Stereoselective Synthesis of Stable Isotope Labeled L-α-Amino Acids: Synthesis of L−[4−13C] and L−[3,4−13C2]Aspartic Acid

We have developed a stereoselective route to isotopically labeled L-aspartic acid using L-serine as a chiral precursor. Labeled serine, prepared biosynthetically was N-protected by conversion to the N-t-Boc derivative. (N-t-Boc)-[3-C-13]Serine is cyclized to its beta-lactone which was treated with potassium [C-13]cyanide to yield L-beta-[3,4-C-13(2)]cyanoalanine. Hydrolysis of the cyanoalanine yielded L-[3,4-C-13(2)]aspartic acid. Similarly, L-[4-C-13]aspartate was produced from L-serine and K13CN. Using this route, the L-enantiomer was produced in 96% excess.