Cyclic Terpenes Research Articles

Heterologous regulation of anion transporters by menthol in human airway epithelial cells

The present study concerns previously unreported effects of menthol, a cyclic terpene alcohol produced by the peppermint herb, on anion transporters in polarized human airway Calu-3 epithelia. Application of menthol (0.01–1 mM) attenuated transepithelial anion transport, estimated as short-circuit currents ( I SC), after stimulation by forskolin (10 µM) but not before. In contrast, menthol potentiated forskolin-stimulated and -unstimulated apical Cl − conductance, which reflected the cystic fibrosis transmembrane conductance regulator (CFTR: the cAMP-regulated Cl − channel)-mediated conductance, without correlation to changes in cytosolic cAMP levels. These results indicate that menthol-induced attenuation of forskolin-induced I SC despite CFTR up-regulation was due to cAMP-independent inhibition of basolateral anion uptake, which is the rate-limiting step for transepithelial anion transport. Analyses of the responsible basolateral anion transporters revealed that forskolin increased both bumetanide (an inhibitor of the basolateral Na +–K +–2Cl − cotransporter [NKCC1])- and DNDS (an inhibitor of basolateral HCO 3 −-dependent anion transporters [NBC1/AE2])-sensitive I SC in the control whereas only the former was prevented by the application of menthol. Neither the bumetanide- nor DNDS-sensitive component was, however, reduced by menthol without forskolin. These heterologous effects of menthol were reproduced by latrunculin B, an inhibitor of actin polymerization. F-actin staining showed that menthol prevented forskolin-stimulated rearrangements of actin microfilaments without affecting the distribution of forskolin-unstimulated microfilaments. Collectively, menthol functions as an activator of CFTR and prevents activation of NKCC1 without affecting NBC1/AE although all of these transporters are commonly cAMP-dependent. The heterologous effects may be mediated by the actin cytoskeleton, which interacts with CFTR and NKCC1.

Transdermal Delivery of Ketorolac

A reservoir type transdermal patch for delivery of ketorolac, a potent analgesic agent was studied. The low permeability of skin is the rate-limiting step for delivery of most of the drugs. Studies were carried out to investigate the effect of permeation enhancers on the in vitro permeation of ketorolac across rat skin. The reservoir type transdermal patch was fabricated and the core was filled with gel system of a non ionic polymer HPMC (hydroxypropyl methyl cellulose) formulated in PBS (phosphate buffer saline) solution of pH of 5.4 along with isopropyl alcohol at 25% w/w concentration. Various permeation enhancers' viz. dimethyl sulphoxide, d-limonene, eucalyptus oil and transcutol (diethylene glycol monoethyl ether) were incorporated into the gel system. Permeation enhancement of ketorolac with different enhancers followed the order eucalyptus oil> transcutol> DMSO> d-limonene. Cyclic terpene containing eucalyptus oil was found to be the most promising chemical permeation enhancer for transdermal delivery of ketorolac. The increase in concentration of eucalyptus oil further enhanced drug permeation with maximum flux being achieved at 10% w/w of 66.38 microg/cm(2)/h. Further enhancement of permeation rate of ketorolac across skin was attained by application of abrading gel containing crushed apricot seed onto the skin. There was 5.16 times enhancement and flux of 93.10 microg/cm(2)/h was attained. A reservoir type transdermal patch for delivery of ketorolac thus appears to be feasible of delivering ketorolac across skin.

Fatty acid composition and volatile compounds of selected marine oils and meals

AbstractBACKGROUND: Although volatile compounds characterising seafood have been studied extensively, no similar data are available regarding the volatiles of raw materials used in fish feed. Therefore the aim of this study was to make an initial screening of the volatiles of various common marine raw materials used in the aquaculture feed industry. Nine commercial marine oils (German (GFO1, GFO2 and GFO3) and Norwegian (NFO) fish oils and salmon (SO1 and SO2), tuna (TO), sardine (SRDO) and shrimp (SHO) oils) and eight commercial marine meals (Peruvian (PFM1 and PFM2), Danish (DFM1 and DFM2) and prime quality (PQFM1 and PQFM2) fish meals and Antarctic krill meals (KM1 and KM2)) were analysed for their fatty acid profiles and volatile flavour compounds. The relation between fatty acids and volatiles was examined.RESULTS: The highest polyunsaturated fatty acid and eicosapentaenoic acid (20:5ω3) contents and ω3/ω6 ratio were found in NFO. The fatty acid composition of all marine meals except krill meals was found to be more variable among batches than that of marine oils. Regarding volatiles, all marine raw materials were characterised by the complete absence or negligible levels of eight‐ and nine‐carbon alcohols and carbonyls. All marine oils were found to have high 2‐ethyl furan, 2‐methylenebutyl cyclopropane, hexanal, 2,4‐octadiene and 3,5‐octadiene contents. Marine meals, unlike marine oils, were characterised by the almost complete absence of unsaturated and cyclic hydrocarbons and terpenes and very low levels of furans.CONCLUSION: Volatiles of marine meals differ from those of marine oils. Unlike fatty acids which give useful traceability information, volatiles seem to fail in this role owing to their strong variability. Copyright © 2008 Society of Chemical Industry

Linear and cyclic C18 terpenoids from the southern Australian marine brown alga Cystophora moniliformis.

Chemical investigation of the Southern Australian marine brown alga Cystophora moniliformis resulted in the isolation of two new cyclic epimeric terpene diols, moniliforminol A (25) and moniliforminol B (26), a new linear farnesylacetone derivative (27), and the previously described terpenoids 19-24. This study also resulted in the first complete 2D NMR characterization for compounds 21 to 24 as well as the first report of 24 as a natural product. All structures were elucidated by detailed spectroscopic analysis, with the relative configurations of 25 and 26 being established by selective 1D NOE NMR experiments. The absolute configuration of 26 was assigned on the basis of circular dichroism (CD), which also permitted that of 25 to be tentatively assigned.

Cloning, expression and characterisation of CYP102A7, a self-sufficient P450 monooxygenase from Bacillus licheniformis

Cytochrome P450 monooxygenases of the CYP102A subfamily are single-component natural fusion proteins consisting of a heme domain and a diflavin reductase. The characterised CYP102A enzymes are fatty acid hydroxylases with turnover rates of several thousands per minute. In search of new P450s with similar activities, but with a broader substrate spectrum, we cloned, expressed and characterised CYP102A7 from Bacillus licheniformis. As expected, CYP102A7 was active towards medium-chain fatty acids but showed a strong preference for saturated over unsaturated fatty acids, which could not be observed for either of the CYP102A members so far. Besides fatty acids, CYP102A7 was able to catalyse the oxidation of cyclic and acyclic terpenes with high activity and coupling efficiency. For example, (R)-(+)-limonene was converted with activity of 220 nmol nmol P450(-1) min(-1) and 80% coupling. Unusual for enzymes of the CYP102A subfamily was the deethylation activity of CYP102A7 towards 7-ethoxycoumarin. Furthermore, this monooxygenase, though having a moderate thermal stability, exhibited 50% of its initial activity in the presence of 26% DMSO. Comparison of the homology models of CYP102A7 and other members of the CYP102A subfamily revealed distinct differences in the shape of the substrate access channel and the active site, which might explain differences in catalytic properties of these homologous enzymes.

Inhibitory effect of cyclic terpenes (limonene, menthol, menthone and thymol) on Fusarium verticillioides MRC 826 growth and fumonisin B1 biosynthesis

The minimum inhibitory concentration (MIC) of cyclic terpenes (limonene, menthol, menthone and thymol) against Fusarium verticillioides MRC 826 was assessed by using the semisolid agar antifungal susceptibility (SAAS) technique. Limonene, menthol, menthone and thymol were evaluated at final concentrations of 25, 50, 75, 150, 200, 250, 500 and 1000 μL/L of culture medium. Limonene and thymol showed the highest inhibitory effects on F. verticillioides development. Thus, the effects of monoterpenes on fumonisin B1 (FB1) biosynthesis were evaluated by using corn grain ( Zea mays) as substrate. The monoterpenes were inserted on maize 1 day before inoculation with a conidial suspension of F. verticillioides to give final concentrations of 75 ppm. At this concentration, thymol was the most active inhibitor on FB1 biosynthesis.

Effect of physicochemical properties of cyclic terpenes on their ex vivo skin absorption and elimination kinetics

The terpenes disturb lipid arrangement in the intercellular region of the stratum corneum (SC) that leads to the increased permeability of the skin. This effect is used in technology of transdermal drug forms and depends on physicochemical properties of terpenes and their amounts penetrated to the stratum corneum; however terpenes do not need penetrate into viable skin tissue and this event is not even desired. To correlate skin absorption and elimination kinetics of four cyclic terpenes, namely alpha-pinene, beta-pinene, eucalyptol and terpinen-4-ol, applied as neat substance with their physicochemical properties. The terpenes were applied onto the human skin in vitro, and after 1-4 h their content in the separated by a tape-stripping method stratum corneum layers and in the epidermis/dermis was determined using GC. Similarly, the amounts of terpenes in the skin were analysed during 4 h following 1 h absorption. The fastest and progressive penetration into all skin layers was observed for terpinen-4-ol. All studied terpenes are absorbed in the viable epidermis/dermis, however penetration into this layers is time-dependent process, constantly increasing during 4 h. Like for stratum corneum, the largest cumulation in epidermis/dermis was observed for terpinen-4-ol. The elimination of terpenes from the stratum corneum was fast, especially in deeper layers, and much faster if the initial cumulation was small. Investigated cyclic terpenes represent different penetration and elimination characteristics and do not permeate across the skin to the acceptor medium due to large cumulation in the skin tissue. The penetration of terpenes into stratum corneum is greater if their log P-value is close to 3.

Spatial representation of hydrocarbon odorants in the ventrolateral zones of the rat olfactory bulb.

The glomerular sheet of the olfactory bulb (OB) forms odorant receptor maps that are parceled into zones. We previously reported the molecular receptive range (MRR) property of individual glomeruli in the dorsal zone (zone 1) of the OB and showed that polar functional groups play a major role in activating glomeruli in this zone. However, the MRR property of glomeruli in zones 2-4 is not well understood yet. Using the method of intrinsic signal imaging, we recorded odorant-induced glomerular activity from the ventrolateral surface (zones 2-4) of rat OB. While hydrocarbon odorants that lack polar functional groups activate only a few glomeruli in zone 1, we found that a series of hydrocarbon odorants consistently activated many glomeruli in the ventrolateral surface. The hydrocarbon-responsive glomeruli were grouped into two clusters; glomeruli in one cluster (cluster H) responded to benzene-family hydrocarbons but not to cyclic terpene hydrocarbons. Glomeruli in the other cluster (cluster I) responded to both classes of hydrocarbons. Detailed analyses of MRR properties of individual glomeruli using hydrocarbon odorants and polar-functional-group-containing odorants showed that the common and characteristic molecular features effective in activating glomeruli in the clusters H and I are the hydrocarbon skeleton. These results suggest that ORs represented by glomeruli in these clusters recognize primarily the hydrocarbon skeleton of odorants, and thus imply a systematic difference in the manner of recognizing odorant molecular features between ORs in zone 1 and ORs in zones 2-4.

Effect of azorellanone, a diterpene from Azorella yareta Hauman, on human sperm physiology.

Previous studies have shown that cyclic terpenes extracted from plants decrease sperm motility and concentration in rats. In this work, we studied the effect 13-alpha-hydroxy-7-oxoazorellano (azorellanone), a cyclic diterpene extracted from Azorella yareta Hauman, on in vitro human sperm physiology. Sperm aliquots, capacitated for 4.5 or 20 hours, were incubated for 15 minutes with different concentrations of azorellanone. Then, the effects of azorellanone on sperm motility, viability, binding to the human zona pellucida, progesterone-induced acrosome reactions and increase in intracellular Ca(2)(+) concentration, and trypsin and chymotrypsin-like protease activities were evaluated. Sperm motility was evaluated according to World Health Organization (WHO) guidelines; sperm viability with the supravital dye Hoescht 33258; sperm-zona binding with the hemizona assay; progesterone-induced acrosome reaction with fluorescent lectin; intracellular Ca(2)(+) level with fura 2; and protease activity with the synthetic substrates N-t-Boc-Gln-Ala-Arg-Amido-4-methylcoumaryn and Succinyl-Leu-Leu-Val-Tyr-Amido-4-methylcoumaryn. The results obtained indicate that azorellanone inhibited sperm motility in a concentration-dependent manner at 0.15, 1.5, and 3 mM, while sperm viability was only inhibited at 3 mM. Treatment with azorellanone significantly inhibited sperm-zona binding, progesterone-induced acrosome reactions, and intracellular Ca(2)(+) concentration. Treatment of free-swimming sperm with azorellanone did not affect protease activity; however, the incubation of sperm extracts with azorellanone significantly inhibited both trypsin-like and chymotrypsin-like protease activities. In conclusion, azorellanone has a significant effect on the different parameters that characterize human sperm physiology.

Vanadium haloperoxidase-catalyzed bromination and cyclization of terpenes.

Marine red algae (Rhodophyta) are a rich source of bioactive halogenated natural products, including cyclic terpenes. The biogenesis of certain cyclic halogenated marine natural products is thought to involve marine haloperoxidase enzymes. Evidence is presented that vanadium bromoperoxidase (V-BrPO) isolated and cloned from marine red algae that produce halogenated compounds (e.g., Plocamium cartilagineum, Laurencia pacifica, Corallina officinalis) can catalyze the bromination and cyclization of terpenes and terpene analogues. The V-BrPO-catalyzed reaction with the monoterpene nerol in the presence of bromide ion and hydrogen peroxide produces a monobromo eight-membered cyclic ether similar to laurencin, a brominated C15 acetogenin, from Laurencia glandulifera, along with noncyclic bromohydrin, epoxide, and dibromoproducts; however, reaction of aqueous bromine with nerol produced only noncyclic bromohydrin, epoxide, and dibromoproducts. The V-BrPO-catalyzed reaction with geraniol in the presence of bromide ion and hydrogen peroxide produces two singly brominated six-membered cyclic products, analogous to the ring structures of alpha and beta snyderols, brominated sesquiterpenes from Laurencia, spp., along with noncyclic bromohydrin, epoxide, and dibromoproducts; again, reaction of geraniol with aqueous bromine produces only noncyclic bromohydrin, epoxide, and dibromoproducts. Thus, V-BrPO can direct the electrophilic bromination and cyclization of terpenes.

Epoxidation on titanium-containing silicates: do structural features really affect the catalytic performance?

Five titanium-containing silicates, with different structural features, were compared: Ti–MCM-41, ordered titanium-grafted mesoporous silica, Ti–SiO 2 Davison, nonordered titanium-grafted porous silica, Ti–SiO 2 Aerosil, nonporous pyrogenic titanium-grafted silica, MST, nonordered in-framework mesoporous material, and TiO 2–SiO 2 Grace, commercial amorphous porous mixed oxide. They were tested in the liquid-phase epoxidation reaction on six unsaturated cyclic terpenes. Good performances were obtained on the commercial mixed oxide and also on the three grafted silicates. The in-framework MST showed the worst activity results. Under these conditions, the porosity features do not affect the catalytic performances noticeably and the use of an ordered mesoporous material is not strictly required. Likewise, a very high surface area is not mandatory in order to have an efficient titanium-grafted catalyst in the epoxidation of these substrates.

Lewis Acid Activated Chiral Leaving Group: Enantioselective Electrophilic Addition to Prochiral Olefins.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Lewis acid-activated chiral leaving group: enantioselective electrophilic addition to prochiral olefins.

A new strategy using a BINOL derivative as a chiral leaving group and Lewis acid has been developed for enantioselective alkylation of prochiral olefins. (R)-2,2'-Bis[2-(trimethylsilyl)ethoxymethyl]-1,1'-binaphthol is demonstrated to be an effective reagent for enantioselective hydroxymethylation of silyl enol ethers and trisubstituted alkenes. Electrophilic addition to prochiral olefins is accompanied by cleavage of an acetal that is dual activated by SnCl4 and the delta-effect of silicon through the S(N)2 substitution process. Enantioselective synthesis of cyclic terpenes is also described using this strategy.

Menthol: A Review of Its Sensitization Potential

Menthol, a cyclic terpene alcohol found in high concentrations in oils of peppermint and cornmint, has been widely used in over-the-counter medications, cosmetics and confectionery for over a century. However, its clinical pharmacology remains incompletely understood and its sensitization potential and irritant properties have not been thoroughly studied. Analysis of the menthol structure in a quantitative structure-activity relationship model does not identify any protein-reactive functions. Considering the extensive use of menthol there have been only few reports of adverse dermatological effects. After performing an extensive review of the reported cases of sensitization to menthol, we concluded that the literature does not adequately document the clinical relevance of the patch test reactions nor the impact of irritant reactions. We propose a comprehensive approach when testing with a nonstandard substance such as menthol.

“Gated Migration” for Enantioselective Synthesis of Palladium Allyls Using a “PdHBr” Synthon

The synthesis of enantiomerically pure palladium cyclic allyl complexes is accomplished by reaction of “PdHBr” with several chiral cyclic terpenes. The strategy used involves a 100% stereoselective Pd-migration from an attached chain to the ring through a chiral carbon (“gated migration”). “PdHBr” species are produced by β-H elimination in the benzylic moiety of [Pd2(μ-Br)2(η3-PfCH2CHPh)2] (1, Pf = C6F5). The allylic complexes prepared are transformed by carbonylation reactions into chiral unsaturated methyl esters.

Zeolite titanium beta as a selective catalyst in the epoxidation of bulky alkenes

The catalytic potential of aluminum-free zeolite titanium beta (Ti-beta) is demonstrated by its facile catalysis of the epoxidation of alkenes with aqueous hydrogen peroxide. The Ti-beta catalyst is compared with TS-1, Ti,Al-beta and Ti-MCM-41 in the epoxidation of 1-octene and norbornene. The advantage of the larger pore size of Ti-beta is illustrated by the facile epoxidation of norbornene in which TS-1 displayed no activity. Rate differences in the epoxidation of terminal or internal alkenes are very small for Ti-beta, indicating that the Ti-site is rather spacious. The catalytic properties of Ti-beta were further investigated in the epoxidation of bulky alkenes such as cyclohexenes, cyclic terpenes and allylic alcohols. Ti-beta was found to catalyze the epoxidation of a wide variety of alkenes with aqueous hydrogen peroxide. In the epoxidation of linear alkenes two trends were observed. The lower alkenes were epoxidized fastest and the internal alkenes were slightly faster than the alkenes with a terminal double bond. The reactivity of methylenecyclohexane is about twice that of 1-methylcyclohexene. Based on electronic effects of substituents the reverse order would be expected, which suggests that here steric effects at the titanium site can play a dominant role in determining reactivity. Pronounced electronic effects were observed to be more important in the epoxidation of allylic alcohols: more highly substituted allylic alcohols are more reactive, whereas the reactivity of the substrates bearing a terminal, unsubstituted double bound is over an order of lower magnitude.

Structural basis for cyclic terpene biosynthesis by tobacco 5-epi-aristolochene synthase.

Terpene cyclases catalyze the synthesis of cyclic terpenes with 10-, 15-, and 20-carbon acyclic isoprenoid diphosphates as substrates. Plants have been a source of these natural products by providing a homologous set of terpene synthases. The crystal structures of 5-epi-aristolochene synthase, a sesquiterpene cyclase from tobacco, alone and complexed separately with two farnesyl diphosphate analogs were analyzed. These structures reveal an unexpected enzymatic mechanism for the synthesis of the bicyclic product, 5-epi-aristolochene, and provide a basis for understanding the stereochemical selectivity displayed by other cyclases in the biosynthesis of pharmacologically important cyclic terpenes. As such, these structures provide templates for the engineering of novel terpene cyclases.

De Novo Biosynthesis of Volatiles Induced by Insect Herbivory in Cotton Plants.

In response to insect feeding on the leaves, cotton (Gossypium hirsutum L.) plants release elevated levels of volatiles, which can serve as a chemical signal that attracts natural enemies of the herbivore to the damaged plant. Pulse-labeling experiments with [13C]CO2 demonstrated that many of the volatiles released, including the acyclic terpenes (E,E)-[alpha]-farnesene, (E)-[beta]-farnesene, (E)-[beta]-ocimene, linalool, (E)-4,8-dimethyl-1,3,7-nonatriene, and (E/E)-4,8,12-trimethyl-1,3,7,11-tridecatetraene, as well as the shikimate pathway product indole, are biosynthesized de novo following insect damage. However, other volatile constituents, including several cyclic terpenes, butyrates, and green leaf volatiles of the lipoxygenase pathway are released from storage or synthesized from stored intermediates. Analysis of volatiles from artificially damaged plants, with and without beet armyworm (Spodoptera exigua Hubner) oral secretions exogenously applied to the leaves, as well as volatiles from beet armyworm-damaged and -undamaged control plants, demonstrated that the application of caterpillar oral secretions increased both the production and release of several volatiles that are synthesized de novo in response to insect feeding. These results establish that the plant plays an active and dynamic role in mediating the interaction between herbivores and natural enemies of herbivores.

Identifying functional domains within terpene cyclases using a domain-swapping strategy.

Cyclic terpenes and terpenoids are found throughout nature. They comprise an especially important class of compounds from plants that mediate plant- environment interactions, and they serve as pharmaceutical agents with antimicrobial and anti-tumor activities. Molecular comparisons of several terpene cyclases, the key enzymes responsible for the multistep cyclization of C10, C15, and C20 allylic diphosphate substrates, have revealed a striking level of sequence similarity and conservation of exon position and size within the genes. Functional domains responsible for a terminal enzymatic step were identified by swapping regions approximating exons between a Nicotiana tabacum 5-epi-aristolochene synthase (TEAS) gene and a Hyoscyamus muticus vetispiradiene synthase (HVS) gene and by characterization of the resulting chimeric enzymes expressed in bacteria. While exon 4 of the TEAS gene conferred specificity for the predominant reaction products of the tobacco enzyme, exon 6 of the HVS gene conferred specificity for the predominant reaction products of the Hyoscyamus enzyme. Combining these two functional domains of the TEAS and HVS genes resulted in a novel enzyme capable of synthesizing reaction products reflective of both parent enzymes. The relative ratio of the TEAS and HVS reaction products was also influenced by the source of exon 5 present in the new chimeric enzymes. The association of catalytic activities with conserved but separate exonic domains suggests a general means for generating additional novel terpene cyclases.

Diversity in cyclic sesquiterpene production by Gossypium hirsutum

Major sesquiterpene components of oil of Texas Race Stock 810 of Gossypium hirsutum were α- and β-selinene. This is the seventh cyclic terpene type found to date in this genus. Both α- and β-selinene, along with aromadendrene, were found but only as minor components of extracts of several domestic cultivars of G. hirsutum.