Absolute Stereostructures and Syntheses of Saussureamines A, B, C, D and E, Amino Acid–Sesquiterpene Conjugates with Gastroprotective Effect, from the Roots of Saussurea lappa

From the methanolic extract of the dried roots of Saussurea lappa Clarke, Saussureae Radix, five amino acid–sesquiterpene conjugates, saussureamines A, B, C, D and E, were isolated together with a lignan glycoside, (−)-massoniresinol 4″-O-β-d-glucopyranoside. Their stereostructures were determined on the basis of chemical and physicochemical evidence. In addition, saussureamines and the related amino acid–sesquiterpene conjugates were synthesized using a Michael type addition reaction of amino acid to the α-methylene-γ-lactone moiety of sesquiterpenes. Saussureamines A, B and C, costunolide and dehydrocostus lactone showed a gastroprotective effect on acidified ethanol-induced gastric mucosal lesions in rats. Saussureamines A also exhibited an inhibitory effect on gastric mucosal lesions induced by water-immersion stress in mice.