Pankaj Kumar Chaurasia

Syntheses of Aromatic Aldehydes by Laccase of Pleurotus ostreatus MTCC-1801

Abstract Selective bioconversion of the aromatic methyl group to its aldehyde group is one of the best applications of the laccases. In the present communication, crude laccase, obtained from the liquid culture medium of the fungal strain Pleurotus ostreatus MTCC-1801, has been used for the selective bioconversion of toluene, 3-nitrotoluene, 4-nitrotoluene, 2-fluorotoluene, 4-fluorotoluene, 2-chlorotoluene, 3-chlorotoluene, 4-chlorotoluene, and 3,4-dimethoxytoluene to benzaldehyde, 3-nitrobenzaldehyde, 4-nitrobenzaldehyde, 2-fluorobenzaldehyde, 4-fluorobenzaldehyde, 2-chlorobenzaldehyde, 3-chlorobenzaldehyde, 4-chlorobenzaldehyde, and 3,4-dimethoxybenzaldehyde, respectively, in the presence of 2,2′-azino-bis (3-ethylbenzthiazoline-6-sulfonic acid) diammonium salt (ABTS) as a mediator molecule. Time taken by these conversions was 1–2 h, and average yield of products was more than 93%. GRAPHICAL ABSTRACT

Purification and characterization of laccase secreted by Phellinus linteus MTCC-1175 and its role in the selective oxidation of aromatic methyl group

A laccase from the culture filtrate of Phellinus linteus MTCC-1175 has been purified to homogeneity. The method involved concentration of the culture filtrate by ammonium sulphate precipitation and an anion exchange chromatography on DEAE-cellulose. The SDS-PAGE and native-PAGE gave single protein band indicating that the enzyme preparation was pure. The molecular mass of the enzyme determined from SDS-PAGE analysis was 70 kDa. Using 2.6-dimethoxyphenol, 2.2′[azino-bis-(3-ethylbonzthiazoline-6-sulphonic acid) diammonium salt] (ABTS) and 4-hydroxy-3,5-dimethoxybenzaldehyde azine as the substrates, the Km, kcat and kcat/Km values of the laccase were found to be 160 μM, 6.85 s−1, 4.28 × 104 M−1 s−1, 42 μM, 6.85 s−1, 16.3 × 104 M−1 s−1 and 92 μM, 6.85 s−1, 7.44 × 104 M−1 s−1, respectively. The pH and the temperature optima of the P. linteus MTCC-1175 laccase were 5.0 and 45°C, respectively. The activation energy for thermal denaturation of the enzyme was 38.20 kJ/mole/K. The enzyme was the most stable at pH 5.0 after 1 h reaction. In the presence of ABTS as the mediator, the enzyme transformed toluene, 3-nitrotoluene and 4-chlorotoluene to benzaldehyde, 3-nitrobenzaldehyde and 4-chlorobenzaldehyde, respectively.

Selective oxidation and N-coupling by purified laccase of Xylaria polymorpha MTCC-1100

The chemical route of oxidation of methyl group to its aldehyde is inconvenient because once a methyl group is attacked, it is likely to be oxidized to the carboxylic acid and it is very difficult to stop the reaction at the aldehyde stage. Fungal laccases can be used for such oxidation reaction and the reaction can be completed sharply within 1–2 h. Coupling of amines are another important reactions known for fungal laccases; coupling reactions generally take 3–7 h. We have used the purified laccase of molecular weight 63 kDa obtained from the fungal strain Xylaria polymorpha MTCC-1100 with activity of 1.95 IU/mL for selective oxidation of 2-fluorotoluene, 4-fluorotoluene, and 2-chlorotoluene to 2-fluorobenzaldehyde, 4-fluorobenzaldehyde, and 2-chlorobenzaldehyde, respectively, and syntheses of 3-(3, 4-dihydroxyphenyl)-propionic acid derivatives by N-coupling of amines. In each oxidation reactions, ABTS was used as mediator molecule. All the syntheses are ecofriendly and were performed at room temperature.

ROLE OF LACCASE FROM CORIOLUS VERSICOLOR MTCC-138 IN SELECTIVE OXIDATION OF AROMATIC METHYL GROUP

Now a day, laccases are the most promising enzymes in the area of biotechnology and synthesis. One of the best applications of laccases is the selective oxidation of aromatic methyl group to aldehyde group. Such transformations are valuable because it is difficult to stop the reaction at aldehyde stage. Chemical methods used for such biotransformations are expensive and give poor yields. But, the laccase-catalyzed biotransformations of such type are non-expensive and yield is excellent. Authors have used crude laccase obtained from the liquid culture growth medium of fungal strain Coriolus versicolor MTCC-138 for the biotransformations of toluene, 3-nitrotoluene, and 4-chlorotoluene to benzaldehyde, 3-nitrobenzaldehyde, and 4-chlorobenzaldehyde, respectively, instead of purified laccase because purification process requires much time and cost. This communication reports that crude laccase can also be used in the place of purified laccase as effective biocatalyst.

Syntheses of aromatic aldehydes by laccase without the help of mediators

This communication reports the selective bioconversions of substituted toluenes to substituted benzaldehydes without the help of any mediators by purified laccase of indigenous fungal strain Fomes durissimus microbial type culture collection (MTCC)-1173. Molecular mass of laccase purified by sodium dodecyl sulfate-polyacrylamide gel electrophoresis was found to be 74.86 kDa (∼75 kDa). By using this purified laccase, selective bioconversions of 3-nitrotoluene to 3-nitrobenzaldehyde, 2-fluorotoluene to 2-fluorobenzaldehyde, 4-fluorotoluene to 4-fluorobenzaldehyde, 2-chlorotoluene to 2-chlorobenzaldehyde and 4-chlorotoluene to 4-chlorobenzaldehyde have been done without the help of mediator molecules within 1–2 hrs at room temperature and pressure with high yields (>90%). All the above bioconversions are good examples of green chemistry.

Synthetic applications of purified laccase from Pleurotus sajor caju MTCC-141

The study is devoted to the role of laccase, purified from the liquid culture medium of the indigenous fungal strain Pleurotus sajor caju MTCC-141, in selective bioconversion of toluene derivatives into substituted benzaldehydes with high yield. Coupling reactions of 3-(3,4-dihydroxyphenyl)propionic acid with 4-aminobenzoic, 4-aminoacetophenone and 1-hexylamine proceeded at room temperature under the action of laccase to give the corresponding products with excellent yields.

Amination of p-hydroquinone by laccase of Xylaria polymorpha MTCC-1100

The communication is devoted to the study of activity of crude laccase obtained from the liquid culture growth media of fungal strain Xylaria polymorpha MTCC-1100 in coupling processes of aromatic amines with p-hydroquinone. Products of monoamination were obtained under mild condition with high yields.

Some novel organometallic Mn III complexes with porphine and 1,6-diaminohexane

A novel series of MnIII complexes with 5,10,15,20-tetra(p-tolylporphine) and 1,6-diaminohexane has been synthesized. These complexes have been characterized by UV/Vis, IR, ESI-mass spectra, elemental analysis, conductivity and magnetic susceptibility measurements. These MnIII porphyrins exhibited a blue shift in soret band in comparison to non-metallated porphyrins. The molar conductance values of these complexes show their non-electrolytic nature in ethanol. The tentative structures have also been proposed. All the complexes have good level of water solubility due to which they may have medicinal as well as other valuable biological applications.