Penicillamine thiyl radicals

Sevilla MD, Becker D, Yan M (1990a) The formation and structure of the sulfoxyl radicals RSO, RSOO, RSCV, and RS0200 from the reaction of cysteine, glutathione and penicillamine thiyl radicals with molecular oxygen. Int J Radiat Biol 57 65-81... 

Subsequently, two pathways may be entered, one leading to perthiyl (plus thio-late), while the other results in thiyl radicals (plus perthiolate). An example shedding light on the strong influence of structural parameters on the relative yields of these two options has been described by Everett et alJ who report reaction 31a to dominate for penicillamine derivative (> 95%), as opposed to an only =20% yield of this process in the reduction of cysteine trisulfide. A similarly striking difference between these two trisulfides was found with respect to the OH-induced formation of perthiyl radicals (63% for R=Pen and 10% for R=Cys). 

Pulse radiolysis of penicillamine in aqueous solution gives thiyl radicals RS% Amax 330 nm, and the radical anion RSSR-, Amax 450 nm, formed from RS and RS / Photolysis of propanethiol tritiated at SH, in the presence of a hydrogen donor, results in tritium scrambling in the propyl group and in the hydro n donor, suggesting that such a system is a useful source of H atoms in solution. In eased yields of the products of sensitized photodecarboxylation of R X CHj COaH (X = O, S, or NH) are obtained in the presence of thiophenol as hydrogen donor. Butane-thiol quenches triplet acetophenone only slowly (At = 1.4 x 10 1 mol s ), and it can be included in the reaction systems of ketone photo-reactions as a radical trap without interfering with the photo-excited substrate. ... 

The radiochemlstty of the drugs themselves is of interest. Thiyl radicals formed by the radiolysis of cysteine, M A, and the related disulfides in aqueous solution can build up a steady-state concentration and "scramble" many disulfide groups.The radlolysls of aqueous mixtures of cystine and penicillamine disulfide gave a spectrum of products very similar to that obtained from the mixed disulfide of the two components. Cystine alone gave sulfonic acids, while penicillamine difulside, which is not radioprotective, gave none. Perhaps the ability to form sulfonic acids is characteristic of protective disulfides.68... 

In general these data are comparible with the absorption spectra of thiyl radicals detected by the pulse radiolysis technique in dilute aqueous solutions [10, 56-58]. The spectra typically display fairly weak and poorly resolved absorption with a maximum around 330 nm. The only species showing a well-defined absorption maximum is the radical derived from penicillamine... 

Ionizing radiation has been applied successfully to generate thiyl radicals in crystalline cysteine [26, 32-34, 36,42] and penicillamine derivatives [35]. Thiyl radicals in these systems are probably produced through direct ionization of the parent thiols followed by S-deprotonation of the initially formed radical cation ... 

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