The structure-activity relationship analysis has been performed for trans- and cis-hydroxycinnamic acids, to determine their theoretical antioxidant pharmacophore. Based on the detailed conformational studies, the most stable rotamers have been selected. We have analyzed the descriptors of four antioxidant mechanisms important in free radical scavenging: hydrogen atom transfer, sequential proton loss electron transfer, single electron transfer - proton transfer and transition metal chelation, based on the B3LYP/6-311++G(2d,2p) calculations in vacuum and polar media. The results explain the activity difference between cinnamic acid and its derivatives. The descending order of antioxidant potential is as follows: caffeic > sinapinic ~ ferulic > p-coumaric > o-coumaric > m-coumaric ~ phenol. The results have shown that transisomers indicate higher reactivity than cis- and may be considered as good antioxidants. It has been determined that the highest antioxidant ability is related to the hydroxyl group in para position, supported by planar structure and stability of radical forms. π-Type delocalization of unpaired electron on aromatic ring, double bond and para O-atom is the key to radical stabilization. The ortho-dihydroxy substitution in benzene ring positively influences the ability to neutralize free radicals and makes caffeic acid the antioxidant pharmacophore of hydroxycinnamic acids.

Melanoma is one of the most aggressive forms of skin cancer and is characterized by high metastatic potential. Despite improvements in early diagnosis and treatment, the mortality rate among metastatic melanoma patients continues to represent a significant clinical challenge. Therefore, it is imperative that we search for new forms of treatment. Trametes versicolor is a mushroom commonly used in Chinese traditional medicine due to its numerous beneficial properties. In the present work, we demonstrate T. versicolor fruiting body and mycelium ethanol extracts exhibit potent cytotoxic activity towards A375 (IC₅₀ = 663.3 and 114.5 μg/mL respectively) and SK- MEL-5 (IC₅₀ = 358.4 and 88.6 μg/mL respectively) human melanoma cell lines. Further studies revealed that T. versicolor mycelium extract induced apoptotic cell death and poly (ADP-ribose) polymerase cleavage, upregulated the expression of autophagy-associated marker LC3-II, increased the presentation of major histocompatibility complex II and expression of programmed death-ligand receptor, and inhibited cell migration in SK- MEL-5 cells. Therefore, our present findings highlight the therapeutic potential of T. versicolor mycelium extract for the treatment of melanoma and merit further study.

Phenolic acids constitute a family of natural compounds that can be found in a wide variety of plants and food. Among them only ferulic, p -coumaric, chlorogenic, and caffeic acids were recently investigated. There are no data about antioxidant activity of single molecules of fertaric, coutaric, caftaric, dactylifric, and neochlorogenic acids and prenyl caffeate. In a continuation of our attempts to clarify their antioxidant activity, we present herein in silico studies concerning four mechanisms of interaction of phenolic antioxidants with free radicals: hydrogen atom transfer (HAT), (sequential proton loss electron transfer (SPLET), single electron transfer followed by proton transfer, and transition metals chelation, determining several parameters such as bond dissociation enthalpy; proton affinity; adiabatic ionization potential; highest occupied molecular orbital, lowest unoccupied molecular orbital, singly occupied molecular orbital; spin density; stabilization energy (Δ E _ISO ); deprotonation enthalpy/energy (Δ H _acidity and Δ G _acidity ); and second-order perturbation energy E (2). We have proved that for all studied compounds the HAT mechanism was preferred in vacuum as well as in benzene and amyl acetate solvent media, whereas SPLET approach was significantly exposed especially in water. The most active antioxidants (according to the HAT approach) were compounds prenyl caffeate, methyl caffeate, and caffeic acid phenethyl ester, whereas the activity of trans and cis isomers of chicoric derivatives was related to the SPLET protocol. We also observed that trans isomers of caffeic, ferulic, and p -coumaric derivatives were not enough effective in all environments, when compared with other studied molecules. Moreover, we have noticed that the ortho position of the phenylic ring influenced profitably on antioxidant activity in all analyzed compounds.