Synthesis of novel biphenyls containing thiophene, pyridazinimine and 1,3,4-thiadiazole moieties, and their effects on the mortality, oxidative stress and antioxidant enzymes in the desert locust, Schistocerca gregaria (Forskål) (Orthoptera: Acridiidae)

Abstract

Abstract Biphenyls acting on insects are an intensive research area now. In order to search for novel biphenyl candidates, a series of biphenyl derivatives containing thiophene, pyridazinimine and 1,3,4-thiadiazole moieties were synthesized. Their insecticidal activities on the newly molted fifth nymphal instars of the desert locust, Schistocerca gregaria, were screened. Additionally, the effect of the most toxic compound on the level of malondialdehyde (MDA) and on the activity of the antioxidant enzymes, catalase (CAT) and glutathione S-transferase (GST), in the thoracic muscles and the midgut was also evaluated. The synthesized compounds were characterized through 1HNMR, 13C NMR and high-resolution mass spectrometry. Bioassay indicated that they showed insecticidal activity; the compound 11 with thiophene nucleus (8-13), phenylamino group and ethyl carboxylate moiety, in a certain arrangement, in addition to biphenylcarbonyl was the most toxic one, with LC50 of 42.90 ppm using leaf – dip technique. This compound increased the activity of MDA and GST, whereas the activity of CAT decreased. The present work demonstrated that biphenyl derivatives can be used as possible major compounds to develop novel insecticides. Additionally, antioxidant biomarkers such as MDA and GST and CAT were involved in the free radical scavenging in response to exposure of S. gregaria to the target compound 11.