Highly Stereoselective Synthesis of Branched Fructooligosaccharides ABW90-1 and ABW50-1 from Achyranthes bidentatawith Potent Antiosteoporosis Activities

The branched fructooligosaccharides ABW90-1 and ABW50-1 from Achyranthes bidentatawith potent antiosteoporosis activities have been synthesized for the first time. The synthetic approach highlights the following features: (1) 6-O-picoloyl-directed β-d-fructofuranosylation via a hydrogen-bond-mediated aglycone delivery strategy for the highly stereoselective constructions of β-(2 → 6)-d-fructofuranosidic linkages and β-(2 → 1)-d-fructofuranosidic linkages in the internal positions under the reaction conditions (DBDMH, −20 °C, CH2Cl2) and (2) the reaction conditions (DBDMH, −78 °C to −35 °C, toluene) for highly stereoselective formations of β-(2 → 1)-d-fructofuranosidic linkages in the terminal positions.