Cyclic tetrapeptides with -SS- bridging between amino acid side chains for potent histone deacetylases' inhibition.

Cyclic depsipeptide FK228 with an intramolecular disulfide bond is a potent inhibitor of histone deacetylases (HDAC). FK228 is stable in blood because of its prodrug function, whose -SS- bond is reduced within the cell. Here, cyclic peptides with -SS- bridges between a variety of amino acids were synthesized and assayed for HDAC inhibition. Cyclic peptide 3, cyclo(-L-amino acid-L-amino acid-L-Val-D-Pro-), with an -SS- bridge between the first and second amino acids, was found to be a potent HDAC inhibitor. Cyclic peptide 7, cyclo(-L-amino acid-D-amino acid-L-Val-D-Pro-), with an -SS- bridge between the first and second amino acids, was also a potent HDAC inhibitor.