On the presence of 4-O-(1-carboxyethyl)-mannose in the capsular polysaccharide of Rhodococcus equi serotype 3

4-O-[(S)-1-carboxyethyl]-d-mannose and 4-O-[(R)-1-carboxyethyl]-d-mannose were synthesized and their acetylated lactones (1) and (2) prepared and characterized by 1 and 2D NMR spectroscopy and mass spectrometry. NMR spectra of (1) were identical to those of the lactone of a monosaccharide isolated from the exocellular polysaccharide of the cyanobacterium Cyanospira capsulata. The same derivative of a monosaccharide isolated from the capsular polysaccharide of Rhodococcus equi serotype 3, identified as 4-O-[(S)-1–carboxyethyl]-d-mannose [W. B. Severn and J. C. Richards, Can. J. Chem., 70 (1992) 2664–2676], shows instead NMR spectra different from those of both lactones (1) and (2). This proves that 4-O-(1-carboxyethyl)-mannose is not among the constituent sugars of R. equi capsular polysaccharide. As a consequence, the nature of the sugar obtained from R. equi must be reinvestigated.