77
379 and 380, in sample 35 exhibit a 3α,4α-epoxide moiety [112], which is rather
rare in Ligularia. Sample 36 produced five dimeric compounds (570, 615, 619–
621), related to cacalol (316) [12]. Virgaurin A (615), also isolated from sample 28,
is linked between C-6 and C-6′ of two farfugin B (335) units, while, in turn,
adenostin A (570) is linked between C-14 and C-12′ of two cacalol (316) units.
Compound 619 is linked between C-15 of cacalol (316) and C-12′ of compound
338, a quinone derivative of farfugin B (335). The structures of compounds 620
and 621 are complex, since they are hetero-Diels- Alder-type derivatives between a
1(10)-en-9-one moiety and the C-11/C-12 double bond of cacalol or farfugin
B. The relative configurations at C-11′ and C-12′ of 620 and 621 are cis concerning
H 3 -13′ and H-12′. 6α-Hydroxyeremophil-7(11)-en-12,8α-olide (345) proved to be
the major constituent of samples 38 and 39, being grouped into the L type. Five
Fig. 13 10H-Furanoeremophilan-15,6-olides
Chemical Constituents of Ligularia Species (Asteraceae) and Their Diversity…