HPLC Isolation and structural elucidation of diastereomeric niloyl ester tetrasaccharides from Mexican scammony root

The application of preparative-scale recycling HPLC is illustrated by describing the complete resolution of diastereomeric mixtures of niloyl esters involving both of the (2R,3R) and (2S,3S) enantiomers of 3-hydroxy-2-methylbutanoic acid bonded to a macrocyclic tetrasaccharide from the resin of the Mexican scammony root (Ipomoea orizabensis). The characterization of 13 new diastereomeric niloyl ester glycosides, orizabins IX–XXI, based on the same structure of scammonic acid A was performed by high field NMR spectroscopy. The absolute configuration of the stereogenic carbinol center in the saponification-liberated nilic acid residues esterifying each of the individual pure glycolipids has been determined by careful 1H NMR analysis of (S)- and (R)-Mosherʹs ester derivatives.