Selective esterification of methyl 4,6-di-O-benzyl-α-d-mannopyranoside

ROESY and 13C NMR to distinguish between d- and l-rhamnose in the α-d-Manp-(1 → 4)-β-Rhap-(1 → 3) repeating motif

“…Selective anomeric deacetylation using N , N -dimethylaminopropylamine (DMAPA) and treatment of the resulting hemiacetal with trichloroacetonitrile and 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) gave trichloroacetimidate donor 10 in good yield (68%). Known 17 acceptor 11 was glycosylated with trichloroacetimidate donor 10 using either boron trifluoride diethyl etherate (BF 3 ·OEt 2 ) or trimethylsilyl trifluoromethanesulfonate (TMSOTf) as activators. Synthesis of disaccharide 12 proved to be quite difficult due to the high reactivity of the 6-deoxy glucosyl (quinovosyl) donor 10 .…”

“…We prepared disaccharide 2 as a thiophenyl glycoside that could subsequently be used as a glycosyl donor. Synthesis of 2 (Scheme 2) began with the glycosylation of known donor 17 21 and glycosyl acceptor 27 22 using stoichiometric amounts of TMSOTf (1.2 equiv.) for 2 hours at −20 °C in the presence of 4 Å molecular sieves.…”

“…A solution of donor 10 (50 mg, 0.096 mmol, 1 equiv.) and known 17 acceptor 11 (60 mg, 0.126 mmol, 1.3 equiv.) in anhyd DCM (2.4 mL) was heated to 40 °C using an oil bath.…”

“…25 Protection of the free HO-2′ was achieved using benzoyl chloride to give 17 (92%) and selective deacetylation using methanolic HCl gave disaccharide acceptor We prepared disaccharide 2 as a thiophenyl glycoside that could subsequently be used as a glycosyl donor. Synthesis of 2 (Scheme 2) began with the glycosylation of known donor 17 21 and glycosyl acceptor 27 22 using stoichiometric amounts of TMSOTf (1.2 equiv.) for 2 hours at −20 °C in the presence of 4 Å molecular sieves.…”

“…was added dropwise and the reaction was allowed to proceed with stirring for 20 min at −78 °C before being quenched with AcOH (250 μL) and warmed up to rt. Methyl (17). Alcohol 16 (31 mg, 0.041 mmol) was dissolved in anhyd 1,2-dichloroethane (1 mL) and anhyd pyridine (30 μL, 8 equiv.)…”