Prenylated flavonoids are mainly distributed in Leguminosae and Moraceae plants, and they have been reported to possess various biological activities. Previously, we have reported a prenylated isoflavonoid, isoangustone A（IAA） from licorice（Glycyrrhiza uralensis）, which induces apoptosis in colorectal cancer cells by disrupting mitochondrial functions. In the present study, we compared a group of flavonoids from licorice with IAA for their anti-proliferation activities and effects on intracellular signaling. The results indicated that the isoprenyl groups on the A and B rings, the hydroxyl groups at the ortho position of isoprenyl on A ring and the conjugated plane of C ring might contribute to the anti-cancer activity of prenylated flavonoids. Based on the above structure-activity relationship, we further identified four prenylated flavonoids with similar anti-cancer activities from licorice. Taken together, our present study established a preliminary structure-activity relationship of anti-cancer prenylated flavonoids, and our data provided important leading compounds from licorice, which deserved further research and development.
Monoterpene glycosides are the major bioactive compounds of Paeonia lactiflora Pall（P. lactiflora）. Characteristic neutral loss of 30 Da has been extensively reported for monoterpene glycosides in tandem mass spectrometry. However, little is known about mechanism of this fragmentation. The neutral loss of 30 Da was studied for eleven monoterpene glycosides（1–11） from P. lactiflora by ion trap mass spectrometry in this report. Compounds 1–5 with a hemiacetal structure could readily lose 30 Da at low collision energy of 30% in MS/MS by ion trap mass spectrometry. For compounds 6–11, neutral loss of 30 Da could also be observed at low abundance, but the collision energy had to be increased to 60%. In both cases, high-accuracy mass spectrometry assigned the 30 Da as CH_2O. After careful analysis of the structures and mass spectra, we believe that the neutral loss of 30 Da in compounds 1–5 was due to cleavage of the hemiacetal structure, whereas it was ascribed to the cleavage of 5＇-hydroxymethyl group of the glucosyl residue in other monoterpene glycosides. Furthermore, the characteristic neutral loss of 30 Da at low collision energy was used to screen hemiacetals from crude extracts of P. lactiflora and related plant species. Significant differences among Paeonia species were observed by 30 Da neutral loss analysis.
Isoangustone A （1） is an isoprenylated flavonoid isolated from licorice. It has been reported to possess anti-microbial, anti-oxidative, anti-inflammatory, and anti-tumor activities. In order to increase its structural diversity, microbial transformation of 1 was conducted by Mucor hiemalis CGMCC 3.14114 to obtain three new compounds. By extensive NMR and MS spectroscopic analyses, their structures were identified as isoangustone A 7-O-glucoside （2）, isoangustone A 7-O-glucoside-4＇-O-sulfate （3）, and isoangustone A 7,3 ＇di-O-glucoside （4）, respectively. The major biotransformation reaction was glycosylation at C-7. Sulfation is rare for microbial transformation.
