Synthesis and biological evaluation of 3,4-dihydro-1H-[1,4] oxazepino [6,5,4-hi] indol-1-ones and 4,6-dihydrooxepino [5,4,3-cd] indol-1(3H)-ones as Mycobacterium tuberculosis inhibitors

This study focuses on the synthesis of 1,7- and 3,4-indole-fused lactones via a simple and efficient reaction sequence. The functionalization of these "oxazepino-indole" and "oxepino-indole" tricycles is carried out by palladium catalysed CC coupling, nucleophilic substitution or 1,3-dipolar cycloaddition. The evaluation of their activity against Mycobacterium tuberculosis shows that the "oxazepino-indole" structure is a new inhibitor of M. tuberculosis growth in vitro.

Identification of inhibitors of UDP-galactopyranose mutase via combinatorial in situ screening

An in situ screening assay for UDP-galactopyranose mutase (UGM, an essential enzyme of M. tuberculosis cell wall biosynthesis) has been developed to discover novel UGM inhibitors. The approach is based on the amide-forming reaction of an amino acid core with various cinnamic acids, followed by a direct fluorescence polarization assay to identify the best UGM binders without isolation and purification of the screened ligands. This assay allows us to perform one-pot high-throughput synthesis and screening of enzyme inhibitors in a 384-well plate format. UGM ligands were successfully identified by this technology and their inhibition levels were established from pure synthetic compounds in vitro and in a whole cell antibacterial assay. This study provides a blueprint for designing enamide structures as new UGM inhibitors and anti-mycobacterial agents.

Galactofuranose-Related Enzymes: Challenges and Hopes

Galactofuranose is a rare form of the well-known galactose sugar, and its occurrence in numerous pathogenic micro-organisms makes the enzymes responsible for its biosynthesis interesting targets. Herein, we review the role of these carbohydrate-related proteins with a special emphasis on the galactofuranosidases we recently characterized as an efficient recombinant biocatalyst.

Synthetic polyprenol-pyrophosphate linked oligosaccharides are efficient substrates for mycobacterial galactan biosynthetic enzymes

Synthetic glycosyl polyprenol phosphates are substrates for enzymes required for cell wall assembly in mycobacteria, including the organism that causes tuberculosis.

Regioselective 5-O-Opening of Conformationally Locked 3,5-O-Di-tert-butylsilylene-d-galactofuranosides. Synthesis of (1→5)-β-d-Galactofuranosyl Derivatives

The use of thiogalactofuranoside as donors for the construction of internal Galf containing oligosaccharide is limited, probably due to the difficulty to functionalize thiogalactofuranoside derivatives showing O-2, O-3, and O-5 with similar reactivity. An efficient method for complete regioselective 5-O-opening of conformationally restricted 3,5-O-di-tert-butylsilylene-d-galactofuranoside derivatives was developed. The use of a solution nBu₄NF (1.1 equiv) in CH₂Cl₂ on 6 gave the 5-OH free derivative 10 as the only product (90%). 3-O-Di-tert-butylhydroxysilyl derivative 10 was stable upon purification and glycosylation reaction. Preactivation of conformationally restricted thioglycoside 6 employing p-NO₂-benzensulfenyl chloride/AgOTf followed by condensation over the 5-OH thioglycoside acceptor 10 gave the corresponding disaccharide 12 without autocondensation byproduct. Regioselective 5-O-deprotection was also successfully performed over the (1→5)-β-d-galactofuranosyl di- and trisaccharide derivatives 12 and 13. This methodology allowed the differentiation between the secondary hydroxyl groups OH-3 and OH-5 of 1,2-cis or 1,2-trans d-galactofuranoside derivatives, and it still constitutes an innovative approach to access oligosaccharides of pharmacological importance.

Chemical Insight into the Mechanism and Specificity of GlfT2, a Bifunctional Galactofuranosyltransferase from Mycobacteria

Mycobacteria, including the human pathogen Mycobacterium tuberculosis, produce a complex cell wall structure that is essential to survival. A key component of this structure is a glycoconjugate, the mycolyl-arabinogalactan-peptidoglycan complex, which has at its core a galactan domain composed of galactofuranose (Galf) residues linked to peptidoglycan. Because galactan biosynthesis is essential for mycobacterial viability, compounds that interfere with this process are potential therapeutic agents for treating mycobacterial diseases, including tuberculosis. Galactan biosynthesis in mycobacteria involves two glycosyltransferases, GlfT1 and GlfT2, which have been the subject of increasing interest in recent years. This Synopsis summarizes efforts to characterize the mechanism and specificity of GlfT2, which is responsible for introducing the majority of the Galf residues into mycobacterial galactan.