Vicinal Hydroxy Research Articles

Density Functional Theory Study of Deoxydehydration Reaction by TiO2-Supported Monomeric and Dimeric Molybdenum Oxide Catalysts

The development of efficient heterogeneous catalysts for converting biomass into value-added chemical compounds remains at the forefront of catalysis research. Deoxydehydration (DODH) reaction that can transform vicinal hydroxy groups with the cis-configuration to the corresponding C═C bond in a single step is one of the promising techniques, and molybdenum oxide catalysts supported on TiO2 have been reported as an effective catalyst using hydrogen as a reducing agent. Here, using density functional theory calculations, structures of monomeric and dimeric molybdenum oxide catalysts supported on anatase TiO2(101) have been determined, and we decipher the reaction mechanisms of the conversion of 1,4-anhydroerythritol to 2,5-dihydrofuran over these catalysts as a model reaction. We have found that MoO3 and Mo2O5 are the most stable structures for monomeric and dimeric species that exhibit the oxidation states of MoVI and MoV–MoVI, respectively, under the experimental conditions. For monomeric species, it is rather difficult to catalyze DODH reaction due to the instability for MoIV species and also the higher barrier for the C–O bond scission for MoV or MoVI species. For dimeric species, structures with the oxidation state of MoIV–MoV or MoV–MoV that is found in the form of Mo2O4 exhibit promising energy profiles in terms of stability and energy barrier (∼1.0 eV) for the C–O bond dissociation. Considering the experimental facts that MoIV species is responsible for the DODH reaction and Mo–Mo bond is present, the MoIV–MoV structure could be the plausible active species. Our findings would provide useful information for the catalyst design using earth-abundant and less-expensive metal-based catalysts for the DODH reaction.

Complexation of borate with pentitols, hexitols and their derivatives as a functional group of a boron-selective adsorbent

In order to elucidate the characteristics of anchor groups suitable for boron-selective adsorbents, complexation reactions of the borate ion with pentitols, hexitols and their methylamino derivatives were investigated by NMR spectroscopies and DFT calculations. The borate ion bound with these polyols to form various types of complexes, among which the ones binding with vicinal hydroxy groups in an intermediate position of the carbon chain would make a significant contribution to their stability. The threo-form five-membered ring chelate complexes exhibited much higher stabilities compared to the erythro-form ones, which means that the polyol capable of forming more threo-forms and fewer erythro-forms gives a higher affinity toward boron. l-Iditol had the highest affinity toward boron among the studied pentitols and hexitols, because it could form three kinds of threo-form complexes binding at the (C2,C3), (C3,C4) and (C4,C5) positions. Consequently, 1-deoxy-1-methylamino-l-iditol, which is a derivative of l-iditol, will be the best functional group for a boron-selective adsorbent of all the analogous polyol derivatives.

The first total synthesis of rebaudioside R.

With easily available monosaccharides and steviol as starting materials, the first total synthesis of rebaudioside R with a xylosyl core in the C13-OH linked sugar chain was accomplished via two distinct approaches. The first approach features the stepwise installation of branch-sugar residues via an order of C2-OH first and then C3-OH of the xylosyl core, laying a firm foundation for the synthesis of analogues with different branch sugars, while the second route features the introduction of the C13 trisaccharide sugar chain via a convergent strategy, securing the overall synthetic efficiency. Through the synthetic study, the effect of protecting groups (PGs) at the vicinal hydroxy group on the reactivity of OH acceptors was illustrated.

Interpretation of anomeric effect in 2-hydroxytetrahydropyrans based on extensive bond interactions

Recently, exchange repulsion and electron delocalization have been a focus of attention as the origin of the anomeric effect. However, the details of these interactions remain unclear. In this study, to elucidate what exchange repulsion and electron delocalization contribute to anomer stabilities of 2-hydroxytetrahydropyran (2-hydroxy-THP), the electronic structures of the anomers were investigated using bond model analysis. The vicinal bond interactions around the anomeric carbon make the equatorial configuration of the hydroxy group more stable than the axial configuration. Exchange repulsions contribute much to this relative stability of the equatorial configuration. However, exchange repulsion and electron delocalization due to 1,3-diaxial interactions and other interactions involving lone pair electrons of oxygen make the axial configuration more stable overall than the equatorial configuration. The anomeric effect in glucose can also be explained in a manner similar to that in 2-hydroxy-THP. Additionally, interactions between the vicinal hydroxy groups contribute to the stabilization of the axial configuration.

Oxidation of Substituted Catechols at the Air-Water Interface: Production of Carboxylic Acids, Quinones, and Polyphenols.

Anthropogenic activities contribute benzene, toluene, and anisole to the environment, which in the atmosphere are converted into the respective phenols, cresols, and methoxyphenols by fast gas-phase reaction with hydroxyl radicals (HO•). Further processing of the latter species by HO• decreases their vapor pressure as a second hydroxyl group is incorporated to accelerate their oxidative aging at interfaces and in aqueous particles. This work shows how catechol, pyrogallol, 3-methylcatechol, 4-methylcatechol, and 3-methoxycatechol (all proxies for oxygenated aromatics derived from benzene, toluene, and anisole) react at the air-water interface with increasing O3(g) during τc ≈ 1 μs contact time and contrasts their potential for electron transfer and in situ production of HO• using structure-activity relationships. A unifying mechanism is provided to explain the oxidation of the five proxies, which includes the generation of semiquinone radicals. Functionalization in the presence of HO• results in the formation of polyphenols and hydroxylated quinones. Instead, fragmentation produces polyfunctional low molecular weight carboxylic acids after oxidative cleavage of the aromatic bond with two vicinal hydroxy groups to yield substituted cis,cis-muconic acids. The generation of maleinaldehydic, maleic, pyruvic, glyoxylic, and oxalic acids confirms the potential of oxy aromatics to produce light-absorbing aqueous secondary organic aerosols in the troposphere.

Strategies to limit colour changes when fortifying food products with iron

Iron, vitamin A, zinc and iodine have been recognized to be the micronutrients with the largest deficiencies worldwide. Among these, iron is highly reactive and may lead to negatively perceived organoleptic changes in products such as dull colour and off-taste. The colour change originated in fortified fruit-containing food products was confirmed to be the result of the complexation of iron and polyphenols. Phenolic compounds with two or more vicinal hydroxy benzyl moieties in their structure, such as catechols and pyrogallols were investigated for their ability to give bathochromic shift phenomena when mixed with iron salts. Furthermore, strategies for limiting colour development were based on: 1) pH adjustment; 2) saturation of polyphenols with unreactive divalent metal ions; 3) suppression of iron reactivity through complexation. Some of these strategies showed a significant improvement in colour stability, with the best results achieved by the latter. The findings in model systems gave a good insight of the mechanisms involved in colour changes, and results were transferable to iron fortified banana puree.

Synthesis of panaxytriol and its stereoisomers as potential antitumor drugs

An efficient synthesis of panaxytriol and its seven stereoisomers was achieved, and four unnatural diastereomers of 2a were prepared. The key steps involved the opening of vicinal hydroxy epoxides, the stereospecific opening of the epoxides with perchloric acid, and the Cadiot–Chodkiewicz cross-coupling of chiral terminal alkynes with bromoalkynes. Preliminary antitumor activity investigations indicated that some synthetic panaxytriols exhibited promising cytotoxic activity against three human cancer cell lines.

PNA-based DNA assay with attomolar detection limit based on polygalacturonic acid mediated in-situ deposition of metallic silver on a gold electrode

An electrochemical method is described for the ultrasensitive determination of sequence-specific DNA by using polysaccharide-mediated in-situ deposition of metallic silver on a gold electrode. Specifically, a thiolated peptide nucleic acid (PNA) is immobilized on the gold electrode via formation of a self-assembled monolayer. Following hybridization between PNA and target single-stranded DNA (ssDNA), polygalacturonic acid (PGUA) is introduced to the PNA/DNA heteroduplexes via phosphate-zirconium-carboxylate coordination interaction. Next, the vicinal hydroxy groups of the polysaccharide backbone are cleaved and oxidized into aldehyde groups. These act as reductants and convert added silver ions into metallic silver which in-situ deposits on the gold electrode, and then is stripped off electrochemically into a solution of KCl where it is accurately determined by differential pulse voltammetry. Under optimal conditions, this assay exhibits a wide linear response range in that the stripping current is related to the logarithm of the concentration of target ssDNA in the 0.1 fM to 10 pM range, with a detection limit as low as 2.5 aM. The method displays excellent specificity in clearly differentiating mismatched oligonucleotide fragments. We therefore believe that this method has a large potential in terms of genotyping of single-nucleotide polymorphism. Moreover, this kind of signal amplification possesses a very large capability with respect to ultrasensitive quantitation of low-abundant biomarkers.

Modification of guanosine with cyanopropargylic alcohols

Guanosine has been modified with tertiary cyanopropargylic alcohols under mild conditions (1:1.1–2molar ratio, K2CO3, DMF, 20–25°C, 19–50h) to simultaneously give two modifications. The first product (1:1 adduct) is formed by the stereoselective addition of the amide function of the purine ring to the triple bond (38–43% yields), and the second product is the 1:2 adduct, with a second molecule of cyanopropargylic alcohol having reacted with the two vicinal hydroxy groups of the ribose moiety to give a functionalized 1,3-dioxolane ring (29–50% yields).

Intramolecular Glycosidation by Click Reaction Mediated Spacer Generation Followed by Spacer Cleavage

Abstract2‐O‐Propargyl‐substituted glycosyl donors and O‐(2‐azidobenzyl)‐substituted acceptors having a vicinal hydroxy group readily underwent the click reaction. Intramolecular glycosidation with N‐iodosuccinimide/trifluoromethansulfonic acid as the activating system afforded β‐(1–3)‐ and α‐(1–2)‐linked disaccharides as part of 14‐membered macrocycles. Descriptors for these reactions are proposed that consider the donor and acceptor attachment sites and the stereochemistry of the functional groups. Investigation of the influence of 2‐O‐linked 1‐aryl‐1,2,3‐triazol‐4‐ylmethyl groups, as contained in the spacer, on the anomeric selectivity exhibited no anchimeric assistance. In addition, it was shown that the spacer group can be readily cleaved under Birch reduction conditions.

Сhemo- and regioselective modification of adenosine with tertiary cyanopropargylic alcohols

Adenosine reacts with tertiary cyanopropargylic alcohols under mild conditions (K2CO3, DMF, 20–25°C, 4–30h) with 100% chemo- and regioselectivity by the way of two vicinal hydroxy groups of the ribose moiety to afford (in 52–72% yield) a novel family of adenosine cyclic ketals possessing cyano and hydroxyalkyl functions.

ChemInform Abstract: Synthesis of Enantiopure Protected 3-Hydroxy-4-amino Pyrroline N-Oxides.

Abstract The synthesis of new five-membered enantiopure cyclic nitrones bearing protected cis vicinal amino and hydroxy functionalities is reported. The key step was a Mitsunobu reaction, which allowed placement of an azido group, with inversion of configuration, at the reacting centre. Cycloaddition of the novel nitrones to but-3-en-1-ol followed by simple elaboration of the adducts readily afforded protected amino dihydroxy indolizidines.

ChemInform Abstract: Synthesis of Oligopeptides Containing an Oxirane Ring in the Place of a Peptidic Bond

Oligopeptides containing an oxirane ring have recently been identified as inhibitors of a variety of proteases (1-3). These peptidomimetics have the potential to coordinate with metal present in the active site and, after nucleophilic ring opening, irreversibly blocking the enzyme. For this reason, oxirane containing peptidomimetics are good candidates to became transition states analogs or suicide inhibitors with long term efficacy in vivo (3). Synthetic routes to a variety of terminal (4-8) and internal epoxide peptidomimetics (9-11) have been reported but there are no examples of incorporation of such epoxides into oligopeptides. The focus of this chapter will be on the preparation of oligopeptides (up to a three-peptide) containing an epoxide in the place of the peptide bond. The structures prepared here can be identified, using the notation suggested by Spatola (12) as AAxψ[traws-epoxy]-AAy. The general synthetic approach described in this chapter is based on the aldol type reaction of a silylketene thioacetal and a β-amino α-selenyl aldehyde derived from an oligopeptide. This reaction stereoselectively generates a vicinal hydroxy selenide which can be further oxidized to epoxide (Fig. 1). Fig. 1. Retrosynthetic analysis of oxirane peptidomimetrics.

Temporary Carbohydrate Diol Protection with Ester Groups – Orthogonality under Solid‐Phase Oligosaccharide Synthesis Conditions

AbstractFor regioselective deprotection studies under SPOS conditions the glucosamine derivatives 4ab/4ba, 4ac/4ca and 4ad/4da – with Fmoc/PA, Fmoc/Lev or Fmoc/Alloc, respectively, as temporary ester protecting groups at 3‐O and 4‐O – were prepared. Fmoc cleavage with triethylamine in 4ab or 4ba led to PA migration, so the Fmoc/PA pair does not permit regioselective access to the vicinal hydroxy groups. Under the same reaction conditions no Lev migration in 4ac/4ca or Alloc migration in 4ad/4da was observed. Lev removal with hydrazinium acetate in 4ac/4ca and Alloc removal with Pd0 and dimedone as nucleophile in 4ad/4da was also not accompanied by Fmoc migration, so the Fmoc/Lev pair and the Fmoc/Alloc pair can be successfully employed for regioselective access to the 3‐hydroxy or the 4‐hydroxy group, respectively. However, Fmoc cleavage with piperidine in 4ac/4ca led to Lev migration, and the use of a basic nucleophile for Alloc cleavage also led to Fmoc migration in 4ad. 4‐O‐Fmoc protection was also combined with Nap ether protection in 4ea. These two groups could be readily and regioselectively removed, thus providing another useful pair for temporary protection of vicinal diols.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

Antineoplastic Agents. 578. Synthesis of Stilstatins 1 and 2 and Their Water-Soluble Prodrugs

Efficient syntheses of 3,4-methylenedioxy-4',5-dimethoxy-2',3'-dihydroxy-Z-stilbene (stilstatin 1, 2), 3,4,4'-trimethoxy-2',3',5-trihydroxy-Z-stilbene (stilstatin 2, 5), and respective phosphate prodrugs have been summarized. Both 2 and 5 were accessed via a convergent step synthesis using phosphonium bromides 6 and 21 in Wittig reactions with 2,3-bis(tert-butyldimethylsilyloxy)-4'-methoxybenzaldehyde 14. Deprotection of silyl ethers 15 and 26 with TBAF furnished 2 and 5, respectively. Phosphorylation of 2 and 5 afforded the phosphoric acid intermediates 17 and 28 for prodrug development. These phosphoric acid precursors were employed in parallel series of reactions to produce a selection of metal cation prodrug candidates. The biological activities of stilstatins 1 (2) and 2 (5) and their respective prodrugs were evaluated against a panel of one murine (P388) and six human cancer cell lines. Compared to combretastatin A-2 (1), stilstatin 1 (2) has an additional vicinal hydroxy group on the B ring, the presence of which was detrimental to the cancer cell line potency; in vivo, however, compound 2 would be predicted to have greater anticancer activity resulting from the o-quinone mechanism of action analogous to that of combretastatin A-1 (4). The substitution of a hydroxy group for a methoxy group on the A ring of combretastatin A-1 (4), resulting in stilstatin 2 (5), gave rise to a modest level of inhibition consistent with that found for 4 against cancer cell lines.

Peptide‐Bond Synthesis on the Ribosome: No Free Vicinal Hydroxy Group Required on the Terminal Ribose Residue of Peptidyl‐tRNA

OH?—OH no! The generally accepted explanation for peptide transfer in ribosomal peptidyltransferase is that the 2′-OH group of the adenosine residue (Ad) in the P site accepts a proton from the incoming α-amino group and transfers it to the outgoing deacylated tRNA (left). However, it has now been shown that peptide transfer still takes place in the absence of the 2′-hydroxy group (right: proposed alternative mechanism).

Construction of an aminooxy derivative for RNA and DNA labeling

We previously reported that the reactivity of a primary amine is increased by connecting the amine to an aromatic residue with an alkyl linker. This strategy was applied to the construction of a reagent that could form a covalent bond with an aldehyde group. We synthesized a new reagent that consisted of aminooxy and aromatic groups and biotin. The new reagent showed a higher reaction rate to apurinic/apyrimidinic (AP) sites in DNA than a conventional aldehyde-reactive probe (ARP). This reagent also efficiently reacted with 2', 3'-dialdehyde groups, which were generated by the oxidation of the 2', 3'-terminal vicinal hydroxy groups of RNA. The reaction efficiency of the reagent closely related to the structure of the target molecules. We describe the synthesis and chemical properties of the new reagent.

Adsorption Properties of the Natural Carbon–Mineral Sorbent Shungite

Physicochemical methods were used for a comprehensive study of the structural/sorption properties of the natural mineral shungite. It was shown that the composite structure of the mineral determines its main physicochemical characteristics. The isosteric heat of adsorption of water vapour was estimated by calorimetric methods as 70 kJ/mol. This value corresponds to the interaction of water molecules with the vicinal hydroxy groups of the silica constituent of shungite; adsorption heats with values in the range 40-45 kJ/mol are characteristic of the carbon constituent of the sorbent. The heat of adsorption of benzene onto shungite was higher than that for hexane adsorption onto the mineral, indicating that specific interaction occurs between the benzene molecules and the active centres which exist on both the carbon and silica constituents of the mineral. It was shown that the adsorption parameters of shungite with respect to organic compounds which dissociate in an anionic manner suggest that the mineral ...

Post-column deprotonation and complexation in HPLC as a tool for identification and structure elucidation of compounds from natural dyes of historical importance

Flavonoids, anthraquinoids and hydroxybenzoic acids were investigated by reversed phase HPLC analysis with UV and fluorescence detection. Post-column deprotonation with a borax buffer faciliates structure elucidation, particularly with respect to obtaining information about the presence of free 4′- and 3-hydroxy groups in flavonoids and identifying hydroxy groups in 1,4 positions in anthraquinone derivatives. Complexation with aluminum(III) and zirconyl ions was applied in order to lower detection limits. Al(III) is a slow post-column complexing agent whereas the zirconyl ion instantaneously forms fluorescent complexes that can be easily observed. Complexation could be useful in preliminary identification of flavonols and in identification of vicinal hydroxy groups in anthraquinones. The zirconyl ion is also superior to Al(III) in enhancement of fluorescence detection of flavonols, mono- and dihydroxybenzoic acids.

Preparation of [5,6]‐ and [6,6]‐Oxahomofullerene Derivatives and Their Interconversion by Lewis Acid Assisted Reactions of Fullerene Mixed Peroxides

[60]Fullerene mixed peroxides C60(O)(OOtBu)4 exhibit chemo- and regioselective reactions under mild conditions. The epoxy moiety is opened by ferric chloride to form vicinal hydroxy chloride C60Cl(OH)(OOtBu)4. BF3 is also effective in opening the epoxy moiety. The O-O bond of the fullerene mixed peroxide is cleaved by aluminum chloride to form both [5,6]- and [6,6]-fullerene hemiketals (oxohomo[60]fullerenes). A Hock-type rearrangement is proposed for the formation of the hemiketals, in which a fullerene C-C bond is cleaved. Lewis acids and/or visible light can initiate isomerization of the hemiketal isomers. Single-crystal X-ray analysis and theoretical calculations confirmed the results.