A useful synthesis of nopaline, a crown gall tumor metabolite

Nopaline, a reductive conjugate of arginine and α-ketoglutaric acid found in plant tumors incited by Argobacterium tumefaciens, has been synthesized. Three routes were studied. Reduction of L-arginine and α-ketoglutaric acid with sodium cyanoborohydride gave an 80% yield of the diastereomers nopaline and isonopaline. This was by far the best method. The synthetic mixture of diastereomers is capable of replacing purified natural nopaline in biological experiments.