A New Pseudoguaianolide from Postia bombycina

The small genus Postia (tribe Inuleae) with four species, distributed over Syria and Iran, was previously placed in the subtribe Buphthalminae next to Anisopappus. Recently, however, both were transferred to the subtribe Inulinae sensu amplo in the Inula group. Further investigation of the aerial parts of Postia bombycina Boiss. Hausskn. in addition to the known compounds, afforded a new sesquiterpene lactone type pseudoguaianolide. The aerial parts of P. bombycina were extracted with hexane/methanol/diethyl ether by immersion in the solvent. To determine the number of natural compounds in each fraction, thin layer chromatography was prepared. The obtained extract was evaporated to dryness, defatted with methanol and separated by column chromatography over silica gel. The structure of pseudoguaianolide was elucidated by high field 1H-NMR, 13C-NMR, 135-DEPT and FT-IR spectroscopy techniques. Previously, three pseudoguaianolides, four guaianolides, a Seco guaianolide, the known elemanolide and the xanthanolide tomentosin was isolated from P. bombycina. Therefore P. bombycina is a rich source of sesquiterpenes, especially guaianolide structure.