Photodynamic Herbicides - Chlorophyll Biosynthesis and Technological Applications - page 367

structurally related to one quadrant of a tetrapyrrole molecule, i.e. to an individual
pyrrole, such as picolinic acid, nicotinic acid and substituted pyridyls (Fig. 17.4 ).
This in turn suggested that this similarity between the chemical structures of the
templates and between tetrapyrrole halves or quadrants may be essential to the
TDPH activity of the templates, as it may facilitate the binding of the templates to
or close to the reaction sites of specific enzymes of the chlorophyll biosynthetic
pathway. It was possible to visualize how such enzymes may be fooled by the
structural similarities between the templates and those parts of the tetrapyrrole
substrates that bind to the chlorophyll biosynthetic enzymes. What was not clear at
this stage was the way that such a template-enzyme binding may modulate the
activity of chlorophyll biosynthetic enzymes.
The aforementioned template-enzyme binding hypothesis led in turn to the
discovery of an important novel template. It was conjectured that substituted
5-membered N-containing rings, i.e. substituted pyrroles (Fig. 17.3 ) may prove to
Fig. 17.3 (continued)