Diagnosis and therapy exploiting overexpressed receptors on the cell surface is one important strategy in medicine. Determination of the over expression level of a particular receptor is prerequisite for it to be of clinical use. Differentiation between FR-positive (FR=folate receptor) and -negative cells via fluorescence microscopy using a substrate mimetic fluorophore is presented in this work. The strategy adopted here is not the classical FA-conjugated (FA=folic acid) fluorescent probe but a small and environment-sensitive pterin-based (pterin is part of folate, i.e., vitamin B9) fluorescent probe. Electronically diverse pterin-based fluorescent probes have been designed and synthesized to understand the effect of the binding environment on the receptor-substrate interactions. By utilizing steady-state UV/Vis and fluorescence along with time-resolved fluorescence spectroscopy, the effects on the electronic and acid-base properties of the substrate were investigated. Evidently, one synthesized probe showed FA-mimicking behavior with strong binding interaction with FR.

Molybdenum cofactor (Moco) deficiency is a lethal hereditary metabolic disease. A recently developed therapy requires continuous intravenous supplementation of the biosynthetic Moco precursor cyclic pyranopterin monophosphate (cPMP). The limited stability of the latter natural product, mostly due to oxidative degradation, is problematic for oral administration. Therefore, the synthesis of more stable cPMP analogues is of great interest. In this context and for the first time, the synthesis of a cPMP analogue, in which the oxidation‐labile reduced pterin unit is replaced by a pyrazine moiety, was achieved starting from the chiral pool materials D‐galactose or D‐arabitol. Our synthesis, 13 steps in total, includes the following key transformations: i) pyrazine lithiation, followed by acylation; ii) closure of the pyrane ring by nucleophilic aromatic substitution; and iii) introduction of phosphate.