Reduction Of Double Bond Research Articles

Introduction of Methyl Groups at C2 and C6 Positions Enhances the Antiangiogenesis Activity of Curcumin.

Curcumin has diverse biological activities, but is known to undergo rapid metabolism via reduction of vinylic double bonds and phase II conjugation. To prevent reductive metabolism of curcumin, we introduced a methyl group at both C2 and C6 positions (compound 1) or at the C2 position (compound 2) of curcumin, creating steric hindrance on double bonds against metabolizing enzymes. As predicted, these compounds were resistant to reduction by alcohol dehydrogenase. Compound 1 was further evaluated for its antiangiogenesis activity in vitro and in vivo. It exhibited significantly greater inhibitory activity than curcumin against endothelial cell migration, invasion, and tube formation. Similarly, the in vivo Matrigel plug assay in C57BL/6 mice showed more pronounced reduction of blood vessels in the plugs containing 1 than those containing curcumin. Moreover, 1 suppressed tumor growth more effectively than curcumin in a U87MG mouse xenograft model by inhibiting angiogenesis. In vivo metabolite analysis by liquid chromatography/mass spectrometry demonstrated that 1 underwent markedly slower reductive metabolism than curcumin. Taken together, our results indicate that 1 has enhanced antiangiogenesis activity and suppression of tumor growth compared with curcumin, reflecting diminished reductive metabolism owing to the introduction of methyl groups at the C2 and C6 positions of curcumin.

Biotransformations of organic compounds mediated by cultures of Aspergillus niger.

Many different organic compounds may be converted by microbial biotransformation to high-value products for the chemical and pharmaceutical industries. This review summarizes the use of strains of Aspergillus niger, a well-known filamentous fungus used in numerous biotechnological processes, for biochemical transformations of organic compounds. The substrates transformed include monocyclic, bicyclic, and polycyclic aromatic hydrocarbons; azaarenes, epoxides, chlorinated hydrocarbons, and other aliphatic and aromatic compounds. The types of reactions performed by A. niger, although not unique to this species, are extremely diverse. They include hydroxylation, oxidation of various functional groups, reduction of double bonds, demethylation, sulfation, epoxide hydrolysis, dechlorination, ring cleavage, and conjugation. Some of the products may be useful as new investigational drugs or chemical intermediates.

In vitro metabolism studies of desoxy-methyltestosterone (DMT) and its five analogues, and in vivo metabolism of desoxy-vinyltestosterone (DVT) in horses.

The positive findings of norbolethone in 2002 and tetrahydrogestrinone in 2003 in human athlete samples confirmed that designer steroids were indeed being abused in human sports. In 2005, an addition to the family of designer steroids called 'Madol' [also known as desoxy-methyltestosterone (DMT)] was seized by government officials at the US-Canadian border. Two years later, a positive finding of DMT was reported in a mixed martial arts athlete's sample. It is not uncommon that doping agents used in human sports would likewise be abused in equine sports. Designer steroids would, therefore, pose a similar threat to the horseracing and equestrian communities. This paper describes the in vitro metabolism studies of DMT and five of its structural analogues with different substituents at the 17α position (RH, ethyl, vinyl, ethynyl and 2 H3 -methyl). In addition, the in vivo metabolism of desoxy-vinyltestosterone (DVT) in horses will be presented. The in vitro studies revealed that the metabolic pathways of DMT and its analogues occurred predominantly in the A-ring by way of a combination of enone formation, hydroxylation and reduction. Additional biotransformation involving hydroxylation of the 17α-alkyl group was also observed for DMT and some of its analogues. The oral administration experiment revealed that DVT was extensively metabolised and the parent drug was not detected in urine. Two in vivo metabolites, derived respectively from (1) hydroxylation of the A-ring and (2) di-hydroxylation together with A-ring double-bond reduction, could be detected in urine up to a maximum of 46 h after administration. Another in vivo metabolite, derived from hydroxylation of the A-ring with additional double-bond reduction and di-hydroxylation of the 17α-vinyl group, could be detected in urine up to a maximum of 70 h post-administration. All in vivo metabolites were excreted mainly as glucuronides and were also detected in the in vitro studies. Copyright © 2015 John Wiley & Sons, Ltd.

Biotransformation of Steroids and Flavonoids by Cultures of Aspergillus niger.

Steroids are derivatives of the triterpenoid squalene, containing three fused cyclohexane rings and a cyclopentane ring, and flavonoids are derivatives of L-phenylalanine, containing two aromatic rings joined by a three-carbon bridge that may form part of a heterocyclic ring. A great variety of steroids and flavonoids are produced by plants, and many additional steroids are produced by animals or fungi. Because these compounds have many nutritional and pharmaceutical values, and many of them cannot be produced by chemical synthesis, biotechnological processes are being developed that use cultures of Aspergillus niger and other fungi to transform steroids and flavonoids to a variety of metabolites. These biochemical reactions, including hydroxylation, dehydrogenation, O-methylation, demethylation, cleavage of rings, epoxide hydrolysis, double bond reduction, and others, may be used for the production of higher-value compounds.

Unraveling the interactions between cold atmospheric plasma and skin-components with vibrational microspectroscopy.

Using infrared and Raman microspectroscopy, the authors examined the interaction of cold atmospheric plasma with the skin's built-in protective cushion, the outermost skin layer stratum corneum. Following a spectroscopic analysis, the authors could identify four prominent chemical alterations caused by plasma treatment: (1) oxidation of disulfide bonds in keratin leading to a generation of cysteic acid; (2) formation of organic nitrates as well as (3) of new carbonyl groups like ketones, aldehydes and acids; and (4) reduction of double bonds in the lipid matter lanolin, which resembles human sebum. The authors suggest that these generated acidic and NO-containing functional groups are the source of an antibacterial and regenerative environment at the treatment location of the stratum corneum. Based upon the author's results, the authors propose a mechanistic view of how cold atmospheric plasmas could modulate the skin chemistry to produce positive long-term effects on wound healing: briefly, cold atmospheric plasmas have the potential to transform the skin itself into a therapeutic resource.

Development and Evaluation of a Borohydride-palladium System for Selective Reduction of the C=C Bond of α,β-unsaturated Carbonyl Compounds

Selective reduction of the carbon-carbon double bond of α,β-unsaturated carbonyl compounds is most commonly and reliably effected using a palladium metal catalyst together with molecular hydrogen from a pressurized tank. Sodium borohydride, like other hydrides, is ordinarily associated with reduction of the more polarized carbonyl of such compounds. However, we have developed an alternative means of employing sodium borohydride in combination with palladium metal to selectively reduce the carbon-carbon double bonds of these compounds. In this survey study, we introduce sodium borohydride as an alternative hydrogen source for such selective, palladium-catalyzed reductions. We also compare the results of this new, heterogeneous borohydride-palladium method with that of traditional palladium-catalyzed hydrogenation. A third method using only sodium borohydride with no palladium is included for comparison.

Continuous flow reduction of artemisinic acid utilizing multi-injection strategies-closing the gap towards a fully continuous synthesis of antimalarial drugs.

One of the rare alternative reagents for the reduction of carbon-carbon double bonds is diimide (HN=NH), which can be generated in situ from hydrazine hydrate (N2H4⋅H2O) and O2. Although this selective method is extremely clean and powerful, it is rarely used, as the rate-determining oxidation of hydrazine in the absence of a catalyst is relatively slow using conventional batch protocols. A continuous high-temperature/high-pressure methodology dramatically enhances the initial oxidation step, at the same time allowing for a safe and scalable processing of the hazardous reaction mixture. Simple alkenes can be selectively reduced within 10-20 min at 100-120 °C and 20 bar O2 pressure. The development of a multi-injection reactor platform for the periodic addition of N2H4⋅H2O enables the reduction of less reactive olefins even at lower reaction temperatures. This concept was utilized for the highly selective reduction of artemisinic acid to dihydroartemisinic acid, the precursor molecule for the semisynthesis of the antimalarial drug artemisinin. The industrially relevant reduction was achieved by using four consecutive liquid feeds (of N2H4⋅H2O) and residence time units resulting in a highly selective reduction within approximately 40 min at 60 °C and 20 bar O2 pressure, providing dihydroartemisinic acid in ≥93% yield and ≥95% selectivity.

Vibrational circular dichroism (VCD), VCD exciton coupling, and X-ray determination of the absolute configuration of an α,β-unsaturated germacranolide.

The absolute configuration of was deduced by vibrational circular dichroism together with the evaluation of the Flack and Hooft X-ray parameters. Vibrational circular dichroism exciton coupling, using the carbonyl group signals, confirmed the absolute configuration of . In addition, sodium borohydride reduction of the 11,13-double bond of 6-epi-desacetyllaurenobiolide () yields an almost equimolecular mixture of C11 epimers, while reduction of the same double bond of 6-epi-laurenobiolide () provided almost exclusively the (11S) diastereoisomer .

Iron-Sulfur Cluster-dependent Catalysis of Chlorophyllide a Oxidoreductase from Roseobacter denitrificans

Bacteriochlorophyll a biosynthesis requires the stereo- and regiospecific two electron reduction of the C7-C8 double bond of chlorophyllide a by the nitrogenase-like multisubunit metalloenzyme, chlorophyllide a oxidoreductase (COR). ATP-dependent COR catalysis requires interaction of the protein subcomplex (BchX)2 with the catalytic (BchY/BchZ)2 protein to facilitate substrate reduction via two redox active iron-sulfur centers. The ternary COR enzyme holocomplex comprising subunits BchX, BchY, and BchZ from the purple bacterium Roseobacter denitrificans was trapped in the presence of the ATP transition state analog ADP·AlF4(-). Electron paramagnetic resonance experiments revealed a [4Fe-4S] cluster of subcomplex (BchX)2. A second [4Fe-4S] cluster was identified on (BchY/BchZ)2. Mutagenesis experiments indicated that the latter is ligated by four cysteines, which is in contrast to the three cysteine/one aspartate ligation pattern of the closely related dark-operative protochlorophyllide a oxidoreductase (DPOR). In subsequent mutagenesis experiments a DPOR-like aspartate ligation pattern was implemented for the catalytic [4Fe-4S] cluster of COR. Artificial cluster formation for this inactive COR variant was demonstrated spectroscopically. A series of chemically modified substrate molecules with altered substituents on the individual pyrrole rings and the isocyclic ring were tested as COR substrates. The COR enzyme was still able to reduce the B ring of substrates carrying modified substituents on ring systems A, C, and E. However, substrates with a modification of the distantly located propionate side chain were not accepted. A tentative substrate binding mode was concluded in analogy to the related DPOR system.

A facile and convenient synthesis and photovoltaic characterization of novel thieno[2,3-b]indole dyes for dye-sensitized solar cells

Two novel dyes IK-1,2 bearing the 8-alkyl-8H-thieno[2,3-b]indole unit as an electron-donating part of the push–pull system have been designed and prepared, as promising sensitizers for solar cells. The key steps of the synthesis involve the crotonic condensation of 1-alkylisatins with 2-acetylthiophene, followed by reduction of the CC double bond and further cyclization through the Paal–Knorr reaction with the Lawesson reagent, thus leading to the formation of 2-(thien-2-yl) substituted thieno[2,3-b]indole derivatives. The optical and electrochemical properties of these dyes have been investigated by using spectrophotometry and cyclic voltammetry respectively, while their photovoltaic performance was evaluated by a device fabrication study. The DSSCs based on IK-1 and IK-2 have demonstrated an efficiency of η=0.37% (FF=73%) and η=0.79% (FF=69%) under 100mWcm−2 simulated AM 1.5G solar irradiation, respectively.

ChemInform Abstract: A Versatile Synthesis of “Tafuramycin A”: A Potent Anticancer and Parasite Attenuating Agent.

AbstractThe improved synthesis of tafuramycin A (I) includes a regioselective bromination step, a controlled aryl radical alkene cyclization to prevent dechlorination, and a new protection/deprotection method to avoid double bond reduction of the furan ring during deprotection of the benzyl group.

Reduction of N-allylamides by LiAlH4: unexpected attack of the double bond with mechanistic studies of product and byproduct formation.

The reduction of secondary allyl amides with LiAlH4 can lead to a concomitant reduction of the double bond. Previously, an excess of LiAlH4 in hazardous solvents was used for the reduction. This work discusses optimized reaction conditions in tBuOMe as a safe solvent, with only a 1.5-fold excess of LiAlH4, without reduction of the double bond in most cases. (1)H and (2)D NMR spectroscopic studies give evidence for the mechanism of the reduction of the amide as well as the double bond: Amide reduction generally precedes double bond reduction. Sterically hindered allylamides are an exception. They are reduced considerably more slowly at higher temperatures, and double bond reduction is observed before amide reduction has gone to completion.

Ring-closing metathesis and glycosylation reactions: synthesis and biophysical studies of polyether-linked carbohydrate-based macrocyclic nucleosides.

Bis-, tris-, and tetrakisuracil-substituted 12-, 13-, 17-, and 21-membered macrocyclic nucleoside analogues with polyether linkages, including C2-symmetric molecules, have been synthesized through coupling of two appropriately allylated sugar derivatives, derived from D-glucose, followed by a sequential ring-closing metathesis reaction using Grubbs catalysts, double-bond reduction, and nucleoside base insertion under Vorbrüggen reaction conditions. Spectroscopic studies on the interaction of these nucleoside analogues with small molecules, such as the alkaloids berberine and palmatine and the DNA intercalator ethidium bromide, revealed a change in the absorbance and fluorescence of the small molecules suggesting the potential use of these nucleoside molecules as a carrier of small molecules in biological systems. Circular dichroism studies indicated that the complexes of the nucleosides with small molecules undergo aggregation/self-organization. This has been further evidenced by a SEM experiment showing the binding of berberine with one of the nucleoside derivatives, which confirms the occurrence of secondary structure reorganization.

ChemInform Abstract: Organocatalytic Strategies for Enantioselective Metal‐Free Reductions

AbstractReview: 107 refs.

The aldo-keto reductases (AKRs): Overview

The aldo-keto reductase (AKR) protein superfamily contains >190 members that fall into 16 families and are found in all phyla. These enzymes reduce carbonyl substrates such as: sugar aldehydes; keto-steroids, keto-prostaglandins, retinals, quinones, and lipid peroxidation by-products. Exceptions include the reduction of steroid double bonds catalyzed by AKR1D enzymes (5β-reductases); and the oxidation of proximate carcinogen trans-dihydrodiol polycyclic aromatic hydrocarbons; while the β-subunits of potassium gated ion channels (AKR6 family) control Kv channel opening. AKRs are usually 37kDa monomers, have an (α/β)8-barrel motif, display large loops at the back of the barrel which govern substrate specificity, and have a conserved cofactor binding domain. AKRs catalyze an ordered bi bi kinetic mechanism in which NAD(P)H cofactor binds first and leaves last. In enzymes that favor NADPH, the rate of release of NADP+ is governed by a slow isomerization step which places an upper limit on kcat. AKRs retain a conserved catalytic tetrad consisting of Tyr55, Asp50, Lys84, and His117 (AKR1C9 numbering). There is conservation of the catalytic mechanism with short-chain dehydrogenases/reductases (SDRs) even though they show different protein folds. There are 15 human AKRs of these AKR1B1, AKR1C1–1C3, AKR1D1, and AKR1B10 have been implicated in diabetic complications, steroid hormone dependent malignancies, bile acid deficiency and defects in retinoic acid signaling, respectively. Inhibitor programs exist world-wide to target each of these enzymes to treat the aforementioned disorders. Inherited mutations in AKR1C and AKR1D1 enzymes are implicated in defects in the development of male genitalia and bile acid deficiency, respectively, and occur in evolutionarily conserved amino acids. The human AKRs have a large number of nsSNPs and splice variants, but in many instances functional genomics is lacking. AKRs and their variants are now poised to be interrogated using modern genomic and informatics approaches to determine their association with human health and disease.

Synthesis and electrochemical investigation of chromium(0) ferrocenyl-substituted carbene complexes

The series [(CO)5CrC(R)Fc], (1, R=OEt; 2, R=NHnBu) as well as [(OC)5CrC(R)Fc′(R)CCr(CO)5], (3, R=OEt; 4, R=NHnPr) of mono- and biscarbene chromium(0) complexes with Fc=FeII(C5H5)(C5H4) and Fc′=FeII(C5H4)2, were synthesized and characterized spectroscopically, electrochemically and computationally. Electrochemical studies on the new aminocarbene complexes revealed that 2 and 4 are oxidized (and reduced) at lower potential than the EtO derivatives 1 and 3 while the biscarbene complexes 3 and 4 provided evidence for interaction between different redox sites, including the Cr-centers. The Cr0/I couples are electrochemically reversible with the difference in formal potentials ΔE°′ for the consecutive oxidations of the chromium carbene entities being 151 and 105mV in 3 and 4, respectively. Computational and electrochemical results were mutually consistent in showing unambiguously that the Cr(0) center is oxidized before the ferrocenyl group in the carbene complexes 2, 3 and 4. Electrochemical experiments on 1 were also consistent with this redox sequence of events, but differently, our calculations suggest that for 1, the ferrocenyl group may be oxidized before Cr(0) oxidation. The ethoxycarbenes 1 and 3 also showed a carbene double bond reduction to an anion radical, −CrC, while the new aminocarbene 4 was the only derivative to show irreversible Cr(I) oxidation to Cr(II) within the potential window of the solvent.

Rate of steroid double-bond reduction catalysed by the human steroid 5β-reductase (AKR1D1) is sensitive to steroid structure: implications for steroid metabolism and bile acid synthesis.

Human AKR1D1 (steroid 5β-reductase/aldo-keto reductase 1D1) catalyses the stereospecific reduction of double bonds in Δ4-3-oxosteroids, a unique reaction that introduces a 90° bend at the A/B ring fusion to yield 5β-dihydrosteroids. AKR1D1 is the only enzyme capable of steroid 5β-reduction in humans and plays critical physiological roles. In steroid hormone metabolism, AKR1D1 serves mainly to inactivate the major classes of steroid hormones. AKR1D1 also catalyses key steps of the biosynthetic pathway of bile acids, which regulate lipid emulsification and cholesterol homoeostasis. Interestingly, AKR1D1 displayed a 20-fold variation in the kcat values, with steroid hormone substrates (e.g. aldosterone, testosterone and cortisone) having significantly higher kcat values than steroids with longer side chains (e.g. 7α-hydroxycholestenone, a bile acid precursor). Transient kinetic analysis revealed striking variations up to two orders of magnitude in the rate of the chemistry step (kchem), which resulted in different rate determining steps for the fast and slow substrates. By contrast, similar Kd values were observed for representative fast and slow substrates, suggesting similar rates of release for different steroid products. The release of NADP+ was shown to control the overall turnover for fast substrates, but not for slow substrates. Despite having high kchem values with steroid hormones, the kinetic control of AKR1D1 is consistent with the enzyme catalysing the slowest step in the catabolic sequence of steroid hormone transformation in the liver. The inherent slowness of the conversion of the bile acid precursor by AKR1D1 is also indicative of a regulatory role in bile acid synthesis.

Iridium-catalyzed H/D exchange: ligand complexes with improved efficiency and scope.

Hydrogen isotope exchange (HIE) is one of the most attractive tools for the introduction of deuterium or tritium to an organic compound. Herein, iridium complexes with N,P-ligands, highly active catalysts for asymmetric double bond reductions, have been tested for their HIE capabilities. Electron-rich ligands, containing dicyclohexylphosphines or phosphinites, have been identified as excellent ligands for efficient deuterium incorporation. Substrates with strong directing groups, that is, pyridines, ketones, and amides, as well as weak ligating units, such as, nitro, sulfones, and sulfonamides, could be labeled efficiently. With the addition of tris(pentafluorophenyl) borane to the reaction mixture, also highly deactivating nitrile substituents were well tolerated in the reaction. Based on the excellent results obtained with the chiral ThrePhox ligand, a structurally simpler, achiral ligand was developed. The iridium complex containing this ligand, proved to be a powerful catalyst for HIE reactions.

Constructing Tailored Isoprenoid Products by Structure-Guided Modification of Geranylgeranyl Reductase

The archaeal enzyme geranylgeranyl reductase (GGR) catalyzes hydrogenation of carbon-carbon double bonds to produce the saturated alkyl chains of the organism's unusual isoprenoid-derived cell membrane. Enzymatic reduction of isoprenoid double bonds is of considerable interest both to natural products researchers and to synthetic biologists interested in the microbial production of isoprenoid drug or biofuel molecules. Here we present crystal structures of GGR from Sulfolobus acidocaldarius, including the structure of GGR bound to geranylgeranyl pyrophosphate (GGPP). The structures are presented alongside activity data that depict the sequential reduction of GGPP to H6GGPP via the intermediates H2GGPP and H4GGPP. We then modified the enzyme to generate sequence variants that display increased rates of H6GGPP production or are able to halt the extent of reduction at H2GGPP and H4GGPP. Crystal structures of these variants not only reveal the structural bases for their altered activities; they also shed light onto the catalytic mechanism employed.

Recombinant S. cerevisiae expressing Old Yellow Enzymes from non-conventional yeasts: an easy system for selective reduction of activated alkenes.

BackgroundOld Yellow Enzymes (OYEs) are flavin-dependent enoate reductases (EC 1.6.99.1) that catalyze the stereoselective hydrogenation of electron-poor alkenes. Their ability to generate up to two stereocenters by the trans-hydrogenation of the C = C double bond is highly demanded in asymmetric synthesis. Isolated redox enzymes utilization require the addition of cofactors and systems for their regeneration. Microbial whole-cells may represent a valid alternative combining desired enzymatic activity and efficient cofactor regeneration. Considerable efforts were addressed at developing novel whole-cell OYE biocatalysts, based on recombinant Saccharomyces cerevisiae expressing OYE genes.ResultsRecombinant S. cerevisiae BY4741∆Oye2 strains, lacking endogenous OYE and expressing nine separate OYE genes from non-conventional yeasts, were used as whole-cell biocatalysts to reduce substrates with an electron-poor double bond activated by different electron-withdrawing groups. Ketoisophorone, α-methyl-trans-cinnamaldehyde, and trans-β-methyl-β-nitrostyrene were successfully reduced with high rates and selectivity. A series of four alkyl-substituted cyclohex-2-enones was tested to check the versatility and efficiency of the biocatalysts. Reduction of double bond occurred with high rates and enantioselectivity, except for 3,5,5-trimethyl-2-cyclohexenone. DFT (density functional theory) computational studies were performed to investigate whether the steric hindrance and/or the electronic properties of the substrates were crucial for reactivity. The three-dimensional structure of enoate reductases from Kluyveromyces lodderae and Candida castellii, predicted through comparative modeling, resulted similar to that of S. cerevisiae OYE2 and revealed the key role of Trp116 both in substrate specificity and stereocontrol. All the modeling studies indicate that steric hindrance was a major determinant in the enzyme reactivity.ConclusionsThe OYE biocatalysts, based on recombinant S. cerevisiae expressing OYE genes from non-conventional yeasts, were able to differently reduce the activated double bond of enones, enals and nitro-olefins, exhibiting a wide range of substrate specificity. Moreover whole-cells biocatalysts bypassed the necessity of the cofactor recycling and, tuning reaction parameters, allowed the synthetic exploitation of endogenous carbonyl reductases. Molecular modeling studies highlighted key structural features for further improvement of catalytic properties of OYE enzymes.