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.