Transient radical species catalysis

Lactobacillus leichmanii ribonucleotide reductase has a molecular weight of 76 000, with a single polypeptide chain of about 690 amino acids. The large size of the apoenzyme probably reflects the need for it to have sites to interact with the coenzyme, a dithiol, a substrate and allosteric effectors. A transient radical species was observed during catalysis. 

In 2007, the groups of MacMillan and Sibi almost simultaneously introduced a new mode of organocatalytic activation, termed SOMO (singly occupied molecular orbital) catalysis, which was founded upon the transient production of a 37r-electron radical cation species that could function as a generic platform of induction and reactivity. This new mode of organocatalytic activation, was founded upon the mechanistic hypothesis that one-electron oxidation of a transient enamine intermediate, derived from the aldehyde and the chiral amine catalyst, rendered a 37i -electron SOMO-activated species, which could readily participate in asymmetric bond construction. 

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