Seed Dormancy Breaking Diterpenoids, Including Novel Brassicicenes J and K, from Fungus Alternaria brassicicola, and their Necrotic/Apoptotic Activities in HL-60 Cells

Abstract

To find new metabolites similar to cotylenins and fusicoccins from the fungus Alternaria brassicicola, screening tests were carried out using the lettuce seed dormancy breaking assay. Activity-guided fractionation of the EtOAc extract from the culture using the assay afforded the isolation of two novel fusicoccane diterpenoids named brassicicenes J (1) and K (2), along with three known brassicicenes A (3), B (4), and F (5). Their structures were elucidated from extensive NMR spectral data and by comparison of these with those reported in the literature. Brassicicenes (1–5) exhibited weak to moderate seed dormancy breaking activities against lettuce seeds in the presence of abscisic acid. In addition, the necrotic/apoptotic activities of the brassicicenes (1–5), fusicoccin A (6) and cotylenin A (7) were evaluated by determining their cytotoxicity, cell viability and caspase-3/7 activation on the HL-60 cell line. Brassicicene K (2) exhibited similar cytostatic profiles to that of cotylenin A (7), and brassicicenes J (1), A (3), B (4), and F (5) exhibited necrotic activity. This is the first report of the seed dormancy breaking activity of brassicicenes in plants, and of necrotic/apoptotic activity in mammalian cells.