New Sesquiterpene Lactones From the Genera Calea and Berlandiera (Asteraceae) and the Fragmentation Reactions of 1,3-Dihydroxyeudesmanolide Derivatives.

Chemical analysis of Calea ternifolia var. calyculata (syn. Calea hypoleuka, Calea salmaefolia, and Calea albida) yielded the known sesquiterpene lactone calein A (21) and the atripliciolide derivatives, 11,13-dyhydro-11(alpha),13-epoxyatripliciolide-8(beta)-O-angelate (51), 11,13-dihydro-11(alpha),13-epoxyatripliciolide-8(beta)-O-methacrylate (52), and 9(alpha)-hydroxy-11,13-dihydro-11(alpha),13-epoxyatripliciolide-8(beta)-angelate (54). In addition, three new germacranolides, 8(beta)-angeloyloxy-9(alpha)-{2-methylbutanoyloxy} ternifolin (32), 8(beta)-angeloyloxy-9-acetoxyternifolin (33) and five furanoheliangolides, 9(alpha)-acetoxyzexbrevin (36), 9(alpha)-hydroxyzexbrevin (37), 8(beta)-angeloyloxy-9(alpha)-hydroxycalyculatolide (38), 9(alpha)-hydroxy-11,13-dihydro-11(alpha),13-epoxyatripliciolide 8(beta)-O-methacrylate (55) and 15-hydroxy-11,13-dihydro-11(alpha),13-epoxyatripliciolide (56) were isolated. The structures of the new compounds were elucidated by NMR and mass spectral methods. Single crystal X-ray diffraction of the lactones 36 and 55 established their molecular structure. Calea ternifolia var. ternifolia (syn. Calea liebmanii) provided the new sesquiterpene lactone 2,3-epoxycalein A (81). Epoxidation of calein A (21) gave the epoxyangelate derivative (91) but not the expected 2,3-epoxycalein A (81). Acid-mediated chromate oxidation of 8(beta)-O-angeloyloxy-9(alpha)-acetoxy-ternifolin (33) provided the furan-type germacranolide (89). The isolation and structure determination of two new guaianolides, pumilin (95) and 3(alpha)-epoxypumilin (94) from Berlandiera texana and B. lyatra are described. Their structures were determined by NMR and mass spectral methods, and single crystal X-ray analyses. Epoxidation of dihydrosantamarine tosylate (119) followed by treatment with aluminum isopropoxide gave in high yield (11S)-1(beta)-tosyl-3(alpha)-hydroxyeudesmano-4(15)-eno-12,6(alpha)-lactone (111). The latter compound was also obtained in good yield from dihydroreynosin tosylate (117) by SeO(,2) oxidation. Hydrogenation of lactone 111 with Adam\u27s catalyst provide the (11S)-1(beta)-tosyl-3-hydroxeudemano-12,6(alpha)-lactone (121). Based-mediated fragmentation reactions of (11S)-1(beta)-tosyl-3-hydroxyeudesmano-4(15)-eno-12,6(alpha)-lactone 111 and (11S)-1(beta)-tosyl-3-hydroxyeudesmano-12,6(alpha)-lactone (121) using t-BuOK in t-BuOH provided 15-oxo-saussurea lactone (112) and the hemiacetal (142), respectively. Hydroboration-oxidation of the mesylate of dihydrosantamarine (115) gave a 1,3-elimination product, the cyclopropyl-type acid (131) in low yield