Scalar, dipolar‐correlated and J‐resolved 2D‐NMR spectroscopy of the specific phenolic mycoside of Mycobacterium tuberculosis

Abstract

Two-dimensional chemical shift correlated (COSY), nuclear Overhauser (NOESY) and J-resolved spectroscopy were used to determine the complete structure of the major triglycosyl dimycocerosyl phenol phthiocerol of the tubercle bacillus (strain Canetti) without any other analytical technique. The COSY spectrum of the native glycolipid allowed the composition of the trisaccharide and the location of one methoxyl group to be determined through the assignment of the resonances of the non-anomeric methine protons. Information with respect to the configuration of the sugar residues, the pyranose structure and the linkage sites of the trisaccharide were obtained by the analysis of the COSY spectrum of the peracetylated glycolipid. The NOESY spectrum confirmed the linkage sites through the inter-residue connectivity across glycosidic linkages and allowed the determination of the sequence of the oligosaccharide and the configuration of its sugar residues from the through-space connectivities. The J-resolved spectroscopy was used to elucidate the structure of the glycolipid and gave additional data showing the presence of 11 non-equivalent methyl groups and allowing the recognition of two other analogues of the phenol phthiocerol derivative in the mixture. Thus, the non-destructive 2D-NMR spectroscopy was found to be satisfactory for the analysis of mycobacterial mycosides.