A simple synthesis of L‐[ 35 S]cysteine sulfinic acid

The synthesis of L‐[ 35 S]cysteine sulfinic acid (L‐2‐amino‐3‐[ 35 S] sulfino‐propanoic acid) in 65% yield from S‐[ 35 S]cystine is described. The procedure was designed for use with milligram quantities of starting material and requires no purification of intermediates. L‐[ 35 S]Cystine was converted first to its thiosulfonate. Subsequent reaction of the thiosulfonate with ammonium hydroxide generated L‐[ 35 S]cysteine sulfinic acid and L‐[ 35 S]cystine as the major products. The L‐[ 35 S]cystine was recovered and reprocessed thereby increasing the yield.