Total synthesis and anticancer activities of (-)- and (+)-thespesone

The natural p-naphthoquinone (-)-thespesone 1 and its (+)-enantiomer were synthesized for the first time by bisacylation of a 5-lithiodihydrobenzofuran 2' with 4-methyl-3-tert-butoxycyclobut-3-ene-1,2-dione 3. The racemate of the required 2-arylpropan-1-ol precursor 10 was kinetically resolved by an enzyme-catalyzed acetylation exclusively of the (S)-enantiomer. Saponification of this acetate mediated by the same enzyme, porcine pancreas lipase (PPL), afforded the (S)-2-arylpropan-1-ol in 96% ee. Its unreacted (R)-enantiomer could be obtained with 77% ee. (-)-(S)-thespesone was far more efficacious against a panel of six cancer cell lines including multiresistant ones than its (+)-enantiomer and also when compared to thymoquinone, an established natural antitumoral p-quinone from Nigella sativa. Unlike the latter, (-)-thespesone was well tolerated by nonmalignant fibroblasts.