Synthesis of N-15-labelled D-isovaline and alpha-aminoisobutyric acid

[N-15]-D-isovaline was prepared from DL-[alpha-N-15]-alpha-aminoisovalerami de by enzymatic resolution with Mycobacterium neoaurum. The N-15-isotope wa s introduced during the Strecker synthesis of its precursor, e.g. aminoisov aleronitrile. Attempts to prepare the amino nitrile precursor of [N-15]-alp ha-aminoisobutyric acid (Aib) led to a poor yield and loss of the label. Si gnificantly, improved results were obtained when a cosolvent is present dur ing formation of aminoisobutyronitrile.