Isolation and structure elucidation of the major photodegradation products of seratrodast

Photodegradation of seratrodast ([±]-7-(3,5,6-trimethyl-1,4-benzoquinone-2-yl)-7-phenyl-heptanoic acid, SD), a p-benzoquinone anti-asthmatic drug, has been investigated in different solutions. HPLC analysis showed that SD was degradated under UV irradiation at 254 nm to afford three major products (SD1, SD2 and SD3) in methanol and in acetonitrile/H2O solutions, while only two of them (SD2 and SD3) could be detected in acetonitrile solution. Furthermore, SD1 was unstable even when the samples were protected from light, so the acetylated SD1 (Ace-SD1) together with SD2 and SD3 were isolated by semi-preparative reversed-phase HPLC. The structures were elucidated as 6-(2,5-diacetoxy-3,4,6-trimethyl-phenyl)-7-phenyl-hept-6-enoic acid (Ace-SD1), 7-phenyl-6-(2,4,5-trimethyl-3,6-dioxo-cyclohexa-1,4-dienyl)-hept-6-enoic acid (SD2) and 5-(5-hydroxy-4,6,7-trimethyl-2-phenyl-benzofuran-3-yl)-pentanoic acid (SD3) based on the spectral data of MS, UV spectrum, IR spectrum and NMR spectrum. Meanwhile, a possible route for the formation of these photoproducts was proposed, which might explain the generation procedure of SD1, SD2 and SD3 during UV irradiation.