Semi-Synthesis of Chloroxaloterpin A and B and Their Antifungal Activity against .

Chloroxaloterpin A () and B () are two diterpenoids with potent inhibitory activities against spore germination of , which were identified from sp. SN194 as minor products previously. In order to overcome the poor yields, and were synthesized using viguiepinol (), the major metabolite of sp. SN194, as the precursor compound. Scanning electron microscope and transmission electron microscope observations revealed that after treating spores with and , spores were obviously aberrant, the cytoplasm appeared withdrawn, and plasma membranes were blurred. Propidium iodide fluorescence assay indicated that and damaged plasma membranes of spores. In vivo assays showed that compounds and could effectively inhibit the sporulation of on tomato fruits, with sporulation inhibitory rates reaching 98.8% at 100 μg/mL. These findings provide new insights into chloroxaloterpin A and B and demonstrate their potential as lead candidates for novel fungicides.