Synthesis and biological activity of peptide proline-boronic acids as proteasome inhibitors

On the basis of the application of proline-boronic acid as pharmacophore in the kinase inhibitors and our previous research results, using proline-boronic acid as warhead, two series of peptide proline-boronic acids, dipeptide proline-boronic acids (I) and tripeptide proline-boronic acids (II), were designed and synthesized. All the synthesized compounds were first evaluated for their biological activity against MGC803 cell, and then, the best compound II-7 was selected to test its anti-tumor spectrum on six human tumor cell lines and proteasome inhibition against three subunits. The results indicated that series II have much better biological activities than series I. The compound II-7 exhibited not only excellent biological activities with IC₅₀ values of nM level in both cell and proteasome models, but also much better subunit selectivity. Thus, proline-boronic acid as warhead is reasonable in the design of proteasome inhibitors.