Pogonatherumol , a Novel Highly Oxygenated Norsesquiterpene with Flavone C-Glycosides from Pogonatherum crinitum

A novel highly oxygenated norsesquiterpene, pogonatherumol (1), with two known flavone C-glycosides (2-3), was isolated from Pogonatherum crinitum. .e structure of the new compound was illuminated based on its spectroscopic data and X-ray analysis. Compounds 1 and 3 inhibited NO production in the mouse peritoneal macrophage (64.5± 7.2% and 61.6± 5.8%, respectively, at a concentration of 50μM)..e three compounds were inactive when tested against two human cancer cell lines (IC50 values> 50μM).


Introduction
Pogonatherum crinitum, is one of the species in the genus Pogonatherum of Gramineae family, which has been used as a natural medicine in Chinese folk [1], for treatment of diabetes, urinary tract infection, jaundice hepatitis, and nephritis [2][3][4][5].Previous phytochemical studies on this plant have led to a series of flavones and lignins, some of which showed anti-inflammatory and antifungal activities [6,7].In order to discover structurally and biologically interesting compounds from P. crinitum, a novel highly oxygenated norsesquiterpene, pogonatherumol (1) with two known flavone C-glycosides was investigated (Figure 1).Herein, the isolation and structural characterization of the compounds and their biological activities are reported in this paper.

Experimental
2.1.General Experimental Procedures.X-ray dif-segment intensity data of 1 were collected on an MAC DIP-2030K diffractometer with graphite-monochromated Mo Kα radiation and were corrected by Lorentz and polarization.An XT-5B micromelting point apparatus was used to determine the melting point.JEOL ECZ-400S, JASCO V-650, and Nicolet iS5N spectrophotometers manufactured by ermo Scientific were used to record NMR, UV, and IR spectra, respectively.

Plant Material. Pogonatherum crinitum was collected in
Jianyang, Fujian, China, in September 2015.Professor Xiaoxing Zou, from the Fujian Agriculture and Forestry University (FAFU), People's Republic of China (PRC), identified the plant.e plant specimen was deposited at the lab of the material basis and utilization of TCM, College of Plant Protection, FAFU, PRC. e crystallographic data of the structure of pogonatherumol (deposition number: CCDC 1842928) were deposited at the Cambridge Crystallographic Data Centre.

Biological Activities.
Two cell lines, human ovarian neoplasm cell (A2780) and human colon cancer cell line (HCT-116), were used to test the tumor cytotoxic activities, and Taxol was used as a positive control.e method was according to the previously described [8].LPS-induced RAW264.7 macrophage was used to evaluate the NO production inhibition activity of the three compounds.Dexamethasone was used as a positive control, and the test method was according to the literature [9,10].

Journal of Chemistry
In addition to pogonatherumol, two known C-glycosides, schaftoside (2) [11] and isoschaftoside (3) [12], were identified by comparing their ESIMS and 1 H and 13 C NMR data with those reported in the literature.
Pogonatherumol (1) with a fused indanone skeleton has not been previously reported as a natural product.Notably, it seems to be a novel rearrangement of norsesquiterpene.
Meanwhile, the inhibited NO production and the tumor cytotoxic activities of three compounds were evaluated.Compounds 1 and 3 inhibited NO production in the mouse peritoneal macrophage (64.5 ± 7.2% and 61.6 ± 5.8%, respectively, at a concentration of 50 μM), while the positive control dexamethasone gave an inhibitory ratio of 59.4.1 ± 6.2% at a concentration of 10 μM.All compounds were also evaluated in vitro for cytotoxicity against A2780 and HCT-116 cell lines employing an MTT assay with Taxol as the positive control.e three compounds were inactive when tested against the two human tumor cell lines (IC 50 values ≥ 50 μM).

Table 1 :
1H and 13 C NMR data of compound 1.