Characterisation of ( E )‐2‐styrylchromones by electrospray ionisation mass spectrometry: singular gas‐phase formation of benzoxanthenones

RATIONALE The electrospray ionisation (ESI) mass spectra (ESI‐MS n , n = 2 and 3) of six ( E )‐2‐styrylchromones containing electron‐donating and electron‐withdrawing groups were studied for the first time. The potential application of these compounds as drug candidates brings a need for the development of an analytical method to ensure a detailed knowledge of their structures. METHODS ESI‐MS, CID‐MS 2 and MS 3 spectra of all the studied compounds were acquired using a LXQ linear ion trap mass spectrometer with an electrospray source, operating in the positive ion mode. ESI conditions were: nitrogen 8.00 sheath gas flow rate (arb), spray voltage 5 kV, heated capillary temperature 275 °C, capillary voltage 10.99 V and tube lens voltage 75.01 V. CID‐MS 2 and MS 3 experiments were performed on mass‐selected precursor ions using standard isolation and excitation procedures (activation q value of 0.25, activation time of 30 ms). RESULTS A comparable pattern of product ions was observed for all the studied compounds. Only the product ion (1,2)(3,4) A + is common to all the studied compounds. Common to compounds 1 (R 2  = H), 1a (R 2  = OMe) and 1c (R 2  = Cl) are the product ions formed by loss of H 2 O, CO, C 6 H 5 OH, and the product ions (1,2)(2,3) B + and (1,2)(3,4) B + . Among all compounds, 2‐SC 1b (R 2  = NO 2 ) shows an obvious differentiation showing the lowest number of product ions under CID‐MS 2 conditions. CONCLUSIONS The analysed compounds revealed a comparable pattern of product ions formed for each compound only different in what concerns the relative abundance of these formed product ions. A rather interesting and unexpected loss of 2 Da was observed for some compounds. The structure of a benzoxanthenone was proposed for this product ion based on evidence obtained by synthesised benzoxanthenone as a model compound. Copyright © 2012 John Wiley & Sons, Ltd.