The Biologically and Ecologically Important Natural Products from the Chinese Sea Hare Bursatella leachii: Structures, Stereochemistry and Beyond

A novel amide alkaloid bursatamide A (1), possessing an undescribed propyl-hexahydronaphthalene carbon framework, was isolated from the rarely investigated sea hare Bursatella leachi, along with a new 3-phenoxypropanenitrile alkaloid bursatellin B (2) and twelve known compounds. The structures of 1 and 2 were determined by the extensive spectroscopic data analyses, and the relative and absolute configurations were established by total synthesis and a series of quantum chemical calculations, including calculated ECD spectra, optical rotatory dispersion methods and DP4 + probability analyses. Bursatamide A (1) exhibited inhibitory efforts on the human pathogenic bacterium Listeria monocytogenes and Vibrio cholerae. Erythro-bursatellin B (21), the diastereoisomer of 2, displayed an interesting antibacterial activity against fish pathogenic bacteria Streptococcus parauberis FP KSP28, with MIC₉₀ value of 0.0472 μg/mL.