Purification of 2-Aminopyridine Derivatives of Oligosaccharides and Related Compounds by Cation-Exchange Chromatography

A simple method for efficient removal of a large matography (HPLC)on an octadecylsilyl (ODS)column excess of 2-aminopyridine from the reaction mixture and an amide column. This strategy has been recently of pyridylamination of carbohydrates and related extended to include an additional HPLC with a diethylcompounds by cation-exchange chromatography is aminoethyl column for analyses of sialyl-oligosacchapresented. The method is especially suitable for purifi- rides (7). More than 300 neutral and sialyl oligosacchacation and separation of small-sized pyridylaminated- rides have been analyzed by th is approach (5-7), (PA-)derivatives and large-scale preparations. Sepa- attesting to the usefulness of the method. The pyridyration of PA-derivatives from 2-aminopyridine was lamination method has been also used for separation accomplished by a Dowex 50X8 column (NH/4 -form)and purification of oligosaccharides for analyses by eluted with 20 mM ammonium acetate buffer (pH 8.5). NMR and mass spectrometry (8). The PA derivatives thus purified can be used for high- performance liquid chromatography analysis directly. Since more than a 2000-fold excess of 2-aminopyri The method requires only 10 min to purify a sample, in dine (2-AP)is customarily used for the pyridylaminacontrast to an hour or longer required by the gel filtra- tion to obtain quantitative yields (9), removal of the tion method. Unlike the existing methods for purifica- excess reagent from the reaction mixture is an imtion of PA-oligosaccharides, which are applicable only portant step prior to chromatography of the derivatized in the range of 0.05-100 nmol, the cation-exchange products. Gel filtration (5)is effective for removal of method allows processing of much larger quantities of 2-AP from relatively large PA-oligosaccharides, but a PA-derivatives. For example, PA-L-glyceraldehyde (10 complete removal of 2-AP is difficult when small commmol)was successful purified by a Dowex 50X8 column pounds, such as monosaccharides and disaccharides, (1.5 1 17 cm)eluted with 20 mM ammonium acetate are derivatized. Extraction of the reactionmixture with buffer (pH 8.75)within 3 h.