Screening of tricyclic quinazoline alkaloids in the alkaloidal fraction of Adhatoda beddomei and Adhatoda vasica leaves by high-performance liquid chromatography/electrospray ionization quadrupole time-of-flight tandem mass spectrometry.

Adhatoda beddomei and Adhatoda vasica are popular Ayurvedic medicinal plants in India, belonging to the family Acanthaceae. Tricyclic quinazoline alkaloids are found to be the most abundant in these plants which are responsible for broad-spectrum medicinal properties. This study aims to seek identification and characterization of those alkaloids based on their fragmentation patterns. A method was developed to elucidate the main fragmentation pathways of tricyclic quinazoline alkaloids in positive ion mode using high-performance liquid chromatography coupled with electrospray ionization quadrupole time-of-flight tandem mass spectrometry (HPLC/ESI-QTOF-MS/MS). Chromatographic separation was carried on a Supelco Discovery HS C18 column (15 cm × 4.6 mm, 3 µm) with 0.1% formic acid aqueous solution and acetonitrile as a mobile phase. In full scan mass spectra, protonated molecules were observed for all the quinazoline alkaloids. Ring cleavages of the tricyclic quinazoline moiety were observed in MS(2) spectra and the characteristic ions provide valuable structural information of these alkaloids. Fragmentation pathways and fragment ion structures were proposed in two groups of quinazoline alkaloids. The established fragmentation patterns have been successfully used to identify 23 tricyclic quinazoline alkaloids in the alkaloidal fraction of A. beddomei and A. vasica.