Structures and anti-lipid droplets accumulation activity of ceramicines from Chisocheton ceramicus

抄録

In the era of ever improving living status, lifestyle disease such as diabetes and obesity has become one of the major health problems for people living in developed countries. These health problems are often associated with increased adipocyte differentiation or accumulation of lipid. In effort to provide new lead compound that can improve the symptoms of lifestyle disease, we focused on species from the Meliaceae family due to their various significant biological activities. We subsequently identified Chisocheton ceramicus bark extracts to possess in vitroanti-lipid droplets accumulation (LDA) activity on pre-adipocyte cell line. Following research led to identification of 12 limonoids, ceramicines A-L (Fig. 1) ^1-4. Their relative structures were elucidated by using 1D and 2D NMR data.

Structure Elucidation of Ceramicine B from C. ceramicus Bark

Ceramicine B (2) was isolated as a colorless amorphous solid with molecular formula, C₂₆H₃₂O₄as determined by high resolution-electrospray ionization-time of flight-mass spectra. The planar structure was elucidated with 1D and 2D NMR data (Figure 2). Thus, 2 was established as a new limonoid with cyclopenta[α]phenanthren ring system with a β-furyl ring at C-17 and a tetrahydofuran ring. The relative stereochemistry of 2 was elucidated by NOESY correlations as shown in computer-generated 3D rendering (Figure 2). NOESY correlations of H-6/Hb-28, H₃-19, and H₃-30, H-7/H-15, and H-12/H-17 together with ³J proton coupling constants (³J_H-5/H-6 = 12.4 Hz and ³J_H-6/H-7 = 3.8 Hz) suggested that H-6, H-7, and H-17 adopts β-configuration. While NOESY correlation of H-5/H-9 indicates both H-5 and H-9 adopt α-configuration.

Absolute Configuration of Ceramicine B

The absolute configuration of 2, a major limonoid from C. ceramicus, was elucidated by X-ray crystallography and CD spectrum of p-Br-benzoyl derivative results (Fig. 3). The CD spectrum of p-Br-benzoyl derivative of 2indicated that the mutual relationship of dipole moment of the benzoate and α,β-unsaturated ketone chromophores was oriented in a counter clockwise manner, indicating absolute configuration at C-7 as S configured. Further X-ray crystallography analysis results confirmed the total structure of 2 including its absolute structure [Flack parameter, c = -0.0(2)].

Ceramicines with Anti-Lipid Droplets Accumulation Activity

The LDA activities were examined on murine pre-adipocyte cell line, MC3T3-G2/PA6, and measured via nile red lipid droplets staining. Results showed that ceramicine B was demonstrated as most potent (IC₅₀= 1.8 μM) among the ceramicine compound series ⁵. The potency prompted us to further investigate the structural-activity relationship of ceramicines. Nine derivatives based on the potent ceramicine B were synthesized, and the summaries of ceramicines and its derivatives SAR were shown at Fig. 4.

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