NEUROPEPTIDE-Y ACYLATION CHEMISTRY IN AQUEOUS-SOLUTION - SIGNIFICANCETO SYNTHESIS OF A PEPTIDE-BASED PHOTOAFFINITY LABEL

Treatment of neuropeptide Y (NPY, 1) for 20 hr with a 20 equivalent ex cess of N-propionyl succinimide (2) in 10 mM phosphate buffer, pH 6.0, yields NPY and N(alpha)-propionyl-NPY (3) as major products, and at p H 7.5 the major product is N(alpha), N(epsilon)-dipropionyl-NPY. Howev er, acylation of NPY with one equivalent of N-(5-azido-2-nitrobenzolyl oxy)-succinimide (5) is more rapid, yielding N(alpha)-(5-azido-2-nitro benzoyl)-NPY (6) in 70% conversion yield after only 5 min. Thus, in sp ite of its increased reactivity, the N-hydroxysuccinimide active ester shows enhanced alpha- vs. epsilon-NH2 selectivity relative to 2. The activities of 3, 4, and 6 as reversible, competitive ligands at rat br ain NPY binding sites and of 6 as an irreversible photoaffinity label are reported.