Abstract

Emergence of multidrug-resistant and extreme-drug-resistant strains of Mycobacterium tuberculosis (MTb) can cause serious socioeconomic burdens. Arabinogalactan present on the cellular envelope of MTb is unique and is required for its survival; access to arabinogalactan is essential for understanding the biosynthetic machinery that assembles it. Isolation from Nature is a herculean task and, as a result, chemical synthesis is the most sought after technique. Here we report a convergent synthesis of branched heneicosafuranosyl arabinogalactan (HAG) of MTb. Key furanosylations are performed using [Au]/[Ag] catalysts. The synthesis of HAG is achieved by the repetitive use of three reactions namely 1,2-trans furanoside synthesis by propargyl 1,2-orthoester donors, unmasking of silyl ether, and conversion of n-pentenyl furanosides into 1,2-orthoesters. Synthesis of HAG is achieved in 47 steps (with an overall yield of 0.09%) of which 21 are installation of furanosidic linkages in a stereoselective manner.

Highlights

  • Emergence of multidrug-resistant and extreme-drug-resistant strains of Mycobacterium tuberculosis (MTb) can cause serious socioeconomic burdens

  • The complete structure of the cell wall of MTb has been unravelled to observe that it has two major components termed as mycolylarabinogalactan and lipoarabinomannan wherein arabinose and galactose are in furanosyl and mannose in the pyranosyl form9–14

  • In this Article, we show that the highly branched heneicosafuranosyl arabinogalactan (HAG) can be synthesized by the repeated use of gold-catalysed activation of alkynyl 1,2-O-orthoester chemistry that was developed in our laboratory35–40

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Summary

Introduction

Emergence of multidrug-resistant and extreme-drug-resistant strains of Mycobacterium tuberculosis (MTb) can cause serious socioeconomic burdens. Gold-catalysed glycosidation conditions36 were employed on glycosyl donor 8b to obtain n-pentenyl furanoside 13 followed by the deprotection of TBDPS group using Py Á HF to obtain the desired building block 8a in very high yields.

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