Abstract
Various ferulic acid (FA) dimers occurring in plant cell walls, such as 8-5-, 8-O-4-, 5-5-, and 8-8-coupled dimers, are effective antioxidants and potential antimicrobials. It is necessary to access these diferulates as reference compounds to validate those isolated from plants. 3,6-bis(4-hydroxy-3-methoxyphenyl)-tetrahydrofuro-[3,4-c]furan-1,4-dione, a 8-8-coupled FA dilactone generated from ferulic acid via radical coupling, has been used to synthesize 8-8-coupled FA dimers although few reports investigated the distribution of products and mechanisms involved in the transformation of FA dilactone. In this work, the FA dilactone, obtained from FA by a peroxidase-catalyzed radical coupling, was reacted under various base/acid conditions. Effects of reaction conditions and workup procedures on the distribution of products were investigated by GC-MS. The isolated products from such treatments of FA dilactone were characterized by NMR. New derivatives of FA dimer including 2-(4-hydroxy-3-methoxybenzylidene)-3-(hydroxyl-(4-hydroxy-3-methoxyphenyl)methyl)succinic acid and 2-(bis(4-hydroxy-3-methoxyphenyl)-methyl)-succinic acid were produced from NaOH treatment. Another novel 8-8-coupled cyclic FA dimer, diethyl 6-hydroxy-1-(4-hydroxy-3-methoxyphenyl)-7-methoxy-1,2-dihydronaphthalene-2,3-dicarboxylate was identified in products from FA dilactone treated by dry HCl in absolute ethanol. Mechanisms involved in such transformations were proposed.
Highlights
Natural phenolics, the secondary metabolites extracted from plants, such as gallic acid [1] and ellagic acid [2], have been shown to have various biological activities including antioxidant, antimicrobial, and anticancer capacities [3,4]
In addition to monomeric Ferulic acid (FA), various FA dimers occurring in plant cell walls, including 5-5, 8-8, 8-5, and 8-O-4-coupled dehydrodimers [6] were demonstrated to have potential antimicrobial properties
FA dimers found in hydrolysate of corn Stover were showed to inhibit the growth of S. cerevisiae revealing that poacic acid, an 8-5-coupled decarboxylated ferulic acid dimer (8-5 DC), had the greatest antifungal activity with an IC50 of 111 μg/mL (324 μM) against S. cerevisiae
Summary
The secondary metabolites extracted from plants, such as gallic acid [1] and ellagic acid [2], have been shown to have various biological activities including antioxidant, antimicrobial, and anticancer capacities [3,4]. FA dimers found in hydrolysate of corn Stover were showed to inhibit the growth of S. cerevisiae revealing that poacic acid, an 8-5-coupled decarboxylated ferulic acid dimer (8-5 DC), had the greatest antifungal activity with an IC50 of 111 μg/mL (324 μM) against S. cerevisiae. This inhibition is comparable to that of the widely used fungicides picoxystrobin (IC50 of 308 μM) or polyoxin D (IC50 of 340 μM) and substantially lower than that of the primary fungicide used in organic agriculture, copper sulfate (IC50 of 2.4 mM) [7]. IInntthhiisswwoorrkk,, FFAA ddiillaaccttoonnee wwaass rreeaacctteedd uunnddeerr vvaarriioouuss ccoonnddiittiioonnss.
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