Antitumor agents. 89. Psychorubrin, a new cytotoxic naphthoquinone from Psychotria rubra and its structure-activity relationships

A new naphthoquinone, isolated from the alcoholic extract of Psychotria rubra, exhibited significant cytotoxicity in the KB cell assay (ED50 = 3.0 micrograms/mL). Spectral data was used to assign the structure of psychorubrin as 2. Naphthoquinone derivatives 6, 8, 13, and 14 were prepared and exhibited superior cytotoxic activity to that of psychorubrin. All were potential Michael acceptors whose conjugation had been extended. However, when a hydrophilic hydroxy group was present in such compounds, reduced in vitro activity was observed.