Asymmetric synthesis and structure elucidation of a glycerophospholipid from Mycobacterium tuberculosis

Abstract

A glycerophospholipid (1-O-tuberculostearoyl-2-O-palmitoyl-sn-glycero-3-phosphoethanolamine) from Mycobacterium tuberculosis was isolated from the reference strain H37Rv. The molecular structure of this tuberculostearoyl [(R)-10-methyloctadecyl] and palmitoyl containing phosphatidylethanolamine (PE) has been resolved. The substitution pattern on the glycerol backbone could be determined by comparison of the isolate to the two synthetically prepared regioisomers. MS/MS analysis was used to determine its molecular structure. Production of this synthetic version of mycobacterial PE in high yield, with a stereochemically correct and pathogen-specific fatty acyl group, can be used as a standard in LC-MS based lipidomic analyses to detect trace amounts of mycobacterial PE in human blood, sputum, or tissues as a marker of infection by mycobacteria.

Fig. 1.

Total synthesis of (R)-TBSA (3).

Fig. 2.

Synthesis of 1-O-TBSA-2-O-palmitoyl-sn-phos­pho­lipid (1).

Fig. 3.

The two possible structures of the natural phospholipid; 1-O-TBSA-2-O-palmitoyl-sn-phospholipid (1) and 1-O-palmitoyl-2-O-TBSA-sn-phospholipid (2).

Fig. 4.

A: Negative mode mass analysis of detected M. tuberculosis phosphatidylethanolamines (PE). B: Extracted ion chromatograms of PE's detected in M. tuberculosis compared to mammalian PE's from non-infected mouse lung homogenate, no ion at m/z 732.55 was detected in this region of the chromatogram for the mammalian PEs.

Fig. 5.

MS/MS (ESI) in negative mode.