Synthesis and Evaluation of 9--Koshidacin B As Selective Inhibitor of Histone Deacetylase 1

A concise synthetic route to an epimer of the recently isolated biologically active cyclic tetrapeptide koshidacin B has been developed, which featured a late-stage functionalization of a macrocyclic scaffold through a cross metathesis reaction. The synthetic 9--koshidacin B showed marginal differences in spectroscopic behavior with that of the natural product but exhibited conformational preferences similar to those reported for analogous substrate chlamydocin. Moreover, it exhibited a useful level of selective inhibition of biologically relevant enzyme histone deacetylase 1 with an IC value of 0.145 μM over two other isoforms. Docking studies indicate that the natural product as well as its 9-epimer binds very similarly to the active site of HDAC1 indicating little influence of the configuration of the C9-stereocenter.