Synthesis of the unusual α-amino acid component of some novel histone deacetylase inhibiting cyclic peptides

Synthesis and Evaluation of 9-epi-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-epi-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 IC50 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.

α,ß-Didehydrosuberoylanilide hydroxamic acid (DDSAHA) as precursor and possible analogue of the anticancer drug SAHA

An alternate synthetic route to the important anticancer drug suberoylanilide hydroxamic acid (SAHA) from its α,ß-didehydro derivative is described. The didehydro derivative is obtained through a cross metathesis reaction between a suitable terminal alkene and N-benzyloxyacrylamide. Some of the didehydro derivatives of SAHA were preliminarily evaluated for anticancer activity towards HeLa cells. The administration of the analogues caused a significant decrease in the proliferation of HeLa cells. Furthermore, one of the analogues showed a maximum cytotoxicity with a minimum GI₅₀ value of 2.5 µg/mL and the generation of reactive oxygen species (ROS) as some apoptotic features.

Divergent Access to Histone Deacetylase Inhibitory Cyclopeptides via a Late-Stage Cyclopropane Ring Cleavage Strategy. Short Synthesis of Chlamydocin

A unified step-economical strategy for accessing histone deacetylase inhibitory peptides is proposed, based on the late-stage installation of multiple zinc-binding functionalities via the cleavage of the strained cyclopropane ring in the common pluripotent cyclopropanol precursor. The efficacy of the proposed diversity-oriented approach has been validated by short stereoselective synthesis of natural product chlamydocin, containing a challenging-to-install fragment of (2S,9S)-2-amino-8-oxo-9,10-epoxydecanoic acid (Aoe) and a range of its analogues, derivatives of 2-amino-8-oxodecanoic and 2-aminosuberic acids.

Cross metathesis-mediated synthesis of hydroxamic acid derivatives

An alternative synthesis of α,ß-unsaturated hydroxamates via cross metathesis between a class-I olefin and N-benzyloxyacrylamide is reported. The reaction proceeds better in the presence of Grubbs’ second generation catalyst within short time and in good yields (57–85%) with a range of substrates. Subsequent hydrogenation of each of the CM products delivers the title compounds in moderate to very good yield (70–89%). An important demonstration of the protocol is the preparation of the unusual amino acid component of the bioactive cyclic peptide Chap-31.