New antibiotics, miyakamides A
1, A
2, B
1, and B
2, were isolated from the cultured broth of
Aspergillus flavus Link var.
columnaris FKI-0739 together with known compounds, parasiticolide A, hydroxyaspergillic acid, and kojic acid. The structure of miyakamide A
1 is
N-acetyl-L-phenylalanyl-
N-methyl-L-phenylalanyl-(α
Z)-α, β-didehydrotryptamine, and miyakamide A
2 is
E isomer of A
1 at didehydrotryptamine. The structure of miyakamide B
1 is
N-acetyl-L-tyrosyl-
N-methyl-L-phenylalanyl-(α
Z)-α, β-didehydrotryptamine, and B
2 is
E isomer of B
1. Both miyakamides A
1 and B
1 existed as equilibrium isomers in solvents, and this isomerism was associated with
cis-trans rotation of the amide bond between two amino acids. Conformational isomerism between two amino acids of miyakamides A
2 and B
2 is
cis-form. Miyakamides showed growth inhibitory activity against brine shrimp,
Artemia salina.
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