Does anyone know why several sources (including the 12th edition of the Merck Index) show that the C-6 carbon atom of vancomycin as an "S" configuration? Vancomycin is a glycopeptide antibiotic, a compound based on a defined glycopeptide core. The structure of the core glycopeptide skeleton was known, and the sterechemistry at the C-6 position of the glycopeptide core was known to be R.
So, which is the correct stereochemistry, S or R? Can it exist in both configurations, and are both active?