Methionine and cystine residues have been speculated to be involved in long-range electron transfer between redox centers in oxidoreductases in spite of their high oxidation potentials. In the study of neighboring group participation in sulfide oxidation it was revealed that the stability of the transient sulfur radical cation was attributed to the fomation of 2-center 3-eletron (2c3e) sulfur-oxygen (SO) bond by neighboring carbonyl group participation. Here we present syntheses of conformationally-constrained disulfide derivatives shown in Figure 1 and electrochemical oxidation of these compounds. It is possible for endo compounds to juxtapose disulfide bond and neighboring group in order to form 2c3e SO bond, while it is not for exo compounds. These new compounds were successfully synthesized. Moreover, in the course of the syntheses we found that disulfide moiety was unexpectedly nucleophilic. For example, disulfide moiety reacted with neighboring acid chloride moiety to form thiolactone (Scheme 1), which generally requires metal activation of disulfide bond. Electrochemical oxidation of these compounds were measured by cyclic voltammetry using Pt microelectrode. The results showed that oxidation potentials of disulfides with endo-CONH2 and endo-CON(CH2)4 were 0.88 and 0.85 V, respectively. Considering that oxidation of potetials of all the other compounds were about 1.0 V, those amide neighboring groups clearly have an effect on stabilizing disulfide radical cation by 2c3e SO bond formation, which may be relevant to the long-range electron-transfer mechanism.

Syntheses and electrochemical oxidation of disulfide compounds juxtaposing carbonyl groups

254th National Meeting (2017)

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