Reduction of a 4-pyrrole phenylacyl-containing peptide with trifluoroacetic acid–triisopropylsilane–phenol–H2O during solid-phase peptide synthesis and its protein kinase C α inhibitory activity

Cleavage of 4-pyrrole phenylacyl TentaGel-appended peptide (5) containing Arg(Pbf) with trifluoroacetic acid/triisopropylsilane/phenol/H2O (90/2/4/4) gives the 4-pyrrole phenylacyl peptide (3). However, cleavage of 4-pyrrole phenylacyl Rink-appended peptide (7) containing Arg(Pbf) using the same reagents furnishes the 4-pyrrolidine phenylacyl peptide (8), which contains the reduced pyrrole ring. Compound 8 displays a Ki of 2.32 μM, approximately fivefold less potent than compound 3.