Insignoic acids A – E, unusual α, β-unsaturated keto fatty acids isolated from the exocarp of Australian rainforest tree Endiandra insignis (Lauraceae)

Anti-inflammatory bioassay-guided compound isolation from the exocarp of the Australian rainforest tree Endiandra insignis (family Lauraceae) has led to the discovery and structural elucidation of unusual α, β-unsaturated twenty-four carbon fatty acids and their positional isomers, insignoic acids A – E (1a – 5c). The stereochemistry and position of the double bond within the aliphatic chain were independently determined via NMR spectroscopy and Ozone-Induced Dissociation (OzID) Mass Spectrometry, respectively. Compounds (1a – 5c) displayed good to moderate anti-inflammatory activity in the range of 8–84 μM. The low therapeutic index observed when assessing the cell viability in the RAW macrophage cell lines, prompted us to investigate the anticancer potential of these unusual fatty acids. The anti-cancer activity was assessed in A-431 carinoma cell lines and MM649 melanoma cell lines. Insignoic acid C (3a-f) exhibited the highest level of potency with an IC50 value of 5–7 μM against both the cell lines. The insignoic acids are the first of their kind known for incorporating an alpha-beta unsaturated system flanked next to a keto group with an additional level of oxygenation at C-6 in a 24‑carbon fatty acid backbone.