Azaphilone α-Bromoacetates (AzαBs): Fluorescent Linchpin Reagents for the Inter- and Intramolecular Cross-Linkage of Primary Amines to Thiols

alpha-Bromoacetate esters of the azaphilone isochromene-6,8-dione core exhibit a pH-dependent orthogonal reactivity allowing for the one-pot cross-linkage of primary amines to thiols in an inter- or intramolecular fashion to afford fluorescent products. This represents a new potential strategy for bioconjugate chemistry.