p-Nitromandelic acid as a highly acid-stable safety-catch linker for solid-phase synthesis of peptide and depsipeptide acids.

[reaction: see text] p-Nitromandelic acid as a safety-catch linker for Boc/Bzl-SPPS of base-labile compounds like peptides and depsipeptides is described. This linker permits acidic removal of side-chain protection groups from the resin. For cleavage from the solid support, the p-nitro group was reduced with tin(II) chloride. After washing off the reducing agents, the (depsi)peptide acids with or without the side-chain protection schemes were obtained by microwave irradiation at 50 degrees C with 5% TFA in dioxane.