Nunavik, a vast subarctic territory located in northern Quebec (Canada), had been phytochemically marginally investigated despite its unique environmental conditions. Since the organisms living in those type of ecosystems are subject to extreme environmental stress (intense UV radiations, cold, predation, etc.), they adapted over time by developing unique biochemical pathways to survive. More specifically, lichen represent promising targets in the search of new bioactive molecule from this ecosystem. In addition of being dominant in Nordic ecosystems, those organisms, via the unique combination of metabolic pathway from two symbiotic partners (fungus and alga), can produce a plethora of unique secondary metabolites. However, the chemodiversity of northern territory is now threaten by the effect of climate changes. Facing this imminent ecosystem mutation, the Voyer group decided to investigate the phytochemistry of the Nordic lichen Stereocaulon paschale. This study resulted in the discovery of 13 lichen metabolites, two of which were new dibenzofurans (1 and 2, Fig. 1). Although these compounds showed some bioactivity in preliminary assays, their low abundance limited their study. In a way to allow an easier access to these new natural products as well as analogs, our group designed a synthetic route towards heavily functionalized dibenzofurans. Our convergent strategy involves two key steps. First, a biphenyl moiety is prepared by a Suzuki-Miyaura cross-coupling involving polyfunctionalized aryl rings (5 and 6, Fig. 1). One of these precursors is an aryl bromide (7 and 8, Fig. 1), while the second is an arylboronic acid (9 and 10, Fig. 1). Afterward, the dibenzofuran moiety is obtained via an intramolecular O-Arylation lead by a palladium-catalyzed C-H activation. Our latest progress in the application of this synthetic route as well as some challenges met along the way will be discussed in this presentation.

Total synthesis of highly functionalized dibenzofuran natural products isolated from the northern lichen Stereocaulon paschale

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