Griseofamines A and B: Two Indole-Tetramic Acid Alkaloids with 6/5/6/5 and 6/5/7/5 Ring Systems from Penicillium griseofulvum

Two novel indole-tetramic acid alkaloids—griseofamine A (1) and griseofamine B (2)—and (R)-N-(2-methylbutanoyl)-l-tryptophan (3), were isolated from the fungus Penicillium griseofulvum. Compounds 1 and 2 feature a 6/5/6/5 and 6/5/7/5 tetracyclic ring systems formed by the fusion of an indole unit and a tetramic acid via a six or seven-membered N-heterocyclic ring, respectively. The plausible biosynthetic pathways of 1–3 are proposed. Compound 1 shows a weak anti-inflammatory activity by inhibition of NO and TNF-α production.