Diterpenoid glycosyl esters from Phlomis younghusbandii and P. medicinalis roots.

From the roots of Phlomis younghusbandii collected in Tibet, new furanolabdane-type diterpenoid glycosides named phlomisosides III and IV were isolated together with a known sweet furanolabdane-type diterpenoid glycoside, phlomisoside I. The structure of the common aglycone of phlomisosides III and IV, which we have named phlomisoic acid, was established as 15,16-epoxy-8,13(16),14-labdatrien-19-oic acid by MS and NMR spectroscopy. Phlomisosides III and IV are tasteless and the structures of these were determined to be the beta-D-xylopyranosyl(1-->2)-beta-D-glucopyranosyl and the alpha-L-rhamnopyranosyl(1-->2)-beta-D-glucopyranosyl ester of phlomisoic acid by chemical and spectroscopic methods, respectively. The diterpenoid glycoside constituents of the roots of P. medicinalis collected in Tibet were also elucidated, and baiyunoside and phlomisosides II and III were isolated and identified.