Schematic preparation of a novel aminopyridine-based fluorescent reporter (ADP) and LAP substrates. Reagents and conditions: (a) DMSO/150-160 °C, overnight, 60%; (b) Pt/H2 in CH3OH, 4 h, 90%; (c) (N-(tert-butoxycarbonyl)-L-leucine monohydrate, DBU, 1,3-diisopropylcarbodiimide/CH2Cl2, 2h, 96%; (d) TFA, 2 h, 55%.