Indeed, almost quantitative yield and conversion (Fig. , Tables 1 and 2) and good mass balance (Fig. ) under the optimized conditions will exclude other potential side reactions, including Kolbe-type reactions and polymerization. Hydrogen atom abstraction at the α-position of amino acids may lead to a transient species, but the subsequent shift from strong carbon-centered radicals to weaker sulfur-centered radicals would afford the catalytically essential thiyl group, as in the case of glycyl radical enzymes, including benzylsuccinate synthases. Thus, the mild reactivity of thiyl radicals with moderate bond dissociation energies (BDEs) of ~ 87 kcal mol -1 for the RS-H bonds could also explain the high selectivity.