Polyketides from the marine-derived fungus Ascochyta salicorniae and their potential to inhibit protein phosphatases

Chemical investigation of the marine fungus Ascochyta salicorniae led to the isolation of two new epimeric compounds, ascolactones A ( 1) and B ( 2), in addition to the structurally-related polyketides hyalopyrone ( 3), ascochitine ( 4), ascochital ( 5) and ascosalipyrone ( 6). The absolute configurations of the epimeric compounds 1 and 2 were assigned as (1R, 9R) and (1S, 9R), respectively, through simulation of the chiroptical properties using quantum-chemical CD calculations, and chiral GC - MS subsequent to oxidative cleavage (Baeyer - Villiger oxidation) of the side chain. In silico screening using the PASS software identified some of the A. salicorniae compounds ( 1 - 6) as potential inhibitors of protein phosphatases. Compound 4 was found to inhibit the enzymatic activity of MPtpB with an IC50 value of 11.5 mu M.