Practical approach to solid‐phase synthesis of C‐terminal peptide amides under mild conditions based on a photolysable anchoring linkage

Several 3‐nitro‐4‐(N‐protected aminomethyl)benzoic acids, with protection provided by tert.‐butyloxycar‐bonyl (Boc), 9‐fluorenylmethyloxycarbonyl (Fmoc), trifluoroacetyl (Tfa), dithiasuccinoyl (Dts), or phthaloyl (Phth), have been prepared by reproducible routes. Synthesis of Dts‐handle 6 illustrates some particularly novel and efficient chemistry, and is preferred over more intricate routes to Boc‐handle 3 and Fmoc‐handle 4. The five handles were each evaluated for their application to the synthesis of peptide amides. Coupling onto amino‐functionalized supports provided a general starting point for peptide chain assembly. The handle amino function was deblocked (Boc, Fmoc, Dts), the C‐terminal residue was coupled as its N^x‐protected free acid, and ultimately the ortho‐nitrobenzylamide anchoring linkage was cleaved photolytic‐ally to give the corresponding amide. Starting with handles 3, 4, and 6, several free and protected peptide amides were synthesized.