Lipid oxidation is the major cause of the deterioration of fat-containing foods, especially those containing polyunsaturated fatty acids (PUFAs). Antioxidant additives of synthetic origin are added to matrices rich in PUFAs, such as sunflower oil (SO). However, there is controversy regarding their safety, and their low solubility in both water and fat has led to the search for new covalent modifications through lipophilicity. This work presents the synthesis of O-alkyl acid derivatives from ferulic and syringic acids and the study of their antioxidant capacity and effect on the thermoxidative degradation of SO. Antioxidant activities were evaluated by employing ferric reducing antioxidant power (FRAP) and 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging assays in a concentration range of 10-100 mu g mL(-1). The IC50 values for DPPH scavenging activity ranged from 15.61-90.43 mu g mL(-1). The results of the FRAP assay for both O-alkyl ferulic (3a-f) and syringic (5a-f) series revealed a "cut-off" effect on antioxidant activity in carbon five (C5). Thermoxidation study of additives 3b-c and 5b-c showed a decrease in the slope of extinction coefficients K-232 and K-270 in comparison with SOcontrol. Furthermore, 3c presented higher antioxidant activity than 3b and 1, with a power to decrease the thiobarbituric acid reactive species (TBARS) 6 times higher than SOcontrol at 220 degrees C. Additives 5b-c exerted a protective effect on the thermoxidation of SO. The results suggest that increasing lipophilic and thermal properties of antioxidants through O-alkyl acid derivatization is an effective strategy for accessing lipophilic antioxidant additives with potential use in food matrices. C1 [Forero-Doria, Oscar; Echeverria, Javier] Univ Santiago Chile, Fac Quim & Biol, Dept Ciencias Ambiente, Santiago 9170022, Chile. [Forero-Doria, Oscar] Univ Santo Tomas, Fac Ciencias, Dept Ciencias Bas, Talca 3460000, Chile. [Guzman, Luis; Zapata-Gomez, Felipe] Univ Talca, Fac Ciencias Salud, Dept Bioquim Clin & Inmunohematol, Talca 3460000, Maule, Chile. [Venturini, Whitney] Univ Catolica Maule, Fac Med, Dept Ciencias Preclin, Talca 3460000, Chile. [Duarte, Yorley] Univ Andres Bello, Fac Ciencias Vida, Ctr Bioinformat & Integrat Biol, Ave Republ 330, Santiago 8370146, Chile. [Camargo-Ayala, Lorena] Univ Talca, Lab Sintesis Organ & Act Biol LSO Act Bio, Inst Quim Recursos Nat, Casilla 747, Talca 3460000, Chile. [Echeverria, Cesar] Univ Atacama, Fac Med, Lab Biol Mol & Genom, ATACAMA OMICS, Copiapo 1532502, Chile. C3 Universidad de Santiago de Chile; Universidad Santo Tomas; Universidad de Talca; Universidad Catolica del Maule; Universidad Andres Bello; Universidad de Talca; Universidad de Atacama