LC–HRESI–MS/MS Profiling of Flavonoids from Chlorophora regia (Moraceae)

Aims: This study was undertaken to characterize flavonoids from the stem bark of Chlorophora regia based on their HRESI–MS/MS fragmentation pattern in positive mode.

Study Design: Isolation and identification of flavonoids from the methanol–chloroform extract of the stem bark and the HRESI–MS/MS characterization of the flavonoids.

Place and Duration of Study: Faculty of Pharmacy and Pharmaceutical Sciences, Kwame Nkrumah University of Science and Technology, Ghana, Technische Universität Dortmund, Germany, between July 2014 and October 2016.

Methodology: Six flavonoids were isolated and purified using various chromatographic techniques. Their structures were elucidated by extensive analyses of their spectroscopic data (UV, 1D and 2D NMR, MS). Tandem mass spectroscopy was further employed to characterize the isolated flavonoids.

Results: Three flavonols including 3,5,7,4ʹ–Tetrahydroxy–2ʹ–methoxyflavonol, quercetin, kaempferol and three flavanones, 5,7,4ʹ–Trihydroxy–2ʹ–methoxyflavanone, 5,7,3ʹ,5ʹ–Tetrahydroxyflavanone, naringenin were isolated. The MS fragmentation patterns of the flavonoids, in positive mode, were proposed. Retro Diels–Alder (RDA) fragmentation of the dihydropyran ring (ring C) of the chromane substructure of the flavonoids led to characteristic fragments that were used to identify the major flavonoid subgroup of the isolated compounds. Furthermore, the substitution pattern of the benzo (ring A) and phenyl (ring B) residues of the flavonoid nucleus was obtained through the RDA fragmentation.

Conclusion: The RDA fragments of the flavonoids obtained from the HRESI–MS/MS spectrum, could be employed in the identification and the determination of the substitution pattern of flavonoids in medicinal plants without the necessity of isolating them.