Synthesis of Potassium (2R)-2-O-α-D-Mannopyranosyl-(1→2)-α-D-glucopyranosyl-2,3-dihydroxypropanoate: A Naturally Compatible Solute

Octanoylation of early intermediates of mycobacterial methylglucose lipopolysaccharides

Mycobacteria synthesize unique intracellular methylglucose lipopolysaccharides (MGLP) proposed to modulate fatty acid metabolism. In addition to the partial esterification of glucose or methylglucose units with short-chain fatty acids, octanoate was invariably detected on the MGLP reducing end. We have identified a novel sugar octanoyltransferase (OctT) that efficiently transfers octanoate to glucosylglycerate (GG) and diglucosylglycerate (DGG), the earliest intermediates in MGLP biosynthesis. Enzymatic studies, synthetic chemistry, NMR spectroscopy and mass spectrometry approaches suggest that, in contrast to the prevailing consensus, octanoate is not esterified to the primary hydroxyl group of glycerate but instead to the C6 OH of the second glucose in DGG. These observations raise important new questions about the MGLP reducing end architecture and about subsequent biosynthetic steps. Functional characterization of this unique octanoyltransferase, whose gene has been proposed to be essential for M. tuberculosis growth, adds new insights into a vital mycobacterial pathway, which may inspire new drug discovery strategies.

Regioselective one-pot protection, protection-glycosylation and protection-glycosylation-glycosylation of carbohydrates: a case study with D-glucose

Well-defined oligosaccharides are important requirements in evaluating structure-activity relationships to decipher the roles of carbohydrates in various physiological processes. These oligosaccharides are accessed mainly through chemical synthesis, which nonetheless remains a huge undertaking despite the many advances in recent years. A combinatorial and regioselective one-pot protection strategy was previously disclosed by us to reduce the effort and wastes associated with carbohydrate synthesis. With the tetra-trimethylsilylated 4-methylphenyl thioglucoside as the starting material, we herein show the one-pot preparations of diols, triols and fully protected derivatives of thioglucosides, and, more importantly, we generated building blocks in situ that effectively acted as glycosyl donors and glycosyl acceptors for further coupling with other monosaccharide building blocks. Our one-pot protection-glycosylation and protection-glycosylation-glycosylation approaches made use of the perceived reactivity differences between thioglycoside donors to conveniently supply disaccharide and trisaccharide skeletons as well as the backbone of a recently discovered compatible solute from two thermophilic bacteria of the Petrotoga species. The demonstrated protocol is another step in reducing the enormous work in carbohydrate synthesis and efficiently delivering sugar constructs for application in other areas of glycobiology.