Oxidative Coupling Of Phenols Research Articles

Ipobscurines C and D: macrolactam-type indole alkaloids from the seeds of Ipomoea obscura

Separation of the methanolic seed extract of Ipomoea obscura afforded five indole alkaloids, three of them (ipobscurines B-D) being new natural products of a unique structural type characterized as serotonin hydroxycinnamic acid amide-type conjugates with a second phenylpropanoid moiety forming an ether with the 5-OH position of the indole nucleus. Due to an oxidative phenolic coupling between the two phenylpropanoid moieties of the supposed precursor ipobscurine B two 21-membered macrolactams with a phenol ether partial structure are formed: the trans–cis isomers ipobscurines C and D. Their structures were established on the basis of spectral data. Moreover, total synthesis of the racemic erythro- and threo-ipobscurine B 4′,4″-dimethyl ethers and the comparison with the corresponding derivative of natural (−)-ipobscurine B proved an erythro configuration of the latter.

Reactions Catalyzed by Bacterial Cytochromes P450

The cytochromes P450 are a large family of oxidative haemoproteins that are responsible for a wide variety of oxidative transformations in a variety of organisms. This review focuses upon the reactions catalyzed specifically by bacterial enzymes, which includes aliphatic hydroxylation, alkene epoxidation, aromatic hydroxylation, oxidative phenolic coupling, heteroatom oxidation and dealkylation, and multiple oxidations including C–C bond cleavage. The potential for the practical application of the oxidizing power of these enzymes is briefly discussed.

New Perspectives for Iodine (III) Reagents in (Hetero)Biaryl Coupling Reactions

The biomimetic phenolic and non-phenolic oxidative coupling approach to the construction of biaryl connections represents an alternative to other known methodologies, such as Ullmann or Stille reactions, with the advantage that no functionalization at the coupling positions is required. However, most of the reagents commonly used for oxidative bond formation are highly toxic and environmentally harmful. This review focuses on the use of easily handle and less toxic hypervalent iodine reagents phenyliodine(III)bis(trifluoroacetate) or PIFA and phenyliodine(III)diacetate or PIDA, to perform such a key transformation as the formation of the biaryl linkage is in Synthetic Organic Chemistry. This methodology has been used in the synthesis of symmetric and unsymmetric biaryl compounds in both inter- and intramolecular fashion with high yields and complete regioselectivity. Moreover, chiral biaryl derivatives have been successfully synthesized employing these reagents. On the other hand, recent results have demonstrated that a combination of the advantages shown by this type of reagents, with those derived from solid phase organic synthesis can be successfully applied to improve the construction of derivatives incorporating the biaryl framework. Finally, this methodology had not been applied to perform the synthesis of aryl-heteroaryl bonds so far. This review also summarizes our recent advances toward this end.

Crystal Structure of OxyB, a Cytochrome P450 Implicated in an Oxidative Phenol Coupling Reaction during Vancomycin Biosynthesis

Gene-inactivation studies point to the involvement of OxyB in catalyzing the first oxidative phenol coupling reaction during glycopeptide antibiotic biosynthesis. The oxyB gene has been cloned and sequenced from the vancomycin producer Amycolatopsis orientalis, and the hemoprotein has been produced in Escherichia coli, crystallized, and its structure determined to 1.7-A resolution. OxyB gave UV-visible spectra characteristic of a P450-like hemoprotein in the low spin ferric state. After reduction to the ferrous state by dithionite or by spinach ferredoxin and ferredoxin reductase, the CO-ligated form gave a 450-nm peak in a UV-difference spectrum. Addition of putative heptapeptide substrates to resting OxyB produced type I changes to the UV spectrum, but no turnover was observed in the presence of ferredoxin and ferredoxin reductase, showing that either the peptides or the reduction system, or both, are insufficient to support a full catalytic cycle. OxyB exhibits the typical P450-fold, with helix L containing the signature sequence FGHGXHXCLG and Cys(347) being the proximal axial thiolate ligand of the heme iron. The structural similarity of OxyB is highest to P450nor, P450terp, CYP119, and P450eryF. In OxyB, the F and G helices are rotated out of the active site compared with P450nor, resulting in a much more open active site, consistent with the larger size of the presumed heptapeptide substrate.

Synthesis and Resolution of BICOL, a Carbazole Analogue of BINOL.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Response to Comment on “Peroxidase-Catalyzed Oxidative Coupling of Phenols in the Presence of Geosorbents: Rates of Non-extractable Product Formation”

Response to Comment on “Peroxidase-Catalyzed Oxidative Coupling of Phenols in the Presence of Geosorbents: Rates of Non-extractable Product Formation”

Synthesis and Resolution of BICOL, a Carbazole Analogue of BINOL

The synthesis and resolution of a novel chiral C2-symmetric bicarbazolediol (BICOL), is reported. The key step in the synthesis is the copper(II)-catalysed oxidative phenol coupling of 3-hydroxycarbazole. Menthyl chloroformate is used as resolving agent for the separation of the two enantiomers of BICOL. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

Peroxidase-catalyzed oxidative coupling of phenols in the presence of geosorbents: rates of non-extractable product formation.

Oxidative coupling processes in subsurface systems comprise a form of natural contaminant attenuation in which hydroxylated aromatic compounds (HACs) are incorporated into soil/sediment organic matter matrices. Here we describe the oxidative coupling of phenol catalyzed by horseradish peroxidase (HRP) in systems containing two geosorbents having organic matter of different composition; specifically Chelsea soil, a near-surface geologically young soil having a predominantly humic-type soil/sediment organic matter (SOM) matrix, and Lachine shale, a diagenetically older natural material having a predominantly kerogen-type SOM matrix. It was found that each of these two different types of natural geosorbents increased the formation of non-extractable coupling products (NEPs) over that which occurred in solids-free systems. The extent of coupling was higher in the systems containing humic-type Chelsea SOM than in those containing kerogen-type Lachine SOM. It was observed that HRP inactivation by free radical attack was significantly reduced in the presence of each geosorbent. A rate model was developed to facilitate quantitative evaluation and mechanistic interpretation of such coupling processes. Experimental rate measurements revealed thatthe greater extent of reaction observed in the presence of Chelsea soil than in the presence of Lachine shale can be attributed to two factors: (i) more effective protection of HRP from inactivation by the Chelsea SOM and (ii) the greater reactivity of Chelsea SOM with respect to cross-coupling. Interrelationships among enzyme protection, cross-coupling reactivity, and SOM chemistry are discussed.

ChemInform Abstract: An Efficient Synthesis of (.+‐.)‐Narwedine and (.+‐.)‐Galanthamine by an Improved Phenolic Oxidative Coupling.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

An Efficient Synthesis of (±)-Narwedine and (±)-Galanthamine by an Improved Phenolic Oxidative Coupling

An Efficient Synthesis of (±)-Narwedine and (±)-Galanthamine by an Improved Phenolic Oxidative Coupling

An Efficient Synthesis of (±)-Narwedine and (±)-Galanthamine by an Improved Phenolic Oxidative Coupling

Old problems, new ideas! The biomimetic phenol coupling of norbelladine derivatives such as 1 (Bn = benzyl) to form galanthamine (2), a drug used in the treatment of Alzheimer's disease, has been greatly improved by the use of the hypervalent-iodine oxidation reagent phenyliodine(III) bis(trifluoroacetate) (PIFA).

An Efficient Synthesis of (±)‐Narwedine and (±)‐Galanthamine by an Improved Phenolic Oxidative Coupling

Old problems, new ideas! The biomimetic phenol coupling of norbelladine derivatives such as 1 (Bn = benzyl) to form galanthamine (2), a drug used in the treatment of Alzheimer's disease, has been greatly improved by the use of the hypervalent-iodine oxidation reagent phenyliodine(III) bis(trifluoroacetate) (PIFA).

Biomimetic Formation of Macrocyclic Spermine Alkaloids

Dihydroxyverbacine (10), a precursor for oxidative phenol coupling, was obtained via (±)-buchnerine (14), whose synthesis is described. The oxidizing system hemin (ferriprotoporphyrin IX chloride)/H2O2 promoted intramolecular coupling of 10 to give the alkaloids aphelandrine (1), orantine (2), and chaenorpine (7). The alkaloids were identified by on-line coupled HPLC and atmospheric-pressure chemical-ionization (APCI) mass spectrometry.

Phenol oxidative coupling in the biogenesis of the macrocyclic spermine alkaloids aphelandrine and orantine in Aphelandra sp.

A crucial step in the biosynthesis of the spermine alkaloid aphelandrine and its diastereoisomer orantine is an intramolecular cyclization of the intermediate (S)-dihydroxyverbacine. In order to elucidate this step of the biosynthetic pathway, microsomes from the roots of Aphelandra squarrosa Nees were incubated with unlabeled and (D8)-labeled (S)-dihydroxyverbacine. It was shown that the microsomal fraction catalyzes the intramolecular coupling of (S)-dihydroxyverbacine to aphelandrine. This was proven by microsomal transformation of (D8)-labeled (S)-dihydroxyverbacine to (D8)-labeled aphelandrine. The reaction absolutely requires NAPDH and O2. The underlying reaction mechanism is probably an oxidative phenol coupling catalyzed by an aphelandrine synthase. This enzyme is proposed to be a cytochrome P-450 oxidase. The intramolecular cyclization of (S)-dihydroxyverbacine represents an important point in the biogenesis of the aphelandrine-type alkaloids.

New reagent for oxidative phenol coupling. The transformation of the monocyclic spermine base ( S)-dihydroxyverbacine to the bicyclic alkaloid ( S, S, S)-aphelandrine by cell free extract of barley seedlings

The soluble protein fraction of barley seedlings ( Hordeum vulgare, Gramineae) in the presence of O 2 stereoselectively catalyzes the intramolecular phenol coupling of the monocyclic spermine base ( S)-dihydroxyverbacine to the bicyclic aphelandrine in preparative yield. The expected microsomal-bond cytochrome P-450 enzyme system does not contribute to this reaction. The nature of the involved biocatalyst still remains uncertain. The catalytic potential of the cell free extract of barley seedlings suggests its possible use as an efficient tool for large scale stereoselective chemoenzymatic synthesis of aphelandrine type alkaloids.

Smart peptide libraries are accessible via enzymatic modifications

The minireview summarizes the recent preparation of the following unusually modified combinatorial peptide collections useful for diagnostics and screening in drug finding. Tissue transglutaminase catalyzes cross couplings with transamidation between Gln and Lys peptide chains resulting in libraries with isopeptide bonds. The enzyme is involved in the triggering of autoantigenic B- and T-cell epitopes of coeliac disease. The microbial enzyme EpiD involved in lantibiotic biosynthesis catalyzes oxidative decarboxylation of C-terminal cysteine residues in peptide libraries transforming peptidyl-cysteines to peptide (2-mercaptovinyl)amides. Novel backbone modified peptide libraries are prepared using oxazole and thiazole building blocks carrying amino acid side chains. These amino acids have been found in many biologically active natural products from marine and microbial organisms such as microcin B17. Dityrosine and isodityrosine linked peptide dimer libraries are accessible by oxidative phenol coupling using horseradish peroxidase. Such structural elements are found for example in the polycyclic glycopeptide antibiotics of the vancomycin type. Microstructured layers of linear and cyclic peptide libraries are generated on transducer surfaces for cellular assays, sensor developments and even chiral recognition. Examples include a light-directed and microstructured electrochemical polymerization of phenol labelled peptides.

ChemInform Abstract: Development of Intramolecular Oxidative Phenolic Coupling Reactions Using Hypervalent Iodine (III) Reagents and Their Application to the Synthesis of Amaryllidaceae Alkaloids

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Regioselectivity in oxidative cross-coupling of phenols. Application to the synthesis of dimeric neolignans

The problems of regioselectivity in oxidative coupling of phenols are outlined, and recent research on the application to the synthesis of lignans and neolignans is reviewed. Lignans and neolignans are dimers that are typically formed by oxidative coupling of propenyl phenols. The coupling of structurally different phenols (cross-coupling) is an extension of this synthesis. Recent results show that cross-coupling can be achieved if the phenols have compatible reactivities. The regioselectivity is often quite different in cross-coupling compared to dimerization. Coupling of phenols with widely different rates of oxidation is difficult but can be achieved if the concentration of the more reactive phenol can be kept low enough during the reaction, for instance by diffusion through a dialysis membrane.

Oxidative aryl coupling reactions: a biomimetic approach to configurationally unstable or axially chiral biaryl natural products and related bioactive compounds

Phenolic and non-phenolic oxidative aryl coupling reactions were successfully used in the efficient synthesis of diverse natural products and related compounds in the fields of biphenyls, biscarbazoles and bisnaphthylisoquinolines. For sterically more hindered biaryls, which consequently show the phenomenon of axial chirality, the products were prepared in an atropisomerically pure form. Their absolute axial configurations were assigned mainly by experimental and computational CD investigations.

Optimizing the kinetics of persulfate-mediated oxidative coupling of phenols to 4-aminoantipyrine

The kinetics of the persulfate oxidation of phenol, p-ethylphenol, and 1-naphthol in the presence of 4-aminoantipyrine under basic condition was studied. Parallel oxidation of 4-aminoantipyrine was observed to influence the rate law in a very complicatedway. The rate law was simplified by limiting the concentration of the phenol, and optimizing the excess persulfate and the 4-aminoantipyrine. Under such condition, the rate law is independent of the concentration of 4-aminoantipyrine. The order of reaction was found to be one with respect to the concentrations of a phenol or persulfate. The second order rate constant was highest for 1-naphthol followed by phenol and p-ethylphenol in that order. © 2001 John Wiley & Sons, Inc. Int J chem Kinet 33: 600–604, 2001