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

Palmarymycins B8 8 (1), 1 ), its regioisomer (2) 2 ) and B7 7 (3) 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 ), 4-hydroxyindanone (12), 12 ), and 2,5-dimethoxybenzaldehyde (20) 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 1 H, 13 C NMR, COSY, HSQC, HMBC and HR-ESI-MS spectral data. The structure of palmarumycin B8 8 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 8 (1) 1 ) showed moderate inhibitory activity against Phytophthora capsica. . Compounds 15 and 16 exhibited excellent in vitro antifungal activities against P. capsica with EC50 50 values of 2.17 and 8.50 mu g/mL, respectively.