Organic Chemistry of L-Tyrosine. 1. General Synthesis of Chiral Piperazines from Amino Acids

Article abstract of DOI:10.1021/jo00224a051

A new method for the conversion of optically active diketopiperazines (cyclo-dipeptides) into optically pure piperazines is described.Due to poor solubility of certain cyclo-dityrosine derivatives, the usual method using lithium aluminum hydride reaction was problematic, giving racemization under forcing conditions.However, the use of borane/tetrahydrofuran for this diketopiperazine to piperazine reduction proceeded well, affording high yields of optically pure materials.In this manner several mixed cyclo-dityrosine derivatives 9a-d were transformed into the piperazines 10a-d, potentially useful intermediates for the synthesis of the antibiotic alkaloids, piperazinomycin (1) and herquline (2).Finally, the naturally occuring alkaloid isolated from Zanthoxylum arborescens, 7b was prepared by this route.