Antifungal Cyclic Peptides Dinemasporins from the Culture of Dinemasporium parastrigosum KT4144.

Cyclic nonapeptides dinemasporins A1 (1), A2 (2), A3 (3), B1 (4), and B2 (5) were isolated from the solid culture of Dinemasporium parastrigosum KT4144. Structures were assigned based on the first elucidation of compound 1 by analysis of spectroscopic data. Dinemasporins A2 (2) and A3 (3) feature a pyridinium cation derived from the δ-amino group of an ornithine residue. The substitution pattern of the aromatic ring moiety in 2 was established by density-functional-theory (DFT)-based 13C NMR chemical shift calculations and corroborated by the identification of the structurally related dinemaxanthone C (6), obtained from the same culture. Dinemasporins B1 (4) and B2 (5) possess a secondary hydroxy group at C-θ of the 2-aminodecanoic acid (ADA) residues in 1 and 2, respectively. Extended Mosher analysis of 7, obtained by acidic hydrolysis of 4 followed by protection of the amino acid moiety in the hydrolysate, revealed that 4 is a diastereomeric pair at C-θ of the ADA residue. Although 1 exhibited potent antifungal activity against rice brown spot fungus Bipolaris oryzae, at 1.0 μg/mL, the other peptides isolated showed very low or no fungal growth inhibition.