Neuropeptide Y acylation chemistry in aqueous solution: Significance to synthesis of a peptide-based photoaffinity label

Treatment of neuropeptide Y (NPY,1) for 20 hr with a 20 equivalent excess of N-propionyl succinimide (2) in 10 mM phosphate buffer,pH 6.0, yields NPY and N-propionyl-NPY (3) as major products, and atpH 7.5 the major product is N, N-dipropionyl-NPY. However, acylation of NPY with one equivalent of N-(5-azido-2-nitrobenzolyloxy)-succinimide (5) is more rapid, yielding N-(5-azido-2-nitrobenzoyl)-NPY (6) in 70% conversion yield after only 5 min. Thus, in spite of its increased reactivity, the N-hydroxysuccinimide active ester shows enhanced- vs.-NH₂ selectivity relative to2. The activities of3, 4, and6 as reversible, competitive ligands at rat brain NPY binding sites and of6 as an irreversible photoaffinity label are reported.Abbreviations used NPY neuropeptide Y - PYY peptide YY - DNFB dinitrofluorobenzene - DNP dinitrophenyl - LAPase leucine aminopeptidase m - HPLC high-performance liquid chromatography - RT retention time - FAB⁺MS positive fast atom bombardment mass spectrometry Taken in part from the Ph.D. dissertation of Longqin Hu, The University of Kansas, 1993.