Protein tyrosine phosphatase 1B inhibitory effects of depsidone and pseudodepsidone metabolites from the Antarctic lichen Stereocaulon alpinum.

Seven phenolic lichen metabolites (1-7) have been isolated from a methanol extract of the Antarctic lichen Stereocaulon alpinum by various chromatographic methods. The structures of these compounds were determined mainly by analysis of NMR spectroscopic data. A depsidone-type compound, lobaric acid (1) and two pseudodepsidone-type compounds, 2 and 3, exhibited potent inhibitory activity against protein tyrosine phosphatase 1B (PTP1B) with IC(50) values of 0.87microM, 6.86microM, and 2.48microM, respectively. Kinetic analyses of PTP1B inhibition by compounds 1 and 2 suggested that these compounds inhibited PTP1B activity in a non-competitive manner.