Abstract Setting out from protected L-cysteine a 2, 5-diketopiperazine V can be synthesized, the reduction of which with NaBH 4/TiCl 4 leads to (6R, 8aR)-7-methyl-6-(sulfanylmethyl)- thiazolidine [3, 4-a] piperazine, L 1 H as well as N, N′-dimethyl-(2R, 5R)-bis (sulfanylmethyl) piperazine, L 2 H 2, which were separated and characterized. L 2 H 2 can be obtained selectively, if V is reduced by NaBH 4/TiCl 4 in the presence of DIEA· HCl, ...