Synthesis of Oligomeric 4-(Glycosyloxy)benzoate Macrocyclic Glycosides

Clemoarmanoside A and Clemahexapetoside A, two novel cyclic dimers of 4-(glycosyloxy)benzoates containing the unusual d-allopyranose as one of the sugar units, were synthesized for the first time. The convenient synthetic approach was adapted to the assembly of the symmetrical trimeric, tetrameric, and pentameric congeners. The synthesis clarified the discrepancy in the NMR data reported for the natural products. X-ray diffraction analysis of Clemahexapetoside A revealed that it adopted an armchair conformation with two carbohydrate rings as the arms and two aromatic rings as the back and seat, respectively.Clemoarmanoside A与Clemahexapetoside A为两类新型4-(糖苷氧基)苯甲酸酯（4-(glycosyloxy)benzoates）环状二聚体，其糖单元之一包含罕见的d-吡喃阿洛糖（d-allopyranose），本研究首次实现了二者的全合成。该便捷合成策略可适配于对称型三聚体、四聚体及五聚体同系物的构建组装。本次合成澄清了此前针对该天然产物的核磁共振（NMR）数据报道中存在的不一致之处。对Clemahexapetoside A的X射线衍射（X-ray diffraction）分析结果显示，该化合物呈现扶手椅式构象：两个碳水化合物环作为扶手，两个芳香环分别充当靠背与座面。