Actinomycetes have provided a diverse array of bioactive secondary metabolites. In particular, those belonging to the genus Streptomyces have been the most promising source of chemically diverse secondary metabolites. Their high capacity of secondary metabolite biosyntheis is largely attributable to the diversity of polyketide synthase (PKS) genes. In our continuing search for novel bioactive secondary metabolited from Streptomyces, we found a novel macrocyclic polyketide with an unprecedented framework from the culture extract of Streptomyces isolated from a leaf of chive Allium sp. For the production of the new compounds, the strain was fermented under a specific co-culturing condition with a bacterium Tsukamurella pulmonis. The 1-butanol extract of whole culture broth was separated by normal- and reversed-phase column chromatographies and HPLC to yield alchivemycins A (1) and B (2). Elucidation of the relative configurations of the alchivemycins was accomplished by a combination of NMR analysis and X-ray crystallography. Here we report the isolation and structure determination of the new compounds. This represents the first example of natural products containing a unique tetronic acid-tetramic acid hybrid substructure. Conpounds 1 and 2 inhibited tumor cell invasion without showing cytotoxic effects.
