Stereocontrol and Biological Activity of Antifeeding Substances with Perhydrofuro[2, 3-b]furan Ring System

Abstract

Diterpenes which have a neoclerodane skeleton such as clerodin, clerodendrin A, and caryoptin show the absolute antifeeding activity for the larvae of Spodoptera litura F. and it is shown that the perhydrofuro[2, 3-b]furan ring in their structures is the active center of the antifeeding activity.
In order t o elucidate the structure-activity relationships of the antifeeding s ubstances, we synthesized the perhydrofuro[2, 3-b]furan derivatives with various phenyl substituents [5], [14], [23] and clerodin homolog [9]. As an approach to clarify quantitatively and rapidly structural factors (steric or electronic effects, etc.) which are essential for the appearance of biological activity of the model compounds, we considered the application of a chemical reaction on the active center, taking the place of their biological reactions on an receptor in vivo. Consequently, a good correlation came out between the chemical stability for mathanolysis of the model compounds by the steric control of their methyl groups and their biological activity. Based on these observations, we proposed the following hypotheses: i ) for the appearance of the biological activity, a definite steric environment around the active center is needed, ii)when the above condition is satisfied, the chemical reactions on the active center hold constant regardless of the supporting structures, the active center holding a constant reactivity represents a constant biological activity. This methodology discusses and compares the dynamic changes (reactivity) of the active center and the variation of biological activity as accompanied by structural changes, being conceptually termed “Dynamic Structure-Activity Relationships”.