PHOTODYNAMIC HERBICIDES .9. STRUCTURE ACTIVITY STUDY OF SUBSTITUTED 1,10-PHENANTHROLINES AS POTENT PHOTODYNAMIC HERBICIDE MODULATORS

o-Phenanthroline, also known as 1,10-phenanthroline, is a potent photodynamic herbicide modulator which induces the accumulation of large amounts of tetrapyrroles in the absence or the presence of exogenous δ-aminolevulinic acid. Relationships between the molecular properties of substituted 1,10-phenanthroline analogues and their herbicidal and tetrapyrrole biosynthesis modulating activities were established. It was observed that the presence of two N atoms, at positions 1 and 10 of the 1,10-phenanthroline macrocycle, were mandatory for the expression of herbicidal activity. Quantitative structure-activity studies suggested that 90-98% of the variance in in vivo herbicidal photodynamic activity could be explained by the pattern of electronic density over specific regions of the molecules. Furthermore, it is suggested that observed variations in the tetrapyrrole modulating activities of substituted 1,10-phenanthrolines are due to alterations in their molecular electrostatic potentials. © 1991.