Design and Synthesis of Phosphonoproline-Proline Bioisosteric Mimetics of Proline Dimers: Pseudopeptide Constructs as Potential Inhibitors of the Zn-Metalloprotease PPEP-1 Associated with Clostridioides difficile

The design, synthesis and preliminary inhibitory activity of novel phosphonoproline–proline-containing pseudohexapeptides against PPEP-1, a metalloprotease secreted by Clostridioides difficile, is reported. Remarkably, the P ( R ) -configured phosphonoproline–proline hexapeptide bioisostere of the synthetic heptapeptide Ac-EVNPPVP-NH 2 is 1000 times more active than the corresponding P ( S ) analogue as measured by a FRET assay, which represents a binding energy of about 12 kJ/mol. Placing an embedded enantiopure phosphonoproline unit to replace a proline within a peptidic construct constitutes a promising venue in the design of proline-containing metalloenzyme inhibitors.