Oxidative Phenol Coupling Reaction Research Articles

Synthetic Studies of Hasubanan Alkaloids Based on Oxidative Phenolic Coupling and Intramolecular Aza-Michael Reaction

Synthetic Studies of Hasubanan Alkaloids Based on Oxidative Phenolic Coupling and Intramolecular Aza-Michael Reaction

Enantioselective Total Synthesis of Cepharatines via Bioinspired Ring Reconstruction.

We describe enantioselective total syntheses of cepharatines A-D, members of the hasubanan alkaloid family, which feature an unusual tetracyclic skeleton including an azabicyclo[3.3.1]nonane motif. A key reaction is a regio-divergent oxidative phenolic coupling reaction that affords the tricyclic core structure of hasubanan with different substitution patterns on the A-ring, including the all-carbon quaternary stereogenic center at C13, in a single step. The characteristic tetracyclic azabicyclo[3.3.1]nonane motif was constructed by means of a bioinspired cascade reaction involving the retro-aza-Michael reaction/hemiaminal formation.

Enantioselective Total Synthesis of (+)-Stephadiamine through Bioinspired Aza-Benzilic Acid Type Rearrangement.

We report the first enantioselective total syntheses of the hasubanan alkaloid (-)-metaphanine and the norhasubanan alkaloid (+)-stephadiamine. Key features of these syntheses include diastereoselective oxidative phenolic coupling reaction and subsequent regioselective intramolecular aza-Michael reaction, which efficiently construct the hasubanan skeleton with the all-carbon quaternary stereogenic center at C13. Based on our hypothesis regarding the biosynthetic pathway of (+)-stephadiamine, we found that (-)-metaphanine is easily converted to (+)-stephadiamine via aza-benzilic acid type rearrangement reaction.

Alatains A and B, unique hetero-dimeric polyphenols from Cassia alata and their anti-tobacco mosaic virus activity

Two structurally unique polyphenols, alatains A (1) and B (2), were isolated from the bark of Cassia alata. Their structures were elucidated on the basis of spectroscopic analysis. Compounds 1 and 2 represent a new type of hetero-dimeric polyphenols with a C-14–C-5′ linkage, biogenetically formed by an unusual intermolecular oxidative phenol-coupling reaction between a chromone unit and an isocoumarin moiety. Moreover, compounds 1 and 2 showed significant anti-tobacco mosaic virus (anti-TMV) inhibition IC50 values of 18.8 and 11.4 μM, respectively. Alatains A and B also exhibited promising protective effects on TMV infection of the host plants (Nicotiana tabacum) with the inhibition rates of 54.6% and 69.7% at the concentration of 20 μM, respectively. The results provided a new structural template for potential anti-TMV agent discovery.

A Fasciclin Protein Is Essential for Laccase-Mediated Selective Phenol Coupling in Sporandol Biosynthesis.

The biaryl scaffold, often showing axial chirality, is a common feature of various fungal natural products. Their biosynthesis requires an oxidative phenol-coupling reaction usually catalyzed by laccases, cytochrome P450 enzymes, or peroxidases. The combination of a laccase and a fasciclin domain-containing (fas) protein is encoded in many biosynthetic gene clusters of biaryls from ascomycetes. However, such phenol-coupling systems including their regio- and stereoselectivity have not been characterized so far. Elucidating the biosynthesis of the antiparasitic binaphthalene sporandol from Chrysosporium merdarium, we demonstrate the combination of a laccase and a fas protein to be crucial for the dimerization reaction. Only the heterologous coproduction of the laccase and the fas protein led to a functional phenol-coupling system, whereas the laccase alone showed no coupling activity. Thus, the laccase/fas protein combination forms an independent group of phenol-coupling enzymes that determines the coupling activity and selectivity of the reaction concurrently and applies to the biosynthesis of many fungal natural products with a biaryl scaffold.

Total Synthesis of (+)-Gracilamine Based on an Oxidative Phenolic Coupling Reaction and Determination of Its Absolute Configuration.

The enantioselective total synthesis of (+)-gracilamine (1) is described. The strategy features a diastereoselective phenolic coupling reaction followed by a regioselective intramolecular aza-Michael reaction to construct the ABCE ring system. The configuration at C3a in 1 was controlled by the stereocenter at C9a, which was selectively generated (91 % ee) by an organocatalytic enantioselective aza-Friedel-Crafts reaction developed by our research group. This synthesis revealed that the absolute configuration of (+)-gracilamine is 3aR, 4S, 5S, 6R, 7aS, 8R, 9aS.

Total Synthesis of (+)‐Gracilamine Based on an Oxidative Phenolic Coupling Reaction and Determination of Its Absolute Configuration

AbstractThe enantioselective total synthesis of (+)‐gracilamine (1) is described. The strategy features a diastereoselective phenolic coupling reaction followed by a regioselective intramolecular aza‐Michael reaction to construct the ABCE ring system. The configuration at C3a in 1 was controlled by the stereocenter at C9a, which was selectively generated (91 % ee) by an organocatalytic enantioselective aza‐Friedel–Crafts reaction developed by our research group. This synthesis revealed that the absolute configuration of (+)‐gracilamine is 3aR, 4S, 5S, 6R, 7aS, 8R, 9aS.

Involucratusins A-H: Unusual Cadinane Dimers from Stahlianthus involucratus with Multidrug Resistance Reversal Activity.

Three novel cadinane dimers, involucratusins A–C (1–3), five unique nor-cadinane-dimers, involucratusins D–H (4–8), together with a known compound (9) were isolated from the rhizomes of Stahlianthus involucratus. Their challenging structures and absolute configurations were determined by spectroscopic data, CD experimentation, chemical conversions and single-crystal X-ray diffraction. Compounds 1–3 are unusual cadinane dimers with new connection and novel cores. Compound 4 is a unique nor-cadinane-dimer, and 5 and 6 are two pairs of hemiketal racemates with novel dinor-cadinane-dimer backbone. Compounds 7 and 8 represent unusual dodecanor-cadinane-dimer and tetradecanor-cadinane-dimer carbon skeletons, respectively. The possible biogenetic pathways of 1–8 were proposed, involving nucleophilic addition, SN2 nucleophilic displacement, [3 + 3] benzannulation, oxidative cleavage, decarboxylation, and oxidative phenol coupling reactions. Multidrug resistance (MDR) reversal activity assay of the isolates were evaluated in doxorubicin-resistant human breast cancer cells (MCF-7/DOX). The combined use of these novel cadinane dimers at a concentration of 10 μM increased the cytotoxicity of doxorubicin by 2.2–5.8-fold. It is the first report about the MDR reversal activity of cadinane dimers.

Substituent Effects on the Phenol Coupling Reaction Catalyzed by the Vancomycin Biosynthetic P450 Enzyme OxyB

Oxidative phenol coupling reactions are required to establish the cross-linked heptapeptide backbone of vancomycin. The first cross-linking reaction, catalyzed by the P450 enzyme OxyB, is dramatically slower when a chlorine substituent is present in the hexapeptide-S-PCP substrate and is abolished when chlorine is introduced into a potential heptapeptide-S-PCP substrate.

Arylglycine-derivative synthesis via oxidative sp3 C–H functionalization of α-amino esters

An efficient method for the synthesis of arylglycine derivatives is described. The oxidative coupling reactions of naphthols and phenols with α-amino esters proceeded smoothly in the presence of meta-chloroperoxybenzoic acid as an oxidant under ambient conditions, to produce arylglycine derivatives in satisfactory yields.

ChemInform Abstract: Novel Anodic Concepts for the Selective Phenol Coupling Reaction

AbstractReview: 66 refs.

ChemInform Abstract: Novel Oxidative Phenol-Coupling Reaction with Phosphomolybdic Acid on Silica Gel Support: Regioselective Biomimetic Synthesis of Dimeric Phenanthrene Derivatives

ChemInform 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.

Novel anodic concepts for the selective phenol coupling reaction

The oxidative phenol coupling reaction of phenols with simple methyl substituents can be difficult due to several by-products. Such a challenging substrate is 2,4-dimethyl-phenol. We studied the electrochemical access to the ortho-coupled dehydrodimer. Anodic treatment in a basic electrolyte supports the formation of a molecular tricyclic architecture called Pummerer’s ketone. Employing a two-step sequence involving anodic conversion of 2,4-dimethylphenol to a preliminary substrate and different workup protocols yield exclusively and diastereoselectively polycyclic architectures. The selective ortho-coupling reaction was achieved by two strategies: A tetraphenoxy borate can be used as template substrate which can be easily made in large scale. Due to the ionic nature of the borate, no supporting electrolyte is required. This methodology can be applied to several related phenolic substrates. The second route is described by the direct conversion of 2,4-dimethylphenol on boron-doped diamond anodes. Surprisingly, the electrochemical transformation does not destruct or mineralize the substrate. Fluorinated additives allow the conversion of a broad scope of substrates.

Monoclinic CuO nanoflowers on resin support: recyclable catalyst to obtain perylene compound

Monoclinic CuO crystallite in grams has been obtained from resin bound Cu(II)-1,10-phenanthroline complex, R(-)[Cu(1,10-phen)(2)](2+) that becomes a recyclable catalyst for oxidative phenol coupling (OPC) reaction. Thus an exclusively intuitive blue fluorescing perylene derivative is derived from colorless 2,7-dihydroxynaphthalene (2,7-DHN) in high yield.

First Total Synthesis of (±)-Powelline

The first total synthesis of (±)-powelline is reported in 10% overall yield over eight steps using an intramolecular oxidative phenolic coupling reaction as the key reaction.

Synthesis of Superparamagnetic β-MnO2 Organosol: a Photocatalyst for the Oxidative Phenol Coupling Reaction

Superparamagnetic monodispersed spherical beta-MnO 2 nanoparticles of approximately 10 nm size with a band gap of 2.52 eV have been synthesized in toluene and support the oxidative phenol coupling reaction as a photocatalyst.

Exploring the substrate specificity of OxyB, a phenol coupling P450 enzyme involved in vancomycin biosynthesis

OxyB is a cytochrome P450 enzyme that catalyzes the first oxidative phenol coupling reaction during vancomycin biosynthesis. The preferred substrate is a linear peptide linked as a C-terminal thioester to a peptide carrier protein (PCP) domain of the glycopeptide antibiotic non-ribosomal peptide synthetase. Previous studies have shown that OxyB can efficiently oxidize a model hexapeptide-PCP conjugate (R-Leu(1)-R-Tyr(2)-S-Asn(3)-R-Hpg(4)-R-Hpg(5)-S-Tyr(6)-S-PCP) (Hpg = 4-hydroxyphenylglycine) into a macrocyclic product by phenolic coupling of the aromatic rings in residues-4 and -6. In this work, the substrate specificity of OxyB has been explored using a series of N-terminally truncated peptides related in sequence to this model hexapeptide-PCP conjugate. Deletion of one or three residues from the N-terminus afforded a penta- (Ac-Tyr-Asn-Hpg-Hpg-Tyr-S-PCP) and a tri- (Ac-Hpg-Hpg-Tyr-S-PCP) peptide that were also efficiently transformed into the corresponding macrocyclic cross-linked product by OxyB. The tripeptide, representing the core of the macrocycle in vancomycin created by OxyB, is thus sufficient, as a thioester with the PCP domain, for phenol coupling to occur. The related tetrapeptide-PCP thioester was not cyclized by OxyB, neither was a related model hexapeptide containing tryptophan in place of tyrosine-6, nor were tripeptides (related to the natural product K-13) with the sequence Ac-Tyr-Tyr-Tyr-S-PCP cross-linked by OxyB.

Monomeric and dimeric stilbenoids from the orchid Dendrobium amplum

Amplumthrin, a new dimeric 9,10-dihydrophenanthrene derivative, was isolated from the orchid Dendrobium amplum which also afforded the known 9,10-dihydrophenanthrene dimer flavanthrin and the monomeric stilbenoids gigantol, batatasin III, its 3'-O-methyl ether and 3,3'-O,O-dimethyl ether, 2,7-dihydroxy-3,4,6-trimethoxyphenanthrene and its 9,10-dihydro derivative, 2,3,7-trihydroxy-4,6-dimethoxyphenanthrene and its 9,10-dihydro derivative and coelonin. The structure of amplumthrin was established as 2,2',7,7'-tetrahydroxy-3,3',4,4',6,6'hexamethoxy-9,9',10,10'-tetrahydro-1,1'-biphenanthryl from various spectral and chemical evidence. The structure of amplumthrin was finally confirmed by regioselective biomimetic synthesis of the compound from its monomeric congener 2,7-dihydroxy-3,4,6-trimethoxy-9,10-dihydrophenanthrene by oxidative phenol-coupling reaction with CuCl(OH).TMEDA in very good yield (80%). Similar biomimetic synthesis of flavanthrin was also achieved in 82% yield from its monomeric congener coelonin using the same oxidant. The co-occurrence of amplumthrin and flavanthrin with their respective monomers in the same orchid Dendrobium amplum provides a strong circumstantial evidence in support of the proposed biogenesis of the naturally occurring biphenanthryl derivatives assumed to have arisen from their corresponding monomers through enzymatic oxidative phenol-coupling reaction.

Rigidanthrin, a new dimeric phenanthrene derivative of the orchid Bulbophyllum rigidum

: Rigidanthrin, a new dimeric phenanthrene derivative, was isolated from the orchid Bulbophyllum rigidum which also afforded the known monomeric phenanthrenes nudol and gymnopusin and the simple aromatic compound ethyl 4-hydroxy-3-methoxycinnamate. The structure of rigidanthrin was established as 2,2',7,7'-tetrahydroxy-3,3',4,4'-tetramethoxy-1,1'-biphenanthryl from various spectral and chemical evidence. The structure of rigidanthrin was finally confirmed by regio- as well as regio- and enantio-selective biomimetic synthesis from its monomeric congener nudol (2,7-dihydroxy-3,4-dimethoxyphenanthrene) by oxidative phenol-coupling reaction with phosphomolybdic acid (PMA) on silica gel surface and CuCl(OH).(-)-(S)-proline methyl ester, respectively, in very good yields. The optical purity of (-)-rigidanthrin obtained in the latter case was found to be 95.79%. The co-occurrence of rigidanthrin with its monomer nudol in the same orchid Bulbophyllum rigidum provides a strong circumstantial evidence in support of the proposed biogenesis of the naturally occurring biphenanthryl derivatives which are assumed to have been formed from their corresponding monomers by enzymatic oxidative phenol-coupling reaction.

Metabolism of CJ-036878, N-(3-phenethoxybenzyl)-4-hydroxybenzamide, in liver microsomes and recombinant cytochrome P450 enzymes: metabolite identification by LC-UV/MSn and 1H-NMR

The identification of metabolites in the early stages of drug discovery is important not only for guiding structure–activity relationships (SAR) and structure–metabolism relationships (SMR) strategies, but also for predicting the potential for adverse events. The present study investigated the phase I metabolism of CJ-036878 (N-(3-phenethoxybenzyl)-4-hydroxybenzamide), a potent antagonist of the N-methyl-D-asparatate (NMDA) receptor, using liver microsomes and representative recombinant cytochrome P450 enzymes. The structures of the oxidative metabolites M1–M11 were confirmed by LC-UV/MSn and/or 1H-nuclear magnetic resonance (NMR). It was found that CJ-036878 is metabolized through three routes: (1) aliphatic hydroxylation that generates M1 and M2; (2) aromatic hydroxylation that produces M3–M5, M7 and M8; and (3) dimerization through an oxidative phenol coupling reaction that yields M10 and M11. The use of recombinant human cytochrome P450 enzymes suggested that CYP3A4 is the major enzyme involved in the oxidative metabolism of CJ-036878, with minor contributions from CYP1A2, CYP2C19, and CYP2D6.