Fig. 1: Introduction.
From: Bioinspired transfer methylation enabled by a photoactive reagent

A Radical methylation in nature by Tbtl. rSAM, radical S-adenosyl-L-methionine methyltransferase. SAH, S-adenosyl-L-homocysteine. B Radical methylation via methyl radical and its equivalents. C Representative protecting group strategies for radical C4-functionalization of azines. BG, blocking group. Aux, auxiliary group.