Department of Chemistry, Indian Institute of Technology Bombay, Mumbai 400076, India.
J Org Chem. 2021 May 7;86(9):6090-6099. doi: 10.1021/acs.joc.0c02935. Epub 2021 Apr 12.
Zwitterionic polysaccharides isolated from commensal bacteria are endowed with unique immunological properties and are emerging as immunotherapeutic agents as well as vaccine carriers. Reported herein is a total synthesis of the repeating unit of zwitterionic polysaccharide A1 (PS A1). The structurally complex tetrasaccharide unit contains a rare sugar 2-acetamido-4-amino-2,4,6-trideoxy-d-galactose (AAT) and two consecutive 1,2- glycosidic linkages. The repeating unit was efficiently assembled by rapid synthesis of d-galactosamine and AAT building blocks from cheap and abundant d-mannose via a one-pot S2 displacement of 2,4-bistriflates and installation of all of the glycosidic bonds in a highly stereoselective manner. The total synthesis involves a longest linear sequence of 17 steps with 3.47% overall yield.
从共生菌中分离得到的两性离子多糖具有独特的免疫学特性，它们正在成为免疫治疗剂和疫苗载体。本文报道了两性离子多糖 A1（PS A1）重复单元的全合成。结构复杂的四糖单元含有一种罕见的糖 2-乙酰氨基-4-氨基-2,4,6-三脱氧-d-半乳糖（AAT）和两个连续的 1,2-糖苷键。重复单元通过从廉价且丰富的 d-甘露糖一锅法 S2 取代 2,4-双三氟甲磺酸酯和以高度立体选择性方式安装所有糖苷键，从廉价且丰富的 d-甘露糖快速合成 d-半乳糖胺和 AAT 砌块来有效组装。该全合成涉及最长的 17 步线性序列，总收率为 3.47%。
