Brown seaweed defensive chemicals: A structure-activity relationship approach for the marine environment

Abstract

The literature describes several diterpenes from brown seaweeds that act as defensive chemicals against natural enemies, such as competitors, epiphytes, pathogenic bacteria and herbivores. A structure-activity relationship is here presented using a new molecular modeling approach to identify structural and chemical features important to the defensive profile of four structurally related diterpenes (three dolastanes and one seco-dolastane) from Canistrocarpus cervicornis against the feeding process of the omnivorous sea urchin Lytechinus variegatus. Our experimental data revealed the herbivory inhibitory profile (HIE) for three of these evaluated compounds with (4R,7R,14S)-4α,7α- diacetoxy-14-hydroxydolast-1(15),8-diene presenting the highest effect (HIE = 70%). Interestingly, the molecular modeling results infer that this biological activity seems to be related to several different structural features, including HOMO distribution, the molecular structure conformation, and the fulfillment of minimum requirements regarding molecular weight. These results reinforce the hypothesis about the intricate biological mechanism of these molecules due to the complexity of their chemical structures. Our work may help in the understanding of these defensive mechanisms and point to a new perspective of ecological and/or evolutionary evaluation in this area.