Develop of new fluorescent probe to target hDHODH enzyme

Fluorescent imaging is a powerful tool for understanding and visualize biological processes in live organisms [1]. There are several probes that may be used for this purpose; however, they all have disadvantages such as large size and low cell permeability [2]. One approach to minimize interference in the live cell is to include small fluorescent probe into the scaffold of molecules with known affinity for a specific target. Pyrazolo[1,5-a]pyridin-2-ol is a small molecule characterized by a strong emission in the blue field. Its physicochemical features as carboxylic acid isoster have been widely investigated. The effectiveness of this moiety as carboxylic acid bioisoster is highlighted in MEDS433, a potent hDHODH inhibitor [3]. With the purpose of moving the emission profile from blue to red while keeping the scaffold's modest size, two series of compounds were design. In the first series, a yellow-red bathochromic shift was achieved by increasing the π-conjugated network of the scaffold, that was, however, accompanied by a very low quantum yield. In the second series, a scaffold rigidification was used to achieve a yellow-red bathochromic shift and an adequate quantum yield. In this occasion a first biological application of this new fluorescent probe in the design of new hDHODH inhibitor, are here described.