is_reactive_with primary amine reactive PCAS 1 106.02928900000000567 C6 H4 N1 O1 PCAS-H4 PCAS-d0 PCASS Pyridine-3-Carboxylic Acid Succinimide. PyridineCarboxylicAcidSuccinimide XLMOD XLMOD:02051 amino acid reactive