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.

Pyrimidine nucleosides are synthesized by using propargyl 1,2-orthoesters and Au(III) salt as a catalyst. Strategically positioned 1,2-orthoesters are found to yield only 1,2-trans nucleosides and enable preparation of 2'-OH containing pyrimidine nucleosides. The glycosyl donor employed in this study is stable and easily accessible. The identified high-yielding protocol is mild, diastereoselective, and catalytic.

Oligosaccharides are involved in a myriad of biological phenomena. Many glycobiological experiments can be undertaken if homogenous and well-defined oligosaccharides are accessible. Mycobacterial cell walls contain arabinogalactan as one of the major constituents that is challenging for chemical synthesis. Therefore, the major aim of this investigation is to synthesise a major oligosaccharide portion of the arabinogalactan. The pentacosafuranoside (25mer) synthesis involved installation of several arabinofuranosidic linkages through neighbouring group participation for 1,2-trans linkages and oxidation-reduction strategy for the 1,2-cis Araf. A strategically placed n-pentenyl moiety at the reducing end enables ligation of biomolecular probes through celebrated cross metathesis or thiol-ene click reactions. Several linear and branched oligosaccharides were synthesised ranging from trisaccharide to pentadecasaccharide during this endeavour. Synthesis of pentacosasaccharide was accomplished in 77 steps with 0.0012 % overall yield. These oligosaccharides are envisioned to be excellent probes for understanding disease biology thereby facilitating discovery of novel antitubercular agents, vaccines and/or diagnostics.

The total synthesis of TMG-chitotriomycin using an automated electrochemical synthesizer for the assembly of carbohydrate building blocks is demonstrated. We have successfully prepared a precursor of TMG-chitotriomycin, which is a structurally-pure tetrasaccharide with typical protecting groups, through the methodology of automated electrochemical solution-phase synthesis developed by us. The synthesis of structurally well-defined TMG-chitotriomycin has been accomplished in 10-steps from a disaccharide building block.

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