Identification of 3-O-acetylglycerol, a novel structural element in bacterial polysaccharides.

We have discovered a novel bacterial polysaccharide structural element, 3-O-acetylglycerol, in the Streptococcus pneumoniae ST11A polysaccharide: This moiety was elucidated through a combination of homonuclear and heteronuclear 1D and 2D NMR experiments using (1)H, (13)C, and (31)P in various combinations. The 3-O-acetylglycerol moiety is substoichiometrically O-acetylated in ST11A; yet, key connectivities that unequivocally show O-acetylation at the glycerol are provided by the long-range correlations from the acetate methyl groups to the glycerol in the (1)H-(13)C HMBC spectrum. Additionally, we clarify the (1)H-(31)P assignments previously presented.