Antifungal Cyclic Peptides Dinemasporins from the Culture of <i>Dinemasporium parastrigosum</i> KT4144

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