PORPHYRIC INSECTICIDES .8. STRUCTURE-ACTIVITY STUDY OF SUBSTITUTED PYRIDYLS

The porphyric insecticidal modulating activity of 2,2'-dipyridyl and e ight of its analogs was investigated. The insecticidal efficacy of the se compounds was closely associated with their ability to enhance the conversion of exogenous delta-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 Waa ls energy, 1,2,2',1' torsion angles, molecular size, and superdelocali zability over the lowest unoccupied molecular orbitals. Electrostatic field changes in the 2,2'-dipyridyl analogs that appeared to be relate d to reduced insecticidal efficacy included: (a) the appearance of pos itive charge binding volumes at positions 4 and 4' of the dipyridyl ma crocycle, which flanked positive charge repelling volumes; (b) the acq uisition of a fourth phenyl or pyridyl ring which generated alternatin g positive charge binding and repelling electrostatic fields between r ings 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 cha rge repelling volumes at the C5'-C6' or C6' position. (C) 1994 Academi c Press, Inc.