 31.37 mmol) at 0 °C. After being stirred for 12 h, the reaction mixture was washed with saturated aq.…”

“…The residue was www.eurjoc.org purified by silica gel column chromatography (toluene/ethyl acetate, 15:1 to 10:1) to give 10 (5.48 g, 90 %) as a white solid. 1 88, 138.72, 136.79, 133.76, 133.43, 130.03, 129.73, 129.50, 129.33, 128.46, 128.34, 127.83, 126.26, 101.91, 86.76 (C-1), 80.61, 77.21, 77.00, 76.79, 73.73, 73.24, 70.39, 68.50, 21.18 (8): [16] Benzoyl chloride (3.7 mL, 31.37 mmol) was added to a solution of 10 (10.00 g, 20.09 mmol), Et 3 N (17.9 mL, 127.27 mmol), and DMAP (catalytic amount) in anhydrous CH 2 Cl 2 (160 mL) at 0°C. The reaction mixture was stirred for 12 h, then the mixture was washed with saturated aq.…”

Convergent Synthesis of the Hexasaccharide Repeating Unit of the O‐Antigenic OPS of Escherichia coli O133

“…The acetyl groups were then removed by trans‐esterification using NaOMe in MeOH to afford the disaccharide derivative 9 in 96 % yield. Further, reaction with benzaldehyde dimethyl acetal in the presence of CSA afforded the disaccharide derivative 10 in 82 % yield. Chloroacetylation of the free 3‐OH group in 10 using chloroacetic anhydride and pyridine afforded the fully protected disaccharide donor 11 in 89 % yield (Scheme ).…”

α/β-Stereo- and diastereoselective glycosylation with n-pentenyl glycoside donors, promoted by N-iodosuccinimide and catalyzed by chiral Brønsted acid

“…[3][4][5][6][7][8][9][10] Sulfuric acid immobilized on silica as BA in combination with N-iodosuccinimide (NIS) was utilized to activate a thioglycoside for the synthesis of tetrasaccharide fragments. [11][12][13] Furthermore, attempts at achieving α/β-stereoselectivity in glycosylation were made with chiral BAs (CBAs)activation. This involved the use of a tetrazole-amino acid ionic liquid, 9 chiral binaphthol (BINOL) phosphoric acids, [14][15][16] and peptides bearing carboxylic acid groups in combination with an MgBr 2 Lewis acid.…”