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Relevant academic research and scientific papers

An improved method for the rapid preparation of 2-amino-4,4a-dihydro-4a,7-dimethyl-3H-phenoxazine-3-one, a novel antitumor agent

A simple and rapid preparation method for a novel antitumor agent, 2-amino-4, 4a-dihydro-4a,7-dimethyl-3H-phenoxazine-3-one (Phx) was described. The procedure included (1) the reaction of bovine hemolysates with 2-amino-5-methylphenol, (2) one-shot denaturation of hemoglobin and proteins by methanol, and removal of the denatured hemoglobin and proteins, (3) concentration of the reaction products, and (4) purification by a Sephadex column. These procedures yielded Phx in 34% yield.

The first report of a tetra-azide bound mononuclear cobalt(iii) complex and its comparative biomimetic catalytic activity with tri-azide bound cobalt(iii) compounds

Three new azide-bound cobalt(iii) complexes, [Co(HL1)(N3)4] (1), [Co(L2)(N3)3] (2) and [Co(L3)(N3)3] (3), where L1, L2 and L3 are N,N-dimethyldipropylenetriamine, N1-isopropyldiethylenetriamine and N,N-diethyldiethylenetriamine, respectively, were synthesized and structurally characterised. X-ray crystallographic studies reveal that the structures of both 2 and 3 are very similar in which three terminal azide ions together with a triamine coordinate the metal centre. Complex 1 on the other hand is significantly different from the other two as the metal centre in 1 is bonded with four terminal azide ions and two donor sites of triamine L1, leaving the tertiary amine group protonated. All the complexes are stabilized by rich hydrogen bonding interactions, leading to hydrogen bonded supramolecular chain structures. It is worth noting that complex 1 is the first example in cobalt(iii) coordination chemistry in which all four azide ions coordinate the metal centre terminally. All these compounds exhibited efficient catalytic activity towards the oxidative coupling of o-aminophenols to phenoxazinone chromophores under aerobic conditions and the role of the structural factors in the catalytic activity has been explored. A mass spectrometry study was carried out to identify the products and important reactive intermediates and to support the mechanistic proposal. This journal is

Influence of anions and solvents on distinct coordination chemistry of cobalt and effect of coordination spheres on the biomimetic oxidation of o-aminophenols

The present work reports the synthesis and structural characterizations of five new cobalt complexes (1–5) resulting from a N3O donor ligand, a Schiff base condensation product of N,N-dimethyldipropylenetriamine and 3-ethoxysalicylaldehyde, and their catalytic activity for the aerobic oxidation of various substrates, namely o-aminophenols and catechol. X-ray structural studies reveal that the Schiff base ligand can bind the metal centre either in the tetradentate fashion using all the available donor sites of the monoanionic deprotonated form (in 2 and 3) or in the tridentate fashion using the zwitterionic form of the Schiff base ligand with pendent quaternary amine nitrogen (in 1 and 4). Additionally, the monoanionic deprotonated ligand can bind the metal centre in the tridentate fashion (in 4 and 5) where the pendent tertiary amine nitrogen is involved in the intramolecular hydrogen bonding. All these adaptabilities associated with this triamine make it appealing candidate for exploration of the coordination chemistry with diverse structures. All complexes except compound 1 are efficient functional models for phenoxazinone synthase, and as expected the availability of labile sites at the first coordination sphere for the substrate, o-aminophenol, binding is the governing factor for higher catalytic activity in 2 and 3. Requisite of the hydrogen bond acceptor centre as well as proton abstraction centre at the second coordination sphere behind the facile oxidation of the substrate were also explored (reactivity of 1 versus 4 and 5). Moreover, the broader catalytic ability of these complexes was examined with substituted aminophenol and catechol as substrates, and the results were assembled and analysed. Furthermore, emphasis was given to get insight into the mechanistic pathway of functioning phenoxazinone synthase activity, well supported by the mass spectral study.

Silver(I) complex with 2-amino-4,4α-dihydro-4α,7-dimethyl-3H-phenoxazin-3-one (Phx-1) ligand: crystal structure, vibrational spectra and?biological?studies

The first metal complex of Phx-1 ligand, bis(2-amino-4,4α-dihydro-4α,7-dimethyl-3H-phenoxazin-3-one)nitratosilver(I), [Ag(Phx-1)2NO3], has been obtained and investigated by single crystal X-ray diffraction and vibrational spectroscopy methods. The Ag+ is bonded to heterocyclic nitrogen atoms of two organic ligands and one oxygen atom of a nitrate anion. The Phx-1 ligand coordination mode is supported by IR and Raman spectra, interpreted with the help of theoretical DFT studies. The antibacterial activity of the ligand and its Ag(I) complex as well as some reference compounds were screened against Gram-positive and Gram-negative bacteria, applying microdilution procedures. High sensitivity to the studied complex was found for Rhodococcus erythropolis and Bacillus licheniformis strains. Modified Phx-1 ligand preparation procedures are also presented.

Catalytic oxidative cyclocondensation of o-aminophenols to 2-amino-3H-phenoxazin-3-ones

The catalytic oxidative cyclocondensation of the o-aminophenols 1a-f was investigated. The oxidants used were air/laccase, H2O2/horseradish peroxidase, H2O2/ebselen (3), and TBHP/diphenyl diselenide 4. The products obtained were 2-amino-3H-phenoxazin-3-on

Biomimetic catalytic activity and structural diversity of cobalt complexes with N3O-donor Schiff base ligand

This report describes the syntheses and structural characterizations of four new cobalt(III) compounds (1–4) derived from a tetradentate Schiff base ligand and their catalytic oxidation of different o-aminophenols in aerobic condition. X-ray crystal struc

Synthesis, structure and diverse coordination chemistry of cobalt(III) complexes derived from a Schiff base ligand and their biomimetic catalytic oxidation of o-aminophenols

This paper deals with the syntheses and structural characterizations of four new cobalt(III) compounds (1–4) derived from a N3O donor Schiff base ligand and their catalytic activity towards the aerobic oxidation of o-aminophenols. Both counter

P-Quinoneimine as an intermediate in the oxidative coupling of 2-amino-5-methylphenol to 4a,7-dimethyldihydro-2-aminophenoxazinone catalyzed by a monomeric copper(II) complex

Copper(II) complex of a tetradentate N-picolatedbisbenzimidazolyl ligand is synthesized and characterized. XRD study reveals that copper(II) is in a distorted square plane comprising of two imine nitrogen, one oxygen atom from nitrate and another from a water molecule. This complex carries out the oxidative coupling of aminomethylphenol to phenoxazinone through an intermediate p-quinoneimine. The reaction is pseudo first order with respect to the catalyst and is self-inhibiting with increasing substrate concentration. Anion like acetate is found to increase the rate of reaction by nine times. EPR monitoring indicates the formation of a Cu(I) species which is the likely cause of inhibition of the catalytic reaction.

Expansion of the aromatic part of Cinchona alkaloids. Annulation of quinolines with phenoxazine motifs

An oxidative cross-coupling strategy for quinoline ring annulation in Cinchona alkaloids has been developed. Key-reaction optimization by changing oxidants and adjusting the nucleophilicity of the 2-aminophenols led to cupreine and cupreidine expanded with the phenoxazinone unit in 56–75% yield. The stereochemical integrity of the obtained alkaloid structures was confirmed by combined experimental and computed CD and NMR data. The conformational study revealed a fast equilibrium of the three conformers, differing in the orientation of the pyrido[a-3,2]phenoxazine moiety.

2-Amino-4,4α-dihydro-4α,7-dimethyl-3H-phenoxazin-3-one as an unexpected product from reduction of 5-methyl-2-nitrophenol

When attempting to synthesize symmetric 2,2′-dihydroxy-4,4′-dimethyl-azobenzene from 5-methyl-2-nitrophenol by reductive methods based on two literature procedures, an unexpected product was isolated in 30% yield. Full analysis by mass spectrometry, NMR spectroscopy, and single-crystal X-ray structure analysis, proved this product to be tricyclic 2-amino-4,4α-dihydro-4α,7-dimethyl-3H-phenoxazin-3-one. This Letter conveys a warning regarding reductive synthetic routes toward azobenzenes. We also present a novel reductive synthetic route for phenoxazines, an important class of tricyclic compounds.