Acidic properties of N,N-naphthoquinonylamines

Temtsin, Galina; Gorohovsky, Sofia; Bittner, Shmuel

doi:10.1016/s0040-4020(02)00533-1

Cited by 3 publications

(4 citation statements)

References 17 publications

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“…This is probably due to formation of a highly conjugated resonance-stabilized anionic form 12B. 26,27 In the case of compound 11a such phenomena were not observed. …”

Section: Methodsmentioning

confidence: 90%

2-Oxiranecarbonitriles in the synthesis of linked quinono heterocyclic derivatives

Volmajer¹,

Toplak

Bittner³

et al. 2003

Arkivoc

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“…This is probably due to formation of a highly conjugated resonance-stabilized anionic form 12B. 26,27 In the case of compound 11a such phenomena were not observed. …”

Section: Methodsmentioning

confidence: 90%

2-Oxiranecarbonitriles in the synthesis of linked quinono heterocyclic derivatives

Volmajer¹,

Toplak

Bittner³

et al. 2003

Arkivoc

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“…In comparison, the pK a of the corresponding semiquinone (radical‐anion) is much smaller, 4.0 [12a,d] . Therefore, various protonated intermediates of diquinones in various stages can be formed under the present electrochemical conditions [14g] …”

Section: Electrochemical Properties Of Diquinonyl Derivatives Involving An Internal Proton Sourcementioning

confidence: 98%

“…In fact, a strong mesomeric (of the vinylogous imide) and inductive (of the chlorine atoms) effects result in unusually high acidity of the compound. Its pKa value (7.51) in methanol is several orders of magnitude lower than that of normal aliphatic or aromatic imides, and it is even a stronger acid than aliphatic carboxylic acids [14g] . That was also the only derivative that afforded an initial irreversible reduction wave in its cyclic voltammogram, that was attributed to the cleavage of the N−H bond prior to the reduction of the quinonyl moiety.…”

Section: Electrochemical Properties Of Quinones In Non‐aqueous Mediamentioning

confidence: 99%

“…Their unique behavior stems from the ability of the amino ‘NH’ group that links the two quinonyl moieties to undergo a rapid deprotonation in the presence of base even in non‐aqueous solvents. For example, the triethyl ammonium salt of N,N ‐bis(3‐chloro‐1,4‐naphthoquinonyl) amine 1 could be formed easily even in chloroform or methanol [14g] . Furthermore, the initial irreversible reduction step in all of 1 – 6 involves the reduction of the acidic N−H bond to generate their corresponding monoanions.…”

Section: Electrochemical Properties Of Diquinonyl Derivatives Involving An Internal Proton Sourcementioning

confidence: 99%

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Electrochemistry of Quinones with Respect to their Role in Biomedical Chemistry

Krayz

Bittner

Dhiman

et al. 2021

The Chemical Record

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Quinones are ubiquitous in nature and form one of the largest class of antitumor agents approved for clinical use. They are known to be efficient in inhibiting cancer cells growth. Under physiological conditions they can undergo non‐enzymatic one‐electron reduction to give the moderately toxic species of semiquinone radical‐anion. Thus, electrochemical study of quinones might provide a basic knowledge on semi‐quinone radicals formation in both in vivo and in vitro under different media. Several processes are outlined briefly and discussed in the present article. Previously we investigated the electrochemical and spectral properties of ω‐N‐quinonyl amino acids. Such quinone‐bearing peptides are known to be cytotoxic and of potential clinical significance. We were able to prove that the ω‐amino quinonyl compounds are very effective in producing stable semiquinone radicals. Moreover, a direct relation was found between the first reduction potentials of the quinonyl moiety and their reactivity towards the ω‐amino acids. In order to increase our knowledge of such amino quinonyl compounds and enlarge the arsenal of such cytotoxic compounds, a series of N,N‐diquinonyl amines (1–6) bearing an internal proton (stems from the NH moiety) were synthesized. Their electron‐transfer capabilities were probed by cyclic voltammetry measurements, in dichloromethane. It was found that the acidic NH group linking the two quinonyl moieties undergoes an initial electrochemical reduction step and generates a nitride anion. This step is followed by further reductions to yield quasi‐stable semiquinone radicals and polyanions, Since these acidic diquinones (1–6) serve also as a source of internal proton donors even in non‐polar medium, they might cause protonation of basic radical‐anions and polyanion intermediates during the various electrochemical stages. The processes are demonstrated and discussed by analyzing different mechanistic schemes. The successful generation of relatively stable semiquinone radicals is a prerequisite for the manifestation of site directed antitumor activity by these bis‐quinonyl amino derivatives. Based on the values of their redox potentials some of them could be promising candidates for clinical development.

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