Generation of novel bioactive “unnatural” natural products through biotransformation by the enzymatic secretome of Botrytis cinerea

Biotransformation can be defined as the use of an intact whole organism or an isolated enzyme system to induce chemical modifications in organic compounds. Biotransformation has a number of advantages when compared to classical organic chemistry. The reactions can occur in mild conditions, near neutral pH, ambient temperatures, and atmospheric pressure, and protection of certain functional groups is often not necessary. For performing biotransformation of NPs, or NP extracts, the protein secretome from fungi could be considered as a promising tool. Fungi are indeed of interest since they synthetized diverse and complementary extracellular proteins to permit host penetration and further successful colonization. This group of secreted proteins released in the extracellular space is defined as the secretome and constitutes the pathogenicity factors in the host-pathogen interaction mechanisms.¹ In the present work, the protein secretome of Botrytis cinerea was used to perform the biotransformation of resveratrol, pterostilbene, and a mixture of both. The reactions were optimised with minimal amounts of NPs for monitoring at the analytical scale. Metabolite profiling by UHPLC-HRMS revealed the presence of compounds with unusual molecular formula, suggesting the existence of new products. The reactions were scaled-up and twenty-one analogues were isolated and fully characterized by NMR and HRESIMS analyses. The reaction with pterostilbene afforded five new compounds, while the reaction with a mixture of pterostilbene and resveratrol afforded seven unusual stilbene dimers. The antifungal properties of these compounds were evaluated using in vitro bioassays against Plasmopara viticola. Some of the isolated compounds present a strong antifungal activity showing that an inactive molecule, such as resveratrol, can be modified into more toxic compounds after enzymatic biotransformation. Our results suggest that biotransformation by usage of crude fungal secretomes represents an efficient way to create chemodiversity with enhanced biological activity.

[1] Gonzalez-Fernandez, R. et al V. Front Plant Sci 2015, 6, 839.