Homoisoflavonoids from the medicinal plant Portulaca oleracea
Graphical abstract
A rare subclass of homoisoflavonoids 1–4 along with nine other known compounds were isolated from the aerial parts of Portulaca oleracea. Compounds 2–5 selectively showed in vitro cytotoxicity towards four cancer cell lines.
Highlights
► Four homoisoflavonoids and nine known compounds were isolated from Portulaca oleracea. ► Each of the homoisoflavonoids is featured with a rare 2′-OH substituent in ring B. ► This is the first finding of homoisoflavonoids from the plant family Portulacaceae. ► Four compounds selectively showed in vitro cytotoxicity towards four cancer cell lines.
Introduction
Portulaca oleracea (purslane, Portulacaceae) is an annual green herbaceous medicinal plant widespread in temperate and tropical regions of the world (Yang et al., 2009). As a traditional Chinese folk medicine, it has been used as a diuretic, antiseptic, antiscorbutic, febrifuge, antispasmodic and vermifuge with a long history (Lim and Quah, 2007). Previously, pharmacological researches have indicated that P. oleracea produces a wide range of pharmacological effects such as anti-inflammatory (Chan et al., 2000), anti-bacterial (Zhang et al., 2002), skeletal muscle relaxant (Parry et al., 1993), wound-healing (Rashed et al., 2003) and in vitro anti-tumor (Yoon et al., 1999) activities. Although many chemical constituents including terpenoids (Xin et al., 2008a), alkaloids (Yang et al., 2009), cerebroside (Xin et al., 2008b), coumarins and flavonoids (Xiang et al., 2006) have quite recently been reported from this plant, most of the biologically active compounds associated with the aforementioned multi-pharmacological effects of P. oleracea have not been addressed thus far. With the aim of identifying those potentially additional and bioactive natural products of this plant a phytochemical study on fresh aerial parts of P. oleracea has been carried out and resulted in the isolation of four unusual homoisoflavonoids, named portulacanones A−D (1–4), together with nine known compounds (5–13, see Fig. 1). Homoisoflavonoids are derivatives of 3-benzylchrom-4-ones which were mainly discovered from plants belonging to the Liliaceae family and a few other plant species (Sievänen et al., 2010). This group of compounds have been reported to show multiple biomedical properties such as cough relief (Ishibashi et al., 2001), antioxidative (Zhou et al., 2008), anti-allergic, anti-inflammatory, anti-histaminic, angioprotective (Shim et al., 2004) and inhibition of platelet aggregation activities (Kou et al., 2006) and etc. To the best of our knowledge, portulacanones A−D are the first group of homoisoflavonoid constituents so far reported from plants belonging to the Portulacaceae family. Herein, the isolation and structural elucidation of these compounds, as well as their cytotoxic activities against several human cancer cell lines are described.
Section snippets
Results and discussion
The EtOH extract of fresh plants of P. oleracea was partitioned between water and EtOAc. The EtOAc-soluble fraction was then subjected to repeated column chromatography over silica gel to yield four compounds 1–4 along with nine other known metabolites, viz. 2,2′-dihydroxy-4′,6′-dimethoxychalcone (5) (Miyaichi et al., 1999), 3-quinolinecarboxylic acid (6) (Ukrainets et al., 2010), indole-3-carboxylic acid (7) (Agemeier et al., 2001), thymine (8) and uracil (9) (Lao et al., 2001), N
Concluding remarks
Four homoisoflavonoids, portulacanones A−D (1–4), together with nine known metabolites (5–13) were isolated and identified from the medicinal plant P. oleracea. The four compounds represent a rare subclass of homoisofalvonoids in nature with a structure characteristic of solely one hydroxyl group substituted at C-2′ rather than at C-4′ in ring B of the molecule. Portulacanones A−D are also the first group of homoisoflavonoids so far identified from plants of the Portulacaceae family. Compounds 2
General experimental procedures
Melting points (m.p.) were obtained on a Sichuan micro-melting-point apparatus (XRC-1), uncorrected. Optical rotations were measured with a Horiba SEPA-300 polarimeter (Horibia, Kyota), with UV spectra being obtained using a Shimadzu UV-2401A spectrophotometer. Circular dichroism (CD) spectra were measured on a JASCO J-810 spectropolarimeter. IR spectra (KBr) were recorded on a Bruker Tensor 27 spectrophotometer whereas, NMR spectra were obtained in either CD3OD or CDCl3 on a Bruker AV-400
Acknowledgements
We thank Prof. Ruiqiang Chen, Guangzhou Institute of Chemistry, Chinese Academy of Sciences, Guangzhou, China, for NMR spectroscopic measurements. This work was supported by the Knowledge Innovation Program of the Chinese Academy of Sciences (KSCX2-YW-N-0804 and KSCX2-EW-J-28), the National Natural Science Foundation of China (No. 30870248 and 30900125), Key Laboratory of Plant Resources Conservation and Sustainable Utilization, South China Botanical Garden, CAS (No. 200920 to J.Y.) and the
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Those authors contributed equally.