Total Synthesis, structure revision and antifungal activity of palmarumycin B₈ and B₇

Palmarymycins B₈ (1), its regioisomer (2) and B₇ (3) were synthesized via 10-, 9-, and 11-steps in 6.5 %, 2.3 % and 0.54 % overall yields from chroman-4-one (4), 4-hydroxyindanone (12), and 2,5-dimethoxybenzaldehyde (20) as the starting materials, using benzyl protection, enol trimethylsilyl ether by TMSOTf, Rubottom oxidation and deprotection with hydrogenation under Pd/C catalyst as the key steps, respectively. Their structures were characterized by ¹H, ¹³C NMR, COSY, HSQC, HMBC and HR-ESI-MS spectral data. The structure of palmarumycin B₈ was revised from 1 to 2 based on the total synthesis, 2D NMR analysis and DFT calculation. The antifungal assay results indicated that palmarumycin B₈ (1) showed moderate inhibitory activity against Phytophthora capsica. Compounds 15 and 16 exhibited excellent in vitro antifungal activities against P. capsica with EC₅₀ values of 2.17 and 8.50 μg/mL, respectively.