Synthesis And Activity Of Phenoloxidase Inhibitors On Pieris Rapae (L.)

Phenoloxidase(PO, EC.1.14.18.1), also known as tyrosinase, is a copper-containing enzyme that widely distributed in plants, microorganisms animals and human. The enzyme possesses an important function in meta- morphism developing and immunity system. This multifunctional enzyme catalyzes two distinct reactions, the hydroxylation of monophenol to o-diphenol(monophenolase activity) and the conversion of o-diphenol to the corresponding o-quinone(diphenolase activity). Further, it is involved in formation of pigments such as melanin. In insects, phenoloxidase is also a widely distributed enzyme playing important roles in normal developmental processes, such as cuticular tanning, scleration, wound healing, production of opsonins, encapsulation and nodule formation for defense against foreign pathogens. This is a useful basis for designing effective, selective, and environment-friendly PO inhibitors.In previous studies, we investigated the inhibition of compounds such as substituted benzaldehydes, substituted benzoic acids, kojic acid, apigenin, quercetin, rutin and flavonoids against PO activity. Most of them inhibit the PO by chelating with Cu(II) ions. Two Cu(II) ions are defined in the active site of the PO. The contents and results were summarized as follows:1. Three series of 57 compouds containing 21 substituted benzaldehyde thiosemicarbazones, 21 substituted salicyl schiff bases and 15α-mercapto-β-aryl acrylic acids were synthesized, including 37 new compounds, which were characterized by IR, 1HNMR and elemental analysis. Synthesis condition, physicochemical properties, and spectrum properties of the compounds were reported.2. PO was extracted and primary purified from the 5th instar Pieris rapae(L.), then, target compounds against the phenoloxidase were tested. Primary results showed that the compounds displayed good inhibitory activity. The inhibitory effects on the PO activity by substituted benzaldehyde thiosemicarbazones andα-mercapto-β-aryl acrylic acids were determined, the IC50 were 0.26 ~ 100μmol·L-1 and 0.37 ~ 6.30 mmol·L-1, respectively. At the concentration of 0.10 mmol·L-1 and 0.20 mmol·L-1 of substituted salicyl schiff bases, inhibitory activity of the IIn and IIo were 55% ~ 70%.At the same time, the relationships of the activity and structure of three series target compounds were analyzed and discussed. These not only supported some reffences to more design on new high biological activity and low toxicity inhibitors of the PO, but also some of the compounds possibly have the practical application in the fields of medical treatments and agriculturel insecticides.