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 Bipolar's colds. The absolute configurations in 1 and 4 were assigned by electronic circular dichroism (ECD) calculations. Compounds 1 and 2 were transformed into 4 and 5 by treatment with acetyl chloride, respectively. Compounds 1-4 showed moderate inhibitory activity against NO release with IC50 values of 16.34 +/- 1.12, 23.55 +/- 1.37, 10.82 +/- 0.83, and 54.20 +/- 2.82 mu M, respectively.