Synthesis of 3-(4-bromobenzyl)-5-(arylmethylene)-5H-furan-2-ones and their activity as inhibitors of the photosynthetic electron transport chain.

A series of 12 3-(4-bromobenzyl)-5-(arylmethylene)-5H-furan-2-one lactones, designed using the naturally occurring toxin nostoclides as a lead structure, were synthesized and screened as potential inhibitors of photosynthetic electron transport. The structures were confirmed by 1H and 13C NMR, MS, and IR analyses. Their biological activity was evaluated both in vitro, as the ability to interfere with light-driven reduction of ferricyanide by isolated spinach chloroplasts, and in vivo, as the capability to inhibit the oxygen production by intact Chlorella cells. Some of the compounds exhibited inhibitory properties in the micromolar range against basal and phosphorylating electron flow from water to K3[Fe(CN)6], with no effect on uncoupled electron flow. Thus, they seem to behave as energy-transfer inhibitors. Although poor solubility in water may limit their effectiveness, the active derivatives could present structures to be exploited for the design of new substances endowed with herbicidal activity.