Biosynthesis of Aspergillic Acid

SUMMARY 1. When Aspergillus flavus was grown on media containing nL-leucine-l-C~4, n-leucine-1-Cr4, uniformly labeled L-leucine-Cl4 or L-isoleucine-C!r4, significant amounts of radioactivity were found in mycelial leucine or isoleucine, and in aspergillic acid. 2 When the aspergillic acid isolated from medium containing nn-leucine-l-C4 was degraded to leucine and isoleucine isomers, the radioactivity was found in carbon atom 1 of leucine and none in the isoleucine isomers. 3. When the aspergillic acid isolated from medium containing uniformly labeled L-isoleucine-Cl4 and a small amount of leucine- Cl4 was degraded, most of the radioactivity was found in isoleu- tine isomers and a small amount in leucine. 4. The set-butyl side chain of aspergillic acid has the same optical configuration as that of carbon atom 3 of L-isoleucine. 5. The results support the hypothesis that aspergillic acid is synthesized by A. flavus from lcucine and isoleucine.