Constituents of Helenium amarum, IV. Desacetyl-1-Epiisotenulin

Abstract

In previous communications from our laboratories (1-4), we reported isolation of the sesquiterpene lactones tenulin, heleniamarin, isoheleniamarin, aromaticin, mexicanin I, and amarilin from leaves of Helenium amarum (Rafin.) H. Rock (bitterweed). Chromatography of the tenulin mother liquors also yielded, in addition to amarilin, a very small amount (ca. 20 mg) of an unknown compound, mp 101-105°(3). We now describe identification of this substance as the previously unreported desacetyl-1epiisotenulin (la).Structure and stereochemistry of the new lactone, C15H20O4 (high resolution mass spectrum), were deduced on the basis of the 270 MHz pmr spectrum in CDC13 (la in Table 1); extensive spin decoupling and the cd curve, which exhibited a very weak negative maximum at 325 nm ( = -349); and a posi-