ABSTRACT
Polyketides form a structurally diverse and pharmaceutically important class of secondary metabolites. Both diversity and biological activity are largely facilitated by post-polyketide synthase tailoring including methylation, oxidation, reduction, glycosylation, and dimerization. Cytochrome P450 enzymes (CYPs), flavin-dependent monooxygenases (FMOs), and laccases are known to catalyze phenol coupling in the biosynthesis of polyketide dimers. Polyketide homodimers resulting from enzyme catalysis are often formed in a highly regio- and stereoselective manner, in contrast to analogous nonenzymatic dimerization. Although it is known that CYPs and FMOs are capable of selectively generating one of several putative isomers, hitherto described laccases depend on auxiliary proteins to achieve similar selectivity. Herein, regioselective phenol coupling catalyzed by a fungal laccase is demonstrated. The heterologously produced Av-VirL from Aspergillus viridinutans selectively generated the 6,6'-homodimer of (R)-semivioxanthin. Genome analysis is used to show that laccase-based phenol-coupling systems are widespread in fungi. Homologues of Av-VirL were identified in the putative biosynthetic gene clusters of vioxanthin, xanthomegnin, and xanthoepocin, and of the perylenequinones hypocrellinâ A, elsinochromeâ A, and cercosporin. These findings show that laccases are capable of selective phenol coupling in the absence of auxiliary proteins.
Subject(s)
Laccase/chemistry , Phenols/chemistry , Polyketides/chemistry , Aspergillus/enzymology , Biocatalysis , Laccase/genetics , Laccase/metabolism , Molecular Conformation , Phenols/metabolism , Polyketides/metabolism , StereoisomerismABSTRACT
The synthesis and enzymatic reduction of several 6-substituted dioxohexanoates are presented. Two-step syntheses of tert-butyl 6-bromo-3,5-dioxohexanoate and the corresponding 6-hydroxy compound have been achieved in 89% and 59% yield, respectively. Regio- and enantioselective reduction of these diketones and of the 6-chloro derivative with alcohol dehydrogenase from Lactobacillus brevis (LBADH) gave the (5S)-5-hydroxy-3-oxo products with enantiomeric excesses of 91%, 98.4%, and >99.5%, respectively. Chain elongation of the reduction products by one carbon via cyanide addition, and by more than one carbon by Julia-Kocienski olefination, gave access to well-established statine side-chain building blocks. Application in the synthesis of the cholesterol-lowering natural compound solistatin is given.
Subject(s)
Amino Acids/chemistry , Hydroxymethylglutaryl-CoA Reductase Inhibitors/chemical synthesis , Lovastatin/analogs & derivatives , Alcohol Dehydrogenase/chemistry , Alcohol Dehydrogenase/metabolism , Amino Acids/chemical synthesis , Amino Acids/metabolism , Caproates/chemical synthesis , Caproates/chemistry , Caproates/metabolism , Hydroxymethylglutaryl-CoA Reductase Inhibitors/chemistry , Hydroxymethylglutaryl-CoA Reductase Inhibitors/metabolism , Levilactobacillus brevis/enzymology , Lovastatin/chemical synthesis , Lovastatin/chemistry , Lovastatin/metabolism , Models, Molecular , NADP/chemistry , NADP/metabolism , Oxidoreductases/metabolismABSTRACT
Investigations of the marine-derived fungus Monodictys putredinis led to the isolation of two novel dimeric chromanones (1, 2) that consist of two uniquely modified xanthone-derived units. The structures were elucidated by extensive spectroscopic measurements including NOE experiments and CD analysis to deduce the configuration. The compounds (1, 2) were examined for their cancer chemopreventive potential and shown to inhibit cytochrome P450 1A activity with IC(50) values of 5.3 and 7.5 µM, respectively. In addition, both compounds displayed moderate activity as inducers of NAD(P)H:quinone reductase (QR) in cultured mouse Hepa 1c1c7 cells, with CD values (concentration required to double the specific activity of QR) of 22.1 and 24.8 µM, respectively. Compound 1 was slightly less potent than compound 2 in inhibiting aromatase activity, with IC(50) values of 24.4 and 16.5 µM.