In this review we examine the fascinating array of microbial and enzymatic transformations of ferulic acid. Ferulic acid is an extremely abundant, preformed phenolic aromatic chemical found widely in nature. Ferulic acid is viewed as a commodity scale, renewable chemical feedstock for biocatalytic conversion to other useful aromatic chemicals. Most attention is focused on bioconversions of ferulic acid itself. Topics covered include cinnamoyl side-chain cleavage; nonoxidative decarboxylation; mechanistic details of styrene formation; purification and characterization of ferulic acid decarboxylase; conversion of ferulic acid to vanillin; O-demethylation; and reduction reactions. Biotransformations of vinylguaiacol are discussed, and selected biotransformations of vanillic acid including oxidative and nonoxidative decarboxylation are surveyed. Finally, enzymatic oxidative dimerization and polymerization reactions are reviewed.

Alfa grass lignin obtained by the acetic acid/formic acid/water CIMV pulping process was characterized by FTIR and (1)H, (13)C-(1)H 2D HSQC, and (31)P NMR spectroscopies. Lignin samples purified by further dissolution/precipitation or basic hydrolysis steps were also analyzed. The CIMV alfa lignin is a mixture of low molar mass compounds (M(n) = 1500 g/mol) of SGH type with β-O-4 ether bonds as the major interunit linkage. The crude lignin contains fatty acids and residual polysaccharides. It also contains large amounts of acetate and hydroxycinnamates, mostly in the γ-position of β-O-4 interunit linkages. Although partial acetylation induced by the process cannot be excluded, the absence of aromatic acetates and acetylated polysaccharides in crude lignin demonstrates the mildness of the process. By combining smooth alkaline hydrolysis and dissolution/precipitation steps to the CIMV pulping, it is possible to produce a purified lignin with a composition and a structure quite analogous to that of the native polymer in the plant.

Ferulic acid was reacted with nitrite under acidic conditions to give complex mixtures of products. Chromatographic purification afforded products that were characterized by 1H- and 13C-NMR spectral analyses. The major fluorescent product was identified as 7-hydroxy-6-methoxy-1,2(4H)-benzoxazin-4-one along with 3-methoxy-4-hydroxybenzaldehyde (vanillin) and 2-methoxy-4,6-dinitrophenol. The structure of the unusual benzoxazinone was confirmed by its chemical degradation in base to methyl-2,4-dihydroxy-5-methoxybenzoic acid. Keywords: Ferulic acid; 7-hydroxy-6-methoxy-1,2(4H)-benzoxazin-4-one; 2-methoxy-4,6-dinitrophenol; vanillin