Synthesis, electrochemical and spectral properties of some ω-N-quinonyl amino acids

Abstract

Four series of omega-N-quinonyl amino acids were synthesized by Michael-like additions. The quinones include 2-phenylthio-1,4-benzoquinone, 1,4-naphthoquinone, 2-methyl-1,4-naphthoquinone and 2,3-dichloro-1,4-naphthoquinone. These modified amino acids can be used for post chain assembly modifications of biologically active peptides, which target the quinonic drug to a cancer damaged area. The electron-transfer capabilities of the modified amino acids were probed by cyclic voltammetry measurements. The results described in this paper show that the novel N-quinonyl amino acids are effective in producing semiquinone radicals similarly to the unconjugated quinones themselves. A direct relation was found between the first reduction potentials of the quinones and their reactivity towards the omega-amino acids. The successful generation of stable semiquinone radicals by the novel quinone derivatives is a prerequisite for the manifestation of site-directed antitumor activity of corresponding quinone-peptide conjugates.

Electrochemical investigations of dissolved and surface immobilised 2-amino-1,4-naphthoquinones in aqueous solutions

“…This is in contrast with the behaviour recorded in non-aqueous aprotic solvent, in which NQ1 displays three reduction waves, two of them being irreversible [34]. A decomposition of the compound was suggested to explain the nonreversibility of the first reduction process and the appearance of a third wave [34]. The formal redox potential, E°' = À0.420 V (vs. SCE), is in good agreement with the values reported for other structurally close 2-amino-1,4-naphthoquinones, ranging between À0.419 and À0.476 V (vs. SCE, at pH 7) [37] depending on the investigated compound.…”

“…This is in contrast with the behaviour recorded in non-aqueous aprotic solvent, in which NQ1 displays three reduction waves, two of them being irreversible [34]. A decomposition of the compound was suggested to explain the nonreversibility of the first reduction process and the appearance of a third wave [34].…”

New evidence for covalent coupling of peptides to humic acids based on 2D NMR spectroscopy: A means for preservation

“…This reaction would involve loss of the 15 N-1 H cross peak for G1. The Michael reaction is well known to occur between primary amines and quinones at near neutral pH (Bittner et al, 2002;Sridhar et al, 2001) or ␣,␤ unsaturated ketones and involves a 1,4 addition as shown in Figure 3 for the case of quinones. We can find no reports of amide nitrogens reacting in this manner.…”

Synthesis, electrochemical and intramolecular charge-transfer properties of ‘calix[4]arene-acceptor’ diad and triad derivatives

“…However, the ratio of the current amplitudes between the two reduction processes is not equal to unity because of fast disproportionation of the anion radical, making the ratio usually greater than unity in favor of the first redox couple, depending on scan rate. 19 As mentioned above, calixarene derivatives are widely used in supramolecular chemistry for the construction of various receptors for charged or neutral guest molecules. Such host -guest interaction can be controlled and detected electrochemically when organic, organometallic or inorganic redox-active centers are incorporated into calix[4]-arene framework.…”