Aureoquinone

Secreted aspartic proteases (Saps) represent an important virulence factor facilitating fungal adherence. Several protease inhibitors (PIs), including HIV PIs, have been shown to reduce Candida adhesion. The aim of this study was to ascertain whether or not the recently discovered PIs Aureoquinone and Laccaridiones A and B, isolated from Basidiomycete cultures, or Bestatin, act as Sap-inhibitors and/or inhibitors of fungal adhesion. Drug effects on candidial Sap-production were determined by Sap-ELISA. Control tubes, in the absence of drug, served as positive controls, while tubes excluding both drug and proteinase induction medium were used as negative controls. Aureoquinone as well as Laccaridiones A and B, but not Bestatin, significantly inhibited Candida albicans adhesion to both epithelial and endothelial cells in a dose dependent manner and also reduced Sap-release (effects were not because of a direct interaction of the Basidiomycete metabolites with secreted Saps). Laccaridione B was consistently found to be the most effective PI tested. Interestingly, these drugs are neither fungistatic nor fungicidal at the concentrations applied. Laccaridione B may represent a promising novel type of antimycotic drug--targeting virulence factors without killing the yeast.

A concise formal total synthesis of the cytotoxic bisnaphthazarin derivative hybocarpone has been completed through the development of routes to the synthetic precursor, 3-ethyl-2-hydroxy-5,7,8-trimethoxy-6-methyl-1,4-naphthoquinone. The oxidation of 3-ethyl-1,2,4,5,7,8-hexamethoxy-6-methylnaphthalene under Rapoport conditions gave 3-ethyl-2-hydroxy-5,7,8-trimethoxy-6-methyl-1,4-naphthoquinone in modest yields after basic hydrolysis. In addition, treatment of 3-ethyl-1,2,4,5,7,8-hexamethoxy-6-methylnaphthalene with boron tribromide provided access to the naturally occurring naphthazarin, boryquinone. The analogous oxidative demethylation of 3,6-dimethyl-1,2,4,5,7,8-hexamethoxynaphthalene and 3-ethyl-1,2,4,5,7,8-hexamethoxynaphthalene resulted in the synthesis of 2,5,7,8-tetrahydroxy-3,6-dimethyl-1,4-naphthoquinone (aureoquinone) and 3-ethyl-2,5,7,8-tetrahydroxy-1,4-naphthoquinone, respectively. An alternative selective synthetic route to 3-ethyl-2-hydroxy-5,7,8-trimethoxy-6-methyl-1,4-naphthoquinone was also developed utilizing an intramolecular Claisen condensation of methyl 2-butyryl-3,5,6-trimethoxy-4-methylphenylacetate with concomitant in situ aerial oxidation.