Coicenals A–D, Four New Diterpenoids with New Chemical Skeletons from the Plant Pathogenic Fungus Bipolaris coicis.

Coicenals A–C (1–3) possessing a previously undescribed 10-(sec-butyl)-6-hydroxy-1,7,9-trimethyl-1,6,7,8,9,9a-hexahydro-1,4-methanobenzo[d]oxepin-2(4H)-ylidene)acetaldehyde skeleton and coicenal D (4) with a new 2-(sec-butyl)-5-hydroxy-1,6,8-trimethyl-2,5,6,7,8,8a-hexahydro-1H-4a,1-(epoxymethano)naphthalen-10-ylidene)acetaldehyde skeleton were isolated from the solid culture of the plant pathogenic fungus Bipolaris coicis. The absolute configurations in 1and 4were assigned by electronic circular dichroism (ECD) calculations. Compounds 1and 2were transformed into 4and 5by treatment with acetyl chloride, respectively. Compounds 1–4showed moderate inhibitory activity against NO release with IC50values of 16.34 ± 1.12, 23.55 ± 1.37, 10.82 ± 0.83, and 54.20 ± 2.82 μM, respectively. [ABSTRACT FROM AUTHOR]