Structures of novel epipolythiodioxopiperazines, emethallicins B, C, and D, potent inhibitors of histamine release, from Emericella heterothallica

Novel compounds designated emethallicins B (1), C (2), and D (3), along with emethallicin A (4), were isolated from the mycelium of the heterothallic fungus, Emericella heterothallica (mating type a). The structures of emethallicins B (1), C (2), and D (3) were determined on the basis of spectroscopic and chemical investigations. Emethallicins B (1) and C (2) are epitetrathiodioxopiperazines, which have the same basic carbon skeleton as apoaranotin (19) and acetylaranotin (17), respectively, whereas emethallicin D (3) is an epitrithiodioxopiperazine derivative, which has the same carbon skeleton as apoaranotin (19). It is very interesting that a large amount of the disulfide, emethallicin A (4), was isolated from the strain of mating type A and that the corresponding tetrasulfide, emethallicin B (1), and trisulfide, emethallicin D (3), were isolated from the other mating type strain, along with a small amount of the disulfide (4). Emethallicins B (1), C (2), and D (3) have potent inhibitory activity against compound 48/80-induced histamine release from mast cells, like emethallicin A (4).