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. 2016 Dec 22:6:39815.
doi: 10.1038/srep39815.

New Formyl Phloroglucinol Meroterpenoids from the Leaves of Eucalyptus robusta

Zhi-Chun Shang  1 , Ming-Hua Yang  1 , Rui-Huan Liu  1 , Xiao-Bing Wang  1 , Ling-Yi Kong  1
Affiliations

New Formyl Phloroglucinol Meroterpenoids from the Leaves of Eucalyptus robusta

Zhi-Chun Shang et al. Sci Rep. .

Abstract

Seven new formyl phloroglucinol meroterpenoids (FPMs), namely eucalrobusones J-P (1-7), as well as three known ones (8-10) were isolated from the leaves of Eucalyptus robusta. Their structures were elucidated by spectroscopic data analysis, and their absolute configurations were determined by applications of the Snatzke's helicity rule and the electron circular dichroism (ECD) calculation. These FPMs are diverse in coupling patterns between phloroglucinol and sesquiterpenoid units, forming novel polycyclic ring systems. Compound 1 possesses a new carbon skeleton that a 1-oxaspiro[5.6]dodecane core is formed through C-14 rather than C-4 of the aromadendrane moiety. Compound 2 features a novel 6/7/5 ring-fused 6-oxabicyclo[3.2.2]nonane skeleton. Compounds 3-5 are rare aristolane-based FPMs. By forming different oxo bridges, compound 3 is the first sample of FPM with benzo-dihydrofuran structure, and compound 4 possesses a novel 6/6/6/6/3-fused pentacyclic skeleton. Compounds 1, 6, and 8 exhibited significant antifungal activities against Candida glabrata with MIC50 values of 2.57, 1.95, and 2.49 μg/mL, respectively.

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Figures

Figure 1
Figure 1. Structures of compounds 1–10.
Figure 2
Figure 2. Key 1H-1H COSY, HMBC, and ROESY correlations of 1.
Figure 3
Figure 3. Key 1H-1H COSY, HMBC, and ROESY correlations of 2.
Figure 4
Figure 4. Key 1H-1H COSY, HMBC, and ROESY correlations of 3.
Figure 5
Figure 5. Key 1H-1H COSY, HMBC, and ROESY correlations of 4.
Figure 6
Figure 6
The P/M-helicity rules and ECD spectra of 1 (A), 4 (B), 6 (C), and 7 (D).
Figure 7
Figure 7. Plausible biosynthetic pathways of 1–7.
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