Chemical Tagging of N -Alkylamine-Containing Natural Products and Pharmaceuticals through C( sp 3 )–H Functionalization

-alkylamines. The transformation proceeds under mild, aerobic conditions with blue-light irradiation: flavin analogues mediate sequential α- and β-amino C-H bond scission to generate enamines, which undergo inverse electron-demand Diels-Alder reactions with tetrazine- or nitroalkene-based tagging agents. We assessed biological consequences by cytotoxicity and ligand-binding assays, revealing examples in which tagging either preserves or alters bioactivity. The method's versatility is demonstrated by the efficient synthesis of antibody-drug conjugates derived from the anticancer agent irinotecan.