Abstract
As a major group of algae, diatoms are responsible for a substantial part of the primary production on the planet. Pennate diatoms have a predominantly benthic lifestyle and are the most species-rich diatom group, with members of the raphid clades being motile and generally having heterothallic sexual reproduction. It was recently shown that the model species Seminavis robusta uses multiple sexual cues during mating, including cyclo(l-Pro-l-Pro) as an attraction pheromone. Elaboration of the pheromone-detection system is a key aspect in elucidating pennate diatom life-cycle regulation that could yield novel fundamental insights into diatom speciation. This study reports the synthesis and bio-evaluation of seven novel pheromone analogs containing small structural alterations to the cyclo(l-Pro-l-Pro) pheromone. Toxicity, attraction, and interference assays were applied to assess their potential activity as a pheromone. Most of our analogs show a moderate-to-good bioactivity and low-to-no phytotoxicity. The pheromone activity of azide- and diazirine-containing analogs was unaffected and induced a similar mating behavior as the natural pheromone. These results demonstrate that the introduction of confined structural modifications can be used to develop a chemical probe based on the diazirine- and/or azide-containing analogs to study the pheromone-detection system of S. robusta.
Highlights
Diatoms play a key role in the biosphere
As an important group of phytoplankton, they account for about one-fifth of the photosynthesis on earth and form the basis of many of the aquatic ecosystems that exist on our planet [1,2]
There was no significant correlation found between the torsion angles and the bioactivity of the analogs (Pearson correlation coefficient = 0.41, p = 0.3). These observations suggest that the introduced chemical moieties could have a minor to no effect on the diketopiperazine conformation
Summary
Diatoms play a key role in the biosphere. As an important group of phytoplankton, they account for about one-fifth of the photosynthesis on earth and form the basis of many of the aquatic ecosystems that exist on our planet [1,2]. Parison: the pseudo‐axial positioning of the methoxy group (7) seems to have less impact on the pheromonal activity It is not clear how much of the interference effect of 7 is caused by the toxic nature of this compound. There was no significant correlation found between the torsion angles and the bioactivity (data presented in Figure 6) of the analogs (Pearson correlation coefficient = 0.41, p = 0.3) These observations suggest that the introduced chemical moieties could have a minor to no effect on the diketopiperazine conformation. The results of diazirine and azide analogs 3 to 5 demonstrate that these substituents can be incorporated into the cyclo(L-Pro-L-Pro) scaffold to probe the putative diatom pheromone receptor and to possibly characterize the action of 1 on other organisms as well
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