13C labeling indicates that the epoxide-containing amino acid of HC-toxin is biosynthesized by head-to-tail condensation of acetate.

HC-toxin, cyclo(D-Pro-L-Ala-D-Ala-L-Aeo), where Aeo stands for 2-amino-9,10-epoxi-8-oxodecanoic acid, is a potent inhibitor of histone deacetylase. Previous molecular genetic studies indicated that HC-toxin biosynthesis requires a dedicated fatty acid synthase. The incorporation of [13C]acetate into HC-toxin was studied using NMR. The pattern of incorporation of 13C was consistent with the carbons of Aeo being derived from head-to-tail condensation of acetate.