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Diels–Alder reaction of furanoeremophilan-6β-ol (petasalbin) and its synthetic analogue, 4-hydroxy-4,5,6,7-tetrahydrobenzofuran, was studied using N-ethyl- and N-phenylmaleimides as the dienophiles...

Three Ligularia species (L. tongolensis, L. cymbulifera, and L. atroviolacea) were examined with respect to the chemical composition and nucleotide sequence. Furanoeremophilanes were found to be produced in the root of all samples of the three species collected in northwest Yunnan and southwest Sichuan. Eight furanoeremophilanes were identified, two of which were new. Most of the identified furanoeremophilanes were oxygenated at 3, 6, and 15-positions. The nucleotide sequence of the atpB-rbcL intergenic region was found to be essentially the same in the three species. These similarities imply that the three Ligularia species, all belonging to the section Corymbosae, are close to one another. The intra-specific diversity in the two widely distributed species in the Hengduan Mountains area, L. tongolensis and L. cymbulifera, were in contrast. Four out of 19 L. tongolensis samples contained a strongly Ehrlich-positive compound besides a number of positive compounds, and five variants of the atpB-rbcL sequence were found in these samples. In contrast, no variation was observed in 13 L. cymbulifera samples with respect to the furanoeremophilane composition or the atpB-rbcL sequence. The lack of diversity in L. cymbulifera probably resulted from the uniformity of its habitat.

Pairs of the skeletal isomers of eremophilane-type lactones were synthesized from furanofukinol via photosensitized oxygenation, followed by lactone cleavage and reformation. Their stereochemistry has been clarified so as to be consistent with a classification method outlined in our earlier papers.

A new modified furanoeremophilane type sesquiterpene, (+)-14-methoxy-1,2-dehydrocacalol methyl ether (2), isolated from Trichilia cuneata exhibited inhibitory activity for mitochondrial lipid perox...

The recent findings of antihyperglycemic and antimicrobial activities for a modified furanoeremophilane sesquiterpene cacalol (1) prompted us to achieve the first total synthesis of five cacalol fa...

Three new furanosesquiterpenes have been isolated from Ligularia japonica LESS., and their structures including absolute configurations have been determined as furanoeremophilane-6β-diol (1), 10β-hydroxyfu-ranoeremophilan-6β-yl 2′ξ-methylbutanoate (2), and 10β-hydroxy-6β-methoxyfuranoeremophilane (3).

Mass spectral fragmentations of furanoeremophilane derivatives bearing oxygen-function on B ring were investigated. It was found that mass spectra measured by direct inlet system gave characteristic retro-Diels-Alder fragmentations, while indirect introduction of the samples afforded intense peaks at m/e 159 and m/e 145 containing the furan moiety. Fragmentation patterns of other poly-functional derivatives were examined by measurements of accurate masses and metastable ions.

Two new furanoeremophilane derivatives isolated from Farfugium japonicum Kitamura have been shown to be 3β-angeloyloxy-10β-hydroxy-9β-senecioyloxyfuranoeremophilane and 3β-angeloyloxy-10β-hdroxyfuranoeremophilane.

The dye-sensitized oxygenation of furanofukinin, and furanoeremophilane, in methanol gave, quantitatively, crystalline mixtures of two isomeric hydroperoxides each consisting of a pair of 8α-methoxy-12β-hydroperoxy and 8β-methoxy-12α-hydroperoxy derivatives respectively. The hydroperoxides were readily transformed to the corresponding lactones with acetic anhydride-pyridine through dehydration. The stereochemistry of the hydroperoxides and the corresponding lactones has been elucidated by spectral and chemical methods according to a previously outlined generalization. Further, furanofukinin, furanoeremophilane, and 8β-hydroxyeremophilenolide, have been synthesized from petasalbin, fukinone, and an epimeric mixture of 8α- and 8β-methoxy lactones, respectively.

(±)-14-Norfuranoeudesmane-4,6-dione, (±)-furanoeremophilane-3,6-dione, and (±)-furanoeremophilan-14, 6α-olide were synthesized by a route involving alkylation of a dianion obtained from 2,4-dimethyl-3-furoic acid.

Five new furanoeremophilane derivatives, I, II, III, IV, and V, have been isolated from Farfugium japonicum Kitamura, and their structures have been determined. Conformations of some furanoeremophilane derivatives are discussed.

Treatment of furanoeremophilane-6β,10β-diol (1; R=H) with phosphoryl chloride in pyridine at 110 °C gave farfugin A (2; yield: 23%), farfugin B (3; y: 34%), and 6-[(4R)-4-chloropentyl]-3,5-dimethylbenzofuran (4; y: 15%). A mechanism of formation of these three compounds (2, 3, and 4) is discussed.

Pulegone was transformed into isopulegone enol acetate or isopulegone ethylene acetal, which was treated with m-chloroperbenzoic acid and then with acid to give menthofuran. Fukinone was converted into furanoeremophilane by the same procedure.

Treatment of a dianion generated from 2,4-dimethyl-3-furoic acid with 3-methoxy-2-methyl-2-cyclohexen-1-one gave 4-methyl-2-(3-oxo-2-methyl-1-cyclohexenylmethyl)-3-furoic acid. Catalytic hydrogenation of the alkylated product followed by dehydrative annelation yielded 14-norfuranoeremophilane-4,6-dione, which was converted in five steps into (±)-furanoeremophilane-3,6-dione. (±)-Ligularone has been derived from the 3,6-dione.