Veratryl aldehyde oxidation

Fig. 5.5 Oxidation of veratryl alcohol to a radical cation that can oxidize other substrates (RX) or can be further oxidized to give veratryl aldehyde...

LiP catalyzes the oxidation of 3,4-dimethoxybenzyl alcohol (veratryl alcohol) to veratryl aldehyde. Since this reaction can be easily followed at 310 nm, it is the basis for the standard assay for this enzyme (26,27). The enzyme exhibits normal saturation kinetics for both veratryl alcohol and H202 (28,43). Steady-state kinetic results Indicate a ping-pong mechanism in which H202 first oxidizes the enzyme and the oxidized intermediate reacts with veratryl alcohol (43). The enzyme has an extremely low pH optimum ( 2.5) for a peroxidase (43,44) however, the rate of formation of compound I (kx, Fig. 2) exhibits no pH dependence from 3.0-7.0 (45,46). Addition of excess veratryl alcohol at pH 3.0 results in the rapid conversion of... 

Another iron porphyrin complex with 5,10,15,20-tetrakis(2, 6 -dichloro-3 -sulfonatophenyl)porphyrin was applied in ionic liquids and oxidized veratryl alcohol (3,4-dimethoxybenzyl alcohol) with hydrogen peroxide in yields up to 83% to the aldehyde as the major product [145]. In addition, TEMPO was incorporated via... 

In this scheme veratryl alcohol was viewed to be metabolized by the combined action of oxidative systems (the lignin peroxidase and possibly other active oxygen species) and reductive conversions (aldehyde and quinone reductions). A possible route via veratric acid was discounted because both veratraldehyde and veratric acid were not substrates for the lignin peroxidase under the condition studied. However, both veratraldehyde and veratric acid were rapidly and quantitatively reduced by ligninolytic cultures of P. chrysosporium (21). 

Lignin peroxidase activity, (i.e., peroxide-dependent oxidation of veratryl alcohol at pH 3) was not detected over the 30 days tested, while laccase appeared at day 7. Culture medium from day 7 onwards could also oxidize veratryl alcohol to aldehyde with concomitant conversion of oxygen to hydrogen peroxide. This activity, which was optimal at pH 5.0, was named veratryl alcohol oxidase (VAO). The extracellular oxidative enzyme activities (laccase and veratryl alcohol oxidase) could be separated by ion-exchange chromatography (Figure 2). Further chromatography of the coincident laccase and veratryl alcohol oxidase (peak 2), as described elsewhere (25) resulted in the separation of two veratryl alcohol oxidases from the laccase. 

Upon acylation of some benzyl carbonyl compounds (25, R = H, Me 51, R = OH) dibenzo[a,tropylium salts 65 have been isolated in low yields (5-15 %) along with the major products, 2-benzopyrylium salts. Veratryl acetone 25 (R = Me) as well as homoveratric aldehyde 25 (R = H) (or carboxonium ions 31 which are formed from them) may undergo an oxidative a-cleavage, resulting in the benzyl cation 64. The formation of the same cation from homoveratric acid 51 is the result of decarbonylation of the acylium ion 63. Further interaction of the benzyl cation 64 with the substrate, followed by cyclization and oxidation, results in the polycyclic tropylium salts 65 (82ZOR589). 

LiP catalyzes the degradation of lignin. The enzyme is commonly assayed by its ability to oxidize veratryl alcohol to a diffusible veratryl radical cation that can either oxidize other substrates or is further converted by a second electron removal to the aldehyde (Fig. 5.5). This reaction is thought to mimic the in vivo operation of... 

Kervinen et al. (2005) investigated a homogeneous catalytic reaction, namely, the oxidation of veratryl alcohol to its aldehyde in the liquid phase. In this case, UV-vis spectroscopy, performed by immersing a fiber probe in the reacting medium, allowed detection of changes in the Co (salen) catalyst as well as monitoring of product formation. 

Oxidation with ceric nitrate has been developed as a new degradative procedure in the study of bisbenzylisoquinoline alkaloids. This reagent splits lau-danosine to veratric aldehyde and the N-methyl-6,7-dimethoxy-3,4-dihy-droisoquinolinium ion, isolated as veratryl alcohol and N-methyl-3,4-dimethoxytetrahydroisoquinoline after reduction. In the same way, tetrandrine, hernandezine, and O-methylmicranthine have been degraded to the bis-tetra-hydroisoquinolines (48 R = H), (48 R = OMe), and (49), the second product in each case being the diphenyl ether (50). ... 

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