Self-restricted oxazolone GFP chromophore for construction of reaction-based fluorescent probe toward dopamine

The β-barrel provides a confined environment for chromophores of the green fluorescent protein (GFP) family, defining their emission profiles by the chromophore/β-barrel interactions. Here, we describe the generation of self-restricted oxazolone GFP chromophore (GFPc) for construction of reaction-based fluorescent probe toward dopamine by mimicking the confinement effect of the β-barrel. Through standard synthetic method, the first self-restricted GFPc oxazolone analogue (MBDO) and the conventional pyrenyl-based chromophore (PDO) were prepared respectively. Under the same condition, MBDO shows much better emission response with fluorescent quantum yield (QY) over one order of magnitude higher than that of PDO due to the generation of the self-restricted effect. And, the fluorescent QY of MBDO reaches above 30% in dimethyl sulfoxide, which is the largest ever recorded for unlocked GFPc analogues in highly polar solvents. Moreover, theoretical calculations further reveal that the enhanced emission of MBDO is due to the inhibition of conformational motions around the exocyclic CC bonds. Combination the enhanced emission and the reactivity of the lactone, MBDO is applied to construct reaction-based fluorescent probe toward dopamine via a ring-opening reaction of the lactone. Prospectively, the destruction of the oxazolone would break the effective conjugated structure of the chromophore, which can decrease the corresponding fluorescence. This work puts forward a novel approach to generate highly emissive GFPc oxazolone analogue, which can be used to fabricate reaction-based fluorescent probe toward dopamine, potentially promoting the biochemical applications using synthetic GFP chromophore analogues.