Development and Scaling-Up of the Fragrance Compound 4‑Ethylguaiacol Synthesis via a Two-Step Chemo-Enzymatic Reaction Sequence

The transformation of (abundant) oxygenated biomass-derived building blocks via chemo-enzymatic methods is a valuable concept for accessing useful compounds, as it combines the high selectivity of enzymes and the versatility of chemical catalysts. In this work, we demonstrate a straightforward combination of a phenolic acid decarboxylase (PAD) and palladium on charcoal (Pd/C) that affords the flavor compound 4-ethylguaiacol from ferulic acid. The use of a two-phase system proved to be advantageous in terms of enzyme activity, stability, and volumetric productivity and allows us to carry out the hydrogenation step directly in the organic layer containing exclusively the intermediate, vinylguaiacol. The enzymatic decarboxylation step in the biphasic system afforded 89% conversion of 100 mM (19 g L^–1) ferulic acid with an isolated yield of 75%. By extracting 4-vinylguaiacol continuously into the organic phase, conversion was enhanced to 92% using 170 mM (33 g L^–1) ferulic acid, which was only possible in the continuous extraction and distillation setup developed. The reaction cascade (PAD–Pd/C) is demonstrated at gram scale, affording the target product 4-ethylguaiacol (1.1 g) in 70% isolated yield in a two-step two-pot process. The enzymatic step was characterized in detail to overcome major constraints, and the process favorably compares in terms of the environmental impact with traditional approaches

Carbon Nanotubes as Activating Tyrosinase Supports for the Selective Synthesis of Catechols

A series of redox catalysts based on the immobilization of tyrosinase on multiwalled carbon nanotubes has been prepared by applying the layer-by-layer principle. The oxidized nanotubes (ox-MWCNTs) were treated with poly­(diallyl dimethylammonium chloride) (PDDA) and tyrosinase to yield ox-MWCNTs/PDDA/tyrosinase <b>I</b>. Catalysts <b>II</b> and <b>III</b> have been prepared by increasing the number of layers of PDDA and enzyme, while <b>IV</b> was obtained by co-immobilization of tyrosinase with bovine serum albumin (ox-MWCNTs/PDDA/BSA-tyrosinase). Attempts to covalently bind tyrosinase provided weakly active systems. The coating of the enzyme based on the simple layer-by-layer principle has afforded catalysts <b>I–III</b>, with a range of activity from 21 units/mg (multilayer, <b>II</b>) to 66 units/mg (monolayer, <b>I</b>), the best system being catalyst <b>IV</b> (80 units/mg). The novel catalysts were fully characterized by scanning electron microscopy and atomic force microscopy, showing increased activity with respect to that of the native enzyme. These catalysts were used in the selective synthesis of catechols by oxidation of <i>meta</i>- and <i>para</i>-substituted phenols in an organic solvent (CH₂Cl₂) as the reaction medium. It is worth noting that immobilized tyrosinase was able to catalyze the oxidation of very hindered phenol derivatives that are slightly reactive with the native enzyme. The increased reactivity can be ascribed to a stabilization of the immobilized tyrosinase. The novel catalysts <b>I</b> and <b>IV</b> retained their activity for five subsequent reactions, showing a higher stability in organic solvent than under traditional buffer conditions

Chemical investigations of male and female leaf extracts from <i>Schinus molle</i> L.

<p>The pepper-tree <i>Schinus molle</i> is an evergreen ornamental plant with various and diversified list of medical uses. In this article we analysed the chemical composition of male and female leaves of this plant during the off-flowering and flowering seasons. The leaf extracts were obtained by using a sequential extraction with solvents of different polarities and the chemical composition was investigated by GC-MS. The results showed a total of twenty-three components, <b>in which elemol is the most abundant constituent followed by bicyclogermacrene, γ-eudesmol, α-eudesmol, β-eudesmol and isocalamendiol</b>. The petroleum ether and diethyl ether extracts from male and female flowering and off-flowering leaves consisted of sesquiterpene hydrocarbons as a major constituent followed by monoterpene hydrocarbons, while the acetone extracts showed a different composition. The obtained results show differences in the chemical composition between male and female and flowering and not flowering.</p