Emissive Synthetic Cofactors: Enzymatic Interconversions of tz A 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 tz AD + , which can be enzymatically phosphorylated by NAD + kinase and ATP or tz ATP to the corresponding N tz ADP + . The latter can be engaged in NADP‐specific coupled enzymatic transformations involving conversion to N tz ADPH by glucose‐6‐phosphate dehydrogenase and reoxidation to N tz ADP + by glutathione reductase. The N tz ADP + / N tz ADPH cycle can be monitored in real time by fluorescence spectroscopy.