3-[(tert-Butoxycarbonyl)amino]-2-methylpropanoic-d3 Acid is labelled (R)-3-((tertButoxycarbonyl)amino)-2-methylpropanoic Acid (B692230), which has been used as a reactant in the preparation of cryptophycin B and arenastatin A, potent antiumor macrolides. 3-[(tert-Butoxycarbonyl)amino]-2-methylpropanoic-d3 Acid is an intermediate in the synthesis of labelled 3-Aminoisobutyric Acid (A611587). Unlabelled 3-Aminoisobutyric Acid (A611585) is a substituted β-alanines and is used for preparation and isolation of D(-)-β-Aminoisobutyric Acid.