1-Methylinosine-d3 (N1-MetHYlinosine-d3) is the deuterium labeled 1-Methylinosine. 1-Methylinosine is a modified nucleotide located at position 37 of eukaryotic tRNA, 3 to the tRNA anticodon. 1-Methylinosine is a minor metabolite of 1-methyladenosine (HY-113081). The level of 1-Methylinosine is significantly elevated in urine samples from breast cancer models.