Do cinnamylideneacetophenones have antioxidant properties and a protective effect toward the oxidation of phosphatidylcholines?

Cinnamylideneacetophenones (CA) are an important group of α,β,γ,δ-diunsaturated ketones that have been widely used in a variety of synthetic transformations. Biological studies concerning these compounds are scarce and refer mainly to antiviral and antibacterial evaluations. Curcumin (CR), a natural polyphenol, is a yellow pigment extracted from the plant Curcuma longa, which is one of the major spices used in the Indian culinary. It has been reported that CR has cancer chemopreventive properties in a range of animal models of chemical carcinogenesis, along with antioxidative and anti-inflammatory properties. Inspired by the biological activity shown by CR and their structural resemblance with CA, it was considered to study the ability of the latter molecules to inhibit lipid oxidation induced by the hydroxyl radical (Fenton reaction) by electrospray ionization (ESI) mass spectrometry (MS) using phosphatidylcholine (PC) liposomes as a model of cell membrane. Compound 4, holding a methylated hydroxy group in the position R(2), and CR showed similar effects in inhibiting lipid peroxidation. In the presence of 7, the extension of oxidation was higher than the one verified in all other compounds. Other methodologies, namely DPPH radical scavenging and oxygen radical absorption capacity (ORAC) assays, were performed to complement and clarify the results attained by oxidation of PC monitored by ESI-MS and to evaluate the antioxidant profile of compounds. For both assays, compound 7 showed to be rather efficient due to its specific structure. This derivative can form a quite stable allylic radical by abstraction of a hydrogen atom which accounts for these results.