Cyclic Monoterpenes Research Articles

Diversity of volatile organic compounds in 14 rose cultivars

ABSTRACT This study illustrates the importance of multivariate analysis in profiling the levels of 104 volatiles across 14 modern rose cultivars obtained using headspace gas chromatography–mass spectrometry analysis. Despite differences in the abundance of volatiles, the cultivars ‘Lady Emma Hamilton’, ‘Golden Celebration’ and ‘The Poet’s Wife’ share similar profiles of volatile organic compounds (VOCs) and the absence of phenethyl alcohol, which is usually associated with a characteristic ‘rose’ fragrance. R. ‘Hansa’ is the cultivar with the greatest abundance of volatiles, with high levels of acyclic monoterpenes and aromatic compounds. No monoterpenes were detected from the climbing rose R. ‘August Gervais’. The study revealed that highly fragrant cultivars tend to produce VOCs in higher intensity and greater diversity. These findings also demonstrate the potential of using headspace analysis to compare the natural aromas of rose cultivars, which provides information to inspire innovation in the perfumery and food industries. Abbreviations AMT, acyclic monoterpenes; ARM, aromatic compounds; CMT, cyclic monoterpenes; GLV, green leaf volatiles; HEX, C6 lipid derivatives; OTH, other volatiles; PCoA, principal coordinates analysis; PEA, phenethyl alcohol; RI, retention index; SSQ, sesquiterpenes; TD-GC-MS, thermal desorption-gas chromatography-mass spectrometry; VOC, volatile organic compounds.

Encapsulation of D-Limonene into O/W Nanoemulsions for Enhanced Stability

The present study aimed to investigate the physical stability in terms of (droplet size, pH, and ionic strength) and chemical stability in terms of (retention) of D-limonene (LM) in the nanoemulsions after emulsification as well as after storing them for 30 days under different temperatures (5 °C, 25 °C, and 50 °C). LM is a cyclic monoterpene and a major component extracted from citrus fruits. The modification of disperse phase with soybean oil (SB) and a nonionic emulsifier (Tween 80) was adequate to prepare stable LM-loaded nanoemulsions. LM blended with SB-loaded nanoemulsions were stable against droplet growth over pH (3-9) and ionic strength (0-500 mM NaCl). Regarding long-term storage, the prepared nanoemulsions demonstrated excellent physical stability with droplet size ranging from 120-130 nm during 30 days of storage at both 5 °C and 25 °C; however, oiling off started in the emulsions, which were stored at 50 °C from day 10. On the other hand, the retention of LM in the emulsions was significantly impacted by storage temperature. Nanoemulsions stored at 5 °C had the highest retention of 91%, while nanoemulsions stored at 25 °C had the lowest retention of 82%.

Selective dehydroisomerization of cyclic monoterpenes to p-cymene over silica-supported CdO

Cadmium oxide supported on silica is a highly active and selective bifunctional catalyst for the clean synthesis of p-cymene using dehydroisomerization of cyclic monoterpenes such as α-pinene, β-pinene, limonene, α-terpinene, γ-terpinene, and terpinolene. The dehydroisomerization occurs via acid-redox bifunctional catalysis at the gas-solid interface involving isomerization of monoterpenes to p-menthadienes on acid sites of silica support followed by p-menthadiene dehydrogenation to p-cymene on oxo-metal sites of CdO. The less reactive bicyclic monoterpenes, such as α-pinene and β-pinene, give 91–95% p-cymene yields at 325–375 °C, whereas more reactive monocyclic monoterpenes, such as limonene, α-terpinene, γ-terpinene, and terpinolene, give a 100% yield at 200–250 °C. To the best of our knowledge, CdO/SiO2 has the highest efficiency in monoterpene-to-p-cymene dehydroisomerization among the catalysts reported so far. The catalyst was characterized by BET, TGA, XRD, DRIFTS, H2-TPR, and ICP–OES.

Mechanism and kinetics of atmospheric degradation of menthol initiated by hydroxyl radical

Menthol is a naturally occurring compound belonging to the cyclic monoterpene family and is one of the main constituents of peppermint oil, recognized worldwide as a cooling agent.

Review on Pharmacological Activity of Cymbopogon Citratus

Cymbopogon citratus belonging to the family Gramineae is an herb worldwide known as lemongrass. The prefix ‘lemon’ owes to its typical lemon like odor, which is mainly due to the presence of citral, a cyclic monoterpene. Cymbopogon citratus a fast growing, perennial aromatic grass is native to South India and Sri Lanka, now widely cultivated in the tropical areas of America and Asia. Freshly cut and partially dried leaves are used medicinally and are the source of the essential oil. The plant is used extensively in Ayurvedic medicine. Studies indicate that Cymbopogon citratus possesses various pharmacological activities such as anti-amoebic, anti-bacterial, anti-diarrheal, anti-filarial, anti-fungal and anti-inflammatory properties. Various other effects like anti-malarial, anti-mutagenicity, anti-mycobacterial, anti-oxidants, hypoglycemic and neurobehavioral have also been studied. These results are very encouraging and hence this literature review was intended to study about the plant more extensively to confirm these results and reveal other potential therapeutic effects.

Alpha-Phellandrene and Alpha-Phellandrene-Rich Essential Oils: A Systematic Review of Biological Activities, Pharmaceutical and Food Applications.

Alpha-phellandrene is a very common cyclic monoterpene found in several EOs, which shows extensive biological activities. Therefore, the main focus of the present systematic review was to provide a comprehensive and critical analysis of the state of the art regarding its biological activities and pharmaceutical and food applications. In addition, the study identified essential oils rich in alpha-phellandrene and summarized their main biological activities as a preliminary screening to encourage subsequent studies on their single components. With this review, we selected and critically analyzed 99 papers, using the following bibliographic databases: PubMed, SciELO, Wiley and WOS, on 8 July 2022. Data were independently extracted by four authors of this work, selecting those studies which reported the keyword “alpha-phellandrene” in the title and/or the abstract, and avoiding those in which there was not a clear correlation between the molecule and its biological activities and/or a specific concentration from its source. Duplication data were removed in the final article. Many essential oils have significant amounts of alpha-phellandrene, and the species Anethum graveolens and Foeniculum vulgare are frequently cited. Some studies on the above-mentioned species show high alpha-phellandrene amounts up to 82.1%. There were 12 studies on alpha-phellandrene as a pure molecule showed promising biological functions, including antitumoral, antinociceptive, larvicidal and insecticidal activities. There were 87 research works on EOs rich in alpha-phellandrene, which were summarized with a focus on additional data concerning potential biological activities. We believe this data is a useful starting point to start new research on the pure molecule, and, in particular, to distinguish between the synergistic effects of the different components of the OEs and those due to alpha-phellandrene itself. Toxicological data are still lacking, requiring further investigation on the threshold values to distinguish the boundary between beneficial and toxic effects, i.e., mutagenic, carcinogenic and allergenic. All these findings offer inspiration for potential applications of alpha-phellandrene as a new biopesticide, antimicrobial and antitumoral agent. In particular, we believe our work is of interest as a starting point for further studies on the food application of alpha-phellandrene.

Fundamental insights into the effect of blending hydrogen flames with sooting biofuels

A major challenge to using hydrogen as a carbon-free energy carrier to replace fossil fuels in high-temperature practical processes is the reduced thermal radiative transfer of hydrogen flames due to the absence of soot. To address the potential issue of low radiative heat transfer from hydrogen flames, the effect of blending highly sooting biofuels to turbulent nonpremixed hydrogen-based flames on flame luminosity and radiant heat flux enhancement is investigated in this paper. The sooting propensities of aromatic bio-oil surrogates (toluene, anisole and guaiacol) and monoterpene essential oil surrogates (eucalyptol and D-limonene) are evaluated. The Threshold Sooting Index (TSI) and Oxygen Extended Sooting Index (OESI) are calculated and compared with the data sets in the literature. The sooting propensities of the reported fuels are found to follow a decreasing order: aromatics > monoterpenes > alkenes > alkanes > aldehydes. The effect of chemical structure and functional group on sooting propensity tends to be more significant than the oxygen content and effective C/H ratio. Turbulent nonpremixed hydrogen–nitrogen (9:1 mol) jet flames are blended with 0.2 and 1 mol% (based on the molar concentration of hydrogen) vapourised biofuels. The results show that adding 0.2 and 1 mol% vapourised biofuels to the hydrogen-based flame non-linearly improves the flame luminosity and radiant fraction by 61%–253% and 2%–19%, respectively. Toluene is the most effective additive in luminosity and radiant fraction enhancement among all tested biofuels. Adding biofuels with an aromatic structure increases the radiant fraction by 10%–19%, which is more effective than cyclic monoterpenes (2%–9%). Adding non-oxygenated biofuels generally have larger increases in radiant fraction (9%–19%) than oxygenated biofuels (2%–10%).

Regiospecific C–H amination of (−)-limonene into (−)-perillamine by multi-enzymatic cascade reactions

Background(−)-Limonene, one of cyclic monoterpenes, is an important renewable compound used widely as a key building block for the synthesis of new biologically active molecules and fine chemicals. (−)-Perillamine, as derived from (−)-limonene, is a highly useful synthon for constructing more complicated and functionally relevant chemicals.AimWe aimed to report a more sustainable and more efficient method for the regiospecific C–H amination of (−)-limonene into (−)-perillamine.ResultsHere, we report an artificial penta-enzymatic cascade system for the transformation of the cheap and easily available (−)-limonene into (−)-perillamine for the first time. This system is composed of cytochrome P450 monooxygenase, alcohol dehydrogenase and w-transaminase for the main reactions, as well as formate dehydrogenase and NADH oxidase for cofactor recycling. After optimization of the multi-enzymatic cascade system, 10 mM (−)-limonene was smoothly converted into 5.4 mM (−)-perillamine in a one-pot two-step biotransformation, indicating the feasibility of multi-enzymatic C7-regiospecific amination of the inert C–H bond of (−)-limonene. This method represents a concise and efficient route for the biocatalytic synthesis of derivatives from similar natural products.

Shared phytochemicals predict efficacy of essential oils against western flower thrips (Frankliniella occidentalis) in the greenhouse

Western flower thrips (Frankliniella occidentalis; Thysanoptera: Thripidae), or WFT, are a global pest of commercial crops, particularly those grown in greenhouses. Current management recommendations often involve judicious use of pesticides to which WFT have evolved multiple resistance phenotypes. Essential oils (EOs) have shown promise as a less toxic alternative for WFT greenhouse management. However, challenges remain in predicting which EOs are most likely to be insecticidal to WFT and ensuring that the efficacy of EOs under bioassay conditions reflect performance in whole-plant application scenarios. To address these challenges, 9 EOs were tested for contact toxicity against WFT in small container assays, then gas chromatography–mass spectroscopy (GC–MS) profiles of each EO were used to quantify concentrations of 22 chemicals shared by at least 5 or more of the plant species. Of these, 13 compounds were positively correlated with thrips mortality. Effective compounds were a mixture of sesquiterpenes, cyclic monoterpenes, and noncyclic monoterpenes. Interestingly, no bicyclic monoterpenes shared among the essential oils tested correlated with thrips mortality. Whole-plant assays of the four best EOs from the container assay showed significant reduction in the number of thrips per plant, although mortality in EO treatments in the whole plant assay was lower than in the container assay. In addition, all four EOs were as efficacious as the conventional insecticide flonicamid. Identifying other EOs with high concentrations of the efficacious compounds that were identified in this study and using container assays to screen these oils for WFT thrip mortality and phytotoxicity could help integrated pest management (IPM) practitioners and greenhouse staff to more rapidly accumulate a suite of EOs as low toxicity alternatives for management of WFT in greenhouse settings.Graphical

Products and Mechanisms of Secondary Organic Aerosol Formation from the NO3 Radical-Initiated Oxidation of Cyclic and Acyclic Monoterpenes

Biogenic sources dominate annual emissions of volatile organic compounds (VOCs) to the atmosphere. A large fraction of these are monoterpenes, which react with OH radicals, NO3 radicals, or O3 to form oxidized products, some of which partition to particles as secondary organic aerosol (SOA). Here, we compare the results of studies of the reaction of NO3 radicals, a nighttime oxidant, with five monoterpenes: Δ-3-carene, β-pinene, α-pinene, limonene, and ocimene. Whereas all of these monoterpenes have the molecular formula C10H16, they differ by having 1, 2, or 3 C═C double bonds and 0, 1, or 2 rings. Experiments were conducted in an environmental chamber under conditions in which RO2• + RO2• reactions were dominant, and gas- and particle-phase products were analyzed using mass spectrometry, gas and liquid chromatography, infrared spectroscopy, and derivatization-spectrophotometric methods. Gas-phase products were first-generation compounds with 2–4 functional groups, whereas SOA products were mostly acetal and hemiacetal dimers formed by particle-phase accretion reactions. The large contribution of dimers formed from hydroxycarbonyl nitrate and hydroxynitrate monomers indicates that they might be used as atmospheric tracers for NO3 radical-initiated reactions of monoterpenes. Conversely, gas-phase formation of ROOR dimers was negligible. Functional group analysis of SOA indicated ∼1 nitrate, ∼0.2–0.7 carbonyl groups, and ∼0–0.4 hydroxyl, carboxyl, ester, and peroxide groups per C10 product for all the monoterpenes. SOA mass yields were 56, 89, 48, 78, and 69% for Δ-3-carene, β-pinene, α-pinene, limonene, and ocimene, which combined with functional group analysis gives lower-limit estimates of organic nitrate yields of 34, 56, 35, 50, and 40%. Results were used to develop reaction mechanisms to explain the formation of gas- and particle-phase products and provide improved understanding of the role of molecular structure in VOC oxidation and particle-phase accretion reactions.

Metabolic engineering of Ashbya gossypii for limonene production from xylose

BackgroundLimonene is a cyclic monoterpene that has applications in the food, cosmetic, and pharmaceutical industries. The industrial production of limonene and its derivatives through plant extraction presents important drawbacks such as seasonal and climate issues, feedstock limitations, low efficiency and environmental concerns. Consequently, the implementation of efficient and eco-friendly bioprocesses for the production of limonene and other terpenes constitutes an attractive goal for microbial biotechnology. In this context, novel biocatalysts with the ability to produce limonene from alternative carbon sources will help to meet the industrial demands of limonene.ResultsEngineered strains of the industrial fungus Ashbya gossypii have been developed to produce limonene from xylose. The limonene synthase (LS) from Citrus limon was initially overexpressed together with the native HMG1 gene (coding for HMG-CoA reductase) to establish a limonene-producing platform from a xylose-utilizing A. gossypii strain. In addition, several strategies were designed to increase the production of limonene. Hence, the effect of mutant alleles of ERG20 (erg20F95W and erg20F126W) were evaluated together with a synthetic orthogonal pathway using a heterologous neryl diphosphate synthase. The lethality of the A. gossypii double mutant erg20F95W−F126W highlights the indispensability of farnesyl diphosphate for the synthesis of essential sterols. In addition, the utilization of the orthogonal pathway, bypassing the Erg20 activity through neryl diphosphate, triggered a substantial increase in limonene titer (33.6 mg/L), without critically altering the fitness of the engineered strain. Finally, the overexpression of the native ERG12 gene further enhanced limonene production, which reached 336.4 mg/L after 96 h in flask cultures using xylose as the carbon source.ConclusionsThe microbial production of limonene can be carried out using engineered strains of A. gossypii from xylose-based carbon sources. The utilization of a synthetic orthogonal pathway together with the overexpression of ERG12 is a highly beneficial strategy for the production of limonene in A. gossypii. The strains presented in this work constitute a proof of principle for the production of limonene and other terpenes from agro-industrial wastes such as xylose-rich hydrolysates in A. gossypii.

Pharmacological and Pharmacognostic review on Cymbopogon citrus

Cymbopogon citratus of the family Gramineae is a plant known worldwide for lemongrass. The origin of the word 'lemon' owes its common lemon as an aroma, largely due to the presence of citral, cyclic monoterpene. Cymbopogon citratus is a fast-growing, perennial herb native to South India and Sri Lanka, now widely grown in tropical America and Asia. Freshly cut and slightly dried leaves are used medicinally and are a source of essential oils. This plant is widely used in Ayurvedic medicine. Studies show that Cymbopogon citratus has various medicinal properties such as anti-amoebic, anti-bacterial, anti-diarrheal, anti-filarial, anti-fungal and anti-inflammatory properties. Various other effects such as anti-malarial, anti-mutagenicity, anti-mycobacterial, anti-oxidants, hypoglycemic and neurobehavioral have also been investigated. These results are very encouraging and that is why this review of the literature was intended to further study the plant to confirm these effects and to highlight other potential therapeutic effects.

Genetic Manipulation of Biosynthetic Pathways in Mint.

In recent years, the study of aromatic plants has seen an increase, with great interest from industrial, academic, and pharmaceutical industries. Among plants attracting increased attention are the Mentha spp. (mint), members of the Lamiaceae family. Mint essential oils comprise a diverse class of molecules known as terpenoids/isoprenoids, organic chemicals that are among the most diverse class of naturally plant derived compounds. The terpenoid profile of several Mentha spp. is dominated by menthol, a cyclic monoterpene with some remarkable biological properties that make it useful in the pharmaceutical, medical, cosmetic, and cleaning product industries. As the global market for Mentha essential oils increases, the desire to improve oil composition and yield follows. The monoterpenoid biosynthesis pathway is well characterised so metabolic engineering attempts have been made to facilitate this improvement. This review focuses on the Mentha spp. and attempts at altering the carbon flux through the biosynthetic pathways to increase the yield and enhance the composition of the essential oil. This includes manipulation of endogenous and heterologous biosynthetic enzymes through overexpression and RNAi suppression. Genes involved in the MEP pathway, the menthol and carvone biosynthetic pathways and transcription factors known to affect secondary metabolism will be discussed along with non-metabolic engineering approaches including environmental factors and the use of plant growth regulators.

Antidiabetic activities of menthone on insulin resistant in 3T3-L1 adipocytes

Background: Diabetes mellitus (DM) is a metabolic disorder characterised by chronic hyperglycaemia and metabolic consequences caused by insulin defects. Adipose tissue is an endocrine organ that influences glucose and lipid metabolism by releasing adipokines; adipose tissue is vital for the life of mammals. It represents the major source of fatty acid. Brown adipose tissue (BAT) and white adipose tissue (WAT) are the basic adipose tissue forms. They have different functions and cellular compositions and localization. They are essentially adversarial in terms of functionality. WAT is known to contain the most body fat; its involvement in the storage of excess dietary triglycerides. It is the source of free fatty aid used as energy substrates for the generation through oxidative phosphate of (ATP) high-energy bonds. During insulin resistance, the secretion of the hormone from the pancreatic islet cells cannot trigger glucose uptake in metabolic tissues, leading to elevated blood glucose and insulin levels. Menthone is cyclic monoterpenes and is reported to have several biological activities. This study, explores the potential antidiabetic effects invitro of menthone in the 3T3L1 adipocytes. Methods: The differentiation of 3T3-L1 preadipocytes into mature adipocytes were cultured and maintained.

Flavonoid and Organosulphur Phytoconstituents From Allium Sativum Inhibits Antiapoptotic Protein Bcl-2: A Computational Molecular Modeling Study

PURPOSE Apoptosis resistance to anticancer treatments can occur due to over-expression of Bcl-2 anti-apoptotic proteins. Studies have shown the use of Allium sativum (garlic) as a herbal supplement among cancer patients. In this study, the inhibitory activity of phytochemicals from Allium sativum against Bcl-2 anti-apoptotic protein was demonstrated using a computational technique. METHODS Identified phytoconstituents from A. sativum were docked in receptor grid generated active sites of Bcl-2 (PDB-ID: 4AQ3) protein using the Glide-Ligand docking tool of Schrödinger Maestro 12.5. Receptor-ligand complex pharmacophore models were generated using the PHASE module, and the binding free energy of the complex was calculated using the MM-GBSA Prime panel. Potential lead compounds were screened for drug likeness using the Lipinski rule of five (RO5) and Veber rule. Absorption, distribution, metabolism, excretion, and toxicity (ADME/T) predictions of the leads were carried out using the PROTOX-II tool. Induced fit docking simulation was performed on the top ranked hit compound. RESULTS Extra precision docking results showed that myricetin, kaempferol, and apigenin (flavonoid); α and β-phellandrene (cyclic monoterpene); 3-vinyl-4H-1,2-dithiin, 3-vinyl-1,2-dithiin and 2-vinyl-4H-1,3-dithiine (organosulphur) were ranked highest, with docking scores range from -6.00 to -3.78 kcal/mol compared with -3.62 kcal/mol demonstrated by co-crystallized ligand. Apigenin (CID: 5280443), 3-vinyl-1,2-dithiin (CID: 10219489), and 3-vinyl-4H-1,2-dithiin (CID: 150636) were identified as the top three lead compounds with free binding energies of -33.83, -30.36, and -29.70 kcal/mol respectively. The identified lead compounds from A. sativum were in accordance with RO5 and Veber rule with good oral bio-availability and ADME/T profile. Similar to the co-crystallized ligand, apigenin interacted with important active site amino acid residues like Try 67, Asp 70, Leu 96, Arg 105, Ala 108 among others. CONCLUSION Some bioactive phytochemicals from A. sativum can be explored for development toward inhibition of antiapoptotic protein Bcl-2 in apoptosis resistance to anticancer treatments.

Menthol Targeting AMPK Alleviates the Inflammatory Response of Bovine Mammary Epithelial Cells and Restores the Synthesis of Milk Fat and Milk Protein.

Mastitis is one of the most serious diseases that causes losses in the dairy industry, seriously impairing milk production and milk quality, and even affecting human health. Menthol is a cyclic monoterpene compound obtained from the stem and leaves of peppermint, which has a variety of biological activities, including anti-inflammatory and antioxidant activity. The purpose of this study was to investigate the preventive effect of menthol on the lipopolysaccharide-induced inflammatory response in primary bovine mammary gland epithelial cells (BMECs) and its anti-inflammatory mechanism. First, BMECs were isolated and amplified from the udders of Holstein cows by enzymatic hydrolysis. BMECs were treated with menthol (10, 50, 100, 200 μM) for 1h, followed by lipopolysaccharide (5μg/ml) for 12 h. Lipopolysaccharide treatment upregulated the protein levels of cyclooxygenase-2 (COX-2) and inducible nitric oxide synthase (INOS) and the mRNA abundance of tumor necrosis factor α (TNF-α), interleukin-6 (IL-6), and interleukin-1β (IL-1β), while menthol was able to inhibit this effect. The inhibitory effect of menthol on proinflammatory factors was significantly reduced when autophagy was blocked using 3-Methyladenine (5μg/ml), an inhibitor of autophagy. Furthermore, lipopolysaccharide treatment reduced the expression levels of milk lipids and milk proteins, which were inhibited by menthol. In addition, menthol (200 μM) treatment was able to significantly upregulate the expression level of autophagy-related protein LC3B, downregulate the expression level of P62, promote the expression abundance of autophagy-related gene mRNA, and enhance significantly enhance autophagic flux. Interestingly, treatment of BMECs with menthol (200 μM) promoted the phosphorylation of AMP-activated protein kinase (AMPK) and unc-51 like kinase 1 (ULK1) and increased the nuclear localization of nuclear factor-E2 associated factor 2 (Nrf-2). When the AMPK pathway was blocked using compound C (10μg/ml), an inhibitor of AMPK, autophagy was significantly inhibited. Autophagy levels were significantly decreased after blocking the Nrf-2 pathway using ML385 (5μg/ml), an inhibitor of Nrf-2. Overall, the data suggest that menthol activates the AMPK-ULK1 pathway to initiate the onset of autophagy and maintains the level of autophagy through the AMPK-Nrf-2 pathway. In conclusion, the findings suggest that menthol may alleviate the inflammatory response in BMECs via the AMPK/ULK1/Nrf-2/autophagy pathway.

Stereospecific Epoxidation of Limonene Catalyzed by Peroxygenase from Oat Seeds.

Limonene is one of the most abundant naturally occurring cyclic monoterpenes and has recently emerged as a sustainable alternative to petroleum-based solvents as well as a chemical platform for the production of value-added compounds. The biocatalytic epoxidation of both enantiomers of limonene was carried out in the presence of a peroxygenase-containing preparation from oat (Avena sativa) flour. Different reaction profiles were observed depending on the starting enantiomer of limonene, but in both cases the 1,2-monoepoxide was obtained as the main product with excellent diastereoselectivity. Trans-1,2-monoepoxide and cis-1,2-monoepoxide were isolated from the reaction of (R)-limonene and (S)-limonene, respectively, and the reactions were scaled-up to 0.17 M substrate concentration. The process is valuable for operational simplicity, lack of toxic metal catalysts, and cost-effectiveness of the enzymatic source. Pure stereoisomers of 1,2-monoepoxides of limonene constitute a useful starting material for biorenewable polymers, but can be also converted into other chiral derivatives by epoxide ring opening with nucleophiles. As a proof of concept, a tandem protocol for the preparation of enantiopure (1S,2S,4R)-1,2-diol from (R)-limonene and (1R,2R,4S)-1,2-diol from (S)-limonene was developed.

Glucosylation of (±)-Menthol by Uridine-Diphosphate-Sugar Dependent Glucosyltransferases from Plants.

Menthol is a cyclic monoterpene alcohol of the essential oils of plants of the genus Mentha, which is in demand by various industries due to its diverse sensorial and physiological properties. However, its poor water solubility and its toxic effect limit possible applications. Glycosylation offers a solution as the binding of a sugar residue to small molecules increases their water solubility and stability, renders aroma components odorless and modifies bioactivity. In order to identify plant enzymes that catalyze this reaction, a glycosyltransferase library containing 57 uridine diphosphate sugar-dependent enzymes (UGTs) was screened with (±)-menthol. The identity of the products was confirmed by mass spectrometry and nuclear magnetic resonance spectroscopy. Five enzymes were able to form (±)-menthyl-β-d-glucopyranoside in whole-cell biotransformations: UGT93Y1, UGT93Y2, UGT85K11, UGT72B27 and UGT73B24. In vitro enzyme activity assays revealed highest catalytic activity for UGT93Y1 (7.6 nkat/mg) from Camellia sinensis towards menthol and its isomeric forms. Although UGT93Y2 shares 70% sequence identity with UGT93Y1, it was less efficient. Of the five enzymes, UGT93Y1 stood out because of its high in vivo and in vitro biotransformation rate. The identification of novel menthol glycosyltransferases from the tea plant opens new perspectives for the biotechnological production of menthyl glucoside.

Single Wavelengths of LED Light Supplement Promote the Biosynthesis of Major Cyclic Monoterpenes in Japanese Mint.

Environmental light conditions influence the biosynthesis of monoterpenes in the mint plant. Cyclic terpenes, such as menthol, menthone, pulegone, and menthofuran, are major odor components synthesized in mint leaves. However, it is unclear how light for cultivation affects the contents of these compounds. Artificial lighting using light-emitting diodes (LEDs) for plant cultivation has the advantage of preferential wavelength control. Here, we monitored monoterpene contents in hydroponically cultivated Japanese mint leaves under blue, red, or far-red wavelengths of LED light supplements. Volatile cyclic monoterpenes, pulegone, menthone, menthol, and menthofuran were quantified using the head-space solid phase microextraction method. As a result, all light wavelengths promoted the biosynthesis of the compounds. Remarkably, two weeks of blue-light supplement increased all compounds: pulegone (362% increase compared to the control), menthofuran (285%), menthone (223%), and menthol (389%). Red light slightly promoted pulegone (256%), menthofuran (178%), and menthol (197%). Interestingly, the accumulation of menthone (229%) or menthofuran (339%) was observed with far-red light treatment. The quantification of glandular trichomes density revealed that no increase under light supplement was confirmed. Blue light treatment even suppressed the glandular trichome formation. No promotion of photosynthesis was observed by pulse-amplitude-modulation (PAM) fluorometry. The present result indicates that light supplements directly promoted the biosynthetic pathways of cyclic monoterpenes.

The Mode of Action of Cyclic Monoterpenes (-)-Limoneneand (+)-α-Pinene on Bacterial Cells.

A broad spectrum of volatile organic compounds’ (VOCs’) biological activities has attracted significant scientific interest, but their mechanisms of action remain little understood. The mechanism of action of two VOCs—the cyclic monoterpenes (−)-limonene and (+)-α-pinene—on bacteria was studied in this work. We used genetically engineered Escherichia coli bioluminescent strains harboring stress-responsive promoters (responsive to oxidative stress, DNA damage, SOS response, protein damage, heatshock, membrane damage) fused to the luxCDABE genes of Photorhabdus luminescens. We showed that (−)-limonene induces the PkatG and PsoxS promoters due to the formation of reactive oxygen species and, as a result, causes damage to DNA (SOSresponse), proteins (heat shock), and membrane (increases its permeability). The experimental data indicate that the action of (−)-limonene at high concentrations and prolonged incubation time makes degrading processes in cells irreversible. The effect of (+)-α-pinene is much weaker: it induces only heat shock in the bacteria. Moreover, we showed for the first time that (−)-limonene completely inhibits the DnaKJE–ClpB bichaperone-dependent refolding of heat-inactivated bacterial luciferase in both E. coli wild type and mutant ΔibpB strains. (+)-α-Pinene partially inhibits refolding only in ΔibpB mutant strain.