isoGTP (Isoguanosine-5'-O-triphosphate) sodium is an isomer of guanosine 5'-triphosphate and a phosphorylated form of Crotonoside. In reverse transcriptase assays, isoGTP sodium inhibits transcription and induces T-to-C mutations. It holds potential for research on substrate specificity of fructose phosphate kinase and mutT homolog 1 (MTH1).