Pseurotin

We report synthesis of two diastereomeric structures previously proposed for the complex secondary metabolite pseurotin A2. Both structures were accessed from the same building blocks taking advantage of a stereodivergent nickel(II)-diamine-catalyzed 1,4-addition of a chiral 2-alkoxycarbonyl-3(2H)-furanone. Late-stage Csp-Csp3 cross-coupling of a highly functionalized bromoalkyne featured in the pseurotin A2 side-chain assembly. The work supports the 2016 stereochemical revision of pseurotin A2 and represents the first chemical synthesis of this natural product.

Pseurotins, secondary metabolites of fungi, represent a group of bioactive natural products with newly recognized biological activities, including the modulation of specific immune response. However, the type of immune response affected by pseurotins and the mechanistic details underlying these effects are still not understood. Thus, the aim of the current study was to examine the effects of pseurotin D on delayed-type IV hypersensitivity (DTH) reaction induced by chicken ovalbumin in vivo and to examine the effects of pseurotin D on major types of leukocytes responsible for DTH development in vitro. Pseurotin D significantly decreased paw swelling, the major symptom of DTH, as well as the DTH-related production of pro-inflammatory cytokine IL-1β, IL-4, IL-6, IFN-γ and anti-inflammatory cytokine IL-10 in paws tissue, spleen enlargement, and DTH-related changes in leukocyte counts in peripheral blood. In vitro, pseurotin D mediated a decrease in the proliferation and differentiation of both Th1 and Th2 cells, as was concluded on the basis of the inhibition of the gene expressions of Gata3 and Tbx21 and the production of effector cytokines IFN-γ and IL-13 in vitro. Further, pseurotin D significantly inhibited the activation and differentiation of B cells, as was documented by the significant inhibition of B cell proliferation, CD138 expression, and IgE production. In conclusion, the results show the potential of pseurotin D to inhibit DTH reaction, this phenomenon involving the inhibition of the activation and differentiation of both T cells and B cells.

Species from the Metarhizium genus are the causal agents of the green muscardine disease of insects. These fungi have been successfully employed for the biological control of pests over decades. Besides the biocontrol applications, recent efforts for genome sequencing of species in this genus have revealed a great diversity of biosynthetic gene clusters potentially associated with secondary metabolite synthesis. Amongst such molecules are the pseurotins, compounds with several activities, as chitin synthase inhibitors, and immunoglobulin E suppressors. Here, we report, for the first time, the isolation of pseurotin A from the culture broth of M. anisopliae, as well as the characterization of the effects of this compound over the model-arthropod Galleria mellonella. Pseurotin A displayed dose-dependent reversible paralysis effects when injected into the larvae hemocoel. However, the posterior challenge of the treated insects with M. anisopliae conidia did not lead to increased mortality, suggesting that pseurotin A treatment did not increase larvae susceptibility to the green muscardine disease. Although apparent insecticidal effects were not observed for pseurotin A, the paralysis effect observed can be important in M. anisopliae infection development.