Fluorophore-Promoted Facile Deprotonation and Exocyclic Five-Membered Ring Cyclization for Selective and Dynamic Tracking of Labile Glyoxals

The lack of effective chemical tools capable of dynamic tracking of labile glyoxal species (GOS) [e.g., methylglyoxal (MGO) and glyoxal (GO)] levels with high selectivity over other relevant electrophilic species, particularly, formaldehyde (FA) and nitric oxide (NO), has significantly hampered the understanding of their roles in a complex metabolic network and disease progressions. Herein, we report the rational design of the bioinspired 4-(2-guanidino)-1,8-naphthalimide fluorescent probes NAP-DCP-1 and NAP-DCP-3 from arginine-specific protein modifications. These probes undergo facile reversible fluorophore-promoted deprotonation-cyclization of a guanidium ion with labile GOS to form exocyclic five-membered dihydroxyimidazolidines. The probe NAP-DCP-1 can differentiate GOS levels in the serum of diabetic mice and patients from nondiabetic ones, which correlate very well with glucose levels, providing the GOS level as a potential new biomarker for diabetes diagnosis. Notably, the endoplasmic reticulum (ER)-targeting probe NAP-DCP-3 enabled the study of GOS perturbation in ER under various stress conditions and led to the discovery that formaldehyde (FA), either exogenously added or endogenously generated, could induce GOS level increases in ER. This finding reveals the previous unknown connection of FA with upregulated GOS levels and suggests that GOS is a key metabolite in bridging one-carbon metabolism with glycolysis and the downstream cell redox status. Moreover, the probes also showed potentials in separate quantification of MGO and GO via ultra-performance liquid chromatography-mass spectrometry (UPLC-MS) and unexpected selectivity modulation for GO over MGO via two-photon excitation. It is expected that probes reported herein provide powerful tools to study GOS level modulations in complex biological networks and would facilitate GOS-associated basic research and discovery.