Derivatization of sugars with N,O-dimethylhydroxylamine. Efficient RP-HPLC separation of sugar mixtures

Sugars were derivatized with N,O-dimethylhydroxylamine (DMHA) using a simple procedure. The disaccharides lactose and chitobiose and the human milk tetrasaccharides lacto-N-tetraose (LNT) and lacto-N-neotetraose (LNnT) were used as examples. The β-glycosylamines were formed exclusively in good yields (80-84%). The derivatives were very well suited for RP-HPLC, giving rise to single peaks for each sugar, without the usual complications caused by mutarotation. The LNT- and LNnT-derivatives separated very well on an ordinary RP-HPLC column, despite their close structural similarity. Also, three human milk pentasaccharides (LNF I, II and III) were derivatized with DMHA. Again, good separation of these isomers was obtained. The DMHA derivatization was easily reversed. The free oligosaccharides were recovered quantitatively by mild acidic hydrolysis. To demonstrate usefulness on a preparative scale, an LNDI-rich human milk oligosaccharide fraction was derivatized, and three HPLC fractions (one major and two minor) were collected. Hydrolysis and desalting gave saccharides LNDI, LNnDII, and LNDII, the latter mixed with minor amounts of LNnDI.