Antioxidants and α-glucosidase inhibitors from “Liucha” (young leaves and shoots of Sibiraea laevigata)
Introduction
In recent years, a growing awareness of the relationship between functional foods and health has led to more and more attention being paid to the development of physiological functional plants due to their potential health benefits. “Liucha” is a kind of tea consumed by local people on the Qinghai-Tibet Plateau. Anecdotally the consumption of “Liucha” has some beneficial effects such as improving digestion and protecting stomach. “Liucha” has long been used as Tibetan folk medicine to treat indigestion and upset stomach. However, mixing “Luchia” into sheep feed is avoided since it has been practically known to cause sheep weight-loss (Ito et al., 2009). “Liucha” is made of the young leaves and shoots of two Sibiraea species, S. laevigata and S. angustata (Duan, Li, Liu, & Yang, 2010). Previous researches of “Liucha” have mainly focused on S. angustata which revealed the chemical components of S. angustata (Ito et al., 2009, Li et al., 2010, Wang et al., 2013) and showed that the extracts of S. angustata exhibited hypolipidemic, antitumor, antidiabetic and anti-obesity effects (Ito et al., 2009, Wei et al., 2011, Xie et al., 2014). However, studies about S. laevigata are quite few (Yu, Shao, & Tao, 2014).
The free radicals and reactive oxygen species are considered to be harmful to human health and trigger many diseases, such as cancer, coronary heart disease, arteriosclerosis, inflammatory disorders, and aging processes (Wang, Yang, & Zhang, 2007). Phenolic components including tocopherols, flavonoids, and polyphenolic compounds are typical natural antioxidants that can potentially provide protection against the development of certain oxidation-linked chronic diseases (Hwang et al., 2014, Spínola et al., 2015). On the other hand, phenolic compounds had been reported as glucosidase inhibitors used to reduce postprandial hyperglycemia induced by the digestion of starch in the small intestine (Benalla et al., 2010, Manzano and Williamson, 2010, Wan et al., 2012). Previous researches showed that a series of unique phenolic compounds were obtained from S. angustata. (Li et al., 2015, Zhang et al., 1993) S. laevigata bears extensive similarity to S. angustata and both of them were used as the materials of “Liucha”. Thus, the main objective of this work was to clarify the chemical constituents of “Liucha” (S. laevigata) which has a variety of pharmaceutical functions and search for new natural antioxidants and α-glucosidase inhibitors from “Liucha” (S. laevigata). In this work, we isolated and identified the phenolic components of S. laevigata and evaluated their antioxidant and α-glucosidase inhibitory activities.
Section snippets
General experimental procedure
Optical rotations were acquired on a Jasco P-1020 digital polarimeter (JASCO Corporation, Tokyo, Japan). Ultraviolet–visible (UV) spectra were measured on a Shimadzu UV2401A ultraviolet–visible spectrophotometer (Shimadzu Corporation, Tokyo, Japan). Circular dichroism (CD) spectra were tested on a Chirascan Circular Dichroism spectrometer (Applied Photophysics Ltd., Surrey, UK). Infrared (IR) spectra were recorded on a Bruker Tensor-27 FI-IR spectrometer (Bruker, Germany) with KBr pellets.
Structure elucidation of compounds
The n-BuOH fraction of S. laevigata was subjected to column chromatography over silica gel, MCI gel CHP 20P, preparative and semi-preparative HPLC to afford compounds 1–25 including seven new sorbitol O-caffeic acid ester derivatives, sorbitol esters A–G (1–7) (Fig. 1) and eighteen known phenolic compounds. The known compounds were each identified as 1,6-sorbitol-O-dicaffeic acid ester (8) (Li et al., 2015), icariside H1 (9) (Matsushita, Miyase, & Ueno, 1991), 9-O-β-d
Conclusions
Considering the various functions and values of “Liucha” (young leaves and shoots of S. laevigata), it is clearly important to figure out its chemical constituents. Phytochemical study of “Liucha” resulted in seven new sorbitol O-caffeic acid ester derivatives (1–7) together with 18 known phenolic compounds. To our knowledge, all compounds were reported from this plant for the first time except 15 and 16. Phenolics have been extensively studied for their human health benefit (Crozier, Jaganath,
Notes
The authors declare no competing financial interest.
Acknowledgements
This work was supported by the Significant Science & Technological Project of Qinghai Province (2014-GX-A3A) and the Project of Discovery, Evaluation and Transformation of Active Natural Compounds, Strategic Biological Resources Service Network Programme of Chinese Academy of Sciences (ZSTH-027).
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These authors contributed equally.