(2S,6R)-6-Benzyl-piperazine-1,2-dicarboxylic acid 1-tert-butyl ester

(R)-4-((R)-2-Hydroxy-1-phenyl-ethyl)-2-methyl-piperazine-1-carboxylic acid tert-butyl ester

(R)-4-((R)-2-Methoxy-1-phenyl-ethyl)-2-methyl-piperazine-1-carboxylic acid tert-butyl ester

(R)-2-Benzyl-4-((R)-2-hydroxy-1-phenyl-ethyl)-piperazine-1-carboxylic acid tert-butyl ester

(2S,6R)-4-((R)-2-Methoxy-1-phenyl-ethyl)-6-methyl-piperazine-1,2-dicarboxylic acid 1-tert-butyl ester