This disclosure relates to libraries of oligosaccharides comprising multiple individual oligosaccharides derived from cells that contain a tag or detectable marker. In certain embodiments, the tag or detectable marker is an oxygen linked to the oligosaccharides through the first carbon of a sugar ring. In certain embodiments, the disclosure relates to methods of generating the libraries of oligosaccharides using saccharides, e.g., monosaccharides, or a disaccharide, in which hydroxyl groups are chemically acetylated.
