| The Turkish traditional medicine Hindiba, prepared from the aerial parts of Cichorium intybus (Asteraceae) has been used for centuries as an anticancer drug. Using the {dollar}sp3{dollar}H-thymidine incorporation bioassay to monitor the inhibition of cell proliferation in several cancer lines to direct the isolation, 11{dollar}beta{dollar},13-dihydrolactucin (1) was isolated as the active constituent. With this lead structure in hand, local collections of C. intybus and related Asteraceae species were examined for guaianolide sesquiterpene lactones similar in structure to 1. Thirteen guaianolide sesquiterpene lactones, including four previously unreported and three artifacts, have been isolated from C. intybus, six known guaianolides from Achillea millefolium, and two known guaianolides from Tanacetum densum subsp. amani. Examination of Matricaria matricarioides and T. densum subsp. sivasicum revealed no guaianolide sesquiterpenes, but instead, five known spiroketal enol ethers from M. matricarioides and a new germacranolide from T. densum subsp. sivasicum were found. Local collections of C. intybus, monitored over three years, contain as their predominant constituents the {dollar}alpha{dollar}-methyleno-{dollar}gamma{dollar}-lactones: lactucin (2), 8-deoxylactucin (3), and lactupicrin (4), which could be selectively hydrogenated over Lindlar's catalyst to their 11{dollar}beta{dollar},13-dihydro analogs in quantitative yield. Thiol nucleophiles underwent conjugate additions to the unsaturated lactones to produce 11{dollar}beta{dollar},13-S-thioether adducts. Initial bioassay results with these structural analogs have shown the thioether adduct improves activity by a factor of {dollar}sim{dollar}10 but also increases cytotoxicity. In an attempt to alter the ratios of unsaturated compounds to their dihydro analogs, callus tissue cultures of C. intybus were grown at pH 4.8, 5.8 and 6.8. Cultures grown on solid medium at pH 4.8 produce 1 and 11{dollar}beta{dollar},13-dihydrolactupicrin (11) as their predominant constituents. Callus cultures grown on solid medium at pH 5.8 and 6.8 produce predominantly 2, 3, and 4. Callus suspension cultures on the other hand, gave a 4-fold increase in the guaianolide sesquiterpene lactone yields with 2 being produced almost exclusively at pH 4.8, 3 predominating at pH 5.8 with other guaianolides in lesser amounts, and the methyl ester artifact 10, which may be derived from 4, predominating at pH 6.8. |
