A novel sesquiterpene alkaloid, Pulchellidine (Ia), C_<20>H_<33>O_4N, mp185-186°, was isolated from Gaillardia pulchella Foug. collected near St. Augustin, Florida, along with a minor epimer, Neopulchellidine (Ib), mp131-134°. Pulchellidine (Ia) was converted to a new pseudo-guaianolide, Epipulchellin (IIa), C_<15>H_<22>O_4, mp162-164° by Hofmann degradation of its methiodide. The structures of Ia and IIa were well established on the basis of chemical transformations and several spectral data for the derivatives of III through X. On the other hand, the cultivated species of the same plant (Tenningiku) yielded, on extensive chromatographic separations, Epipulchellin (IIa) mentioned above and an another new epimer, Neopulchellin (IIb), mp166.5-167.5°, along with certain other constituents. The partial syntheses of Ia and Ib were achieved from IIa and IIb, respectively, by addition of piperidin. The stereochemistry of IIa and IIb have been defined as the followings. 1) cis: C_2-α OH/C_4-α OH by sulfites formation and application of Hydson-Klyne rule for dihydro derivatives, VIIa and VIIb. 2) trans: C_1-α H/C_5-β CH_3 from ORD Cotton Effects with Octant rule for dehydro-dihydro derivatives (IIIa, VIIIa and VIIIb), even cis-relationship observed for an equillibrate of VIIIa (VIIIa') and desoxy derivative of VIII (Xa). 3) trans: C_7-α H/C_8-β H for VIIa and cis: C_7-β H/C_8-β H for VIIb on the basis of lactone sector rule with rotations data and reaction rates. 4) C_<10>-α CH_3 and C_<11>-α CH_3 for VIIIa, VIIIb and VIIa, VIIb from certain NMR analyses. 5) C_<11>-α CH_2NC_5H_<10> for Ia and Ib by thermodynamically controlled additions. Finally, the stereostructure of 11, 13-dibromoepipulchellin (X1) evidenced by a complete three-dimensional X-ray analysis confirmed the absolute configuration and sterochemistry described before for Epipulchellin (IIa) as well as Pulchellidine (Ia).
