5-Deoxy-5-methylthioadenosine-d3 is a stable, deuterium-labeled analogue of the endogenous nucleoside metabolite 5-Deoxy-5-methylthioadenosine (MTA, CAS 2457-80-9). this compound retains the tumor cell proliferation inhibitory effects of the parent molecule and is primarily utilized as an internal standard in mass spectrometry-based metabolomic studies to quantify MTA levels in biological samples.