Mild and efficient oxidation of alcohols with sodium periodate catalyzed by polystyrene-bound Mn(III)porphyrin

Mild and efficient oxidation of primary and secondary alcohols with sodium periodate catalyzed by Mn(TPyP), [manganese(III)tetra(4-pyridyl)porphyrin], supported on chloromethylated polystyrene, [Mn(TPyP)-CMP], at room temperature were reported. This catalyst can be reused consecutively four times in the oxidation of 4-chlorobenzyl alcohol in 97% yield without significant loss of its activity.     

Cytochrome P-450 model reactions: efficient and highly selective oxidation of alcohols with tetrabutylammonium peroxymonosulfate catalyzed by Mn-porphyrins

A novel biomimetic method for rapid oxidation of a wide range of benzylic, allylic, aliphatic, primary and secondary alcohols to the related aldehydes and ketones using Bu(4)NHSO(5) catalyzed by Mn(TPP)OAc/pyridine system with high to excellent yields and excellent selectivity has been developed. The high turnover rates obtained in this catalytic system represent a high efficiency and also relative stability of Mn-porphyrin catalyst towards oxidative degradation. The presence of an electron-withdrawing group on the phenyl ring of both benzyl alcohol and porphyrin ligand increases the reactivity of substrate as well as catalytic activity of Mn-porphyrin catalyst in the oxidation reaction.     

Highly efficient selective oxidation of alcohols to carbonyl compounds catalyzed by ruthenium (III) meso-tetraphenylporphyrin chloride in the presence of molecular oxygen

Efficient selective oxidation of alcohols to carbonyl compounds by molecular oxygen with isobutyraldehyde as oxygen acceptor in the presence of metalloporphyrins has been reported. Ruthenium (III) meso-tetraphenylporphyrin chloride (Ru(TPP)Cl) showed excellent activity and selectivity for oxidation of various alcohols under mild conditions. Moreover, different factors influencing alcohols oxidation, for example, catalyst, solvent, temperature, and oxidant, have been investigated. In large-scale oxidation of benzyl alcohol, the isolated yield of benzaldehyde of 89% was observed.     

Biomimetic degradation of lignin and lignin model compounds by synthetic anionic and cationic water soluble manganese and iron porphyrins.

The biomimetic oxidation of 5-5' condensed and diphenylmethane lignin model compounds with several water soluble anionic and cationic iron and manganese porphyrins in the presence of hydrogen peroxide is reported. The oxidative efficiency of manganese and iron meso-tetra(2,6-dichloro-3-sulphonatophenyl) porphyrin chloride (TDCSPPMnCl and TDCSPPFeCl, respectively), meso-tetra-3-sulphonatophenyl porphyrin chloride (TSPPMnCl) and manganese meso-tetra(N-methylpyridinio)porphyrin pentaacetate (TPyMePMn(CH3COO)5) was compared on the basis of the oxidation extent of the models tested. Manganese porphyrins were found more effective in degrading lignin substructures than iron ones. Among them the cationic TPyMePMn (CH3COO)5, never used before in lignin oxidation, showed to be the best catalyst. The catalytic activity of porphyrins in hydrogen peroxide oxidation of residual kraft lignin was also investigated. The use of quantitative 31P NMR allowed the focusing on the occurrence of different degradative pathways depending on the catalyst used. TPyMePMn(CH3COO)5 was able to perform the most extensive degradation of the lignin structure, as demonstrated by the decrease of aliphatic hydroxyl groups and carboxylic acids. Noteworthy, no significant condensation reactions occurred during manganese porphyrins catalyzed oxidations of residual kraft lignin, while in the presence of iron porphyrins a substantial increase of condensed substructures was detected.     

Parallel mechanistic studies on the counterion effect of manganese salen and porphyrin complexes on olefin epoxidation by iodosylarenes

Counterions of manganese(III) porphyrin complexes influence diastereoselectivity in cis-stilbene epoxidation and product distribution in cyclohexene epoxidation markedly. In the epoxidation of cis-stilbene by iodosylbenzene carried out in a solvent mixture of CH(3)CN and CH(2)Cl(2), trans-stilbene oxide is the major product in the reaction of manganese complexes bearing a ligating anion (i.e., Cl(-)), whereas cis-stilbene oxide is the dominant product in the reactions of manganese complexes bearing a poorly-ligating anion (i.e., CF(3)SO(4)(-)). In cyclohexene epoxidation, the yields of allylic oxidation products such as cyclohexenol and cyclohexenone are higher when the counterion of the manganese catalysts is Cl(-) than when the counterion is CF(3)SO(4)(-). The product selectivities are also dependent on the nature of iodosylarenes and the axial and porphyrin ligands of the manganese porphyrin catalysts. The observation that product selectivities are different depending on the iodosylarenes may indicate the involvement of multiple oxidants in oxygen atom transfer reactions. These results are compared with those observed in manganese salen-catalyzed epoxidation of olefins by iodosylarenes.     

Addition of veratryl alcohol oxidase activity to manganese peroxidase by site-directed mutagenesis

Manganese peroxidase and lignin peroxidase are ligninolytic heme-containing enzymes secreted by the white-rot fungus Phanerochaete chrysosporium. Despite structural similarity, these peroxidases oxidize different substrates. Veratryl alcohol is a typical substrate for lignin peroxidase, while manganese peroxidase oxidizes chelated Mn2+. By a single mutation, S168W, we have added veratryl alcohol oxidase activity to recombinant manganese peroxidase expressed in Escherichia coli. The kcat for veratryl alcohol oxidation was 11 s-1, Km for veratryl alcohol approximately 0.49 mM, and Km for hydrogen peroxide approximately 25 microM at pH 2.3. The Km for veratryl alcohol was higher and Km for hydrogen peroxide was lower for this manganese peroxidase mutant compared to two recombinant lignin peroxidase isoenzymes. The mutant retained full manganese peroxidase activity and the kcat was approximately 2.6 x 10(2) s-1 at pH 4.3. Consistent with relative activities with respect to these substrates, Mn2+ strongly inhibited veratryl alcohol oxidation. The single productive mutation in manganese peroxidase suggested that this surface tryptophan residue (W171) in lignin peroxidase is involved in catalysis.     

Valence-tautomerism in high-valent iron and manganese porphyrins

Iron and manganese hemes are "high-valent" when the valence state of the metal exceeds III. Redox chemistry of the high valent metal complexes involves redistribution of holes and electrons over the metal ion and the porphyrin and axial ligands, defined as valence tautomerism. Thus, catalytic pathways of heme-containing biomolecules such as peroxidases, catalases and cytochromes P450 involve valence tautomerism, as do pathways of biomimetic oxygen transfer catalysis by manganese porphyrins, robust catalysts with potential commercial value. Determinants of the site of electron abstraction are key to understanding valence tautomerism. In model systems, metal-centered oxidation is supported by hard anionic axial ligands that are also strongly pi-donating, such as oxo, aryl, bix-methoxy and bis-fluoro groups. Manganese(IV) is more stable than iron(IV) and metal-centered one-electron oxidations occur with weaker pi-donating axial ligands such as bisazido, -isocyanato, -hypochlorito and bis chloro groups. Virtually all known high-valent iron porphyrin complexes oxidized by two-electrons above the ferric state are coordinated by the strongly pi-donating oxo or nitrido ligands. In all well-characterized oxo complexes, iron is in the ferryl state and the second oxidizing equivalent resides on the porphyrin. Complexes with iron(V) have not been definitively characterized. One-electron oxidation of oxomanganese(IV) porphyrin complexes gives the oxomanganese(IV) porphyrin pi-cation redicals. In aqueous solution, oxidation of Mn(III) complexes of tetra cationic N-methylpyridiniumylporphyrin isomers by monooxygen donors yields a transient oxomanganese(V) species.     

Galactose oxidase and alcohol oxidase: Scope and limitations for the enzymatic synthesis of aldehydes

The utility of both galactose oxidase and alcohol oxidase for alcohol-to-aldehyde oxidation has been investigated, from a synthetic point of view. The speed of reaction and degree of conversion has been measured for 29 different primary alcohols. The two oxidative enzymes show complementary synthetic use, i.e. galactose oxidase for galactose-derived polyols and alcohol oxidase for aliphatic mono- and diols. Alcohol oxidase has been successfully used in combination with the aldolase DERA in a two-step, one-pot reaction cascade.     

Polystyrene-bound Mn(T4PyP): A highly efficient and reusable catalyst for biomimetic oxidative decarboxylation of carboxylic acids with sodium periodate

In this report, highly efficient oxidative decarboxylation of carboxylic acids with sodium periodate catalyzed by a supported manganese(III) porphyrin is described. In the presence of manganese(III) tetra(4-pyridyl)porphyrin supported on cross-linked chloromethylated polystyrene, [Mn(T4PyP)-CMP], as catalyst, carboxylic acids were converted to their corresponding carbonyl compounds via oxidative decarboxylation with sodium periodate using imidazole as axial ligand. The oxidation of anti-inflammatory drugs such Indomethacin and Ibuprofen was carried out successfully and the decarboxylated products were obtained. This catalyst can be reused several times without loss of its catalytic activity in the oxidation reactions.     

Allylic or benzylic stabilization is essential for catalysis by bacterial benzyl alcohol dehydrogenases.

Benzyl alcohol dehydrogenase from Acinetobacter calcoaceticus (AC-BADH) and TOL plasmid-encoded benzyl alcohol dehydrogenase from Pseudomonas putida (TOL-BADH) have previously been shown to oxidize a variety of aromatic alcohols but not aliphatic substrates. Here, we have expressed the genes for AC-BADH and TOL-BADH in Escherichia coli, purified the resulting over-expressed enzymes, and shown that each is an effective catalyst of both benzylic and allylic alcohol oxidation, but not of oxidation of nonallylic analogs. Enzyme specificity (kcat/Km) for both enzymes was higher with an aliphatic, allylic alcohol (3-methyl-2-buten-1-ol) than with benzyl alcohol. These results suggest that bacterial benzyl alcohol dehydrogenases use the resonance stabilization provided by allylic and benzylic alcohols to promote catalysis.     

Bioelectrochemical fuel cell and sensor based on a quinoprotein,alcohol dehydrogenase

A biofuel cell, yielding a stable and continuous low-power output, based on the enzymatic oxidation of methanol to formic acid has been designed and investigated. The homogeneous kinetics of the electrochemically-coupled enzymatic oxidation reaction were investigated and optimized. The biofuel cell also functioned as a sensitive method for the detection of primary alcohols. A method for medium-scale preparation of the enzyme alcohol dehydrogenase [alcohol:(acceptor) oxidoreductase, EC 1.1.99.8] is described.     

The metal complexes of N-confused porphyrin as heme model compounds

Recently, metal complexes of the isomers and analogs of porphyrin have become important model compounds for heme enzymes and proteins. While the chemistry of metalloporphyrins as heme models still attracts attention, the isomers and analogs of porphyrins provide insight into the biological choice of porphine as the macrocycle of choice and also help model reactive intermediates, such as high valent oxidation states. In this mini-review, we discuss the heme-relevant chemistry of N-confused porphyrin, an isomer of porphyrin with an inverted pyrrole ring, and focus on the chemistry of manganese, iron, and cobalt. The metallation chemistry of this macrocycle is more diverse than normal porphyrin, and involves tautomerization, C-H bond activation, the Lewis basicity of the external nitrogen, and issues with nucleophilic sensitivity. Despite the challenges posed by N-confused porphyrin, significant progress has been made toward generating heme-model complexes with this macrocycle.     

Selective oxidation of steroidal allylic alcohols

Pyridinium chlorochromate in CH₂Cl₂ containing pyridine (2%) at 2—3°C has been found to effect the high yield selective oxidation of the hydroxyl function of a number of steroidal allylic alcohols. Under these conditions the oxidation of cholest-4-cn-3β-ol to the corresponding ketone was effected in 92% yield. Only the allylic hydroxyl function of 5α-cholest-8(14)-ene-3β,15α-diol, 5α-cholest-8(14)ene-3β,15β-diol and 5α-cholest-8(14)-ene-3β,7β-diol was oxidized under these conditions to give the corresponding α,β-unsaturated ketones in high yields. 5α-Cholest-8(14)-ene-3β,7α,15α-triol gave 5α-cholest-8(14)-ene-3β,7α-diol-15-one in 82% yield. Attempted oxidations of the 5α-cholestan-3β,15α-diol and 5α-cholest-7-ene-3β,15α-diol, both lacking an allylic hydroxyl function, under these conditions, were unsuccessful. Selective oxidation of the allylic alcohol function of 5α-cholest-8(14)-ene-3β,15β-diol using activated manganese dioxide gave 5α-cholest-8(14)-en-3β-ol-15-one in high yield while oxidation of the corresponding 15α-hydroxy epimer using manganese dioxide was unsuccessful.     

Electrophoretic analysis of substrate specificity of wheat alcohol dehydrogenases]

Electrophoresis in polyacrylamide gel slabs has been used to study the isoform composition and substrate specificity of alcohol dehydrogenases in the embryo and young seedlings of the diploid wheat Triticum monococcum L., the tetraploid T. dicoccon (Schrank) Schuebl and the hexaploid T. spelta L. Three alcohol dehydrogenases of different substrate specificity and developmental pattern were distinguished: a) the NAD-dependent alcohol dehydrogenase, catalyzing the oxidation of different primary and secondary aliphatic and aromatic alcohols, as well as certain compounds with several hydroxyl groups (tris, triethanolamin) and revealing, after electrophoresis, one major band in the diploid wheat and three bands in both polyploid wheats; b) the NADP-dependent aromatic alcohol dehydrogenase (substrate--cinnamic alcohol), revealing, after electrophoresis, one major fast moving band in the diploid wheat and two bands in polyploid wheats; c) an aromatic alcohol dehydrogenase (2-3 bands after electrophoreis) with no specificity to the cofactors (NAD or NADP).     

Characterisation of recombinant human fatty aldehyde dehydrogenase: implications for Sjögren-Larsson syndrome

Fatty aldehyde dehydrogenase (FALDH) is an NAD+-dependent oxidoreductase involved in the metabolism of fatty alcohols. Enzyme activity has been implicated in the pathology of diabetes and cancer. Mutations in the human gene inactivate the enzyme and cause accumulation of fatty alcohols in Sj?gren-Larsson syndrome, a neurological disorder resulting in physical and mental handicaps. Microsomal FALDH was expressed in E. coli and purified. Using an in vitro activity assay an optimum pH of approximately 9.5 and temperature of approximately 35 degrees C were determined. Medium- and long-chain fatty aldehydes were converted to the corresponding acids and kinetic parameters determined. The enzyme showed high activity with heptanal, tetradecanal, hexadecanal and octadecanal with lower activities for the other tested substrates. The enzyme was also able to convert some fatty alcohol substrates to their corresponding aldehydes and acids, at 25-30% the rate of aldehyde oxidation. A structural model of FALDH has been constructed, and catalytically important residues have been proposed to be involved in alcohol and aldehyde oxidation: Gln-120, Glu-207, Cys-241, Phe-333, Tyr-410 and His-411. These results place FALDH in a central role in the fatty alcohol/acid interconversion cycle, and provide a direct link between enzyme inactivation and disease pathology caused by accumulation of alcohols.     

Isolation ofCaenorhabditis elegans mutants lacking alcohol dehydrogenase activity

Alcohol dehydrogenase (ADH) and the genes encoding this enzyme have been studied intensively in a broad range of organisms. Little, however, has been reported on ADH in the free-living nematodeCaenorhabiditis elegans. Extracts of wild-typeC. elegans contain ADH activity and display a single band of activity on a native polyacrylamide gel. Reaction rate for alcohol oxidation is more rapid with higher molecular weight alcohols as substrate than with ethanol. Primary alcohols are preferred to secondary alcohols.C. elegans is sensitive to allyl alcohol, a compound that has been used to select for ADH-null mutants of several organisms. Allyl alcohol-resistant mutant strains were selected from ethylmethanesulfonate (EMS)-mutagenized nematode populations. ADH activity was measured in extracts from eight of these strains and was found to be low or nondetectable. These results form a basis for molecular and genetic characterization of ADH expression inC. elegans.     

Sjögren-Larsson syndrome: accumulation of free fatty alcohols in cultured fibroblasts and plasma

Sj?gren-Larsson syndrome (SLS) is an inherited disorder associated with deficient oxidation of long-chain aliphatic alcohols. Previous studies have reported modest elevations in total (free + esterified) fatty alcohols in SLS, but free fatty alcohols have not been selectively measured, in part because of their low concentrations in most tissues and the presence of trace fatty alcohol contaminants in some solvents used for their analysis. We adapted methods to measure free fatty alcohols in cultured cells and plasma that minimize exogenous alcohol contamination. Fatty alcohols were analyzed as acetate derivatives, using capillary column gas chromatography. By this method, cultured skin fibroblasts from SLS patients were found to have 7- and 8-fold elevations in the mean content of hexadecanol (16:0-OH) and octadecanol (18:0-OH), respectively. The mean plasma 16:0-OH and 18:0-OH concentrations in SLS patients (n = 11) were 9- and 22-fold higher than in normal controls, respectively. In SLS fibroblasts, most of the fatty alcohol (59%) that accumulated was free rather than esterified alcohol, whereas free alcohol accounted for 23% of the total alcohol in normal cells. These results indicate that elevations in free fatty alcohols provide a sensitive marker for the enzymatic defect in SLS. The ability to measure free fatty alcohols in cultured cells and plasma should prove useful for investigations of normal fatty alcohol metabolism and the deranged metabolism in SLS.     

Enantioselective oxidation of secondary alcohols by quinohaemoprotein alcohol dehydrogenase from Comamonas testosteroni

Purified and reconstituted quinohaemoprotein alcohol dehydrogenase (QH-EDH) from Comamonas testosteroni is shown to oxidize secondary alcohols enantioselectively. The products formed during the oxidation of secondary alcohols were positively identified as the corresponding ketones. In the oxidation of chiral secondary n-alkyl alcohols a preference of the enzyme for the S(+)alcohols was found. The apparent kinetic parameters (K_m and K_max) for a range of n-alkyl alcohols depend on the length of the alcohol chain and the location of the hydroxyl function in the chain. The enzyme is stable up to a temperature of 37 °C. Above this temperature the activity is irreversibly lost. The pH optimum of the enzyme in the conversion of secondary alcohols is 7.7.     

Microbial oxidation of methanol: Properties of crystallized alcohol oxidase from a yeast, Pichia sp

Alcohol oxidase (alcohol:oxygen oxidoreductase) was crystallized from a methanolgrown yeast, Pichia sp. The crystalline enzyme is homogenous as judged from polyacrylamide gel electrophoresis. Alcohol oxidase catalyzed the oxidation of short-chain primary alcohols (C₁ to C₆), substituted primary alcohols (2-chloroethanol, 3-chloro-1-propanol, 4-chlorobutanol, isobutanol), and formaldehyde. The general reaction with an oxidizable substrate is as follows: Primary alcohol + O₂ → aldehyde + H₂O₂ Formaldehyde + O₂ → formate + H₂O₂. Secondary alcohols, tertiary alcohols, cyclic alcohols, aromatic alcohols, and aldehydes (except formaldehyde) were not oxidized. The K_m values for methanol and formaldehyde are 0.5 and 3.5 mm, respectively. The stoichiometry of substrate oxidized (alcohol or formaldehyde), oxygen consumed, and product formed (aldehyde or formate) is 1:1:1. The purified enzyme has a molecular weight of 300,000 as determined by gel filtration and a subunit size of 76,000 as determined by sodium dodecyl sulfate-gel electrophoresis, indicating that alcohol oxidase consists of four identical subunits. The purified alcohol oxidase has absorption maxima at 460 and 380 nm which were bleached by the addition of methanol. The prosthetic group of the enzyme was identified as a flavin adenine dinucleotide. Alcohol oxidase activity was inhibited by sulfhydryl reagents (p-chloromercuribenzoate, mercuric chloride, 5,5′-dithiobis-2-nitrobenzoate, iodoacetate) indicating the involvement of sulfhydryl groups(s) in the oxidation of alcohols by alcohol oxidase. Hydrogen peroxide (product of the reaction), 2-aminoethanol (substrate analogue), and cupric sulfate also inhibited alcohol oxidase activity.     

Substrate specificity and properties of the aryl-alcohol oxidase from the ligninolytic fungus Pleurotus eryngii.

The production in a 5-1 fermenter of the extracellular enzymes laccase and aryl-alcohol oxidase by the fungus Pleurotus eryngii was studied. The latter enzyme has been purified 50-fold by Sephacryl S-200 and Mono Q chromatography. Purified aryl-alcohol oxidase is a unique flavoprotein with 15% carbohydrate content, a molecular mass of 72.6 kDa (SDS/PAGE) and a pI of 3.9. The enzyme presents wide specificity, showing activity on benzyl, cinnamyl, naphthyl and aliphatic unsaturated alcohols. Neither activity nor inhibition of veratryl alcohol oxidation was found with saturated alcohols, but competitive inhibition was produced by aromatic compounds which were not aryl-alcohol oxidase substrates, such as phenol or 3-phenyl-1-propanol. From these results, it was apparent that a double bond conjugated with a primary alcohol is necessary for substrate recognition by aryl-alcohol oxidase, and that activity is increased by the presence of additional conjugated double bonds and electron donor groups. Both affinity and maximal velocity during enzymic oxidation of methoxybenzyl alcohols were affected in a similar way by ring substituents, increasing from benzyl alcohol (Km = 0.84 mM, Vmax = 52 U/mg) to 4-methoxybenzyl alcohol (Km = 0.04 mM, Vmax = 208 U/mg). Aryl-alcohol oxidase presents also a low oxidase activity with aromatic aldehydes, but the highest activity was found in the presence of electron-withdrawing groups.