Ulbactins F and G, Polycyclic Thiazoline Derivatives with Tumor Cell Migration Inhibitory Activity from Brevibacillus sp.

Two new structurally unique compounds bearing a nitrogen- and sulfur-containing tricyclic ring system, ulbactin F (1) and its diastereomeric isomer ulbactin G (2), were isolated from the culture extract of a sponge-derived Brevibacillus sp. The structures and absolute configurations of 1 and 2 were determined by NMR analysis and X-ray crystallographic analysis. These compounds inhibit the migration of tumor cells in the submicromolar to micromolar range.