Thermal‐ and Photo‐Induced Isomerization of All‐E‐ and Z‐Isomer‐Rich Xanthophylls: Astaxanthin and Its Structurally‐Related Xanthophylls,Adonirubin, and Adonixanthin

The effects of heating and photo‐irradiation on the stability of all‐E‐isomer‐rich and Z‐isomer‐rich xanthophylls, astaxanthin and its structurally related xanthophylls, adonirubin, and adonixanthin, are investigated. The xanthophylls with high Z‐isomer content are prepared from their high‐purity all‐E‐isomers by thermal isomerization and filtering techniques, that is, total Z‐isomer ratios of adonirubin, astaxanthin, and adonixanthin are 80.9%, 89.5%, and 72.5%, respectively. The all‐E‐ and Z‐isomer‐rich xanthophylls dissolved in ethanol are stored at 4, 30, and 50 °C in the dark and at 30 °C under photo‐irradiation using a fluorescent light for 21 days. In the all‐E‐isomer‐rich xanthophylls, as the storage temperature increases, the total Z‐isomer ratio becomes higher, whereas in the Z‐isomer‐rich xanthophylls, the all‐E‐isomer ratio becomes higher. Photo‐irradiation slightly promotes Z‐isomerization in (all‐E)‐xanthophylls, but highly promotes all‐E‐isomerization in Z‐isomer‐rich xanthophylls. In addition, photo‐irradiation prevents thermal Z‐isomerization of (all‐E)‐xanthophylls. Moreover, it is found that some xanthophyll Z‐isomers such as (9Z)‐astaxanthin are more stable than that of the other Z‐isomers against heating and photo‐irradiation. These findings can contribute not only to establishing suitable storage conditions for Z‐isomer‐rich xanthophylls, but also to developing control techniques for the E/Z‐isomer ratio of the xanthophylls. Practical Applications: The fundamental data on the stability of xanthophyll isomers against heating and photo‐irradiation and finding stable xanthophyll Z‐isomers are very important to develop xanthophyll materials rich in the Z‐isomers. Moreover, this study clearly shows that the heat treatment enhances the Z‐isomerization of xanthophylls, whereas the photo‐irradiation enhances the all‐E‐isomerization and prevents thermal Z‐isomerization of them. This information can be utilized in technology for arbitrarily controlling E/Z‐isomerization of xanthophylls.     

Thermal isomerization of (all-E)-lycopene and separation of the Z-isomers by using a low boiling solvent: Dimethyl ether

Thermal isomerization of (all-E)-lycopene and the separation of generated Z-isomers were conducted using a low boiling solvent, dimethyl ether (DME). Because of the low boiling point (–24.8°C), DME is easily separated from lipids and other residues and is extremely low residual. The efficiency of thermal Z-isomerization of (all-E)-lycopene in DME was almost equivalent to using hexane. The thermally generated lycopene Z-isomers were separated by utilizing the solubility differences among lycopene isomers and a characteristic of DME that allows the solubility of compounds to be controlled by changing the temperature. Finally, a lycopene mixture containing 72.0% Z-isomers was obtained from (all-E)-lycopene.     

Photoinduced Isomerization and Hepatoxicities of Semaxanib,Sunitinib and Related 3‐Substituted Indolin‐2‐ones

3‐Substituted indolin‐2‐ones are an important class of compounds that display a wide range of biological activities. Sunitinib is an orally available multiple tyrosine kinase inhibitor that has been approved by the US Food and Drug Administration (FDA) for the treatment of renal cell cancer. Sunitinib and a related compound, semaxanib, exist as thermodynamically stable Z isomers, which photoisomerize to E isomers in solution. In this study, 17 3‐substituted indolin‐2‐ones were synthesized, and the kinetics of their photoisomerization were studied by ¹H NMR spectroscopy. The rate constants for photoisomerization ranged from 0.009 to 0.048 h^?1. Selected compounds were tested for cytotoxicity in the TAMH liver cell line. E/Z mixtures of four compounds were also assessed for toxicity in the TAMH and HepG2 cell lines. In some cases, the stereochemically pure drug was more toxic than the E/Z mixtures, but a general statement cannot be made. Our studies show that each stereoisomer could contribute differently to toxicity, suggesting that stereochemical purity issues that could arise from isomerization cannot be ignored.     

A New Type of Stereoselectivity in Baeyer–Villiger Reactions: Access to E‐ and Z‐Olefins

A new concept for accessing configurationally defined trisubstituted olefins has been developed. Starting from a common ketone precursor of the type 4‐ethylidenecyclohexanone, Baeyer–Villiger monooxygenases are employed as catalysts in diastereoselective Baeyer–Villiger reactions leading to the corresponding E‐ or Z‐configurated lactones. Wild‐type cyclohexanone monooxygenase (CHMO) as catalyst delivers the E‐isomers and a directed evolution mutant the opposite Z‐isomers. Subsequent transition metal‐catalyzed chemical transformations of a key product containing a vinyl bromide moiety provide a variety of different trisubstituted E‐ or Z‐olefins. A model based on QM/MM sheds light on the origin of this unusual type of diastereoselectivity. In contrast to this biocatalytic approach, traditional Baeyer–Villiger reagents such as m‐CPBA fail to show any selectivity, 1:1 mixtures of E‐ and Z‐olefins being formed.     

Diet‐dependent occurrence of CLA isomers in rumen and duodenal digesta of slaughtered bulls

This study examined the effects of linolenic acid‐rich vs. linoleic acid‐rich feeding system on the occurrence of individual CLA isomers in the rumen and duodenum digesta of German Holstein and German Simmental bulls using Ag⁺‐HPLC/DAD. The diet affected the biosynthesis of individual CLA isomers in the rumen of the bulls of both breeds. The isomer t‐11,c‐13 CLA was detected as the most abundant isomer in the rumen of linolenic acid‐rich diet‐fed bulls, up to six times higher compared to linoleic acid‐rich diet‐fed bulls. However, the main isomer in muscle lipid, c‐9,t‐11 CLA, was produced to a low extent in the rumen of linolenic acid‐rich diet‐fed bulls compared to higher concentrations of this isomer in the rumen of linoleic acid‐rich diet‐fed bulls. The isomers t‐7,c‐9 CLA and t‐8,c‐10 CLA were not present in the rumen samples of bulls fed both diets; however, abundant t‐7,c‐9 CLA was identified in the duodenum. The CLA isomers t‐12,t‐14 CLA and t‐11,t‐13 CLA were identified as the main t,t CLA isomers in the rumen, and were significantly enhanced in the rumen of linolenic acid‐rich diet‐fed compared to linoleic acid‐rich diet‐fed bulls. In contrast to c‐9,t‐11 CLA, the t,t CLA isomers seem to be biosynthesized predominantly in the rumen, further transported via the duodenum and finally deposited in the tissue lipids mainly in linolenic acid‐rich diet‐fed bulls. This was shown earlier for muscle and subcutaneous fat samples from the same animal experiment.     

Enantioselective Reduction of Citral Isomers in NCR Ene Reductase: Analysis of an Active‐Site Mutant Library

A deeper understanding of the >99 % S‐selective reduction of both isomers of citral catalyzed by NCR ene reductase was achieved by active‐site mutational studies and docking simulation. Though structurally similar, the E/Z isomers of citral showed a significantly varying selectivity response to introduced mutations. Although it was possible to invert (E)‐citral reduction enantioselectivity to ee 46 % (R) by introducing mutation W66A, for (Z)‐citral it remained ≥88 % (S) for all single‐residue variants. Residue 66 seems to act as a lever for opposite binding modes. This was underlined by a W66A‐based double‐mutant library that enhanced the (E)‐citral derived enantioselectivity to 63 % (R) and significantly lowered the S selectivity for (Z)‐citral to 44 % (S). Formation of (R)‐citronellal from an (E/Z)‐citral mixture is a desire in industrial (?)‐menthol synthesis. Our findings pave the way for a rational enzyme engineering solution.     

Rubber substrates and their influence on isomerization of conjugated dienes in pheromone dispensers

Release rate and degree of isomerization of pheromones with conjugated double bonds were studied in dispensers prepared from several rubber substrates. The substrates compared were made of rubber, cured with elemental sulfur or accelerators based on organic sulfur compounds or organic peroxides. Isomerization of the double bonds occurs immediately after impregnation of the substrate, and the degree of isomerization increases during field use and/or storage. The propensity of the isomers to isomerize corresponds to their proportion in the equilibrium mixture. AnE,Z isomer is isomerized faster than theE,E isomer, and finally a near-equilibrium mixture of the four isomers is present. Minimal isomerization was found in non-sulfur-cured substrates which are the material of choice.     

Filbertworm sex pheromone

(E,E)- and (E,Z)-8,10-Dodecadien-1-ol acetates were identified in a 14.3 ratio in the extract of abdominal tips of female filbert-worm moths,Melissopus latiferreanus (Walsingham). The identifications were based on electroantennogram (EAG) analysis, gas chromatography, mass spectrometry, ozonolysis, and synthesis. TheE,Z isomer produced the stronger EAG response. In the field tests of various ratios ofE,EE,Z, the ratio found in the extract captured the most males. The pureE,E isomer initially was not attractive by itself (<0.1%E,Z) but became attractive after a few days, presumably because of isomerization. TheE, Z isomer (<0.1%E,E) was attractive initially, but this compound might have isomerized faster than theE,E isomer. A study of the isomerization showed that regardless of the initial mixture of 8,10-dodecadien-1-ol acetate isomers, almost complete equilibration existed after one month. The equilibrium mixture consisted of 9%Z8,E10, 65%E8,E10, 23%E8,Z10, and 3%Z8,Z10. Concentrations in rubber septa (14 ratio ofE,E toE,Z) of 0.03–3.0 mg/septum produced equivalent trap catches.This paper reports the results of research only. Mention of a commercial product in this paper does not constitute a recommendation by the U.S. Department of Agriculture.     

Asymmetric Sharpless epoxidation of 13S‐hydroxy‐ 9Z, 11E‐octadecadienoic acid (13S‐HODE)

The asymmetric Sharpless epoxidation of methyl 13S‐hydroxy‐9Z, 11E‐octadeca‐dienoate (13S‐HODE, 1 ) with tert‐butyl hydroperoxide (TBHP) catalysed by titanium tetraisopropoxide {Ti(ⁱOPr)₄} in the presence of L(+)‐diisopropyl tartrate (L‐DIPT) gave methyl 13S‐hydroxy‐11S, 12S‐epoxy‐9Z‐octadecenoate 2 (erythro isomer) in 84% diastereomeric excess (de). The epoxidation of 1 with TBHP catalysed by Ti(ⁱOPr)₄ in the presence of D(‐)‐DIPT yielded methyl 13S‐hydroxy‐11RR12R‐epoxy‐9Z‐octadecenoate (threo isomer) 3 in 76% de.     

Sex pheromone of Egyptian cotton leafworm (Spodoptera littoralis)

Samples of pheromone carriers, after use for 4–5 weeks in traps in the field, were analyzed. Partial isomerization of prodlure, (Z,E)-9,11-tetradecadienyl acetate (TDDA), the main component of the sex pheromone of femaleSpodoptera littoralis, took place. All three other possible isomers were formed to yield a mixture of 50% (Z,E)-9,11 -TDDA, 30% (E,E)-9,11-, 13% (E,Z)-9,11-, and 7% (Z,Z)-9,11 isomer. The process was found to be photochemically induced; none of these isomers was found under heating alone. Most of the pheromone, however, decomposed under field conditions.     

Expeditious and Practical Synthesis of Lycopene

Our lycopene synthesis highlights the expeditious assembly of the carbon skeleton by the use of a readily available ten‐carbon unit, geraniol, rather than the original natural five‐carbon building block, isopentenyl pyrophosphate. Furthermore, four oxidation steps by the enzyme desaturases to produce the conjugated carbon‐carbon double bonds of lycopene are merged into one‐pot double elimination reactions in our synthesis. These accomplished the highly efficient synthesis of all‐(E)‐lycopene from geraniol through a seven‐step sequence in 51% overall yield.     

Modulation of prostaglandin H synthase activity by conjugated linoleic acid (CLA) and specific CLA isomers

Conjugated linoleic acid (CLA) has been shown to inhibit tumorigenesis in animal models and is cytostatic to numerous cell lines in vitro. However, the mechanism of action is unknown. In the current study, we determined the effects of CLA and specific isomers of CLA on the rate of oxygenation of arachidonic acid by prostaglandin H synthase (PGHS) in ram seminal vesicle microsomes. The enzyme was incubated with 0.1 to 100 μM CLA or specific isomers of CLA for 2 min prior to the addition of 44 to 176 μM arachidonate. The isomers tested were 9(E),11(E) CLA; 9(Z),11(E) CLA; 9(Z),11(Z) CLA, and 10(E),12(Z) CLA. For a positive inhibitor control, flurbiprofen was used at 0.75 to 2.50 μM. Enzyme activity was assessed by measuring the rate of oxygen consumption. Inclusion of CLA or specific isomers of CLA in the incubation mixtures inhibits PGHS. The efficacy differs for each isomer, with the 9(Z),11(E) CLA isomer being the most effective and the 9(Z),11(Z) CLA isomer being the least effective inhibitor among the four CLA isomers tested. The K _i values obtained by Dixon replots range from 18.7 μM for the most effective isomer, 9(Z),11(Z) CLA, to 105.3 μM for the least effective isomer, 9(Z),11(Z) CLA. The K _i value for flurbiprofen with ram seminal vesicle microsomes was 0.33 μM. As the concentration of arachidonate was increased, the CLA-dependent inhibition of PGHS decreased, suggesting competitive inhibition. The results of this study demonstrate the potential of CLA and specific isomers of CLA to modulate prostaglandin biosynthesis.     

Sex pheromone of European grapevine moth (Lobesia botrana) its chemical transformations in sunlight and heat

Photo- and radical isomerization of (E, Z)-7,9-dodecadien-1-yl acetate (DDA) leads to an equilibrium mixture of all four possible geometric isomers of 7,9-DDA in the ratio ofE,E, 69–76%;Z,E, 11–13%;E, Z, 12–15%; andZ, Z, 1–3%. Iodine catalysis of the isomerization takes place even in dark at room temperature and is probably a radical reaction.     

<Emphasis Type="Italic">Trans</Emphasis> and positional ethylenic bonds in two dominant isomers of eicosapentaenoic acid from the freshwater sponge <Emphasis Type="Italic">Baicalospongia bacillifera</Emphasis>

Reinvestigation of the current FA composition of the regional freshwater sponge Baicalospongia bacillifera showed that the main measured isomer of EPA (14% of the total FA now detected) is, in fact, an unusual 5Z,8Z,11Z,14Z,18E-EPA. Two other isomers of this acid also present were identified as a novel 5Z,8Z,11Z,15Z,18E-EPA and the common methylene-interrupted 5Z,8Z,11Z,14Z,17Z-EPA (usually written simply as EPA). Isolation of these acids as their methyl ester derivatives was accomplished with the use of a combination of silver-ion column chromatography and HPLC. The structure of the two new compounds was deduced from GC-MS and detailed NMR data. Partial hydrazine reduction of all three isolated EPA esters followed by separation of cis/trans isomers of the resulting monoenoic acids and GC-MS analysis of their dimethyl disulfide adducts were used for determination of the configuration and position of the double bonds. We may assume that the sponge B. bacillifera cannot receive these unusual EPA isomers directly from food sources (e.g., algal diatoms), and accordingly restructuring of ordinary EPA to novel acids may take place in the sponge tissue.     

Attraction of pea mothCydia nigricana F. (Lepidoptera: Tortricidae) to female sex pheromone (E,E)-8,10-dodecadien-1-YL acetate,is inhibited by geometric isomersE,Z, Z,E, andZ,Z

Field attraction ofCydia nigricana males to synthetic female sex pheromone (E,E)-8,10-dodecadien-1-yl acetate, formulated on red rubber septa, declined continuously during two weeks. This was due to isomerization of (E,E)-8,10-dodecadien-1-yl acetate: eight days after application of purifiedE,E isomer, the proportion ofE,Z;Z,E; andZ,Z isomers in rubber septa aged in the laboratory was 4%; a 5% addition of any one of these isomers to fresh lures of (E,E)-8,10-dodecadien-1-yl acetate significantly reduced male attraction. Stereospecific syntheses of (E,Z)-, (Z,E)-, and (Z,Z)-8,10-dodecadien-1-yl acetate are described. The pheromone gland ofCydia nigricana contains 0.8 ng/female of (E,E)-8,10-dodecadien-1-yl acetate, accompanied by three monounsaturated acetates, (E)-9-dodecen-1-yl acetate, (Z)-5-tetradecen-1-yl acetate, and (Z)-7-tetradecen-1-yl acetate (0.1 ng/female each). These compounds did not augment male trap catch when added to (E,E)-8,10-dodecadien-1-yl acetate.     

Heat-induced geometrical isomerization of α-linolenic acid: Effect of temperature and heating time on the appearance of individual isomers

The formation of linolenic acid geometrical isomers (LAGIs) was studied in linseed oil that was heated under vacuum in sealed ampoules at different temperatures (190–260°C) for several durations (2–16 h). A temperature of about 190°C seems to be necessary to induce the formation of LAGIs. At higher temperatures, disappearance of linolenic acid follows a first-order kinetic. The formation of LAGIs increases with both heating time and temperature, degrees of isomerization of linolenic acid higher than 50–60% could easily be obtained by simply heating the oil under vacuum. Side reactions remain at a low level. The mean probabilities of isomerization of individual ethylenic bonds are similar to those determined in linolenic acid-containing oils marketed in European countries, 41.9, 4.7 and 53.3% for double bonds in positions 9, 12 and 15, respectively. The di-trans t,c,t (trans,cis,trans) isomer is formedvia the mono-trans c,c,t andt,c,c isomers by a two-step reaction. The proportions of thec,c,t andt,c,c isomers (relative to total LAGIs) decrease linearly with the heating time. The proportion of thec,t,c isomer is only slightly affected by this parameter; however, it increases with temperature. The proportion of thet,c,t isomer increases linearly with heating time at each tested temperature, at the expense of thec,c,t andt,c,c isomers. However, there is no simple relationship linking the disappearance of each of the mono-trans isomers and the formation of the di-trans isomer.     

Oxidative degradation kinetics of lycopene, lutein, and 9-cis and all-trans β-carotene

The thermal and oxidative degradation of carotenoids was studied in an oil model system to determine their relative stabilities and the major β-carotene isomers formed during the reaction. All-trans β-carotene, 9-cis β-carotene, lycopene, and lutein were heated in safflower seed oil at 75, 85, and 95°C for 24, 12, and 5 h, respectively. The major isomers formed during heating of β-carotene were 13-cis, 9-cis, and an unidentified cis isomer. The degradation kinetics for the carotenoids followed a first-order kinetic model. The rates of degradation were as follows: lycopene>all-trans β-carotene≈9-cis β-carotene>lutein. The values for the thermodynamic parameters indicate that a kinetic compensation effect exists between all of the carotenoids. These data suggest that lycopene was most susceptible to degradation and lutein had the greatest stability in the model system of the carotenoids tested. Furthermore, there was no significant difference in the rates of degradation for 9-cis and all-trans β-carotene under the experimental conditions.     

Efficient Extraction of Lycopene from Rhodopseudomonas palustris with n‐Hexane and Methanol after Alkaline Wash

Extraction of lycopene from Rhodopseudomonas palustris with various solvents and alkaline wash was investigated. Dichloromethane or benzene as single polar or nonpolar solvent were the most effective solvents. The maximum extraction efficiency was achieved with a combination of n‐hexane and methanol (1:1 v/v). which was approximately one time higher than that obtained with a single solvent. The partitioning behavior of lycopene in n‐hexane/methanol indicated that almost all extracted lycopene from R. palustris cells was dissolved in the n‐hexane phase. Further studies showed that lycopene extraction was much improved after an alkaline wash of R. palustris cells. The measured lycopene content was much higher than that in tomatoes which indicates that R. palustris will become an important biological resource of lycopene.     

Structure‐Based Insight into the Asymmetric Bioreduction of the CC Double Bond of α,β‐Unsaturated Nitroalkenes by Pentaerythritol Tetranitrate Reductase

Biocatalytic reduction of α‐ or β‐alkyl‐β‐arylnitroalkenes provides a convenient and efficient method to prepare chiral substituted nitroalkanes. Pentaerythritol tetranitrate reductase (PETN reductase) from Enterobacter cloacae st. PB2 catalyses the reduction of nitroolefins such as 1‐nitrocyclohexene ( 1 ) with steady state and rapid reaction kinetics comparable to other old yellow enzyme homologues. Furthermore, it reduces 2‐aryl‐1‐nitropropenes ( 4a–d ) to their equivalent (S)‐nitropropanes 9a–d . The enzyme shows a preference for the (Z)‐isomer of substrates 4a–d , providing almost pure enantiomeric products 9a–d (ees up to>99%) in quantitative yield, whereas the respective (E)‐isomers are reduced with lower enantioselectivity (63–89% ee) and lower product yields. 1‐Aryl‐2‐nitropropenes ( 5a , b ) are also reduced efficiently, but the products (R)‐ 10 have lower optical purities. The structure of the enzyme complex with 1‐nitrocyclohexene ( 1 ) was determined by X‐ray crystallography, revealing two substrate‐binding modes, with only one compatible with hydride transfer. Models of nitropropenes 4 and 5 in the active site of PETN reductase predicted that the enantioselectivity of the reaction was dependent on the orientation of binding of the (E)‐ and (Z)‐substrates. This work provides a structural basis for understanding the mechanism of asymmetric bioreduction of nitroalkenes by PETN reductase.     

Structure-activity studies on aggregation pheromone components ofPityogenes chalcographus (Coleoptera: Scolytidae)

Syntheses of all four Stereoisomers (2S,5S; 2S,5R;2R,5R; and2R,5S) of chalcogran, a major component of the aggregation pheromone ofPityogenes chalcographus, and of all four isomers (2Z,4Z; 2Z,4E; 2E,4E; and 2E,4Z) of methyl 2,4-decadienoate (MD), the second major pheromone component, are briefly described. Attraction responses of walking beetles of both sexes were tested to mixtures of the synergistic pheromone components or analogs. These bioassays showed that theE,Z isomer of MD is the most active when tested with chalcogran. When tested with (E,Z)-MD, (2S,5R)-chalcogran was the most active stereoisomer, while 2R,5R and 2R,5S isomers had intermediate activities, and the 2S,5S isomer was inactive. There was no evidence that the relatively less active Stereoisomers of chalcogran inhibited or promoted attraction to (2S,5R)-chalcogran with (E,Z)-MD. Male beetles only produce the activeE,Z isomer of MD (inactive alone) and their hindguts contain the most active (2S,5R)- and least active (2S,5S)-chalcogran. A mixture of all MD isomers with racemic chalcogran was not significantly different in attractivity compared to (E,Z)-MD with racemic chalcogran, indicating no synergistic or inhibitory effects of the inactive isomers of MD.