Abstract
Three novel cadinane dimers, involucratusins A–C (1–3), five unique nor-cadinane-dimers, involucratusins D–H (4–8), together with a known compound (9) were isolated from the rhizomes of Stahlianthus involucratus. Their challenging structures and absolute configurations were determined by spectroscopic data, CD experimentation, chemical conversions and single-crystal X-ray diffraction. Compounds 1–3 are unusual cadinane dimers with new connection and novel cores. Compound 4 is a unique nor-cadinane-dimer, and 5 and 6 are two pairs of hemiketal racemates with novel dinor-cadinane-dimer backbone. Compounds 7 and 8 represent unusual dodecanor-cadinane-dimer and tetradecanor-cadinane-dimer carbon skeletons, respectively. The possible biogenetic pathways of 1–8 were proposed, involving nucleophilic addition, SN2 nucleophilic displacement, [3 + 3] benzannulation, oxidative cleavage, decarboxylation, and oxidative phenol coupling reactions. Multidrug resistance (MDR) reversal activity assay of the isolates were evaluated in doxorubicin-resistant human breast cancer cells (MCF-7/DOX). The combined use of these novel cadinane dimers at a concentration of 10 μM increased the cytotoxicity of doxorubicin by 2.2–5.8-fold. It is the first report about the MDR reversal activity of cadinane dimers.
Highlights
Sesquiterpenoid dimers are some naturally occurring metabolites that have C30 cores, and originate biosynthetically from two sesquiterpenoid molecules1
Its 13C NMR spectrum displayed a total of thirty carbons that, with the aid of HSQC spectrum, were deduced to contain a ketonic, twelve aromatic, and seven methylic carbons (Supplementary Table S1)
According to the data above, compound 1 should contain two aromatic cadinane sesquiterpenoid moieties, which was further confirmed by 2D NMR spectra analysis (1H-1H COSY correlations: H-2/H-4/H3-15, H-8/H2-7/H-6/H-11/H3-12/H3-13, H-2′/H-4′/H3-15′,H2-7′/H-6′/H-11′/H312′/H3-13′; and HMBC correlations: H-2 with C-4/C-10, H-4 with C-6/C-10, H3-14 with C-8/C-9/C-10, H3-15 with C-2/C-3/C-4, H-2′with C-4′/C-10′, H-4′with C-6′/C-10′, H2-14′with C-8′/C-9′/C-10′, H3-15′with C-2′/C-3′/C-4′) (Fig. 2A)
Summary
Qiang-Ming Li*, Jian-Guang Luo*, Rui-Zhi Wang, Xiao-Bing Wang, Ming-Hua Yang, Jun Luo & Ling-Yi Kong. Involucratusins A–C [1,2,3], five unique nor-cadinane-dimers, involucratusins D–H [4,5,6,7,8], together with a known compound [9] were isolated from the rhizomes of Stahlianthus involucratus. As one class of sesquiterpenoid dimers, are of considerable interest due to their ability to induce diverse biological activity (e.g. male antifertility, anticancer, antiviral, and anti-inflammatory)1 Of these naturally occurring cadinane dimers, most are derived from two units of the corresponding monomers by the free-radical coupling reaction, rare example that formed by nucleophilic addition reaction have been reported. We have reported three unprecedented cadinane dimers, involucratustones A–C4, from Stahlianthus involucratus, a folklore medicine to treat inflammation, pain, and fever, as part of a continued program searching for novel terpenoids from Zingiberaceae plants. Are described the isolation, structure elucidation and possible biosynthesis of new metabolites 1–8, as well as MDR reversal activities of the compounds obtained
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