Versatile magnetic resonance singlet tags compatible with biological conditions

The long lifetime of nuclear singlet states holds promise for the development of molecular tracers to study motional processes in proteins with increased precision or to act as imaging contrast agents. We introduce a singlet tag (STAG) based on bromoacrylate that is readily attached to a variety of biomolecules, compatible with biological conditions, and is relatively insensitive to the presence of molecular oxygen. The generality of this approach is demonstrated by tagging buildings blocks for biomolecules using a simple labelling route based on commercially available starting materials. Additionally, we demonstrate a singlet NMR experiment on the endogenous molecule phosphoenolpyruvate.