Identification of a diarylpentanoid-producing polyketide synthase revealing an unusual biosynthetic pathway of 2-(2-phenylethyl)chromones in agarwood.

2-(2-Phenylethyl)chromones (PECs) are the principal constituents contributing to the distinctive fragrance of agarwood. How PECs are biosynthesized is currently unknown. In this work, we describe a diarylpentanoid-producing polyketide synthase (PECPS) identified from Aquilaria sinensis. Through biotransformation experiments using fluorine-labeled substrate, transient expression of PECPS in Nicotiana benthamiana, and knockdown of PECPS expression in A. sinensis calli, we demonstrate that the C6-C5-C6 scaffold of diarylpentanoid is the common precursor of PECs, and PECPS plays a crucial role in PECs biosynthesis. Crystal structure (1.98 Å) analyses and site-directed mutagenesis reveal that, due to its small active site cavity (247 Å3), PECPS employs a one-pot formation mechanism including a "diketide-CoA intermediate-released" step for the formation of the C6-C5-C6 scaffold. The identification of PECPS, the pivotal enzyme of PECs biosynthesis, provides insight into not only the feasibility of overproduction of pharmaceutically important PECs using metabolic engineering approaches, but also further exploration of how agarwood is formed.

Anti-inflammatory dimeric furanocoumarins from the roots of Angelica dahurica.

Seven new dimeric furanocoumarins, dahuribiethrins A-G (1-7), were isolated from the roots of Angelica dahurica. Their structures were determined by chemical derivatization and extensive spectroscopic techniques, including (1)H NMR, (13)C NMR, HSQC, (1)H-(1)H COSY, HMBC, and NOESY experiments. Compounds 2, 3, 4, and 5 exhibited significant inhibition of nitric oxide production in the lipopolysaccharide (LPS)-stimulated RAW264.7 macrophage cells with IC50 values in the range of 8.8-9.8 µM.

Triterpene saponins from the roots of Ilex asprella.

Six new triterpene saponins, ilexasprellanosides A-F (1-6, resp.), together with eleven known compounds were isolated from the roots of Ilex asprella. The new saponins were characterized as ursa-12,18-dien-28-oic acid 3-O-ß-D-xylopyranoside (1), 19α-hydroxyursolic acid 3-O-ß-D-(2'-O-acetylxylopyranoside) (2), 19α-hydroxyursolic acid 3-O-ß-D-glucuronopyranoside (3), 3ß,19α-dihydroxyolean-12-en-23,28-dioic acid 28-O-ß-D-glucopyranoside (4), 19α-hydroxyoleanolic acid 3-O-ß-D-(2'-O-acetylxylopyranoside) (5), 19α-hydroxyoleanolic acid 3-O-ß-D-glucuronopyranoside (6). The structures of the new compounds were elucidated by analysis of their spectroscopic data and chemical degradation. Compounds 2, 4, oleanolic acid 3-O-ß-D-glucuronopyranoside, 3-ß-acetoxy-28-hydroxyurs-12-ene, and pomolic acid showed significant cytotoxic activities against human tumor cell line A549 (IC50 values of 1.87, 2.51, 1.41, 3.24, and 5.63 µM, resp.).

Quinolone alkaloids with antibacterial and cytotoxic activities from the fruits of Evodia rutaecarpa.

Five new quinolone alkaloids, euocarpines A-E (16-20), four new natural products (1, 4, 12, and 14), and eleven known natural products were isolated from the fruits of Evodia rutaecarpa (Juss.) Benth. The structures of the new compounds were elucidated based on spectroscopic evidence. All compounds were evaluated for their antibacterial activity against three strains and for their cytotoxic activity against four human tumor cell lines. The results revealed that 5, 7-11, 13, 14, and 16-20 exhibited moderate antibacterial activities (MIC values: 4-128 µg/mL), and 9, 11, 14, and 17 exhibited moderate cytotoxic activities against HepG-2, Hela, BEL7402, and BEL7403 (IC50 values: 15.85-56.36 µM).

[Study on the chemical constituents of Selaginella tamariscina (Beauv.) Spring].

AIM: To study the chemical constituents of Selaginella tamariscina (Beauv.) Spring. METHODS: Various chromatographic techniques were used to separate and purify the chemical constituents. Their physico-chemical properties and spectral data were used to elucidate the structures. RESULTS: Four compounds were isolated from the n-BuOH fraction of the water-extracts. Their structures were identified as 1-hydroxy-2-[2-hydroxy-3-methoxy-5-(1-hydroxyethyl)-phenyl]-3-(4-hydroxy-3,5-dimethoxy)-propane-1-O-beta-D-glucopyranoside (tamariscinoside B, I), adenosine (II), guanosine (III), arbutin (IV). CONCLUSION: Tamariscinoside B (I) is a new compound, while the others were isolated from Selaginella for the first time.