Study On Antioxidant Property And Selective Synthesis Of Dehydrodiferulates

With the development trendence,that green and sustainsable energy is gradually replacing fossil energy,the research on efficient and value-added utilization of biomass resources has become a hot topic.Maize bran produced in the production of cornstarch contains many phenolic compounds including ferulic acid（FA）with good physiological functions.As a phenolic acid compound,ferulic acid is widely used in food,medicine,nutrition and health care products and cosmetics.In this study,the dehydrogenation dimers of FA and their ethyl esters were synthesized from commercially available FA and ethyl ferulate（FE）.In addition,their antioxidant capacibility and selective preparation were investigated.The proposed here was a preparation method of 8-5 DC DFA dimer based on a green process with scale-up potential,providing with scientific sound basis for value-added utilization of industry maize bran.First of all,the current known 11 kinds of ferulic acid dimers and 8 kinds of ethyl ferulate dimers were synthesized in laboratory,and all the dimers were tested with TEAC method（Trolox equivalent antioxidant capacity）and DPPH method（2,2’-diphenyl-1-picrylhydrazyl）on their antioxidant properties to establish the antioxidant activity relationship with their structures.The results showed that all ferulic acid and ethyl ferulic acid dimer have stronger free radical scavenging ability than the reference Trolox.It also found that 8-8-lactone DC and 8-5 DC DFA showed the best antioxidant activity（with TEAC value 2.88 and 2.31）.Based on the molar concentration,ferulic acid dehydrodimers had better antioxidant activity than corresponding monomers except for 8-8-dilactone,8-5-c DFA and 8-5-c DEF.Secondly,the potential for selectively synthesizing dimers of ethyl ferulate（EF）with various biomimetic oxidants under various conditions was investigated.Identification and quantitation of oxidative coupled dimers from EF with GC-MS indicated that the peroxidasecatalyzed oxidation of EF produced the best yield of 8-5-coupled dehydrogenation dimer 8-5-c DEF in buffer of p H 5.5 with 90% of conversion rate and 80% of total dimers.The addition of organic co-solvents to the enzyme-catalyzed system resulted in lower yields of total dimers.Among the reaction systems with metal-containing oxidant,Ag₂O is the best choice for preparing the 8-5-cDEF with the highest yield of 56%.Mn（OAc）₃ in Et OAc produced 8-O-4-coupled dehydrodimer 8-O-4 DEF with 11.4% yield,the best reported for 8-O-4 coupled dimer to date.The yield of 8-8-coupled dehydrodimer 8-8-o DEF generated in Mn（OAc）3-pyridine system was 31%,making the system the best choice for the preparation of 8-8-o DEF.The yield of 5-5-coupled dehydrodimer 5-5 DEF was 21.6% when CuCl（OH）-TMEDA is used in CH₂Cl₂ solvent,which is the best condition for preparation of 5-5 DEF.Therefore,we demonstrated that certain types of diferulates could be synthesized from oxidative coupling reactions of ferulate when an appropriate oxidation system is chosen.Finally,a process for preparing 8-5 DC DFA with good antioxidant properties was explored using ferulic acid as raw material,and the preparation process was optimized.Thus 8-5-c DFA was made by a peroxidase-catalyzed biomimetic oxidation system,then decarboxylated to produce the target product 8-5 DC DFA.The ideal procedure for FA coupling was as following: the ferulic acid was dissolved in NaHCO₃ solution and kept in solution with pH 6.6 for complete dissolusion.Then 1.3 equivalent of H₂O₂ and 0.5 mg of horseradish peroxidase（HRP）per g of FA were added while maintaining p H at 6.6 with addition of 0.1 M acetic acid.And the reaction mixture was stirred for 4 hours producing 8-5-c DFA with over 60% yield.The best conditions for decarboxylation process found was as follows: the resulted crude product of 8-5-c DFA from above mentioned step was treated directly at 70℃ for 1 hour resulting in 8-5 DC DFA with over 90% yield.In summary,we established the antioxidant activity relationship of dehydrodimers dimers from ferulic acid and its ethyl esters with their structures.The potential of selective synthesis of dehydrogenation dimers from ethyl ferulate was demonstrated under various biomimetic oxidative system.With commercially available ferulic acid as raw material,we designed a synthetic route to production of the good antioxidant 8-5 DC DFA and optimized its conditions being of environmental friendly,green,and scale up potential.All those efforts provide a new idea and scientific basis for value-added development and utilization of industrial maize bran.