Showing papers on "Anthrone published in 2002"
TL;DR: Theexpression of aknX in Escherichia coli indicates that AknX and related gene products such as DnrG and SnoaB are involved in the formation of aklanonic acid from its anthrone precursor, as suggested by their homology with TcmH and ActVA6.
Abstract: In streptomycete anthracycline biosynthetic gene clusters, small open reading frames are located just upstream of minimal polyketide synthase genes. aknX is such a gene found in the aklavinone-aclacinomycin biosynthetic gene cluster of Streptomyces galilaeus . In order to identify its function, the aknX gene was expressed in Escherichia coli . The cell extract prepared from E. coli cells overexpressing AknX protein exhibited anthrone oxygenase activity, which converted emodinanthrone to anthraquinone emodin. This indicates that AknX and related gene products such as DnrG and SnoaB are involved in the formation of aklanonic acid from its anthrone precursor, as suggested by their homology with TcmH and ActVA6. The AknX protein fused with a His 6 tag was efficiently purified to homogeneity by Ni 2+ affinity and anion-exchange column chromatography. The native molecular mass of AknX was estimated to be 42 kDa by gel filtration. Thus, native AknX is considered to have a homotrimeric subunit structure. AknX, like TcmH and ActVA6, possesses no apparent prosthetic group for oxygen activation. Site-directed mutagenesis was carried out to identify the key amino acid residue(s) involved in the oxygenation reaction. Of seven AknX mutants expressed, the W67F mutant showed significantly reduced oxygenase activity, suggesting the important role of the W67 residue in the AknX reaction. A possible mechanism for the reaction via peroxy anion intermediate is proposed.
63 citations
TL;DR: In this article, the equilibrium constant for tautomerization of anthrone to 9-anthrol has been determined as pKE (−log KE) = 2.10 from ratios of rate constants for ketonisation of anthrol and phenolisation in aqueous acetic acid buffers at 25 °C.
Abstract: The equilibrium constant for keto–phenol tautomerisation of anthrone to 9-anthrol (KE
= [phenol]/[ketone]) has been determined as pKE (−log KE) = 2.10 from ratios of rate constants for ketonisation of anthrol and phenolisation of anthrone in aqueous acetic acid buffers at 25 °C. Combining this value with pKa
= 10.0 for the ionization of anthrone, measured spectrophotometrically in piperazine and borate buffers, gives pKa
= 7.9 for the phenolic hydroxy group of anthrol. Measurements of rate constants for tautomerisation showed acid catalysis by H3O+ in aqueous HCl but by the base component only in buffer solutions of weaker acids. The H3O+-catalysed reaction is subject to a solvent isotope effect kH3O/kD3O
=
4.8, consistent with protonation of 9-anthrol at the 10-carbon atom of the anthracene ring in the rate-determining step. Comparison with hydrolysis of the methyl ether of anthrol showed that ketonisation is faster by a factor of 3000. This large rate difference is consistent with NMR measurements which show that deuterium isotope exchange at the 10-position of the anthryl methyl ether occurs in competition with hydrolysis. This accounts for a 60–70 fold of the rate difference. The residue is attributed to (a) a normal difference of 16-fold in protonation rates of phenols and the corresponding methyl ethers and (b) a minor contribution from steric hindrance to resonance stabilisation of the anthracen-9-onium ion intermediate in the hydrolysis reaction from interaction of the conjugating methoxy group with the 1,8-hydrogen atoms of the adjacent phenyl rings.
34 citations
TL;DR: From the roots of Rumex crispus, two known anthraquinones and a new one together with a new anthrone were isolated and the structures of compounds 1 - 4 were elucidated by spectroscopic means.
Abstract: From the roots of Rumex crispus, two known anthraquinones and a new one together with a new anthrone were isolated and the structures of compounds 1 - 4 were elucidated by spectroscopic means. The singlet oxygen generation capacity was tested with 1,3-diphenylisobenzofuran (DPBF) for compounds 1 - 4 .
33 citations
TL;DR: From the aerial parts of Rubus ulmifolius Schott three new anthrones, rubanthrone A, B and C, have been isolated by spectral procedures including 1D and 2D NMR techniques and chemical derivatization.
29 citations
TL;DR: DMSO solvent allows the use of LiCl as the Lewis acid source and can provide greater control of subsequent conversion to Michael adduct and the combination of an amine base and Lewis acid leads to synergistic catalysis of the Diels-Alder reaction.
22 citations
TL;DR: The antiplasmodial activity proved to be a result of the high levels of cytotoxicity displayed by the anthraquinone derivatives and therefore infusions from this crude drug lack the selectivity index needed to be an effective antimalarial agent.
Abstract: Activity-guided investigation of crude extracts prepared from the root bark of Picramnia antidesma, a medicinal plant long used for the treatment of malaria in tropical areas of the Americas, when tested on KB cells led to the isolation of a new compound, 10-epi-uveoside, from a cytotoxic fraction containing a rich mixture of anthrone glycosides The antiplasmodial activity proved to be a result of the high levels of cytotoxicity displayed by the anthraquinone derivatives and therefore infusions from this crude drug lack the selectivity index needed to be an effective antimalarial agent
17 citations
TL;DR: From the roots of Cassia kleinii two new oxanthrone esters have been isolated and their structures were established as 1,8-dihydroxy-3-methyl-9(10H)-anthracenone-10-oxyhexadecanoate 3 and 2,6,7-trihydroxy-1,8
7 citations
TL;DR: The chemotaxonomic value of the only known diglucoside anthrone from Aloe, homonataloside B, is discussed and species included in this chemotype provide chemical evidence of hybridisation in Aloe.
5 citations
1 Jan 2002
TL;DR: A new 10-hydroxyl anthrone glycoside, 1, 8, 10 - trihexyl-1-O-β-D-glucopyrano-syl-3-methyl-10-C (S) - β - D- glucopyranosyl-anthrone-9 1 was isolated from the stem of Cassia siamea Lam as discussed by the authors.
Abstract: A new 10-hydroxyl anthrone glycoside, 1, 8, 10 - trihydroxyl-1-O-β-D-glucopyrano-syl-3-methyl-10- C (S) - β - D- glucopyranosyl-anthrone-9 1 was isolated from the stem of Cassia siamea Lam. The structure was elucidated by spectral evidences, especially by 2 D techniques.
3 citations
2 citations
TL;DR: In this article, the authors studied the kinetics of the liquid phase oxidation of 10-dihydro-9-ketoanthracene (anthrone) by molecular oxygen in dimethylsulfoxide.
Abstract: The kinetics of the liquid-phase oxidation 10-dihydro-9-ketoanthracene (anthrone) by molecular oxygen was studied in dimethylsulfoxide. Anthrone was found to undergo facile oxidation to give anthraquinone in virtually quantitative yield in this highly basic, polar solvent, while the oxidation rates are much lower in acetonitrile and dimethylformamide, which are less polar solvents. A kinetic scheme for this reaction was proposed.
Patent•
13 Feb 2002
TL;DR: In this paper, a method for treating or preventing a disorder alleviated by inhibiting Jun N-terminal kinase (JNK) by administering the isothiazoloanthrones, isoxazolo anthrones, isoindolanthrones, and derivatives thereof is described.
Abstract: Isothiazoloanthrones, isoxazoloanthrones, isoindolanthrones, and derivatives thereof having the general formula (VI), and pharmaceutically acceptable salts thereof, wherein R0 is -CH2-, -SO-, -O-, -SO2-, or -S-; compositions comprising the isothiazoloanthrones, isoxazoloanthrones, isoindolanthrones, and derivatives thereof; and methods for treating or preventing a disorder alleviated by inhibiting Jun N-terminal kinase (JNK) by administering the isothiazoloanthrones, isoxazoloanthrones, isoindolanthrones, and derivatives thereof are described herein.
TL;DR: The reaction of 4'5dichloroanthrone with thionyl chloride results in dimerization of the substrate, formation of the corresponding bianthracenedione as mentioned in this paper.
Abstract: The reaction of anthrone with thionyl chloride in benzene yields 10-(chlorosulfinyl)anthrone, whilein DMF monothioanthraquinone S-oxide is formed; 4-substituted anthrones react with thionyl chloride in DMFin a similar way. The reaction of 4'5-dichloroanthrone with thionyl chloride results in dimerization of thesubstrate, formation of the corresponding bianthracenedione.
1 Jan 2002
TL;DR: In this paper, direct irradiation of carbonyl compounds such as some aldehydes, ketones and anthraquinone in N,N-dimethylamiline (DMA), without using other solvents, gave β-hydroxyamines as the major products.
Abstract: †Direct irradiation of carbonyl compounds such as some aldehydes, ketones and anthraquinone in N,N-dimethylamiline (DMA), without using other solvents, gave β-hydroxyamines as the major products. Irradiation of anthrone and DMA in methanol afforded γ-hydroxyamine. The structure of the photoproduct was confirmed by treatment with an acid to give a bicyclic compound.
TL;DR: The antiplasmodial activity and toxicity data of 34 Aloe species and their main constituents were determined and homonataloin was a more potent inhibitor of parasite growth than aloin.
TL;DR: Methanolic extracts of dried leaves of 53 Aloe species were tested in the cyclooxygenase-1 assay, finding indications that could point to the plants having anti-inflammatory activity.