Characterization of seventy polymethoxylated flavonoids (PMFs) in the leaves of Murraya paniculata by on-line high-performance liquid chromatography coupled to photodiode array detection and electrospray tandem mass spectrometry

A sensitive HPLC-DAD–ESI-MS/MS method was established to screen and identify the polymethoxylated flavonoids (PMFs) in the leaves of Murraya paniculata (L.) Jack. 16 PMF standards were first to be analyzed in positive mode by the CID-MS/MS. For polymethoxylated flavones, the fragments of [M+H−n × 15]+ produced by loss of one or more methyl radicals from the protonated molecule, as well as [M+H−16]+, [M+H−28]+, [M+H−29]+, [M+H−31]+, [M+H−33]+, [M+H−43]+, [M+H−44]+, [M+H−46]+ and [M+H−61]+ fragment ions were detected, which could be taken as their diagnostic characters. For polymethoxylated flavanones and chalcones, their [M+H]+ ions usually underwent RDA cleavage fragmentation of the C-ring prior to the similar loss of diagnostic fragment ions as polymethoxylated flavones, which could be adopted as a shortcut to distinguish them from ordinary flavones rapidly. For the PMF glycosides, the neutral loss of the similar fragments with polymethoxylated flavones from their [aglycone+H]+ could be adopted as a simple method to screen them out from complex mixture. Based on these characterizations of PMFs and the results of EIC-MS/MS experiment, 70 PMFs including 45 flavones, 17 flavanones or chalcones and 8 PMFs glycosides were screened out from the complex extract of the leaves of M. paniculata. Among them, 16 compounds were unambiguously identified by comparison with reference substances. The results indicated that the developed analysis method could be employed as a rapid, effective technique for structural characterization of PMFs.