Structure of a novel epidithiodioxopiperazine, emethallicin A, a potent inhibitor of histamine release from Emericella heterothallica.

A new epidithiodioxopiperazine derivative, emethallicin A (1), was isolated along with ergosterol from the mycelial extract of the heterothallic fungus, Emericella heterothallica (mating type A). The structure of emethallicin A (1) was established on the basis of chemical and spectroscopic investigations and finally by chemical transformation to apoaranotin (11). Emethallicin A (1) has the same basic skeleton as apoaranotin (11), with C6-C2 carboxylic acid (mandelic and phenylacetic acids) diester moieties, and showed a potent inhibitory activity on histamine release from mast cells.