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
A series of polyamides based on Z‐octadec‐9‐enedioic acid, a bio‐based unsaturated monomer, and aliphatic‐, cycloaliphatic‐, or benzylic diamines were synthesized and characterized by 1H and 13C NMR analysis, size exclusion chromatography (SEC), DSC, and dynamic‐mechanical analysis (DMA). The high reaction temperature (250 °C) did not lead to the degradation of diacid unit double bonds and unsaturated polyamides were obtained. The aliphatic unsaturated polyamides are semi‐crystalline polymers of high molar mass, relatively flexible at room temperature. The cycloaliphatic unsaturated polyamides are semi‐crystalline or amorphous, present higher melting and glass transition temperatures and are much more rigid. The aliphatic and aliphatic–aromatic unsaturated polyamides present lower Tg and Tm as compared to their parent saturated polymers.magnified image
Biolignin, a wheat straw lignin produced by acetic acid/formic acid/water hydrolysis, was characterized by (31)P and (13)C-(1)H 2D NMR spectroscopy and by size-exclusion chromatography. Biolignin is a mixture of low molar mass compounds (Mn = 1660 g/mol) made up of S, G, and H units and of coumaric and ferulic acid units. β-5 and β-O-4 interunit linkages are partially acylated in the γ-position by acetate and p-coumarate groups. Deacylated samples with a low content of contaminants were obtained by combining alkaline hydrolysis and solvent extraction. The high phenolic OH content found by (31)P NMR reflects the presence of condensed aromatic units, such as 5-5 units. Reaction of purified lignin with ethanol and ethane-1,2-diol yielded esterified lignins much more soluble than Biolignin in common organic solvents. During this reaction, the secondary OH of β-O-4 linkages was simultaneously etherified. Phenol hydroxyethylation by 2-chloroethanol yielded samples containing only aliphatic hydroxyl groups.
Poly(β-alanine) was successfully synthesized by
an alternative
method, which is the direct polyamidation of β-alanine in ionic
liquids with triphenylphosphite as a condensing agent. It was found
that 1,3-dimethylimidazolium dimethylphosphate was the most suitable
reaction medium, in which a number-average degree of polymerization
up to 49.5 was obtained. It was shown that the method
is also applicable to the direct synthesis of polypeptides, for example,
poly(l-valine) and poly(l-isoleucine).
An efficient and environmentally benign synthesis of 3‐organoselenylchromenones was accomplished via iron(III) chloride/diorganyl diselenides‐promoted intramolecular 6‐endo‐dig cyclization of alkynyl aryl ketone derivatives. The cyclization reactions proceeded cleanly under mild reaction conditions, and the desired chromenone derivatives were smoothly isolated in good yields. The methodology proved to be highly regioselective, giving only the six‐membered regioisomers and was carried out using iron(III) chloride/diorganyl diselenide at room temperature and under ambient atmosphere, which could be considered an economic and eco‐friendly protocol.
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