Naturally occurring quinones.
Part XXV. Pterocarpenequinones 6 H -benzofuro[3,2- c ]benzopyranquinones from Brya ebenus. Margarida A.
Allergic cross reactions could be obtained with 9 out of 14 different napthoquinones. Naturally Occurring Quinones Hardback R. Enter your email address below and we will send you your username. Physical Description vi, p. Gene Ontology GO Terms. Add a tag Cancel Be the first to add a tag for this edition. If you do not receive an email within 10 minutes, your email address may not be registered, and you may need to create a new Wiley Online Library account.
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Walmart Services. Get to Know Us. Customer Service. Several studies showed that density functional theory is a powerful method for predicting the geometry and other features related to the structure. The highlight of this study is that the free radicals can be easily generated in aqueous solution and are more reactive. Tormena et al. The energies of both endo and exo adducts were obtained at CBS-Q level of theory, which showed that endo adduct is more stable than exo.
An NBO electronic structure analysis indicated that the attractive delocalization interaction predominates over the steric repulsive interaction in the endo adducts. Patil and Sunoj reported the substituent effects of retro Diels-Alder reaction in benzoquinones.
A systematic study has been carried out on the retro Diels-Alder reaction of cycloadducts formed between substituted cyclopentadiene and p -benzoquinone 1 based on the hybrid HF-DFT method Scheme The transition state study on the cycloreversion reaction demonstrated that -SiMe 3 substituents are most effective in lowering the activation barrier.
The influence of hydrogen bonds to nearby molecules direct the quinones to perform a desired function. The reaction of quinone mediated reduction of oxygen to peroxide Scheme 46 has been investigated in detail by Wass et al. Many well known quinones such as p -chloranil , 2,3-dichloro-5,6-dicyano- p -benzoquinone DDQ and tetracyano- p -benzoquinone have strong power of oxidation and have been extensively used as oxidants in organic synthesis. Based on this principle, Zhu et al.
A similar study to predict the electron affinities of various methylated and halogenated derivatives of p -benzoquinones has been undertaken by Wheeler and co-workers. Very recently the characterization of semiquinones and quinones formed as intermediates in the oxidation of flavonoid epicatechin has been studied by means of computational chemistry. The results showed that the 4'-OH of the catechol group represents the primary site of deprotonation the most oxidizable , which gives both the most stable and the easiest formed semiquinones.
The biological actions of quinones are linked to their electron transfer rates and redox potentials. Namazian and Almodarresieh extended their study to improve the reduction potential values by including the frequency calculations and relaxation of salvation energy. Recently Pakiari et al. In comparison with other methods DFT-B1B95 is a reliable level of theory and less computer time demanding, which gives moderate accuracy even when ordinary sized basis sets are used. Quinones lead to the generation of reactive oxygen species, through redox cycling in the presence of oxygen.
This property can be related to their biological activity. A simple and practical method for calculating thermodynamic parameters necessary to estimate semiquinone stability constants and redox potentials for quinone natural products has been reported by Cape et al. Accurate calculation of absolute one-electron redox potentials of some p -quinone derivatives in acetonitrile was done by Namazian and Coote.
Tetrafluoro- p -benzoquinone TFBQ has many applications in chemical synthesis owing to the presence of four highly electronegative F atoms. They correlated the charge distribution with the electron affinity. Our group carried out a semiempirical AM1 computational study on the modeling of Diels-Alder cycloadditions at the beginning of this decade.
Then we extended the study to quinoxalin quinones Results of the computational study revealed that by choosing appropriate diene such as electron-withdrawing diene, it is possible to reverse the course of Diels-Alder cycloaddition from quinonoid ring to the heterocyclic moiety. Very recently an interesting DFT study in understanding the influence of Lewis acid in the regioselectivity of the Diels-Alder reactions of 2-methoxymethyl-1,4-benzoquinone Scheme 50 has been reported by Soto Delgado and co-workers.
The theoretical results obtained by DFT-B3LYP level calculation provided a useful tool for the interpretation of the reaction mechanisms. Transition state studies showed that there is a larger activation barrier associated with the uncatalyzed processes.
Naturally Occurring Quinones aims to discuss where quinones, a major group of organic compounds that are considered as pigments, can be found in nature. Naturally Occurring Quinones By Dr. R. H. Thomson. (Organic Chemistry Monographs.) Pp. vii + (London: Butterworths Scientific Publications; New York.
A biradical mechanism is proposed and described in detail by computational studies. The significant finding of the study is an intramolecular hydrogen shift in the triplet excited state which leads to stable biradical. Cycloaddition Reactions of 1,4-Benzoquinones. Various cycloaddition reactions of 1,4-benzoquinones are known, e.
Owing to this synthetic advantage, cycloaddition reactions have been used as the backbone of many artful synthesis of natural products consisting complex structural frameworks. This methodology has been applied to a short enantioselective synthesis of the potent naturally occurring mutagen aflatoxin B 2 Later Engler et al.
The synthetic utility of these cycloaddition reactions has been demonstrated by the synthesis of different antimicrobial pterocarpan phytoxalexins The mechanistic and kinetic aspects of competing metal-ion catalyzed cycloaddition and hydride transfer reactions of NADH analogues with 1,4-benzoquinones have been studied by Fukuzumi et al. The hydride transfer reaction from to 1 also occurs besides the cycloaddition when the Lewis acidity of metal ion decreases.
A change in the type of reaction from a cycloaddition to a hydride transfer depends on the Lewis acidity of metal ions. They reported the unprecedented formation of a benzo-fused 1,3,2-dithiazolium [AsF 6 - ] salt by a one step quantitative cycloaddition of SNSAsF 6 with 1,4-benzoquinone 1 Scheme For instance, recent works have reported an enantioselective and structure-selective Diels-Alder reactions of unsymmetrical quinones Scheme A set of rules has been framed to predict the structure and absolute configuration of the predominant product. Another glorious achievement of this group using the chiral catalyst has been the transformations of some of the classical synthesis of racemic natural products.
Later Corey and co-workers have improved the catalyst by synthesizing chiral oxazaborolidine-aluminium bromide complexes and reported the enantioselective Diels-Alder cycloadditions of cyclopentadiene with various quinones.
Jarvo et al. White and Choi demonstrated the synthetic utility of Diels-Alder reaction of benzoquinone 1 through the asymmetric synthesis of the indole alkaloid - -ibogamine The key step in this synthesis is the Diels-Alder addition of 1 to an achiral diene in the presence of a chiral catalyst, S -BINOL-TiCl 2 to give for the adduct , which on subsequent reactions yielded Scheme Masked 1,4-benzoquinones are quinones in which a carbonyl group is masked by converting into monoketals.
The monoketals of p -benzoquinones have been used as starting materials for the synthesis of a wide range of bioactive natural products including antitumor antibiotic LL-Ca. These cycloadditions may be performed with certain Lewis acid catalyst like ZnBr 2 and give rise exclusively to endo adducts with a good to excellent anti-facial selectivity Scheme Carreno et al.
The reactivity and selectivity of the process proved to be dependent on the electron density of the arylsulfinyl group. Later Carreno and colleges observed that the dienophilic reactivity of the 2-methyl substituted quinones have been increased upon boronic acid substitution. The Diels-Alder reaction of this substrate followed by a spontaneous and stereoselective protodeboronation to give the trans -fused cycloadduct, Scheme The role of boron group in this typical cycloaddition is to act as a temporal regiocontroller and leads to the uncommon meta- regioisomer of the cycloadduct.
Trauner and colleges demonstrated the viability of vinyl quinones in Diels-Alder reactions.
They utilized this strategy to synthesize medicinally significant - -halenaquinone Nolan and Kedrowski , have shown that extremely electron deficient vinylnitroquinone undergoes facile cycloaddition to electron rich furan and indole Scheme Kang et al. Stratakis and co-workers reported an efficient biomimetic route to acremin G featuring a highly regioselective and stereoselective Diels-Alder reaction between a TBS-protected hydroquinone diene and a structurally related alkenyl quinone The construction of complex polycyclic frameworks has also been reported by a double domino Knoevenagel hetero Diels-Alder synthetic strategy.
Jimenez-Alonso et al. Using microwave radiations these reactions proceeded more efficiently and rapidly.