A-Lapachone

Lapachenole — see 2H-Naphtho[l,2-6]pyran a-Lapachone, dehydrosynthesis, 3, 751 Large heterocyelic rings anions, 7, 18 aromatieity, 7, 14, 16 basicities, 7, 24 bond angles, 7, 14-16 bond lengths, 7, 14-16 cations, 7, 18... 

Because of such extensive application in folk medicine, it is easy to understand the interest that the lapachol, the related naphthoquinones a-lapachone, P-lapachone and other naphthoquinones derivatives, have aroused as potential drugs. In fact, a broad variety of biological activities have been described for this kind of compounds. Some examples are antitumor promoting activities [11-12], inactivators of human cytomegalovirus protease [13], antiprotozoal activity [14], trypanocidal activity [15], anticancer activity [16], and antibacterial and antifungal activities [17]. 

The work realized by Dauson et al [127] is of particular interest for the H NMR and 13C NMR assignments of these type of molecules. The isomers a-lapachone and P-lapachone can be easily distinguished, attending to the pattern that present the linear and angular pyranonaphthoquinones in their NMR spectra. In the H NMR spectra, the signals corresponding to the aromatic protons appear in two different forms. In the case of a-cycled compounds, the aromatic protons have a symmetric environment and the hydrogens H5 and Hg are equivalent as... 

Although it presents diverse stereogenic centers, the authors do not indicate if this compound was found as a racemic mixture. Dehydro-a-lapachone (58) and dehydro-p-lapachone (59) are formed by oxidative cyclisation of lapachol with DDQ [134-135]. The reduction of quinones to hydroquinones is a quick, quantitative, and reversible process, which is common both to ortho and para quinones [136]. The transformation of lapachol to p-lapachone in acid media was treated previously in section-2. 

Syntheses of a- and p- lapachones and their homologues were carried out by photochemical side chain introduction to quinone. Thus, 1,4-naphthoquinone photochemically reacted with 3-methyl-2-butenal to give 2-(3-methyl-2-butenoyl)-l,4-naphthalenediol (69), regiospecifically. The product (69) was successively treated with acid, with dichloroaluminiun hydride, and finally with iron (III) chloride to derive in turn to cromanon (70), dihydropyran (71), and P-lapachone (35). P-lapachone was easily transformed to a-lapachone (38) by treating with acid. Likewise, from... 

BIOLOGICAL ACTIVITY OF LAPACHOL, a-LAPACHONE, 0-LAPACHONE AND THEIR DERIVATIVES... 

Biological investigations over the last years have shown that many of the medicinal properties claimed for Lapacho, Taheebo, Pau D Arco or Ipe Roxo are attibuted to the active components lapachol, a-lapachone, P-lapachone and their derivatives. 

There are also natural products of the 3,4-dehydro series (314). 3-Methyl-314 was isolated from heartwood of Paratecoma peroba (68N38), and the 2,2-dimethyl derivative (310, R = H) from wood of Rademachera sinica (81JCS(P1)2764). The last compound (dehydro-a-lapachone) was obtained also from isolapachol and DDQ 311 is formed first and then isomerized to 310 in the presence of acid (62MI1 69JOC120 78CJC517). 

Among related compounds, a-caryopterone (310, R = OH) was isolated from Caryopteris clandonensis (69HCA808), and a-dihydrocaryopterone (315 = 9-hydroxy-a-lapachone), 9-methoxy- (316), and 4,9-dihydroxy-a-... 

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