Abstract
Seven new compounds, including one dimer novel skeleton, chamaecyformosanin A (1); three diterpenes, chamaecyformosanins B–D (2–4); one sesquiterpene, chamaecyformosanin E (5); and two monoterpenes, chamaecyformosanins F and G (6 and 7) were isolated from the methanol extract of the bark of Chamaecyparis obtusa var. formosana. Their structures were established by the mean of spectroscopic analysis and the comparison of NMR data with those of known analogues. Their structures were elucidated on the basis of physicochemical evidence, in-depth NMR spectroscopic analysis, and high-resolution mass spectrometry. Furthermore, the isolated compounds were subjected to an evaluation of their antimicrobial activity. Metabolites 1, 3, and 4 present antibacterial activities. It is worth mentioning that the chemical composition of the bark of C. obtusa var. formosana has never been studied in the past. This is the first time the barks from C. obtusa var. formosana were studied and two new skeleton compounds, 1 and 7, were obtained.
Highlights
The global distribution of plants of the genus Chamaecyparis includes six species and one variety, and they are only distributed in Taiwan [1], Japan, and the United States, except for one species (C. formosensis) and one variety in Taiwan (C. obtusa var. formosana); there are two Japanese species (C. obtusa and C. pisifera) [2,3] and three American species (C. lawsoniana, C. nootkatensis, and C. thyoides) [4]
Taiwan cypress (Chamaecyparis obtusa var. formosana), known as yellow juniper or thick crust, is a specialty of Taiwan in the cloud and fog belt at an altitude of 1500 to 2500 m, and most of it is distributed in the area north of the central part, namely MaKau Ecological National Park
The antimicrobial activities of the five isolates from the barks of C. obtusa var. formosana were tested against bacteria such as Staphylococcus aureus subsp. aureus (BCRC 10451), Bacillus subtilis subsp. subtilis (BCRC-10255), Pseudomonas aeruginosa (BCRC-11633), Klebsiella pneumoniae subsp. pneumoniae (BCRC-16082), and Escherichia coli (BCRC-11634), as well as the following fungi: Aspergillus niger (BCRC-31512), Penicillium italicum (BCRC30567), Candida albicans (BCRC-21538), and Saccharomyces cerevisiae (BCRC-20822)
Summary
The global distribution of plants of the genus Chamaecyparis includes six species and one variety, and they are only distributed in Taiwan [1], Japan, and the United States, except for one species (C. formosensis) and one variety in Taiwan (C. obtusa var. formosana); there are two Japanese species (C. obtusa and C. pisifera) [2,3] and three American species (C. lawsoniana, C. nootkatensis, and C. thyoides) [4]. According to the literature [10], if the steric orientation of the compound (12S) of the labdane structure is determined to be S, the steric orientation makes the hydroxyl group (-OH) closer to the terminal double bond protons, causing one of the 1H-NMR chemical shift values (δ) of C-17 to move to about δH 4.70 (br s) in the low field, and the signal of one of the protons at the C-17 position of compound 5, located at δH 4.66 (br s), is very close to (12S)-hydroxylabda-8(17),13(Z)-dien-12,19-dioic acid, so it is speculated that the C-12 stereo orientation of compound 5 is S. The signal next to the carbonyl group is at δH 2.47 (1H, dd, J = 18.8, 4.8 Hz, CH2-5α) and 2.71 (1H, dd, J = 18.8, 2.4 Hz, CH2-5β), so it was deduced that compound 6 is a monoterpenoid fencane-type structure, and 2D HMBC was further used to confirm this. It was confirmed that the compound 7 is (1,4,8)-octahydro-4,8-dimethyl-1H-indene-1,4-dicarboxylic acid, and it was named as chamaecyformosanin G
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