Isolation, structure elucidation, and determination of absolute configuration of natural products from a Phomopsis sp. endophyte

Abstract

Natural products are a chemically diverse class of metabolites with broad biological activities that remain a foundation for drug discovery and development. Endophytes represent an underexplored source of new natural products with therapeutic potential. Investigation of a Phomopsis sp. endophyte isolated from Sorbus decora yielded three compounds, tropicicolide and oblongolides A and C. However, the structure of tropicicolide has not been fully characterized and was therefore elucidated through extensive use of nuclear magnetic resonance (NMR) and high-resolution mass spectrometry. The absolute configuration of tropicicolide was determined using Mosher’s analysis, quantum chemical calculations followed by DP4 probability analysis, and NMR comparisons with synthetic stereoisomers of a macrocyclic analogue, eushearilide. Upon testing the biological activities of these natural products, tropicicolide displayed moderate antifungal, antibacterial, and antimycobacterial activity, while oblongolide A showed weak inhibition and oblongolide C was inactive.