Structural Revision of Halipeptins: Synthesis of the Thiazoline Unit and Isolation of Halipeptin C

The Structural revision of the anti-inflammatory marine metabolites halipeptin A (1) and B (2) along with the isolation of the new related product halipeptin C (3) are reported. In particular, the heterocyclic portion of the molecule. incorrectly assigned as an oxazetidine ring, has now been characterised as a thiazoline unit by comparison of the spectral data of the natural products (1-3) with an appropriate synthetic model (10). GIAO calculated C-13 NMR chemical shifts for oxazetidine and thiazoline model compounds provide additional support to the revised structure