Ent-kaurane diterpenoids from the cherries of Coffea arabica
Graphical abstract
Introduction
Coffea arabica (Rubiaceae) is one of the most important species cultivated for drinking in genus Coffea [1]. Previous phytochemical investigations on green and roasted coffee beans of C. arbaica had resulted in the isolation of alkaloids, phenolic acids, flavonoids and diterpenoids [[2], [3], [4]]. Coffee diterpenoids are considered to be responsible for some good impacts of coffee consumption on human health, such as anti-hepatitis, anti-oxidant and anti-cancers [[5], [6], [7]], but also they were proved to have the potential to increase serum lipids [8]. Until now, more than 60 diterpenoids have been isolated from C. arabica, including a series of rearranged, oxygenated and degraded ent-kaurane derivatives [[9], [10], [11]]. Among them, 16-ent-kauren-19-ol showed cytotoxic effect against K569 cells (IC50: 6.8 μg/mL) and (2-desoxy-carboxyatractyligenin)-β-D-glucopyranoside showed the inhibition of mitochondrial adenine nucleotide translocase (IC50: 1.0 μM) [12,13]. Meanwhile, mozambioside and mascaroside were two diterpenoid glucosides which was contributed to the bitter taste of coffee brews [11,14]. Therefore, in the course of ongoing investigations on diterpenoids in C. arabica, four new rearranged ent-kaurane diterpenoids (1–4), and eleven known analogues (5–15) were isolated from the cherries of C.arabica (Fig. 1). Herein, we reported the isolation and structural identification of these new compounds and their inhibitory activities on NO production.
Section snippets
General
Ultraviolet spectra were measured by UV-2401 PC spectrophotometers (Shimadzu, Japan). A Bruker Tensor-27 instrument (Bruker, German) was used for recording infrared spectra by using KBr pellets. A Jasco P-1020 polarimeter (Jasco, Japan) was used to obtain optical rotations and HRESIMS data were measured by an API QSTAR Pulsar spectrometer (Waters, UK). The Bruker DRX-600 instrument (Bruker, Switzerland) were used to detect 1D and 2D NMR spectra with TMS as internal standard for chemical shifts.
Results and discussion
Caffruenol A (1) was isolated as colorless prisms and the molecular formula C20H32O2 was assigned by HRESIMS spectrum, representing five degrees of unsaturation. The 1H NMR (Table 1) spectrum of 1 showed the presence of one methyl (δH 0.79, s, H3–20), one olefinic [δH 5.20 (t, J = 7.0 Hz, H-18)] and two methylenes [δH 3.40 (dd, J = 7.7 Hz and 5.3 Hz, H2–17), δH 4.19 (d, J = 7.2 Hz, H2–19)] proton singnals. In the 13C-DEPT NMR (Table 1) spectra, the observed 20 carbon signals consist of one
Conflict of interest
We declare that there is no conflict of interest.
Acknowlegements
This project was supported financially by the National Natural Science Foundation of China, China (No. 31670364), Project of Key New Productions of Yunnan Province, China (No. 2015BB002 and 2016HE004), the STS Programme of Chinese Academy of Sciences, China (KFJ-SW-STS-143-8), Special Fund Project of Pu’er municipal government, China (2017), as well as Foundation of State Key Laboratory of Phytochemistry and Plant Resources in West China, China (P2015-ZZ09).
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