Heterologous combinatorial biosynthesis of daurichromenic acid derivatives from a common metabolite in Rhododendron species and evaluation of their SARS-CoV-2 inhibitory activities.

Rhododendron species, a globally recognized group of medicinal and edible plants, are known to produce a wide array of meroterpenoid natural products. Among these, daurichromenic acid (7) and its derivatives are widely distributed and exhibit diverse biological activities. However, their low natural abundance in plants and the incomplete elucidation of their biosynthetic pathways have hindered further development and application. Capitachromenic acid D (6), a representative chromene compound formed via successive oxidative transformations of 7, was initially isolated from R. capitatum Maxim. and also shows promising biological potential for pharmaceutical applications. In this study, the heterologous combinatorial biosynthesis of compound 6 was achieved in Aspergillus oryzae through the introduction of genes responsible for the biosynthesis of the precursor griffolic acid (2) from Fusarium graminearum 1962, A. oryzae, and Stachybotrys sp. g12, along with a cyclase gene from R. dauricum L. In bioactivity assays, compounds 5 and 6 exhibited notable inhibitory activity against the main protease (Mpro) of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), with IC50 values of 16.5 ± 1.3 μM and 10.7 ± 1.6 μM, respectively, highlighting their potential as promising lead compounds for SARS-CoV-2 Mpro inhibitor development.