Anti-inflammatory Dimeric 2‑(2-Phenylethyl)chromones from the Resinous Wood of Aquilaria sinensis Hui-Xia Huo, † Zhi-Xiang Zhu, † Yue-Lin Song, † She-Po Shi, † Jing Sun, † Hui Sun, † Yun-Fang Zhao, † Jiao Zheng, † Daneel Ferreira, ‡ Jordan K. Zjawiony, ‡ Peng-Fei Tu, † and Jun Li* ,† † Modern Research Center for Traditional Chinese Medicine, School of Chinese Materia Medica, Beijing University of Chinese Medicine, Beijing 100029, People’s Republic of China ‡ Department of BioMolecular Sciences, Division of Pharmacognosy, and Research Institute of Pharmaceutical Sciences, School of Pharmacy, University of Mississippi, University, Mississippi 38677-1848, United States *S Supporting Information ABSTRACT: Sixteen new 2-(2-phenylethyl)chromone dimers, including four pairs of enantiomers (1a/1b, 3a/3b, 6a/6b, and 8a/8b), along with eight optically pure analogues (2, 4, 5, 7, and 9-12) were isolated from the resinous wood of Aquilaria sinensis. Their structures were determined by extensive spectroscopic analysis (1D and 2D NMR, UV, IR, and HRMS) and experimental and computed ECD data. Compounds 1-10 feature an unusual 3,4-dihydro-2H-pyran ring linkage connecting two 2-(2-phenylethyl)chromone monomeric units, while compounds 11 and 12 possess an unprecedented 6,7-dihydro-5H-1,4- dioxepine moiety in their structures. A putative biosynthetic pathway of the representative structures via a diepoxy derivative of a chromone with a nonoxygenated A-ring is also proposed. Compounds 1a/1b, 2, 3a/3b, 5, 7, 8a/8b, and 10-12 exhibited significant inhibition of nitric oxide production in lipopolysaccharide-stimulated RAW264.7 cells with IC 50 values in the range 7.0-12.0 μM. N atural products continue to play a highly significant role in the identi fication of lead compounds for the development of anti-inflammatory drugs. 1 2-(2-Phenylethyl)- chromones are characterized as a class of uncommon chromones possessing a phenylethyl substituent at C-2. This type of natural product has been found from a limited number of plant species such as Aquilaria (Thymelaeaceae), Bothrio- chloa ischaemum (Gramineae), Cucumis melo (Cucurbitaceae), Eremophila georgei (Myoporaceae), Flindersia laevicarpa (Ruta- ceae), and Imperata cylindrica (Gramineae). 2,3 Recently, 2-(2- phenylethyl)chromone derivatives have been reported to possess pronounced anti-inflammatory activities via multiple underlying mechanisms and have the potential to be developed into therapeutic drugs for inflammation-related diseases. 3-6 Aquilaria sinensis (Lour.) Gilg (Thymelaeaceae) is mainly distributed in southern China. Its resinous woods have been used as Chinese agarwood (“Chenxiang” in Chinese) in Traditional Chinese Medicine for centuries to treat inflamma- tion-related disorders such as rheumatism, arthritis, body pain, asthma, and gout. 7 2-(2-Phenylethyl)chromone derivatives and sesquiterpenoids have been reported to be the main active constituents of Chinese agarwood. 8,9 In a continuing search for anti-inflammatory agents from Aquilaria plants, 3-6,10,11 the EtOAc-soluble fraction from a 95% EtOH extract of the resinous wood of A. sinensis was found to inhibit nitric oxide (NO) production in lipopolysaccharide (LPS)-stimulated RAW264.7 cells (95% inhibition at 20 μg/mL). Bioassay- guided separation of this active fraction led to the identification of an active subfraction, containing a variety of 2-(2- phenylethyl)chromone derivatives in trace amounts as revealed by LCMS-IT-TOF analysis. Subsequent LC-MS-guided sepa- ration and purification afforded 16 new 2-(2-phenylethyl)- chromone dimers, including four pairs of scalemic mixtures (1a/1b, 3a/3b, 6a/6b, and 8a/8b), and eight optically pure 2- (2-phenylethyl)chromone dimers (2, 4, 5, 7, and 9-12). Herein, the isolation and structure elucidation of the new compounds as well as their inhibitory effects on NO production Special Issue: Special Issue in Honor of Susan Horwitz Received: November 1, 2017 Article pubs.acs.org/jnp Cite This: J. Nat. Prod. XXXX, XXX, XXX-XXX © XXXX American Chemical Society and American Society of Pharmacognosy A DOI: 10.1021/acs.jnatprod.7b00919 J. Nat. Prod. XXXX, XXX, XXX-XXX