Total synthesis and cytotoxic activity of stellatin

Stellatin (3,4-dihydro-8-hydroxy-7-hydroxymethyl-6-methoxyisocoumarin) (8), an extrolite of fungal genera Emericella and Aspergillus, was synthesized. Thus, Vilsmeier-Haack formylation of methyl ester of 3,5-dimethoxy-4-methylphenylacetic acid (1) to afford the formyl ester (2) followed sulfamic acid-sodium chlorite oxidation of the aldehydic function to yield the carboxy ester (3). Chemoselective reduction of ester function in the latter using NaBH(4)/THF/MeOH furnished the corresponding hydroxy acid (4) that on cyclodehydration afforded the 3,4-dihydro-6,8-dimethoxy-7-methylisocoumarin (5). Benzylic bromination of the C-7 methyl in 5 using NBS/benzoyl peroxide to give the 7-bromomethyldihydroisocoumarin (6) followed the nucleophilic substitution using aqueous acetone to provide 7-hydroxymethyl-dihydroisocoumarin (7). Finally, the regioselective demethylation of 8-methoxyl group using anhydrous magnesium iodide furnished the stellatin (8). The dihydroisocoumarins (5-8) were screened for cytotoxic activity against human keratinocyte cell line and were found to exhibit moderate to good activity.