Porphyric insecticides 8. structure-activity study of substituted pyridyls

The porphyric insecticidal modulating activity of 2,2′-dipyridyl and eight of its analogs was investigated. The insecticidal efficacy of these compounds was closely associated with their ability to enhance the conversion of exogenous δ-aminolevulinic acid to protoporphyrin IX. The relationship between photodynamic damage in Trichoplusia ni and various physical-chemical properties of Dpy analogs was rather complex and involved a multidimensional surface that consisted of van der Waals energy, 1,2,2′,1′ torsion angles, molecular size, and superdelocalizability over the lowest unoccupied molecular orbitals. Electrostatic field changes in the 2,2′-dipyridyl analogs that appeared to be related to reduced insecticidal efficacy included: (a) the appearance of positive charge binding volumes at positions 4 and 4′ of the dipyridyl macrocycle, which flanked positive charge repelling volumes; (b) the acquisition of a fourth phenyl or pyridyl ring which generated alternating positive charge binding and repelling electrostatic fields between rings C and D; and (c) a change in sign and magnitude of the 1,2,2′,1′ torsion angles which was accompanied by the appearance of positive charge repelling volumes at the C5′-C6′ or C6′ position.