The natural p-naphthoquinone (-)-thespesone 1 and its (þ)-enantiomer were synthesized for the first
time by bisacylation of a 5-lithiodihydrobenzofuran 20 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 (þ)-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.