methods for the synthesis of 2 - thiohistidine or a derivative thereof of the formula , or of a physiologically acceptable salt , a tautomer , a stereoisomer or a mixture of stereoisomers in any proportions thereof , from a compound of the formula or a physiologically acceptable salt , a tautomer , a stereoisomer or a mixture of stereoisomers in any proportions thereof , by cleavage reaction in the presence of a thiol at a temperature higher than or equal to 60 ° c . the invention also relates to compounds of the formula and a method for the synthesis thereof .