| dc.description | The C-polysaccharide (PnC) is a common antigen to all known Streptococcus pneumoniae bacteria. Its repeating unit, a pentasaccharide, is comprised of scD-glucopyranose, 2-acetamido-4-amino-2,4,6-trideoxy- scD-galactopyranose, 2-acetamido-2-deoxy- scD-galactopyranose, ribitol phosphate and phosphorylcholine. There was uncertainty about the configuration of the ribitol unit in PnC. An effort was made here to determine the absolute configuration of this ribitol unit. Firstly, scD-ribitol and scL-ribitol derivatives (38 and 39) were designed and synthesized. For the selective protection of scD-ribose diethyldithioacetal (41) at position-5, dibutylstannylene acetal methodology proved to be successful. This is the first time that the dibutylstannylene acetal method has been applied to a dialkyldithioacetal compound. Then disaccharide phosphates (47 and 48) and trisaccharide phosphates (59 and 60) containing scD-ribitol and scL-ribitol residues respectively were designed and synthesized. 2D NMR techniques were used for the complete assignment of their NMR spectra. Comparison of the $\sp $C NMR data of 47 and 48, and the $\sp1$H and $\sp $C NMR data of 59 and 60 with that of the corresponding part of PnC showed that the data for the scD-ribitol derivative 47 is closer to that of PnC than the scL-ribitol derivative (48); the data of 59 being closer than 60. The data of 59 fit almost perfectly with that of PnC, with an average difference of 0.02 ppm of the chemical shifts in the $\sp1$H NMR spectrum and 0.034 ppm in the $\sp $C NMR spectrum, respectively. On this evidence it was concluded that the ribitol unit in PnC has the scD-configuration. | en_US |
