Biosynthetic pathway of cucumber alcohol: Trans-2,cis-6-nonadienol via cis-3,cis-6-nonadienal

cis-3,cis-6-Nonadienal and cis-3-nonenal in Cucumis sativus were identified by comparison with synthetic specimens. The identification of these compounds, combined with biochemical evidence, suggests that cucumber alcohol and trans-2-nonenol are biosynthesized via cis-3-unsaturated aldehydes from linolenic and linoleic acid, respectively.     

Multinuclear NMR study and crystal structures of complexes of the types cis- and trans-Pt(amine)2I2

Complexes of the types cis- and trans-Pt(amine)₂I₂ were studied by spectroscopic methods, especially by multinuclear NMR spectroscopy. In ¹⁹⁵Pt NMR, the cis diiodo compounds with primary amines were observed between −3342 and −3357 ppm in acetone, while the trans compounds were found between −3336 and −3372 ppm. For the secondary amines, the chemical shifts were observed at lower fields. In ¹H NMR, the trans complexes were observed at higher fields than the cis compounds, while in ¹³C NMR, the reverse was observed. The ²J(¹⁹⁵Pt-¹H) and ³J(¹⁹⁵Pt-¹H) coupling constants are larger for the cis compounds (ave. 67 and 45 Hz, respectively) than for the trans isomers (ave. 59 and 38 Hz). In ¹³C NMR, the values of ²J(¹⁹⁵Pt-¹³C) and ³J(¹⁹⁵Pt-¹³C) were also found to be larger for the cis complexes (ave. 17 and 39 Hz versus 11 and 28 Hz). There seems to be a slight dependence of the pK_a values of the protonated amines or the proton affinity in the gas phase with the δ(Pt) chemical shifts. The crystal structures of eight diiodo complexes were determined. These compounds are cis-Pt(CH₃NH₂)₂I₂, cis-Pt(n-C₄H₉NH₂)₂I₂, cis-Pt(Et₂NH)₂I₂, trans-Pt(n-C₃H₇NH₂)₂I₂, trans-Pt(iso-C₃H₇NH₂)₂I₂, trans-Pt(n-C₄H₉NH₂)₂I₂, trans-Pt(t-C₄H₉NH₂)₂I₂ and trans-Pt(Me₂NH)₂I₂. The Pt-N bond distances located in trans position to the iodo ligands were compared to those located in trans position to the amines. The Pt-N bond in cis-Pt(Et₂NH)₂I₂ are much longer than the others, probably caused by the steric hindrance of the two very bulky ligands located in cis positions.     

Different reaction mechanisms for cis- and trans-prenyltransferases

Octaprenyl diphosphate synthase (OPPs) and undecaprenyl diphosphate synthases (UPPs) catalyze consecutive condensation reactions of farnesyl diphosphate (FPP) with 5 and 8 isopentenyl diphosphate (IPP) to generate C₄₀ and C₅₅ products with trans- and cis-double bonds, respectively. In this study, we used IPP analogue, 3-bromo-3-butenyl diphosphate (Br-IPP), in conjunction with radiolabeled FPP, to probe the reaction mechanisms of the two prenyltransferases. Using this alternative substrate with electron-withdrawing bromo group at the C3 position to slow down the condensation step, trapping of farnesol in the OPPs reaction from radiolabeled FPP under basic condition was observed, consistent with a sequential mechanism. In contrast, UPPs reaction yielded no farnesyl carbocation intermediate under the same condition with radiolabeled FPP and Br-IPP, indicating a concerted mechanism. Our data demonstrate the different reaction mechanisms for cis- and tran-prenyltransferases although they share the same substrates.     

Enhancement of antibody synthesis in rats by feeding cis-9,trans-11 conjugated linoleic acid during early life

Previous studies have demonstrated that the intake of a 1% conjugated linoleic acid (CLA) diet in an 80:20 mixture of cis-9,trans-11 and trans-10,cis-12 exerts age-specific effects on the immune system: immunoglobulin enhancement and proliferative down-modulation in neonatal and adult rats, respectively. The present study evaluates the influence of the same diet on antibody synthesis of early infant Wistar rats during suckling and/or after weaning. Dietary supplementation was performed during suckling and early infancy (4 weeks), only during suckling (3 weeks), or only in early infancy (1 week). CLA content in plasma and serum immunoglobulin (Ig) G, IgM and IgA concentration were determined. Proliferation, cytokines and Ig production were evaluated on isolated splenocytes. Cis-9,trans-11- and trans-10,cis-12-CLA isomers were detected in the plasma of all CLA-supplemented animals, and the highest content was quantified in those rats supplemented over the longest period. These rats also exhibited higher concentrations of serum IgG, IgM and IgA. Moreover, splenocytes from CLA-supplemented rats showed the highest IgM and IgG synthesis and interleukin (IL)-6 production, whereas their proliferative ability was lower. In summary, in infant rats, we observed both the enhance antibody synthesis previously reported in neonates, and the reduced lymphoproliferation previously reported in adults.     

Quantifying the trans influence of triphenylarsine. Crystal and molecular structures of cis-[PtCl2(SMe2)(AsPh3)] and cis-[PtCl2(AsPh3)2]·CHCl3

Reaction between a mixture of cis-trans-[PtCl₂(SMe₂)₂] and 1 equiv. AsPh₃ in chloroform gives cis-[PtCl₂(SMe₂)(AsPh₃)] crystallizing in P2₁/n with a=10.397(2), b=14.876(3), c=13.956(3) Å, β=90.86(3)° and Z=4. Selected geometrical parameters are PtAs 2.3531(10), PtS 2.262(2), PtCl (trans to S) 2.301(2), PtCl (trans to As) 2.328(2) Å and SPtAs 88.85(6), SPtCl(2) 90.77(8), AsPtCl(1) 91.07(6) and ClPtCl 89.42(7)°. cis-[PtCl₂(AsPh₃)₂]·CHCl₃ crystallizes in P2₁/c with a=20.557(4), b=9.5951(19), c=20.147(4) Å, β=96.77(3)° and Z=4. Selected geometrical parameters are PtAs(1) 2.3599(9), PtAs(2) 2.3770(9), PtCl(1) (trans to As(1)) 2.3515(18), PtCl(2) (trans to As(2)) 2.3251(18) Å and AsPtAs 97.87(3), As(1)PtCl(2) 88.67(5), As(2)PtCl(1) 84.30(5) and ClPtCl 89.32(7)°. By comparison with related structures from the literature the following trans influence series was established PMe₂Ph>PPh₃>AsPh₃≈SbPh₃>Me₂SO≈SMe₂≈SPh₂>NH₃≈olefin>Cl⁻>MeCN.     

Enzymatic separation of cis and trans isomers of alicyclic alcohols

It has been discovered that phosphatases [alkaline phosphatase, orthophosphoric-monoester phosphohydrolase (alkaline optimum), EC 3.1.3.1, and acid phosphatase, orthophosphoric-monoester phosphohydrolase (acid optimum), EC 3.1.3.2] display a remarkable geometric specificity in the hydrolysis of cis and trans isomers of monoorthophosphate esters of substituted alicy clicalcohols. While steric hindrances prevent potato acid phosphatase from hydrolysing cis-2-methylcyclohexyl and cis-2-methylcyclopentyl phosphates, the corresponding trans isomers are readily hydrolysed by the enzyme (non-enzymatic, acid-catalysed or base-catalysed hydrolyses of the cis and trans isomers occur at similar rates). Cis isomers of methylcyclohexyl phosphates, in which the methyl group is remote from the hydrolysed ester bond, 3- or 4-, have nearly the same reactivities to phosphatases as their trans counterparts. However, if the methyl group in position 4 is replaced by a bulky substituent, e.g. tert-butyl, phosphatases again hydrolyse only the trans and not the cis isomer. These phenomena afford a simple method for preparative separation of cis and trans isomers of alicyclic alcohols: a mixture of the isomers is first phosphorylated with POCl₃ and then hydrolysed by phosphatase. The trans alcohol formed is extracted with CCl₄, followed by alkaline hydrolysis of the remaining cis-tester and subsequent extraction of the cis alcohol produced.     

Effect of cis-9,trans-11 and trans-10,cis-12 isomers of conjugated linoleic acid on the integrity and functionality of cryopreserved bovine spermatozoa

Plasma membranes of sperm subjected to low temperatures undergo changes in their structure and permeability. The addition of fatty acids in semen cryopreservation media may influence the sperm motility after thawing, possibly by maintaining the membrane fluidity due to their incorporation in lipid bilayers. In this work, different concentrations of the isomers cis-9,trans-11 and trans-10,cis-12 of conjugated linoleic acid (CLA) were added in the cryopreservation medium of bovine sperm. Four Jersey bulls were used, and the ejaculates were processed as a pool. The Tris-based extender (Dilutris®) was supplemented with 20% egg yolk (MB). The treatments with CLA (Luta-CLA®), which had oily presentation, were prepared from MB with addition of 1% sodium lauryl sulfate, and denominated MBL. The concentrations of CLA tested were 50, 100, and 150 μM. The motility characteristics of the post-thaw semen were analyzed by computerized analysis system (CASA), and plasma membrane integrity and acrosomal and mitochondrial function assessed by the association of the fluorescent probes propidium iodide, fluorescein isothiocyanate-conjugated Pisum sativum agglutinin (FITC-PSA), JC-1 and Hoechst 33342. No significant differences were observed among treatments, excepting for a decreased mitochondrial potential of cells treated with 150 μM CLA. The addition of CLA, at the concentrations used, showed no advantages on the integrity and functionality of bovine sperm submitted to cryopreservation.     

Synthesis, characterization and kinetic studies of the cis-[RuCl2(cyclen)] complex

We report here the synthesis, characterization and kinetic studies of cis-[RuCl₂(cyclen)]⁺ in aqueous solution, where cyclen is the macrocyclic ligand 1,4,7,10-tetraazacyclododecane. The complex releases one Cl⁻ producing cis-[RuCl(OH)(cyclen)]⁺ in aqueous solution at pH 4.60. The product of this reaction was characterized by Ultraviolet-Visible (UV-Vis) spectrum in comparison to the synthesized cis-[RuCl(OH)(cyclen)](BF₄)·2H₂O. The electrochemical data showed that E_pc of the Ru(III/II) peak increases as the macrocycle ring size decreases and also when the trans conformation is changed to cis. The chloride affinity of Ru(III) depends on the macrocycle ring size since cis-[RuCl₂(cyclam)]⁺ (cyclam=1,4,8,11-tetraazacyclotetradecane) does not release chloride for at least 12 h. The overall effect between cyclam and cyclen reflects the fact that the electron involved in the reduction enters a nonbonding π-d orbital and its energy is affected by the macrocyclic ligand.     

Solvent exchange, solvent interchange, aquation and isomerisation reactions of cis- and trans-[Co(tmen)2(NCMe)2] in water, Me2SO and MeCN: kinetics and stereochemistry

The synthesis and characterisation of cis- and trans-[Co(tmen)₂(NCCH₃)₂](ClO₄)₃ are described. Solvolysis rates have been measured by both ¹H NMR spectroscopy and UV-Vis spectrophotometry in dimethyl sulfoxide at 298.2 K. The cis isomer undergoes solvolysis by consecutive first-order reactions, k₁=5.61 × 10⁻⁴ and k₂=5.35 × 10⁻⁴ s⁻¹, each with steric retention. The measured solvolysis rate (single step reaction) for the trans isomer is k=1.54 × 10⁻⁵ s⁻¹. The solvent exchange rates have been measured by ¹H NMR spectroscopy in CD₃CN at 298.2 K: k_ex(cis)=k_ct + k_cc=2.0 × 10⁻⁵ and k_ex(trans)=k_tc + k_tt=4.56 × 10⁻⁶ s⁻¹. From these data, the measured cis-trans isomerisation rate (1.71 × 10⁻⁶ s⁻¹) and equilibrium position in CH₃CN (17% trans), the steric course for substitution in the exchange processes has been determined: trans reactant - 69% trans product; cis reactant - 99% cis product. Aquation rates for cis- and trans-[Co(tmen)₂(NCCH₃)₂](ClO₄)₃ have also been determined spectrophotometrically and by NMR; k_cis=1.3 × 10⁻⁴ and k_trans=2.7 × 10⁻⁵ s⁻¹. In both cases the steric course for the primary aquation step is indeterminate because the subsequent steps are faster. Where data are available, the [Co(tmen)₂X₂]ⁿ⁺ complexes are found to be consistently much more reactive than their [Co(en)₂X₂]ⁿ⁺ analogues.     

Partial purification and properties of a cis-3: trans-2-enal isomerase from cucumber fruit

An enzyme, which catalyses the isomerisation of cis-3-enals to trans-2-enals, has been partially purified from cucumber fruit. The isomerase activity has been resolved from significant contamination by the related activities, lipoxygenase and hydroperoxide cleavage enzymes. An examination of the substrate specificity of the isomerase enzyme showed it to be specific for the cis-3-enals. The most efficient isomerisation was achieved with cis-3-hexenal and cis-3-nonenal which are, physiologically, the two most significant substrates. The trans-3-enal and cis-3-enol were not suitable substrates for the enzyme.     

Binding affinities of CRBPI and CRBPII for 9-cis-retinoids

Background

Cellular retinol binding-protein I (CRBPI) and cellular retinol binding-protein II (CRBPII) serve as intracellular retinoid chaperones that bind retinol and retinal with high affinity and facilitate substrate delivery to select enzymes that catalyze retinoic acid (RA) and retinyl ester biosynthesis. Recently, 9-cis-RA has been identified in vivo in the pancreas, where it contributes to regulating glucose-stimulated insulin secretion. In vitro, 9-cis-RA activates RXR (retinoid × receptors), which serve as therapeutic targets for treating cancer and metabolic diseases. Binding affinities and structure–function relationships have been well characterized for CRBPI and CRBPII with all-trans-retinoids, but not for 9-cis-retinoids. This study extended current knowledge by establishing binding affinities for CRBPI and CRBPII with 9-cis-retinoids.

Methods

We have determined apparent dissociation constants, K′_d, through monitoring binding of 9-cis-retinol, 9-cis-retinal, and 9-cis-RA with CRBPI and CRBPII by fluorescence spectroscopy, and analyzing the data with non-linear regression. We compared these data to the data we obtained for all-trans- and 13-cis-retinoids under identical conditions.

Results

CRBPI and CRBPII, respectively, bind 9-cis-retinol (K′_d, 11 nM and 68 nM) and 9-cis-retinal (K′_d, 8 nM and 5 nM) with high affinity. No significant 9-cis-RA binding was observed with CRBPI or CRBPII.

Conclusions

CRBPI and CRBPII bind 9-cis-retinol and 9-cis-retinal with high affinities, albeit with affinities somewhat lower than for all-trans-retinol and all-trans-retinal.

General significance

These data provide further insight into structure–binding relationships of cellular retinol binding-proteins and are consistent with a model of 9-cis-RA biosynthesis that involves chaperoned delivery of 9-cis-retinoids to enzymes that recognize retinoid binding-proteins.     

trans- and cis-Ru(II) aminophosphine complexes: Syntheses, X-ray structures and catalytic activity in transfer hydrogenation of acetophenone derivatives

The ability of transition metal catalysts to add or remove hydrogen from organic substrates by transfer hydrogenation process is a valuable synthetic tool. For this aim, a novel Ru(II) complex with the P-N ligand [(Ph₂P)₂NCH₂-C₄H₃S] derived from thiophene-2-methylamine was synthesized starting with the complex [Ru(η⁶-p-cymene)(μ-Cl)Cl]₂ and isolated in two isomeric forms: trans- and cis-[Ru((PPh₂)₂NCH₂-C₄H₃S)₂Cl₂], 2 and 3, respectively. The structures of both isomers were also determined by single crystal X-ray diffraction. The cis-isomer 3 can be isolated from the solution of major trans-isomer 2 as yellow crystals. However, upon dissolution 3 is rapidly converted to the trans-isomer 2. The new ruthenium(II) complex provides high catalytic activity in the transfer hydrogenation of acetophenone derivatives to 1-phenylethanol derivatives in the presence of 2-propanol as the hydrogen source. This transfer hydrogenation is characterized by low reversibility under the experimental conditions.     

CO-loss and geometric isomerization in the frozen matrix photochemistry of cis-Fe(CO)4X2, where X = Br and I, cis-[Et4N][Mn(CO)4Br2], cis-Mn(CO)4(PBu3)Br, and Mn(CO)3(PBu3)2Br

Photolysis of cis-Fe(CO)₄X₂, where X = Br and I, results in low energy, facile rearrangement to the trans isomer with no evidence of CO-loss. In contrast, the isoelectronic cis-Mn(CO)₄Br₂ anion exhibits CO-loss upon photolysis with only weak evidence for the trans isomer. The photolysis of Mn(CO)₅Br, Mn(CO)₄Br(PBu₃) and Mn(CO)₃Br(PBu₃)₂ have also been examined in frozen matrices.     

Synthesis of deuterated methyl 6,9,12-octadecatrienoate geometric isomers

Methyl cis-6,cis-9,cis-12-octadecatrienoate-15,15,16,16-d₄ and the corresponding cis,cis,trans isomer were obtained by coupling hexyl-d₄-triphenylphosphonium bromide and methyl 12-oxo-cis-6,cis-9-dodecadienoate by the Wittig reaction. The deuterated phosphonium salt was prepared from 3-hexynol by catalytic deuteration of the corresponding tetrahydropyranyl ether and intermediate formation of the bromide. The dienoic aldehyde ester was obtained through the intermediate dioxanyl and dimethoxy derivatives from the Wittig coupling of methyl 9-oxo-cis-6-nonenoate with [2-(1,3-dioxan-2-yl)ethyl]-triphenylphosphonium bromide. The monoenoic aldehyde ester was prepared in a similar manner by the Wittig reaction between methyl 6-oxohexanoate and the dioxanylphosphonium salt. The saturated aldehyde ester was obtained, through several steps, from the ozonolysis of cyclohexene. Geometric isomers formed during each of the Wittig reactions were separated by silver resin chromatography. ¹³C Nuclear magnetic resonance chemical shifts for the compounds prepared are presented.     

Characterization of novel 2-oxoglutarate dependent dioxygenases converting l-proline to cis-4-hydroxy-l-proline

Hydroxyprolines are valuable chiral building blocks for organic synthesis of pharmaceuticals. Several microorganisms producing l-proline trans-4- and cis-3-hydroxylase were discovered and these enzymes were applied to the industrial production of trans-4- and cis-3-hydroxy-l-proline, respectively. Meanwhile, other hydroxyproline isomers, cis-4- and trans-3-hydroxy-l-proline, were not easily available because the corresponding hydroxylase have not been discovered. Herein we report novel l-proline cis-4-hydroxylases converting free l-proline to cis-4-hydroxy-l-proline. Two genes encoding uncharacterized proteins from Mesorhizobium loti and Sinorhizobium meliloti were cloned and overexpressed in Escherichia coli, respectively. The functions of purified proteins were investigated in detail, and consequently we detected l-proline cis-4-hydroxylase activity in both proteins. Likewise l-proline trans-4-, cis-3-hydroxylase and prolyl hydroxylase, these enzymes belonged to a 2-oxoglutarate dependent dioxygenase family and required a non-heme ferrous ion. Although their reaction mechanisms were similar to other hydroxylases, the amino acid sequence homology was not observed (less than 40%).     

Synthesis and multinuclear magnetic resonance spectroscopy of the novel ionic Pt(II) mixed-ligands complexes cis- and trans-[Pt(pyrazine)2(Ypy)2](NO3)2 where Ypy = pyridine derivative

Novel ionic mixed-ligands complexes of the types cis- and trans-[Pt(pz)₂(Ypy)₂](NO₃)₂ (where Ypy is a pyridine derivative and pz = pyrazine) were synthesized and studied mainly in the solid state by IR spectroscopy and in aqueous solution by multinuclear (¹⁹⁵Pt, ¹H and ¹³C) magnetic resonance spectroscopy. The trans isomers with ligands containing a methyl group in ortho position on the pyridine ring could not be synthesized. The results of the solution NMR characterization have shown that the isolated compounds are pure. In ¹⁹⁵Pt NMR, the cis complexes containing a methyl group in ortho positions were observed at lower field (average −2337 ppm) than the other cis compounds (average −2427 ppm), which is explained by the solvent effect. The trans isomers were observed at very slightly lower fields (average −2422 ppm) than the equivalent cis complexes (average −2427 ppm). In ¹H NMR, the coupling constants ³J(¹⁹⁵Pt-¹H_Ypy) and ³J(¹⁹⁵Pt-¹H_pz) are larger in the cis compounds (∼40 Hz) than in the trans complexes (∼31 Hz). A few ⁴J(¹⁹⁵Pt-¹H_pz) were observed (∼16 Hz). In ¹³C NMR spectroscopy, the coupling constants ³J(¹⁹⁵Pt-¹³C_pz) and ³J(¹⁹⁵Pt-¹³C_Ypy) are also larger in the cis configuration (∼30 and ∼38 Hz, respectively) than in the trans isomers (∼20 Hz). One ⁴J(¹⁹⁵Pt-¹³C_pz) could be calculated (17 Hz). The presence of the syn and anti rotamers were observed in all the cis complexes containing a pyridine derivative with a -CH₃ group in ortho position. They were observed in ¹⁹⁵Pt, ¹H and ¹³C NMR spectroscopy. The proportion of the two rotamers is about 55% and 45%.     

Study of Pt(II)-cyclic amines complexes of the types cis- and trans-Pt(amine)2I2 and cis- and trans-Pt(amine)2(NO3)2 and their aqueous products by

Complexes of the types cis- and trans-Pt(amine)₂I₂ containing cyclic amines were synthesized and studied mainly by IR and multinuclear NMR spectroscopies. The compounds were converted to cis- and trans-Pt(amine)₂(NO₃)₂, which were also investigated. The hydrolysis and the aquation reactions of the latter compounds were then studied in D₂O in different conditions of pH. In acidic medium, the aqueous product is [Pt(amine)₂(D₂O)₂]²⁺ and for a few amines, [Pt(amine)₂(D₂O)(NO₃)]⁺ was detected. In basic pH, the main product is Pt(amine)₂(OD)₂ and Pt(amine)₂(OD)(NO₃) was detected for several compounds. In neutral pH, the cis isomers form between two and four species in fresh solutions. The most shielded species in ¹⁹⁵Pt NMR is the monoaqua-monohydroxo complex cis-[Pt(amine)₂(D₂O)(OD)]⁺ and the less shielded compound is the dihydroxo-bridged dimer [Pt(amine)₂(μ-OD)₂Pt(amine)₂]²⁺, which were observed for all the compounds. For a few amines, the monohydroxo-bridged dimer [Pt(D₂O)(amine)₂(μ-OD)Pt(OD)(amine)₂]²⁺ was detected and for cyclohexylamine, a fourth signal was assigned to a cyclic hydroxo-bridged trimer [(Pt(amine)₂(μ-OD))₃]³⁺. ¹⁹⁵Pt NMR spectroscopy has shown that the concentration of the monomer decreases with time, while the concentration of the dimers increases. Only one product was observed for the trans isomers in neutral pH. The signal was assigned to the monoaqua-monohydroxo species trans-[Pt(amine)₂(D₂O)(OD)]⁺. The ¹³C and ¹H NMR spectra of most of the complexes were measured. All the coupling constants ^2,3J(¹⁹⁵Pt-¹H) and ^2,3J(¹⁹⁵Pt-¹³C) are larger in the cis compounds than in the trans isomers.     

cis- and trans-phytoene in Verticillium agaricinum

cis-Phytoene and trans-phytofluene were identified in illuminated cultures of Verticillium agaricinum in addition to the other carotenoids     

Cis-4-hydroxypipecolic acid and 2,4-cis-4,5-trans-4,5-dihydroxypipecolic acid from Calliandra

cis-4-Hydroxypipecolic acid and 2,4-cis-4,5-trans-4,5-dihydroxypipecolic acid were isolated from leaves of Calliandra pittieri. A system for resolving the eight imino acids isolated from Calliandra is described.