A New Monoterpene-Flavanone Conjugate from the Aerial Parts of Chimonanthus grammatus
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A NEW MONOTERPENE-FLAVANONE CONJUGATE FROM THE AERIAL PARTS OF Chimonanthus grammatus
Yuxian Li,1 Ke Sun,2 Lin Liang,3 Man Wang,3* and Zhenliang Sun3*
A new monoterpene-flavanone conjugate, grammatin A (1), along with four known compounds (2–5), were isolated from the aerial parts of Chimonanthus grammatus. Their structures were elucidated through extensive analysis of NMR spectroscopic data in combination with the reported literature. All these compounds were isolated from this plant for the first time. Keywords: Chimonanthus grammatus, monoterpene-flavanone conjugate, flavonoid. Chimonanthus grammatus is a Chinese endemic plant with highly restricted geographical distribution in Southern China [1]. Due to the rare distribution, the current research on C. grammatus has focused mainly on its essential oil and biological activities. There are rare reports on other secondary metabolites [2–5]. As part of our ongoing search for active chemical constituents from herbs in China, the native C. grammatus was phytochemically investigated. As a result, a new monoterpene-flavanone conjugate and four known compounds were isolated from the ethanol extract of C. grammatus. Herein, we describe the isolation and structural elucidation of these compounds. Compound 1 was obtained as a faint yellow solid. The IR spectrum showed absorption bands at 3445, 2361, 1631, and 698 cm–1, indicating the existence of hydroxyl, carbonyl, and phenolic functional groups. Three absorption bands in the UV spectrum at 200, 235, and 295 nm supported the presence of the flavonoid nucleus. The molecular formula was established as C25H28O4 on the basis of its 1H and 13C NMR data (Table 1) and an HR-ESI-MS ion peak at m/z 393.2060 [M + H]+ (calcd 393.2060). Compound 1 showed characteristic signals for a flavanone moiety at δ 2.80 (1H, dd, J = 17.0, 2.4 Hz, H-3β), 3.06 (1H, dd, J = 17.0, 13.6 Hz, H-3α), and 5.37 (1H, dd, J = 13.6, 2.4 Hz, H-2) in its 1H NMR spectrum, and at δ 43.8 (C-3) and 78.9 (C-2) in its 13C NMR spectrum. The carbonyl group at C-4 was hydrogen-bonded with the C-5 OH group, as evidenced by a sharp peak that appeared at δ 12.93 in the 1H NMR spectrum. Five aromatic proton signals at δ 7.40–7.45, coupled with the 13C NMR resonances at δ 126.3, 128.9, and 129.0, displayed the presence of a monosubstituted benzene ring. The 1H and 13C NMR spectral data implied that compound 1 possessed a monoterpene-conjugated flavanone skeleton closely related to linderatone [6]. Comparison of the NMR data of 1 with those of linderatone revealed the major difference: the absence of a double bond; instead, a quaternary carbon (δ 37.3) and one methine group (δ 32.6, 1.38) were observed in 1. In addition, the upfield chemical shifts of the methylene group (δH 0.75 and 0.62) and 1H–1H COSY correlations of H-5′′/H-6′′ indicated the presence of a cyclopropane ring. Then one hydrogenated sabinene moiety was established based on 1D and 2D NMR data. In the HMBC spectrum, the key correlations of 5-OH/C-5, C-6, and C-10, as well as CH3-7′′/C-1′′, C-2′′, C-6′′, and
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