Total Synthesis of Brevitaxin

Brevitaxin was prepared in nine steps from commercially available carnosic acid. The construction of the 1,4-benzodioxin moiety involved an unique stepwise ortho-quinone-engaged [4+2] cycloaddition. Two strategic stages were employed to prepare the highly unsaturated cycloaddition precursor 3: (1) synthesizing the diene moiety (C1-C2 and C10-C20 double bonds) by regioselective ortho-quinone tautomerization, and (2) installing four sp2-hybridized carbon atoms (C3, C5, C6 and C7) in one step using a SeO2-promoted chemo- and regioselective oxidation reaction.

Discovery and Bioinspired Synthesis of Salpratone A

Salpratone A (1), a novel abietane diterpenoid containing a unique cis-fused A/B ring, was isolated from Salvia prattii. Bioactivity studies showed that 1 has potent activity in inhibiting platelet aggregation induced by multiple agonists as well as antithrombotic efficacy in the FeCl3-induced rat in vivo thrombosis model. Furthermore, a bioinspired synthesis of 1 from the abundant natural product ferruginol was achieved in 6 steps with a 22% overall yield. The key steps include a stereoselective allyl oxidation and a subsequent regioselective Meinwald rearrangement.

Arylcyanomethylenequinone Oximes: An Overview of Synthesis, Chemical Transformations, and Biological Activity

Quinone methides are a class of biologically active compounds that can be used in medicine as antibacterial, antifungal, antiviral, antioxidant, and anti-inflammatory agents. In addition, quinone methides have the potential to be used as pesticides, dyes, and additives for rubber and plastics. In this paper, we discuss a subclass of quinone methides: methylenequinone oximes. Although the first representatives of the subgroup were synthesized in the distant past, they still need to be additionally studied, while their chemistry, biological properties, and perspective of practical applications require to be comprehensively summarised. Based on the analysis of the literature, it can be concluded that methylenequinone oximes exhibit a diversified profile of properties and outstanding potential as new drug candidates and reagents in organic synthesis, both of electrophilic and nucleophilic nature, worthy of wide-ranging further research.

Bispericyclic Diels-Alder Dimerization of ortho-Quinols in Natural Product (Bio)Synthesis: Bioinspired Chemical 6-Step Synthesis of (+)-Maytenone

Many natural products of plant or microbial origins are derived from enzymatic dearomative oxygenation of 2-alkylphenolic precursors into 6-alkyl-6-hydroxycyclohexa-2,4-dienones. These so-called ortho-quinols cyclodimerize via a remarkably selective bispericyclic Diels-Alder reaction. Whether or not the intervention of catalytic or dirigent proteins is involved during this final step of the biosynthesis of these natural products, this cyclodimerization of ortho-quinols can be chemically reproduced in the laboratory with the same strict level of site-specific regioselectivity and stereoselectivity. This unique yet unified process, which finds its rationale in the inherent chemical reactivity of those ortho-quinols, is illustrated herein by an efficient and bioinspired first chemical synthesis of one of the most structurally complex and synthetically challenging examples of such natural cyclodimers, the bisditerpenoid (+)-maytenone.

Two new troponoides with anti-inflammatory activity from the stems of Juniperus formosana Hayata

Two new troponoides (1-2) were isolated from a 95% ethanol extract of the stems of Juniperus formosana (Cupressaceae), together with six known compounds (3-8). The structures of the new compounds were comprehensively characterized by high resolution electrospray ionization-mass spectrometry (HR-ESI-MS), 1D and 2D nuclear magnetic resonance (NMR). Compounds 1-7 were evaluated for their anti-inflammatory against the expression of IL-1β, IL-6 and TNF-α in lipopolysaccharide (LPS)-induced RAW 264.7 macrophages. The new compounds showed moderate anti-inflammatory effect, while other compounds did show no activity.

Taxodisones A and B: bioactive C30-terpenes with new skeletons from Taxodium distichum and their biosynthetic origin

Herein, taxodisones A and B were isolated from the seeds of T. distichum, and the structures, configurations, bioactivities and origin of these compounds were determined.

Total Synthesis of Antiproliferative Parvifloron F

The first total synthesis of parvifloron F, a bioactive highly oxidized abietane diterpene, was achieved. The abietane skeleton was constructed by Lewis acid promoted cyclization. Preliminary structure-activity relationship correlations were established for the synthetic intermediates against human tumor cell lines. Certain compounds showed unique selective antiproliferative activity against triple-negative breast cancer. The oxidation level of the abietane ring affected the selectivity.

Crystal structure of taxodione isolated from Taxodium ascendens (B.)

The title compound [systematic name: (4bS)-4-hy-droxy-2-isopropyl-4b,8,8-trimethyl-4b,5,6,7,8,8a-hexa-hydro-phenanthrene-3,9-dione], C20H26O3, is an abietane-type diterpene, which was isolated from Taxodium ascendens (B.). In the crystal, mol-ecules are linked by weak C-H⋯O hydrogen bonds, forming supra-molecular chains propagating along the [001] direction.

Elucidation of the biosynthesis of carnosic acid and its reconstitution in yeast

Rosemary extracts containing the phenolic diterpenes carnosic acid and its derivative carnosol are approved food additives used in an increasingly wide range of products to enhance shelf-life, thanks to their high anti-oxidant activity. We describe here the elucidation of the complete biosynthetic pathway of carnosic acid and its reconstitution in yeast cells. Cytochrome P450 oxygenases (CYP76AH22-24) from Rosmarinus officinalis and Salvia fruticosa already characterized as ferruginol synthases are also able to produce 11-hydroxyferruginol. Modelling-based mutagenesis of three amino acids in the related ferruginol synthase (CYP76AH1) from S. miltiorrhiza is sufficient to convert it to a 11-hydroxyferruginol synthase (HFS). The three sequential C20 oxidations for the conversion of 11-hydroxyferruginol to carnosic acid are catalysed by the related CYP76AK6-8. The availability of the genes for the biosynthesis of carnosic acid opens opportunities for the metabolic engineering of phenolic diterpenes, a class of compounds with potent anti-oxidant, anti-inflammatory and anti-tumour activities.

Diterpenes are plant products with high antioxidant properties and potential application as food additives and therapeutics. Here, the authors describe the complete biosynthetic pathway of carnosic acid and reconstruct it in yeast, opening the way to metabolic engineering of phenolic diterpenes.

Two New Diterpenoids from Salvia Przewarskii

One abietane-type and one dinoricetexane-type diterpenoid, salviskin A (1) and salviskin B (2), respectively, together with fourteen known diterpenoids, were isolated from Salvia przewarskii. Structural elucidation of these compounds was performed by spectroscopic methods including 2D NMR. The compounds isolated were evaluated for their cytotoxicity against HeLa and HL-60 cells.

An antibacterial ortho-quinone diterpenoid and its derivatives from Caryopteris mongolica

To identify antibacterial components in traditional Mongolian medicinal plant Caryopteris mongolica, an ortho-quinone abietane caryopteron A (1) and three its derivatives caryopteron B-D (2-4) were isolated from the roots of the plant together with three known abietanes demethylcryptojaponol (5), 6α-hydroxydemethyl cryptojaponol (6), and 14-deoxycoleon U (7). The chemical structures of these abietane derivatives were elucidated on the basis of spectroscopic data. Compounds 1-4 had C-13 methylcyclopropane substructures, and 2-4 had a hexanedioic anhydride ring C instead of ortho-quinone in 1. The stereochemistry of these compound was assumed from NOE spectra and ECD Cotton effects. Compounds 1 and 5-7 showed antibacterial activities against the Gram-positive bacteria Staphylococcus aureus, Staphylococcus epidermidis, Enterococcus faecalis, and Micrococcus luteus, being 1 the more potent.

Taxodione and arenarone inhibit farnesyl diphosphate synthase by binding to the isopentenyl diphosphate site

We used in silico methods to screen a library of 1,013 compounds for possible binding to the allosteric site in farnesyl diphosphate synthase (FPPS). Two of the 50 predicted hits had activity against either human FPPS (HsFPPS) or Trypanosoma brucei FPPS (TbFPPS), the most active being the quinone methide celastrol (IC50 versus TbFPPS ∼ 20 µM). Two rounds of similarity searching and activity testing then resulted in three leads that were active against HsFPPS with IC50 values in the range of ∼ 1-3 µM (as compared with ∼ 0.5 µM for the bisphosphonate inhibitor, zoledronate). The three leads were the quinone methides taxodone and taxodione and the quinone arenarone, compounds with known antibacterial and/or antitumor activity. We then obtained X-ray crystal structures of HsFPPS with taxodione+zoledronate, arenarone+zoledronate, and taxodione alone. In the zoledronate-containing structures, taxodione and arenarone bound solely to the homoallylic (isopentenyl diphosphate, IPP) site, not to the allosteric site, whereas zoledronate bound via Mg(2+) to the same site as seen in other bisphosphonate-containing structures. In the taxodione-alone structure, one taxodione bound to the same site as seen in the taxodione+zoledronate structure, but the second located to a more surface-exposed site. In differential scanning calorimetry experiments, taxodione and arenarone broadened the native-to-unfolded thermal transition (Tm), quite different to the large increases in ΔTm seen with biphosphonate inhibitors. The results identify new classes of FPPS inhibitors, diterpenoids and sesquiterpenoids, that bind to the IPP site and may be of interest as anticancer and antiinfective drug leads.

Total synthesis and biological evaluation of an antifungal tricyclic o-hydroxy-p-quinone methide diterpenoid

A convergent route has been developed to synthesize an antifungal tricyclic o-hydroxy-p-quinone methide diterpenoid and analogues. A Li/naphthalene-mediated reductive alkylation was employed for coupling β-cyclocitral and the corresponding benzyl chloride, while a BBr3-mediated one-pot bis-demethylation and intramolecular Friedel-Crafts alkylation was used to assemble the tricyclic molecular skeleton. The structure-activity relationship of the diterpenoid was assessed on the basis of antiproliferation assays of the natural product and analogues against strains of pathogenic yeasts and filamentous fungi.

Diterpenoids from the twigs and leaves of Fokienia hodginsii

Five new isopimarane diterpenoids, fokihodgins A-E (1-5), four new labdane diterpenoids, fokihodgins F-I (6-9), and one new icetexane diterpenoid, fokihodgin J (10), as well as 18 known diterpenoids were isolated from Fokienia hodginsii. The structures of the new compounds were determined on the basis of their spectroscopic analysis, and the absolute configurations of 1 and 6 were established by X-ray crystallographic analysis. Compound 9 showed moderate cytotoxicity against HL-60 and SMMC-7721 cell lines, with IC50 values of 9.10 and 7.50 μM, respectively.

Antimicrobial and anti-biofilm properties of new taxodione derivative from hairy roots of Salvia austriaca

The aim of the present report was to evaluate antimicrobial/anti-biofilm activity of 7-(2-oxohexyl)-taxodione, a novel taxodione derivative isolated from n-hexane extract of Salvia austriaca hairy roots. Antimicrobial assays showed that 7-(2-oxohexyl)-taxodione was at least 4 times more active than taxodione against methicillin-susceptible as well against methicillin-resistant staphylococci with MIC of 1.25-2.5 μgml(-1). This compound was less active against vancomycin-resistant enterococci (VRE), on the same level as taxodione (MIC ranged 10.0-20.0 μgml(-1)). The presence of 7-(2-oxohexyl)-taxodione in the culture medium (at MIC, ½ MIC or ¼ MIC) decreased adhesion of staphylococci to abiotic surfaces, which in turn caused a reduction in biofilm formation during 24h, by approximately 25-30%. Also, the extent of established biofilm eradication was found to be significant, although it required an increased concentration of the compound. This is the first report on the antimicrobial activity of this, up to now not known compound, isolated from transformed roots of S. austriaca.