75
through a C-6 cation by bond fission and electron transfer. Cacalol (316), farfugin
B (335), an oplopane 725, and an eudesmane 795 were also isolated from sample
32 [118]. Sample 29 produced toluccanolides A–C (434, 436, and 438), as well as
compounds 437, 414, 418, and 420 [198]. It is very interesting to note that the
configurations at C-6 and C-10 of 414 and 420 are completely opposite and also
1-oxo derivatives are not very often reported from Ligularia species. Sample 30
requires a comment, however. Although the structure of compound 646 was
determined by X-ray crystallographic analysis, the structure drawn in Ref. [202]
unfortunately is completely wrong. This is because bakkanes have a spiro carbon,
so sometimes a structural error may become apparent [275]. The corrected structure
646 has been drawn in this contribution, rather than that published in the literature.
Sample 31 probably belongs to the V type, because virgaurenolide B (460) and 458
are included [199]. The dimeric compound 612, connected between C-8/C-8′ and
C-6/C-12′ of eremophilenolide and furanoeremophilane, was isolated. Sample 33
produced five glucosides (93, 900, 1043, 1044, and 1046) and an acid (35) [65]. In
turn, sample 34 produced three dimers, (612, 613, and 617), two 9-ones (236 and
280), and farfugin B (335) [152]. The structural representations of 612 and 613 in
the original paper [152] should be revised as depicted, however, because each part
of a sesquiterpenoid should have the same absolute configuration. The epoxides,
Fig. 11 10H-Furanoeremophilanes (2)
Chemical Constituents of Ligularia Species (Asteraceae) and Their Diversity…
through a C-6 cation by bond fission and electron transfer. Cacalol (316), farfugin
B (335), an oplopane 725, and an eudesmane 795 were also isolated from sample
32 [118]. Sample 29 produced toluccanolides A–C (434, 436, and 438), as well as
compounds 437, 414, 418, and 420 [198]. It is very interesting to note that the
configurations at C-6 and C-10 of 414 and 420 are completely opposite and also
1-oxo derivatives are not very often reported from Ligularia species. Sample 30
requires a comment, however. Although the structure of compound 646 was
determined by X-ray crystallographic analysis, the structure drawn in Ref. [202]
unfortunately is completely wrong. This is because bakkanes have a spiro carbon,
so sometimes a structural error may become apparent [275]. The corrected structure
646 has been drawn in this contribution, rather than that published in the literature.
Sample 31 probably belongs to the V type, because virgaurenolide B (460) and 458
are included [199]. The dimeric compound 612, connected between C-8/C-8′ and
C-6/C-12′ of eremophilenolide and furanoeremophilane, was isolated. Sample 33
produced five glucosides (93, 900, 1043, 1044, and 1046) and an acid (35) [65]. In
turn, sample 34 produced three dimers, (612, 613, and 617), two 9-ones (236 and
280), and farfugin B (335) [152]. The structural representations of 612 and 613 in
the original paper [152] should be revised as depicted, however, because each part
of a sesquiterpenoid should have the same absolute configuration. The epoxides,
Fig. 11 10H-Furanoeremophilanes (2)
Chemical Constituents of Ligularia Species (Asteraceae) and Their Diversity…