Beside the known naphthoquinones, dehydro-cc -1apachone (17) and lapachol (20), four new naphtho[2,3-b]furan-4,9-diones, i. e. the 2-acetyl-S-hydroxy, 2-acetyl-E-hydroxy, (-)-5-hydroxy-2-(l'-hydroxyethyl), and (+)-8hydroxy-2-( 1'-hydroxyethyl) derivatives 16, 15,12, and 13, respectively, and the new compound benzo[b]furan-6carboxaldehyde (8) have been isolated from a CHC1, extract of the inner stem bark of Tabebuiu uuellunedue LORENTZ ex GRISEB., together with four known naphthofurandiones, a dihydroisocoumarin derivative, (-)-6hydroxymellein, and five benzoic-acid and three benzaldehyde derivatives which have not been reported previously from this plant. Structure determination of the isomeric 5-and 8-hydroxynaphtho[2,3-b]furan-4,9-diones was carried out unambiguously by a combination of selective-INEPT experiments and X-ray crystallographic analysis.
Introduction. ~
The stem bark of the South-American tree Tubebuiu avellanedue LORENTZ ex GRISEB., Bignoniaceae (syn. T. impetiginosu MART. ex DC., T. heptuphylla VELL. TOLEDO, and T. I$ MART. ex. SCHUM. [l]), known in folk medicine as Pau d'Arco, IpC Roxo, Taheebo, and Lapacho, is used in North and South America for many years as an anticancer, antifungal, antibacterial, and antiinflammatory drug [2] [3].
Lapachol and dehydro-a -lapachone, the major naphthoquinones of the heartwood of Tubebuiu uvellunedue LORENTZ ex GRISEB., were found to be active against different types of tumors [47]. In viuo antitumor effects were observed using p . 0. administration of 20-30 mg/kg lapachol [8], and de Suntunu et ul. [9] demonstrated in vivo antineoplastic effects on Yoshidu's sarcoma and Walker 256 carcinosarcoma for the lipophilic extract of the inner bark of T. uvellanedue LORENTZ ex GRISEB.
These pharmacological activities, and recent results from our laboratory (Munich) concerning the immunostimulating effects of various naphthoquinones when applied in minute doses [lo] prompted us to initiate a new, thorough investigation of the lipophilic extract of the inner bark of T. uvellunedue LORENTZ ex GRISEB.
Results and Discussion. -Column chromatography (CC) of the CHCl, extract of T. uvellunedue LORENTZ ex GRISEB. stem bark on silica gel, using CHC1, as eluent resulted in five fractions (Fr. I-V) which afforded twenty compounds by further CC, prep. HPLC, and prep. TLC (see Scheme). In the present publication, we describe the structure elucidation of the new compounds 8, 12, 13, 15, 16, and 19 which were obtained from Fr. I, IZ, and IV. The other compounds and their biological activities will be described in a forthcoming paper.
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') The numbering of the side chain is arbitrary.
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The atomic coordinates are deposited at the Cambridge Crystallographic Data Centre