Structural characterization of isoprenylated flavonoids from Kushen by electrospray ionization multistage tandem mass spectrometry.
Eighteen isoprenylated flavonoids (8 flavanones, 3 flavanols, and 7 chalcones) isolated from Kushen or synthesized were studied by positive and negative ion electrospray ionization multistage tandem mass spectrometry (ESI-MS(n)). Plausible fragmentation patterns were obtained by comparing their MS(n) spectra with each other, which were further supported by high-resolution MS data and two model compounds. It was shown that the 2'-OH group would make the C-ring of flavonoids studied more labile through a six-membered mechanism, resulting in base peaks of (1,3)A+ (positive mode) and (1,4)A(-) (negative mode). In addition, the 2'-OH is also responsible for the neutral loss of water in (+)ESI/MS(2) of flavanones. The neutral loss of water (or methanol) in (-)ESI/MS(2) of flavanols was elucidated by a E2 elimination mechanism. Different relative abundances (RA) of (1,3)A(+) and S(+) in (+)ESI/MS(2) spectra were used to discriminate flavanones with their open-ring products, chalcones, since the equilibrium for flavanone<-->chalcone isomerization in ESI ion source could not be obtained in positive mode.
Zhang
Yufeng
Y
College of Pharmaceutical Sciences, Zhejiang University, Hangzhou 310058, PR China.
Zhang
Peng
P
Cheng
Yiyu
Y
D047188:Chalcones / Q000032:analysis; D047309:Flavones / Q000032:analysis; D005419:Flavonoids / Q000737:chemistry*; D007202:Indicators and Reagents; D054876:Prenylation; D012015:Reference Standards; D029909:Sophora / Q000737:chemistry*; D021241:Spectrometry, Mass, Electrospray Ionization; D053719:Tandem Mass Spectrometry
D047188:Chalcones; D047309:Flavones; D005419:Flavonoids; D007202:Indicators and Reagents