Chemical Synthesis of Arabinogalactans from the Mycobacterium tuberculosis Cell Wall up to the 92-mer and...

Arabinogalactans (AG) from the Mycobacterium tuberculosis (Mtb) cell wall represent potential therapeutic agents against the notorious disease tuberculosis (TB). However, the synthetic access to these long, highly branched, and complex arabinogalactans remains a challenging task, hindering structure-activity relationship studies. Here, we report the chemical synthesis of arabinogalactan 92-mer 1 and shorter sequences 14-mer 2, 30-mer 3, and 50-mer 4 from M. tuberculosis cell envelope via an orthogonal one-pot glycosylation strategy based on glycosyl ortho-(1-phenylvinyl)benzoates, which avoids such issues as aglycone transfer inherent to one-pot assemblies based on thioglycosides. The synthetic route also features the following characteristics: 1) highly stereoselective construction of eight 1,2-cis-Araf-(1→2) linkages via hydrogen-bond-mediated aglycone delivery strategy; 2) effective one-pot assembly of several linear and branched glycans by strategic utilizations of glycosyl N-phenyltrifluoroacetimidates, ortho-alkynylbenzoates, and ortho-(1-phenylvinyl)benzoates; 3) a one-pot and convergent [(7 × 2 + 7) × 2 + 50] assembly of arabinogalactan 92-mer with the simultaneous formations of six furanosidic bonds. Conformational analysis using molecular dynamics simulations and NMR spectroscopy, as well as immunological studies of synthetic arabinogalactans 1-4 in human cell models, revealed that the surface-exposed 30-mer 3 epitope induced only a modest NF-κB activation while preserving cell viability.