Artemisia species, widespread in nature, are frequently utilized for the treatment of diseases such as malaria, hepatitis, cancer, inflammation, and infections by fungi, bacteria, and viruses. Furthermore, some Artemisia constituents were found to be potential insecticides and allelopathic chemicals. This genus is receiving growing attention presumably due to: (i) the diversified biology and chemistry of the constituents, (ii) the frequent application in traditional medical practice, and (iii) the rich source of the plant material. This review summarizes mainly the biological results obtained in the past decade. The significance and trends in this field are briefly discussed.

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Pericyclic reactions are powerful transformations for the construction of carbon-carbon and carbon-heteroatom bonds in organic synthesis. Their role in biosynthesis is increasingly apparent, and mechanisms by which pericyclases can catalyse reactions are of major interest 1. [4+2] cycloadditions (Diels-Alder reactions) have been widely used in organic synthesis 2 for the formation of six-membered rings and are now well-established in biosynthesis 3-6. [6+4] and other 'higher-order' cycloadditions were predicted 7 in 1965, and are now increasingly common in the laboratory despite challenges arising from the generation of a highly strained ten-membered ring Reprints and permissions information is available at http://www.nature.com/reprints.

Two homologous meroterpenoid gene clusters consisting of contiguous genes encoding polyketide synthase (PKS), prenyltransferase (PT), terpenoid cyclase (TC) and other tailoring enzymes were identified from two phylogenetically distinct fungi through computational analysis. Media optimization guided by reverse-transcription PCR (RT-PCR) enabled two strains to produce eight new and two known meroterpenoids (1-10). Using gene inactivation, heterologous expression, and biochemical analyses, we revealed a new polyketide-terpenoid assembly line that utilizes a pair of PKSs to synthesize 2,4-dihydroxy-6-alkylbenzoic acid, followed by oxidative decarboxylation, farnesyl transfer, and terpene cyclization to construct the meroterpenoid scaffold. In addition, two of the isolated meroterpenoids (3 and 17 d) showed immunosuppressive bioactivity. Our work reveals a new strategy for meroterpenoid natural products discovery, and reveals the biosynthetic pathway for compounds 1-10.

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Oxidative rearrangements play key roles in introducing structural complexity and biological activities of natural products biosynthesized by type II polyketide synthases (PKSs). Chartreusin (1) is a potent antitumor polyketide that contains a unique rearranged pentacyclic aromatic bilactone aglycone derived from a type II PKS. Herein, we report an unprecedented dioxygenase, ChaP, that catalyzes the final α-pyrone ring formation in 1 biosynthesis using flavin-activated oxygen as an oxidant. The X-ray crystal structures of ChaP and two homologues, docking studies, and site-directed mutagenesis provided insights into the molecular basis of the oxidative rearrangement that involves two successive C-C bond cleavage steps followed by lactonization. ChaP is the first example of a dioxygenase that requires a flavin-activated oxygen as a substrate despite lacking flavin binding sites, and represents a new class in the vicinal oxygen chelate enzyme superfamily.

Genome mining and heterologous expression of an orphan cluster led to the discovery of ashimides featuring an unusual cyclization mechanism.

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