Alpha-keto amide peptides: a synthetic strategy to resin-bound peptide isosteres for protease inhibitor screening on solid support.

A synthetic strategy for the formation of resin-bound internal alpha-keto amide peptides suitable for protease inhibitor screening on solid support is presented. This general approach is based on the incorporation of alpha-keto amide building blocks during solid-phase peptide synthesis (SPPS). Such dipeptidyl building blocks were accessible using the acylcyanophosphorane methodology. The acid-labile alpha-keto carbonyl functionality was protected as a 1,3-dithiolane derivative. This protective group is fully compatible with standard SPPS reaction conditions and can be efficiently removed with N-bromosuccinimide in 10% aqueous acetone. The alpha-keto amide peptides were assembled on SPOCC-1500 resin and were characterized with high-resolution magic angle spinning (HR-MAS) NMR on bead. The methodology was evaluated and tested with a variety of building blocks containing natural and nonnatural amino acid moieties.