Porphyric Insecticides - Chlorophyll Biosynthesis and Technological Applications - page 427

Quantitative structure activity calculations again revealed a potential relationship
between some physico-chemical properties of various analogs and photodynamic
insecticidal activity. For example, substantial increase in the distance between
N1 and N10 which ensued following the insertion of a disulfide bridge between
the two rings, as in 2,2 0 -dipyridyl disulfide, eliminated completely the insecticidal
activity (Fig. 18.6 , Table 18.14 , # 3, 4). As was observed for Oph analogs, electron
density changes in Dpy and its analogs that appeared to be related to reduced efficacy
included, (a) appearance of positive charge binding volumes at position 4 and 4 0 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 0 1 0 torsion angles which was accompanied
by the appearance of positive charge repelling volumes at the C5 0 -C6 0 ,or

C6 0 positions (Gut et al. 1993 ).

18.6.3 Structure-Activity Relationship
of Substituted Pyridiniums

The structure-activity relationships of four substituted Pyridiniums was investigated
(Fig. 18.4 ). Porphyric insecticide damage was positively correlated with Proto
accumulation except for 1,1 0 -diethyl-4,4 0 -carbocyanine iodide (Table 18.14 ,
# 9,10). Although light was absolutely required for the expression of activity,
enhancement of Proto accumulation appeared to be less pronounced than was
indicated by the high insect mortality. The only total loss of insecticidal activity
was observed in 1-(3-sulfopropyl) pyridinium hydroxide (Fig. 18.7 , Table 18.14 ,
# 3, 4). QSAR investigations of this compound revealed a 3.3 fold increase in the
value of its dipole moment (17.03 D) in comparison to 1,1 0 -diethyl-2,4 0 -cyanine
iodide (5.11 D) (Table 18.14 , # 7, 8) that lacked a sulfonyl group at the N + position
(Fig 18.7 ). This was accompanied by a substantial increase in positive charge
binding volumes and a substantial decrease in positive charge repelling volumes
around the molecule. In other words, it appeared that the presence of an unbalanced
positive charge at the N + position was essential for pyridinium activity. This was
also corroborated by the reduced insecticidal activity of Bis-N-methylacridinium
nitrate that has an NO 3 counterion (Table 18.14 , # 5, 6).

18.6.4 Structure-Activity Relationship of Substituted
Quinolines and Oxypyridines

Structure-activity relationships of four substituted 8-hydroxyquinolines, and two
substituted oxypyridines were also investigated (Fig. 18.7 ). Porphyric insecticidal
effects were positively correlated with Proto accumulation, and the presence of both