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Magterpenoid A (1), possessing a rare 4,6,11-trioxatricyclo[5.3.1.01,5]undecane framework with an irregular monoterpenoid moiety, magterpenoid B (2), with an unprecedented 6/6/6/6 polycyclic skeleton, and magterpenoid C (3), a novel terpenoid quinone with a C6-C3 unit, were isolated from the bark of Magnolia officinalis var. biloba. Plausible biogenetic pathways of 1-3 are presented. Compounds 1 and 3 exhibited significant PTP1B inhibitory activities with IC50 values of 1.44 and 0.81 μM, respectively. [ABSTRACT FROM AUTHOR]

Dysiarenone (1), a dimeric C21 meroterpenoid featuring an unprecedented 2-oxaspiro[bicyclo[3.3.1]nonane-9,1'-cyclopentane] carbon skeleton, was isolated from the marine sponge Dysidea arenaria. The structure of 1 was determined by HRMS and NMR spectroscopic analyses coupled with ECD calculations. Dysiarenone showed inhibitory activities against COX-2 expression and the production of prostaglandin E2 with an IC50 value of 6.4 µM in LPS-stimulated RAW264.7 macrophages. [ABSTRACT FROM AUTHOR]

Two novel schinortriterpenoids (SNTs), schincalactones A (1) and B (2), featuring a unique 5/5/6/11/3 ring system, together with schincalide B (3), were isolated from Schisandra incarnata. Their structures were elucidated by detailed spectroscopic analysis, and the absolute configurations of 1 and 3 were confirmed by single-crystal X-ray diffraction. Compounds 1 and 2 possess a 13-membered carbon ring and are the first examples in the SNT family. Plausible biosynthetic pathways of 1-3 were postulated. [ABSTRACT FROM AUTHOR]

Allured by the quest to fabricate sustainable elastomers having tangible applications, the present work reports the study of vulcanization and reinforcement characteristics of several sustainable elastomers derived from β-myrcene—a naturally occurring “waste” monoterpene from plant. The elastomers were synthesized by the environmentally benign and industrially robust emulsion polymerization method. Conventional elastomer processing techniques were employed for the compounding and vulcanization of the synthesized elastomers. The vulcanization characteristics of the synthesized sustainable elastomers are similar to natural rubber. Polymer microstructure, molecular weight, and type and amount of comonomer influence the curing characteristics and physico-mechanical properties of the elastomer vulcanizates. An attempt has been made to elucidate the plausible network structure of the polymyrcene vulcanizate. Because of wide range of polarity, these sustainable elastomers could also aid in dispersion of functional additives. It is thus envisaged that these terpene-based elastomers could replenish the dearth of sustainable elastomers in the near future. [ABSTRACT FROM AUTHOR]

The Brassica rapa oxidosqualene cyclase Bra032185 makes 60% astertarone A (1) and 20 minor triterpenes (0.1–11%). Mechanistic analysis indicates the absence of an enol intermediate to generate the 4S epimer of 1, unless workup involves saponification. Bra032185 and its closest Arabidopsis thaliana homologue diverged markedly in product profiles over a short evolutionary distance, while developing opposite C18 configurations. Active-site residue comparison of Bra032185 with friedelin and shionone synthases suggests convergent evolution to 3-ketotriterpenes. [ABSTRACT FROM AUTHOR]

We report the first chemical syntheses of both (-)-majucin and (-)-jiadifenoxolane A via 10 net oxidations from the ubiquitous terpene (+)-cedrol. Additionally, this approach allows for access to other majucin-type sesquiterpenes, like (-)-jiadifenolide, (-)-jiadifenin, and (-)-(1R,10S)-2-oxo-3,4-dehydroxyneomajucin (ODNM) along the synthetic pathway. Site-selective aliphatic C(sp³)-H bond oxidation reactions serve as the cornerstone of this work which offers access to highly oxidized natural products from an abundant and renewable terpene feedstock. [ABSTRACT FROM AUTHOR]

Laboratory and field measurements have demonstrated that an isoprene-derived epoxide intermediate (IEPOX) is the origin of a wide range of chemical species found in ambient secondary organic aerosol (SOA). In order to explore the potential relevance of a similar mechanism for the formation of monoterpene-derived SOA, nuclear magnetic resonance techniques were used to study kinetics and reaction products of the aqueous-phase reactions of several monoterpene epoxides: β-pinene oxide, limonene oxide, and limonene dioxide. The present results, combined with a previous study of α-pinene oxide, indicate that all of these epoxides will react more quickly than IEPOX with aqueous atmospheric particles, even under low-acidity conditions. As for α-pinene oxide, the observed products can be mainly rationalized with a hydrolysis mechanism, and no long-lived organosulfate or nitrate species nor species that retain the β-pinene bicyclic carbon backbone are observed. As bicyclic ring-retaining organosulfate and nitrate species have been previously observed in monoterpene-derived SOA, it appears that monoterpene-derived epoxides may not be as versatile as IEPOX in producing a range of SOA species, and other mechanisms are needed to rationalize organosulfate and nitrate formation. [ABSTRACT FROM AUTHOR]

Macrophorins are representative examples of isoprenoid epoxycyclohexenones containing cyclized drimane moieties. We located and characterized the biosynthetic gene cluster of macrophorin from Penicillium terrestris. MacJ encoded by this cluster was characterized to be the first example of a membrane-bound type-II terpene cyclase catalyzing the cyclization of meroterpenoids via direct protonation of the terminal olefinic bond in acyclic yanuthones. The late-stage functionalization and substrate promiscuity of MacJ make it a potential biocatalyst for the synthesis of macrophorin analogues. [ABSTRACT FROM AUTHOR]

A divergent entry to the chiral bicyclo[5.3.0]decane skeletons relevant to sesqui- and higher terpenoids has been achieved. Its usefulness was demonstrated by formal synthesis of a guaiane sesquiterpenoid (--)-englerin A. The key reactions are (i) diastereoselective Nazarov cyclization for stereoselective construction of the bicyclo[5.3.0]decane skeleton, (ii) intramolecular C--H amination for tuning an oxidation state, and (iii) introduction of an alkyl group to a β-alkoxy ketone with a zinc(II) ate complex. [ABSTRACT FROM AUTHOR]

The pool of abundant chiral terpene building blocks (i.e., "chiral pool terpenes") has long served as a starting point for the chemical synthesis of complex natural products, including many terpenes themselves. As inexpensive and versatile starting materials, such compounds continue to influence modern synthetic chemistry. This review highlights 21st century terpene total syntheses which themselves use small, terpene-derived materials as building blocks. An outlook to the future of research in this area is highlighted as well. [ABSTRACT FROM AUTHOR]

The year 2017 marks the twentieth anniversary of terpenoid cyclase structural biology: a trio of terpenoid cyclase structures reported together in 1997 were the first to set the foundation for understanding the enzymes largely responsible for the exquisite chemodiversity of more than 80000 terpenoid natural products. Terpenoid cyclases catalyze the most complex chemical reactions in biology, in that more than half of the substrate carbon atoms undergo changes in bonding and hybridization during a single enzyme-catalyzed cyclization reaction. The past two decades have witnessed structural, functional, and computational studies illuminating the modes of substrate activation that initiate the cyclization cascade, the management and manipulation of high-energy carbocation intermediates that propagate the cyclization cascade, and the chemical strategies that terminate the cyclization cascade. The role of the terpenoid cyclase as a template for catalysis is paramount to its function, and protein engineering can be used to reprogram the cyclization cascade to generate alternative and commercially important products. Here, I review key advances in terpenoid cyclase structural and chemical biology, focusing mainly on terpenoid cyclases and related prenyltransferases for which X-ray crystal structures have informed and advanced our understanding of enzyme structure and function. [ABSTRACT FROM AUTHOR]

Phainanolide A (1), a highly modified triterpenoid incorporating an unprecedented 6/9/6 heterotricyclic system and a highly oxygenated 5,5-spirocyclic ketal lactone, along with three new triterpenoids 2-4 were isolated from Phyllanthus hainanensis. Their structures were completely elucidated by a combination of diverse methods including 2D NMR, quantum chemical NMR and ECD calculations, and NMR data analogy with model compounds. Compounds 1-4 exhibited both remarkable cytotoxic and immunosuppressive activities. [ABSTRACT FROM AUTHOR]

Walrobsins A (1) and B (2), two limonoids featuring an unprecedented 5-oxatricyclo[5.4.11,4]hendecane ring system, were isolated from the root barks of Walsura robusta. Their structures, including their absolute configurations, were determined by analyses of HR-ESIMS, 1D/2D NMR, and X-ray crystallography. Compounds 1 and 2 possessed a stable hemiketal structure formed between the OH-11 and 3-carbonyl group in the hexatomic oxoheterocyclic ring. Compound 1 showed significant anti-inflammatory activity with an IC50 value of 7.8 μM and inhibited the expression of iNOS and IL-1β in a dose-dependent manner. [ABSTRACT FROM AUTHOR]

Treatment of the fungal meroterpenoid dhilirolide A (1) with either sodium azide or perchloric acid results in conversion of the dhilirane carbon skeleton of 1 to the 14,15-dinordhilirane carbon skeleton of the products 5-7, with and without concomitant transfer of an acetyl residue to form a C-9 acetate ester. The discovery of these transformations, which are vinylogous retro-Claisen-type condensations, suggests an efficient biogenetic route to 14,15-dinordhiliranes such as dhilirolide K (3). [ABSTRACT FROM AUTHOR]

New experimental data on solid-liquid equilibrium (SLE) phase diagrams for binary systems {(-)-menthol or thymol + n-dodecane, or 1-dodecanol, or 2-phenylethanol} are presented. An influence of chemical structure of both terpenoid and solvent on the solubility curves is established and discussed. The new data are addressed and compared to the SLE data with a different set of solvents published previously. Modeling of SLE in the investigated mixtures with three modern thermodynamic models, namely, modified UNIFAC (Dortmund), perturbed-chain statistical associating fluid theory (PC-SAFT), and conductor-like screening model for real solvents (COSMO-RS), is presented as well. The predictive capacity of the studied approaches is confronted and compared with respect to their physical foundations for representation of components forming the systems as well as relevant intermolecular interactions governing thermodynamic behavior of the mixtures. [ABSTRACT FROM AUTHOR]

The tail-to-head terpene cyclization is arguably one of the most complex reactions found in nature. The hydrogen-bond-based resorcinarene capsule represents the first man-made enzyme-like catalyst that is capable of catalyzing this reaction. Based on noncovalent interactions between the capsule and the substrate, the product selectivity can be tuned by using different leaving groups. A detailed mechanistic investigation was performed to elucidate the reaction mechanism. For the cyclization of geranyl acetate, it was found that the cleavage of the leaving group is the ratedetermining step. Furthermore, the studies revealed that trace amounts of acid are required as cocatalyst. A series of control experiments demonstrate that a synergistic interplay between the supramolecular capsule and the acid traces is required for catalytic activity. [ABSTRACT FROM AUTHOR]

Carvone is a sustainable and readily available starting material for organic synthesis. Herein, we present the syntheses of various natural product scaffolds that rely on a novel benzannulation involving the α-methyl group (C-10) of carvone to afford a versatile tetralin. The utility of our synthetic approach is highlighted by its application to a short synthesis of the ent-3,4-seco-atisane diterpenoid (−)-crotogoudin. The 13-step enantiospecific synthesis features a regioselective double oxidative dearomatization, a Diels−Alder cycloaddition with ethylene gas (to construct the bicyclo[2.2.2]octane framework), and a final acid-mediated lactonization. The versatility of this benzannulation strategy is demonstrated by its utility in the preparation of the carbon skeleton of ent-3,4-seco-abietane diterpenoids using an intramolecular oxidative dearomatization. [ABSTRACT FROM AUTHOR]

Sesquiterpenyl epoxy-cyclohexenoids (SECs) show impressive biological activities. However, the key pathways for SECs still remain unambiguous. Unexpectedly, 11 new SECs and derivatives with diverse oxidation patterns were isolated after the deletion of gene 274. A high accumulation of toluquinol and its new glycosides in mutant Δ276 and further isolation of the most crucial precursors farnesyl hydroquinone, farnesyl quinone, and three new derivatives from mutant Δ278 confirm that farnesylation at toluquinol is the key step for SECs. [ABSTRACT FROM AUTHOR]

Wickerol A (1) is an unusual diterpene with remarkable activity against the H1N1 influenza virus. Its tetracyclic skeleton contains three quaternary carbons and is marked by several syn-pentane interactions which force a six-membered ring into a twist-boat conformation. We present an asymmetric synthesis of wickerol A (1) that is based on a Jung Diels-Alder reaction, an intramolecular alkylation to complete the 6-5-6-6 ring system, and a conjugate addition, all of which overcome considerable steric strain. During the synthesis, we isolated an unexpected cyclopropane that presumably stems from a carbonium ion intermediate. [ABSTRACT FROM AUTHOR]

Monoterpenes, a major class of biogenic volatile organic compounds, are known to produce oxidation products that further react with sulfate to form organosulfates. The accurate quantification of monoterpene-derived organosulfates (OSs) is necessary for quantifying this controllable aerosol source; however, it has been hampered by a lack of authentic standards. Here we report a unified synthesis strategy starting from the respective monoterpene through Upjohn dihydroxylation or Sharpless asymmetric dihydroxylation followed by monosulfation with the sulfur trioxide-pyridine complex. We demonstrate the successful synthesis of four monoterpene-derived OS compounds, including α-pinene OS, β-pinene OS, limonene OS, and limonaketone OS. Quantification of OSs is commonly achieved using liquid chromatography-mass spectrometry (LC-MS) by either monitoring the [M-H]- ion or through multiple reaction monitoring (MRM) of mass transitions between the [M-H]- and m/z 97 ions. Comparison between the synthesized standards and previously adopted quantification surrogates reveals that camphor-10-sulfonic acid is a better quantification surrogate using [M-H]- as the quantification ion, while the highly compound-specific nature of MRM quantification makes it difficult to choose a suitable surrogate. Both could be rationalized in accordance to their respective MS quantification mechanisms. The in-house availability of the authentic standards enables us to discover that β-pinene OS, due to the sulfate group at the primary carbon, partially degrades to a dehydrogenated OS compound during LC/MS analysis and a hydroperoxy OS over a prolonged storage period (>5 month) and forms a regioisomer through intermolecular isomerization. Limonene OS was positively identified for the first time in ambient samples and found to be more abundant than α-/β-pinene OS in the Pearl River Delta, China. This work highlights the critical importance of having authentic standards in advancing our understanding of the interactions between biogenic VOC emissions and anthropogenic sulfur pollution. [ABSTRACT FROM AUTHOR]

Two GFPPS linked (+)-thalianatriene (1) and (-)-retigeranin B (2) sesterterpene synthase genes were identified from the genome of Arabidopsis thaliana. 1 possesses an unprecedented 11-6-5 tricyclic ring system, while 2 contains a characteristic 5-5-5-6-5 pentacyclic ring system. Their structures were determined by extensive NMR spectroscopy, chemical derivatization, and X-ray crystallography. The variable-temp NMR measurement of 3, a diepoxy-bearing derivative of 1, enables us to completely assign the NMR signals of the two conformers as 3a (67%, UUU) and 3b (33%, UUD). A plausible biosynthesis mechanism of 1 was proposed. [ABSTRACT FROM AUTHOR]

Analysis of bioorganic materials by infrared spectroscopy (FT-IR) is frequently limited due to overlapping of diagnostic bands from the various components, which poses a fundamental problem to this analytical technique. The distinction of oxidized di- and triterpenes, for example, is hindered by the superposition of similar absorption bands of carbonyl functional groups summing up to a broad, nondistinctive signal. This study presents a technique for selective fluorination of various carboxylic acids by exposure to gaseous sulfur tetrafluoride. The derivatization treatment leads to characteristic band shifts, allowing the separation of otherwise overlapping bands. Accordingly, the IR bands of primary acids, α,β-unsaturated acids, tertiary acids, peroxy acids, esters, ketones, and α,β-unsaturated ketones are split into distinct absorption bands. The capability of this method is demonstrated on the example of natural resins and their ingredients, which are commonly known to be susceptible to oxidation at ambient conditions. The derivatization method enables one to identify various carbonyl containing functional groups by infrared spectroscopy, even in complex mixtures of terpenes. It unveils previously hidden degradation reactions running in terpenes and natural resins exposed to artificial aging by irradiation with light. New insight is presented on the individual reaction pathways of the terpenes hydroxydammarenone and abietic acid as well as of natural resin varnishes made from dammar and colophony. [ABSTRACT FROM AUTHOR]

Commiphoranes A-D (1-4), four novel aromatic terpenoids with unprecedented carbon skeletons, were isolated from Resina Commiphora. Their structures were identified by spectroscopic and crystallographic methods. Compounds 1 and 2 are dinorditerpenoids characteristic of a 6/6/6/6 ring system. In contrast, compounds 3 and 4 are sesquiterpenoids possessing a 5/6/7 backbone. Biological evaluation reveals that 3 could significantly attenuate overproduction of fibronectin, collagen I, and α-SMA in TGF-β1-induced rat renal proximal tubular cells. [ABSTRACT FROM AUTHOR]

Formal syntheses of tetracyclic terpenoids frondosin B and liphagal are described. Both synthetic routes rely on the use of platinum-catalyzed α,β-unsaturated carbene formation for the key C-C bond forming transformations. The successful route toward frondosin B utilizes a formal (4 + 3) cycloaddition, while the liphagal synthesis features the vinylogous addition of an enol nucleophile as a key step. Both synthetic routes are discussed, revealing insights into structural requirements in the catalytic α,β-unsaturated carbene reaction manifold. [ABSTRACT FROM AUTHOR]

Dimericbiscognienyne A (1), an unusual diisoprenyl-cyclohexene-type meroterpenoid dimer, was isolated from Biscogniauxia sp. together with three new monomeric diisoprenyl-cyclohexene-type meroterpenoids (2-4) and one new isoprenyl-benzoic acid-type meroterpenoid (5). All structures were determined by extensive NMR spectroscopic methods, quantum chemical calculations, chemical derivatization, and X-ray crystallography. The formation of 1 is related to a unique intermolecular redox coupling Diels-Alder adduct reaction. Their cytotoxicities and short-term memory enhancement activities against Alzheimer's disease were assessed. [ABSTRACT FROM AUTHOR]

Two novel C25 terpenoids with a 6/5/5/5/5/3 hexacyclic skeleton including one γ-lactone ring and two tetrahydrofuran rings, hitorins A (1) and B (2), were isolated from the aerial parts of Chloranthus japonicus. The structures of 1 and 2 were elucidated on the basis of spectroscopic analyses as well as TDDFT ECD calculations. Hitorins A (1) and B (2) might be biogenetically derived from eudesmane sesquiterpene and thujane monoterpene. [ABSTRACT FROM AUTHOR]

A novel synthetic approach for the synthesis of bioactive phenolic natural products is reported. This strategy highlights the power of halogenative aromatization reactions recently developed in our group for preparing densely functionalized arenes in a controlled fashion. Five natural products related by an aromatic core and a farnesyl side chain are synthesized. In contrast to prior methods, this synthesis features high efficiency and generality that permits preparation of targets in gram-scale quantities. [ABSTRACT FROM AUTHOR]

Rhodomyrtials A and B (1 and 2), two unprecedented triketone-sesquiterpene-triketone adducts, along with five biogenetically related intermediates, rhodomentone A (3) and tomentodiones A-D (4-7), were isolated from the leaves of Rhodomyrtus tomentosa. Their structures and absolute configurations were determined by a combination of NMR spectroscopy, chemical conversion, and X-ray diffraction analysis. Compounds 1 and 2 were biomimetically synthesized via 5 and 4, respectively, rather than 3, revealing their key ordering of biosynthetic events and confirming their structural assignments. Compound 7 exhibited potent metastatic inhibitory activity against DLD-1 cells by suppressing the activation of matrix metalloproteinase (MMP)-2 and MMP-9. [ABSTRACT FROM AUTHOR]

Five sesquiterpene-based meroterpenoids with three kinds of new skeletons [1, 2, 3, (+)-4, and (−)-4] were isolated from the leaves of Myrtus communis. Compound 1 featured a new carbon skeleton with an unprecedented octahydrospiro[bicyclo[7.2.0]undecane-2,2′-chromene] tetracyclic ring system, which possessed two preferred conformations detected by variable-temperature NMR spectroscopy experiments. In addition, the structure of reported myrtucommulone K was revised to be compound 3. The plausible biosynthetic pathways of these meroterpenoids and their cytotoxicities are discussed. [ABSTRACT FROM AUTHOR]

A four-step total synthesis of paeoveitol (1), a recently disclosed norditerpene natural product from Paeonia vetchii, is reported. This highly concise synthetic route was guided by biosynthetic considerations and enabled by an unusual intermolecular ortho-quinone methide [4 + 2]-cycloaddition reaction, which proceeded with excellent regio- and diastereoselectivity. Density functional theory (DFT) calculations point to a crucial intermolecular hydrogen bond and π-π stacking interaction that govern selectivity in this process. [ABSTRACT FROM AUTHOR]

The structurally intriguing terpenes pallambins C and D have been assembled in only 11 steps from a cheap commodity chemical: furfuryl alcohol. This synthesis, which features a redox-economic approach free of protecting-group manipulations, assembles all four-ring systems via a sequential cyclization strategy. Of these fourring constructing operations, two are classical (Robinson annulation and Mukaiyama aldol) and two are newly devised. During the course of this work a method for the difunctionalization of enol ethers was developed, and the scope of this transformation was explored. [ABSTRACT FROM AUTHOR]

In general, diffusion rates in extractions are enhanced by increasing the temperature. In this study, we instead add compressed liquid carbon dioxide to the extraction phase to accomplish faster mass transfer. The feasibility of using carbon dioxide expanded ethanol (CXE) as the extraction phase was explored, targeting two medium-polar analytes, α-pinene and cis-verbenol in Boswellia sacra tree resin. Hansen solubility parameters (HSP) were first calculated for the analytes and the extraction phases investigated, ethanol, CXE, and supercritical carbon dioxide (scCO2) containing ethanol as a cosolvent. Second, an extraction method with CXE as the extraction phase was optimized using a Box Behnken design, giving optimal conditions of 40 °C, 9.3 MPa, and 0.31 molar fraction of CO2 in ethanol. Third, the developed method was compared with a supercritical fluid extraction (SFE) method and a conventional solid liquid extraction (SLE) method, showing that CXE enables faster and more efficient extraction than both SFE and SLE. In fact, calculations based on Peleg's equation showed that the initial extraction rate of the new method is up to 10 times faster than SFE when using the highest flow rate tested, 3 mL/min. It was also discovered that it is crucial to cool the makeup solvent in the collection system for efficient analyte collection, at least in modern SFE equipment where pressure is regulated by a backpressure regulator. The use of CXE and pertinently also other CO2-expanded liquids in sample preparation shows a great potential in terms of increasing the extraction rate without elevating the temperature. [ABSTRACT FROM AUTHOR]

Hyperjapones A-E (1-5), novel terpenoid polymethylated acylphloroglucinols (TPAPs) with unusual architectures, were characterized from Hypericum japonicum. Their structures and absolute configurations were determined by comprehensive spectroscopic data and X-ray diffractions. Compound 1 was obtained as a racemic mixture and was separated by a column coated with cellulose tris(4-methylbenzoate) after attempts with various chiral materials. Compounds 1, 2, and 4 exhibited moderate antitumor activities in vitro. [ABSTRACT FROM AUTHOR]

The sesquiterpene synthase germacradiene-4-ol synthase (GdolS) from Streptomyces citricolor is one of only a few known high-fidelity terpene synthases that convert farnesyl diphosphate (FDP) into a single hydroxylated product. Crystals of unliganded GdolS-E248A diffracted to 1.50 Å and revealed a typical class 1 sesquiterpene synthase fold with the active site in an open conformation. The metal binding motifs were identified as D80DQFD and N218DVRSFAQE. Some bound water molecules were evident in the X-ray crystal structure, but none were obviously positioned to quench a putative final carbocation intermediate. Incubations in H218O generated labeled product, confirming that the alcohol functionality arises from nucleophilic capture of the final carbocation by water originating from solution. Site-directed mutagenesis of amino acid residues from both within the metal binding motifs and without identified by sequence alignment with aristolochene synthase from Aspergillus terreus generated mostly functional germacradien-4-ol synthases. Only GdolS-N218Q generated radically different products (~50% germacrene A), but no direct evidence of the mechanism of incorporation of water into the active site was obtained. Fluorinated FDP analogues 2F-FDP and 15,15,15-F3-FDP were potent noncompetitive inhibitors of GdolS. 12,13-DiF-FDP generated 12,13-(E)-β-farnesene upon being incubated with GdolS, suggesting stepwise formation of the germacryl cation during the catalytic cycle. Incubation of GdolS with [1-²H2]FDP and (R)-[1-²H]FDP demonstrated that following germacryl cation formation a [1,3]-hydride shift generates the final carbocation prior to nucleophilic capture. The stereochemistry of this shift is not defined, and the deuteron in the final product was scrambled. Because no clear candidate residue for binding of a nucleophilic water molecule in the active site and no significant perturbation of product distribution from the replacement of active site residues were observed, the final carbocation may be captured by a water molecule from bulk solvent. [ABSTRACT FROM AUTHOR]

Two new sesterterpenoids, aspterpenacids A (1) and B (2), with an unusual carbon skeleton of a 5/3/7/6/5 ring system were isolated from the mangrove endophytic fungus Aspergillus terreus H010. Their structures were elucidated on the basis of spectroscopic methods, single-crystal X-ray diffraction analysis, and electronic circular dichroism calculations. A biogenetic pathway for 1 and 2 is proposed. Both 1 and 2 showed no significant antibacterial activity or cytotoxicity at 50 μM. [ABSTRACT FROM AUTHOR]

The nitrate radical (NO3) is the dominant nighttime oxidant in most urban and rural environments and reacts rapidly with biogenic volatile organic compounds toform secondary organic aerosol (SOA) and organic nitrates (ON). Here, we study the formation of SOA and ON from the NO3 oxidation of two monoterpenes (α-pinene and β-pinene) and investigate how they evolve during photochemical aging. High SOA mass loadings are produced in the NO3+β-pinene reaction, during which we detected 41 highly oxygenated gas- and particle-phase ON possessing 4 to 9 oxygen atoms. The fraction of particle-phase ON in the β-pinene SOA remains fairly constant during photochemical aging. In contrast to the NO3+β-pinene reaction, low SOA mass loadings are produced during the NO3+α-pinene reaction, during which only 5 highly oxygenated gas- and particle-phase ON are detected. The majority of the particle-phase ON evaporates from the α-pinene SOA during photochemical aging, thus exhibiting a drastically different behavior from that of β-pinene SOA. Our results indicate that nighttime ON formed by NO3+monoterpene chemistry can serve as either permanent or temporary NOx sinks depending on the monoterpene precursor. [ABSTRACT FROM AUTHOR]

Thesearch for a new sesterterpene synthase in the genome of Emericellavariecolor, which reportedly produces diversesesterterpenoids, is described. One gene product (a chimeric proteinwith prenyltransferase and terpene cyclase domains) led to the synthesisof a novel tricyclic sesterterpene, stellata-2,6,19-triene (1), from DMAPP and IPP, and the hydrocarbon was further transformedinto stellatic acid (2) by cytochrome P450 monooxygenaseencoded by the gene adjacent to the sesterterpene synthase gene. [ABSTRACT FROM AUTHOR]

This study reports the high-temperature,high-pressure densitydata for propane, squalane, and their binary mixtures for five compositionsat temperatures to 520 K and pressures to 260 MPa. The density measurementsare obtained with a floating-piston, variable-volume, high-pressureview cell. From the density data, the isothermal and isobaric excessmolar volumes upon mixing are computed. For the mixture compositionsstudied here, the excess volume is mostly negative, showing a minimumat 0.6550 mole fraction of propane and becomes less negative as thepropane concentration increases. The perturbed-chain statistical associatingfluid theory (PC-SAFT) equation of state (EoS) provides good representationfor the experimental data. A mean absolute percent deviation (δ)of 1.4% is obtained with the PC-SAFT EoS when using propane and squalanepure component parameters fit to density data at high-temperature,high-pressure conditions. [ABSTRACT FROM AUTHOR]

Hydroperoxides can act as specifichaptens and oxidatively modifyproteins. Terpene hydroperoxides trigger unusually high frequenciesof positive skin reactions in human patients if tested at high concentrations.It is unknown whether this is due to specific hapten formation. Here,we show that both terpene hydroperoxides and the endogenous hydroperoxideformed from squalene can oxidatively modify tryptophan. Oxidativemodifications of Trp were recently postulated to explain cross-sensitizationbetween unrelated photosensitizers. Current observations may extendthis hypothesis: Oxidative events triggered by endogenous hydroperoxidesand hydroperoxides/oxidants derived from xenobiotics might lead toa sensitized state detected by patch tests with high concentrationsof hydroperoxides. [ABSTRACT FROM AUTHOR]

Biocompatible colloidal dispersionsof the micro- and nanoemulsiontype based on lemon oil terpenes, polysorbates, water, and glycerolwere used for the formulation of pyrethrins, botanical insecticidesderived from the white pyrethrum daisy, Tanacetum cinerariifolium.The proposed formulation is based on pyrethrin-containing water-in-oil(W/O) microemulsions that could be diluted in one step with an aqueousphase to obtain kinetically stable oil-in-water (O/W) nanoemulsions.Structural characteristics of the micro- and nanoemulsions were evaluatedby electron paramagnetic resonance (EPR) spectroscopy, dynamic lightscattering (DLS), small angle X-ray scattering (SAXS), and electricalconductivity. Dynamic properties of the surfactant monolayer as evidencedby EPR measurements were affected by the water content, the surfactant,and also the presence of the biocide. DLS and SAXS experiments ofthe nanoemulsions indicated the existence of two populations of oildroplets dispersed in the aqueous phase, globular droplets of 36–37nm in diameter, and also larger droplets with diameters >150 nm.Allof the applied techniques for structural determination revealed theparticipation of the biocide in the nanostructure. The insecticidaleffect of the encapsulated natural pyrethrin was evaluated in laboratorybioassays upon a target-insect pest, the cotton aphid AphisgossypiiGlover (Hemiptera: Aphididae) in eggplant, and wasfound to be increased compared to the commercial pyrethrin formulation. [ABSTRACT FROM AUTHOR]

The article offers information on a research on the catalytic upgrading of α-pinene and related terpenes. Topics discussed include heterogeneously catalyzed hydrogenation of terpenes, epoxidation of limonene and camphene, and isomerization of oxygenated terpenoids. Also mentioned are chemical composition of crude turpentine (CT), upgrading process involving primary reaction of α- and β-pinene, and characteristics of two hydrogen forms of ferrierite.

Two novel meroterpenoids, yaminterritrems A (1) and B (2), were isolated from Aspergillus terreus collected from hot spring zones in Yang-Ming Mountain, Taiwan, and cultured at 40 °C. The structures of 1 and 2 were elucidated by NMR, MS spectral and X-ray crystallographic analyses. The biosynthetic route for 1 and 2 involving the conversion of the sesquiterpene with phenyl-a-pyrone is proposed. Besides, 2 exhibited a dose-dependent inhibitory effect on COX-2 expression in LPS-stimulated RAW264.7 macrophages. [ABSTRACT FROM AUTHOR]

The chemical complexity of dissolved organic matter (DOM) obstructs our ability to definitively recover source compounds from within DOM, an objective which has the capacity to alter our understanding of carbon sequestration on a global scale. To advance compositional studies of DOM we have applied a previously published reduction method to an environmental standard, Suwannee River Fulvic Acid (SRFA). The reduction products, comprising 12% of the prereduced carbon, were then separated by comprehensive two-dimensional gas chromatography time-of-flight mass spectrometry (GC×GC-TOF-MS). Results indicate that the majority of observed reduced compounds corresponded to alicyclic hydrocarbons in the size range C10 to C17. Cyclic terpenoids are the only biomolecule class with contiguous, alicyclic carbon backbones of this size. These terpenoid reduction products contain series offset by CH2 and exhibit great isomeric diversity, features previously inferred from ultrahigh resolution mass spectrometry and NMR studies of unreduced SRFA. Reduction of Taxodium leaf litter as a source material to SRFA confirmed the prevalence of terpenoids in SRFA and provided insight into the parent compounds that must be diagenetically modified on relatively short time scales. These data corroborate several recent studies that suggest alicyclic hydrocarbons to be important components of longer-lived DOM. [ABSTRACT FROM AUTHOR]

On the basis of results from quantum chemical calculations, the feasibility of an extensive series of intramolecular proton-transfer reactions postulated to occur during terpene biosynthesis is assessed and guiding principles are proposed. [ABSTRACT FROM AUTHOR]

Applanatumin A (1), a novel meroterpenoid dimer, was isolated from the fungus Ganoderma applanatum. Its structure and absolute configuration were assigned on the basis of spectroscopic and computational data. Notably, 1 possesses a new hexacyclic skeleton containing a spiro[benzofuran-2,1'-cyclopentane] motif. A plausible pathway, involving a key Diels-Alder reaction, is proposed for the biosynthesis of 1. Applanatumin A exhibits potent antifibrotic activity in TGF-β1-induced human renal proximal tubular cells. [ABSTRACT FROM AUTHOR]

Despite the importance of terpenesin biology, the environment,and catalysis, their vibrational spectra remain unassigned. Here,we present subwavenumber high-resolution broad-band sum frequencygeneration (HR-BB-SFG) spectra of the common terpene (+)-α-pinenethat reveal 10 peaks in the C–H stretching region at room temperature.The high spectral resolution resulted in spectra with more and betterresolved spectral features than those of the Fourier transform infrared,femtosecond stimulated Raman spectra in the bulk condensed phase andthose of the conventional BB-SFG and scanning SFG spectroscopy ofthe same molecule on a surface. Experiment and simulation show thespectral line shapes with HR-BB-SFG to be accurate. Homogeneous vibrationaldecoherence lifetimes of up to 1.7 ps are assigned to specific oscillatorsand compare favorably to lifetimes computed from density functionaltight binding molecular dynamics calculations. Phase-resolved spectraprovided their orientational information. We propose the new spectroscopyas an attractive alternative to time domain vibrational spectroscopyor heterodyne detection schemes for studying vibrational energy relaxationand vibrational coherences in molecules at molecular surfaces or interfaces. [ABSTRACT FROM AUTHOR]

The mulinane class of diterpenoids is a set of tricyclic (5-6-7), biologically active natural products whose members exhibit a variety of oxidation states. Herein, we report the inaugural synthesis of four mulinanes employing a divergent approach that relies on a diastereoselective anionic oxy-Cope rearrangement to set the relative configuration of the C8 stereocenter and an unprecedented vinylogous Saegusa dehydrogenation reaction to address C-ring functionality. [ABSTRACT FROM AUTHOR]

A systematic study of the biomimetic pathways to yezo'otogirin C under aerobic and anaerobic conditions has been investigated, and both are found to be feasible pathways to the natural product depending on the physiological conditions. Because of the lower activation energy, the aerobic process would be more favorable when the in vivo oxygen level is high. In the course of this study, a highly efficient synthetic route to (±)-yezo'otogirin C has been established in four steps (31% overall yield) from a readily available compound without using any protecting groups. The natural product and its structural analogues exhibited antitumor activities against several human cancer cell lines and appeared to arrest cell cycles in different phases. [ABSTRACT FROM AUTHOR]

Phainanoids A-F (1-6), six highly modified triterpenoids with a new carbon skeleton by incorporating two unique motifs of a 4,5- and a 5,5-spirocyclic systems, were isolated from Phyllanthus hainanensis. Their structures with absolute configurations were determined by spectroscopic data, chemical methods, and X-ray crystallography. Compounds 1-6 exhibited exceptionally potent immunosuppressive activities in vitro against the proliferation of T and B lymphocytes. The most potent one, phainanoid F (6), showed activities against the proliferation of T cells with IC50 value of 2.04 ± 0.01 nM (positive control CsA = 14.21 ± 0.01 nM) and B cells with IC50 value of <1.60 ± 0.01 nM (CsA = 352.87 ± 0.01 nM), which is about 7 and 221 times as active as CsA, respectively. The structure--activity relationships of 1-6 are discussed. [ABSTRACT FROM AUTHOR]