A nucleoside analogue of adenosine that arises from post-transcriptional modification. In humans, this is mediated by the enzyme CDK5RAP1 in mitochondrial transfer RNA (tRNA) at amino acid 37. Deficiency for this modification, for example due to CDK5RAP1 deficiency, leads to impaired mitochondrial protein synthesis. This has implications for mitochondrial diseases, as well as cancer, type II diabetes and vitiligo. Synthetic ms2i6A can be used to raise monoclonal antibodies against this nucleotide in vivo.