Porphyric Insecticides - Chlorophyll Biosynthesis and Technological Applications - page 425

Table 18.12 Effects of ALA, phenanthrene and 1,10-phenanthroline (Oph) on Proto accumulation
and larval death in T . ni

Proto content
(nmol/100 mg protein)

Larval mortality after 6 days
in the greenhouse (%) Entry Treatment a

1.5a b 1 Control 0.0a

2 ALA 3.0a 15.0abcd

3 2,9-Dimethyl-4,7-diphenyl Oph 0.8a 0.0a

4 Above + ALA 1.6a 10.0abc

5 2,9-Dimethyl-4,7-diphenyl Oph 1.2a 0.0a

6 Above + ALA 1.6a 18.3abcd

7 Phenanthrene 1.0a 0.0a

8 Above + ALA 3.9a 23.3bcd

9 4,7-Diphenyl Oph 1.3a 0.0a

10 Above + ALA 8.6a 36.7 cd

11 3,4,7,8-Tetramethyl Oph 5.1a 11.7abcd

12 Above + ALA 117.0c 95.0e

13 4,7-Dimethyl Oph 15.9a 8.3ab

14 Above + ALA 131.5c 96.7e

15 5-Cl-Oph 2.0a 10.0abc

16 Above + ALA 133.9c 96.7e

17 5-Nitro-Oph 50.4b 41.7d

18 Above + ALA 190.1d 98.3e

19 Oph 8.6a 5.0a

20 Above + ALA 207.0d 100.0e

Correlation coefficient 0.88

Level of significance 0.1 %

Adapted from Gut et al. ( 1993 )
a Treatment consisted of control diet lacking any added ALA or modulator, diet containing 4 mM
ALA, 3 mMmodulator or 4 mM ALA + 3 mMmodulator, in a randomized complete block design
with three replicates. Percent larval death was arcsine transformed prior to statistical analysis
b Means followed by the same letter within a column are not significantly different at the 5 % level
of significance

Quantitative structure activity calculations suggested a relationship between
peripheral group substitution and some physico-chemical properties of the substituted
compounds. Electron density changes in Oph and its analogs that appeared to be
related to reduced efficacy included (Gut et al. 1993 ) (a) Appearance of positive
charge binding volumes at position 4 and 7 of the 1,10-phenanthroline macrocycle,
which flanks positive charge repelling volumes, (b) a dramatic increase in super-
delocalisability (i.e. electron density) over some unoccupied molecular orbitals, and
(c) electronic charge at position 1 and 10 of themacrocycle. Large increases inVan der
Waals volumes also exerted negative effects on insecticidal efficacy (Gut et al. 1993 ).

18.6.2 Structure-Activity Relationship of Substituted Pyridyls

The porphyric insecticide modulating activity of Dpy and eight of its analogs are
depicted below in Table 18.13 . The insecticidal efficacy of Dpy and its analogs was