Introduction of oxygenated functional groups into 3-carene and 2-pinene by cultured cells

Potential enzymes involved in beer monoterpenoids transformation: structures, functions and challenges

Monoterpenes are important flavor and fragrance compounds in food. In beer, the monoterpenes mainly come from hops added during boiling process. Biotransformations of monoterpene which occurred during fermentation conferred beer with various kinds of aroma profiles, which can be mainly attributed to the contribution of enzymes in yeast. However, there are few reports on the identification and characterization of these enzymes in yeast. Illustrating the structure and functions of key enzymes related to transformations will broaden their potential applications in beer or other foodstuffs. Monoterpenoids including terpene hydrocarbons (limonene, myrcene, and pinene) and terpene alcohol (linalool, geraniol, nerol, and citronellol) gave the beer flower-like or fruit-like aroma. The biotransformation of monoterpenes and monoterpene alcohols in bacteria and yeast, and potential enzymes related to the transformation of them are reviewed here. Enzymes primarily are dehydrogenases including linalool dehydrogenase/isomerase, geraniol/geranial dehydrogenase, nerol dehydrogenase and citronellol dehydrogenase. Most of them are substrate-specific or substrate-specific after modifications by biotechnology methods, and part of them have been expressed in E. coli, while the purification and catalytic rate is very low. Efforts should be made to acquire abundant enzymes, and to fabricate enzyme-expressing yeast, which can be further applied in beer fermentation system.highlightsMonoterpenoids contributed to the flavor of food, especially beer.Transformation of monoterpenoids occurred during fermentation.Various kinds of enzymes are involved in the transformation of monoterpenoids in bacteria, yeast, etc.Crystal structures of these enzymes have been partially resolved.Few enzymes are further applied in food system to obtain abundant flavor.

Potent Odorants of Characteristic Floral/Sweet Odor in Chinese Chrysanthemum Flower Tea Infusion

An investigation using the aroma extract dilution analysis (AEDA) technique applied to the aroma concentrates prepared from the tea infusions of two different types of Chinese chrysanthemum flowers (flower buds, blooming flowers) revealed that 29 aroma peaks were detected in the aroma concentrates, and 17 compounds were newly identified or tentatively identified in the chrysanthemum flower tea. AEDA also revealed that the aroma peaks having high flavor dilution factors mainly consisted of a floral/sweet note in addition to metallic and phenol-like/spicy notes. Among them, four aroma peaks having a floral/sweet were identified as verbenone, ethyl 3-phenylpropanoate, propyl 3-phenylpropanoate, and ethyl cinnamate, and a semiquantitative analysis revealed that the flower buds were rich in these compounds. Furthermore, a chiral analysis revealed that (-)-verbenone existed in both flowers at a 3 times higher concentration than (+)-verbenone. Additionally, because the detection threshold of (-)-verbenone was lower than that of the (+)-verbenone, it is concluded that the (-)-isomer was a main contributor of the aroma peak of verbenone in the chrysanthemum flower tea.

Regioselective Hydroxylation and Glucosylation of α- and β-Pinenes with Cultured Cells of Eucalyptus perriniana

Cultured plant cells of Eucalyptus perriniana regioselectively hydroxylated (+)- and (-)-α-pinenes to the corresponding (+)- and (-)-verbenols. In addition, (+)-and (-)-verbenols were converted into mono-β-D-glucosides. On the other hand, (+)- and (-)-β-pinenes were transformed into (+)- and (-)-pinocarveol 3- O-β-D-glucosides via (+)- and (-)-pinocarveols.

Regioselective Hydroxylation and Glucosylation of Flavanones with Cultured Plant Cells of Eucalyptus perriniana

Cultured plant cells of Eucalyptus perriniana catalyzed reduction regioselective hydroxylation and regioselective glycosylation of flavanones. (2 S)-Flavanone was converted into (2 S)-flavan-4-ol (2 S)-flavan-4,7-diol (2 S)-flavan-7-ol (2 S)-flavan-7-yl glucoside and (2 S)-flavan-7-yl gentiobioside. The cells glucosylated (2 S)-flavan-6-ol to (2 S)-flavan-6-yl glucoside. (2 S)-Flavan-2′-ol was transformed to (2 S)-flavan-2′,4-diol (2 S)-flavan-2′,7-diol (2 S)-flavan-2′-yl glucoside. In addition (2 S)-flavan-4′-ol was transformed to (2 S)-flavan-4,4′-diol (2 S)-flavan-4′,7-diol (2 S)-flavan-4′-yl glucoside.

(1) H NMR Spectra. Part 28: Proton chemical shifts and couplings in three-membered rings. A ring current model for cyclopropane and a novel dihedral angle dependence for (3) J(HH) couplings involving the epoxy proton

The (1) H chemical shifts of selected three-membered ring compounds in CDCl(3) solvent were obtained. This allowed the determination of the substituent chemical shifts of the substituents in the three-membered rings and the long-range effect of these rings on the distant protons. The substituent chemical shifts of common substituents in the cyclopropane ring differ considerably from the same substituents in acyclic fragments and in cyclohexane and were modelled in terms of a three-bond (γ)-effect. For long-range protons (more than three bonds removed), the substituent effects of the cyclopropane ring were analysed in terms of the cyclopropane magnetic anisotropy and steric effect. The cyclopropane magnetic anisotropy (ring current) shift was modelled by (a) a single equivalent dipole perpendicular to and at the centre of the cyclopropane ring and (b) by three identical equivalent dipoles perpendicular to the ring placed at each carbon atom. Model (b) gave a more accurate description of the (1) H chemical shifts and was the selected model. After parameterization, the overall root mean square error for the dataset of 289 entries was 0.068 ppm. The anisotropic effects are significant for the cyclopropane protons (ca 1 ppm) but decrease rapidly with distance. The heterocyclic rings of oxirane, thiirane and aziridine do not possess a ring current. (3) J(HH) couplings of the epoxy ring proton with side-chain protons were obtained and shown to be dependent on both the H-C-C-H and H-C-C-O orientations. Both density functional theory calculations and a simple Karplus-type equation gave general agreement with the observed couplings (root mean square error 0.5 Hz over a 10-Hz range).

Biotransformation of (1S)-2-carene and (1S)-3-carene by Picea abies suspension culture

Biotransformation of (1S)-2-carene and (1S)-3-carene by Picea abies suspension culture led to the formation of oxygenated products. (1S)-2-Carene was transformed slowly and the final product was identified as (1S)-2-caren-4-one. On the other hand, the transformation of (1S)-3-carene was rapid and finally led to the formation of (1S)-3-caren-5-one and (1S)-2-caren-4-one as equally abundant major products. The time-course of the reaction indicates that some products abundant at the beginning of the reaction (e.g. (1S,3S,4R)-3,4-epoxycarane and (1R)-p-mentha-1(7),2-dien-8-ol) were consumed by a subsequent transformations. Thus, a precise selection of the biotransformation time may be used for a production of specific compounds.

Regio- and stereoselective oxidation of (+)-Delta(3)-carene by the larvae of common cutworm (Spodoptera litura)

Biotransformation of (+)-Delta(3)-carene (1) and (+)-(1S,3S,4R,6R)-3,4-epoxycarane (1-1) by larvae of Spodoptera litura was investigated. Compound 1 was transformed to (+)-(1S,3S,4R,6R,7S)-3,4-epoxycaran-9-ol (1-2) by S. litura. This structure was established by infrared, electron impact-mass spectrometry, one- and two-dimensional NMR spectral studies, and (+)-(1S,3S,4R,6R)-3,4-epoxycarane (1-1) was transformed for confirmation of a metabolic pathway. The results indicate that the metabolic reaction of compound 1 by the larvae of S. litura was regioselective hydroxylation at the methyl group of the geminal dimethyl (C-9 position) followed by stereoselective epoxidation at the carbon-carbon double bands (C-3 position). (+)-(1S,3S,4R,6R,7S)-3,4-Epoxycaran-9-ol (1-2) was a new compound.

Monoterpenes as novel substrates for oxidation and halo-hydroxylation with chloroperoxidase from Caldariomyces fumago

Chloroperoxidase (CPO) from Caldariomyces fumago was analysed for its ability to oxidize ten different monoterpenes with hydrogen peroxide as oxidant. In the absence of halide ions geraniol and, to a lesser extent, citronellol and nerol were converted into the corresponding aldehydes, whereas terpene hydrocarbons did not serve as substrates under these conditions. In the presence of chloride, bromide and iodide ions, every terpene tested was converted into one or more products. (1S)-(+)-3-carene was chosen as a model substrate for the CPO-catalysed conversion of terpenes in the presence of sodium halides. With chloride, bromide and iodide, the reaction products were the respective (1S,3R,4R,6R)-4-halo-3,7,7-trimethyl-bicyclo[4.1.0]-heptane-3-ols, as identified by 1H and 13C nuclear magnetic resonance. These product formations turned out to be strictly regio- and stereoselective and proceeded very rapidly and almost quantitatively. Initial specific activities of halohydrin formation increased from 4.22 U mg-1 with chloride to 12.22 U mg-1 with bromide and 37.11 U mg-1 with iodide as the respective halide ion. These results represent the first examples of the application of CPO as a highly efficient biocatalyst for monoterpene functionalization. This is a promising strategy for 'green' terpene chemistry overcoming drawbacks usually associated with cofactor-dependent oxygenases, whole-cell biocatalysts and conventional chemical methods used for terpene conversions.

Formation of trans-verbenol and verbenone from alpha-pinene catalysed by immobilised Picea abies cells

Both enantiomers and the racemate of alpha-pinene were transformed by Picea abies cells immobilised on alginate. The main products were cis- and trans-verbenol, the later being further transformed to verbenone. The enantiomeric purity of each product more or less corresponded to that of the substrate. Transformation by free cells was faster than that by the immobilised cells. The ratio of products differed to some extent between the transformation by free and immobilised cells.

Biotransformations using plant cells, organ cultures and enzyme systems: current trends and future prospects

Plants are valuable sources of a variety of chemicals including drugs, flavours, pigments and agrochemicals. Some of the biochemical reactions occurring in plant cells are complex and cannot be achieved by synthetic routes. In vitro plant cell and organ cultures and plant enzymes act as suitable biocatalysts to perform these complex reactions. A wide variety of chemical compounds including aromatics, steroids, alkaloids, coumarins and terpenoids can undergo biotransformations using plant cells, organ cultures and enzymes. The biocatalyst-mediated reactions are regiospecific and stereospecific. Reaction types include oxidations, reductions, hydroxylations, methylations, acetylations, isomerizations, glycosylations and esterfications. Genetic manipulation approaches to biotransformation offer great potential to express heterologous genes and to clone and overexpress genes for key enzymes. Biotransformation efficiencies can further be improved using molecular techniques involving site-directed mutagenesis and gene manipulation for substrate specificity.

Transformation of alpha-pinene using Picea abies suspension culture

alpha-Pinene, both as the pure enantiomers and as the racemate, was transformed mainly to trans-verbenol by treatment with a Picea abies suspension cell culture. These reactions were followed by a slow transformation of the verbenol to verbenone, which was not transformed further. trans-Pinocarveol, myrtenol, cis-verbenol, and alpha-terpineol were byproducts of intermediate abundance. When subjected to the action of the suspension culture, cis-verbenol was not only transformed to verbenone but also isomerized to trans-verbenol. The transformation of alpha-pinene was fast, and the products were detected within one minute. The absolute configuration of the major products corresponded to that of the starting alpha-pinene enantiomer.