Emissive Synthetic Cofactors: Enzymatic Interconversions of tzA Analogues of ATP,NAD+, NADH,NADP+, and NADPH

A series of enzymatic transformations, which generate visibly emissive isofunctional cofactors based on an isothiazolo[4,3‐d]pyrimidine analogue of adenosine ( ^tz A ), was developed. Nicotinamide adenylyl transferase condenses nicotinamide mononucleotide and ^tz ATP to yield N^tzAD⁺ , which can be enzymatically phosphorylated by NAD⁺ kinase and ATP or ^tz ATP to the corresponding N^tzADP⁺ . The latter can be engaged in NADP‐specific coupled enzymatic transformations involving conversion to N^tzADPH by glucose‐6‐phosphate dehydrogenase and reoxidation to N^tzADP⁺ by glutathione reductase. The N^tzADP⁺ / N^tzADPH cycle can be monitored in real time by fluorescence spectroscopy.