Diol Units Research Articles

Investigation of 44-methylgambierone reactivity with periodate: Structural reassignment, solvent instability and formation of a furanoid analogue

Gambierones are sulfated polyethers produced by benthic dinoflagellates in the genera Gambierdiscus, Coolia and Fukuyoa. While relative toxicity data for gambierones suggests they are low compared with ciguatoxin analogues, gambierones have been suggested for use as marker compounds for environmental monitoring programs for the presence of Gambierdiscus in marine waters. The published structure of gambierone and analogues of it, including 44-methylgambierone (44-MeGAM), have been reported to possess 1,2- and 4,5-cis diols, while only the 1,2- diol unit has been shown to undergo periodate oxidation. An in-depth analysis of previously reported NMR data for 44-MeGAM in CD3OD showed that the C-4 stereochemistry of 44-MeGAM and other gamberiones was mis-assigned, that the 4-CH2-CHOH-CH2OH and OH groups are equatorially and axially oriented, respectively, rather than vice versa as previously reported. This re-examination of existing 44-MeGAM NMR data also showed that its C-12 and C-13 assignments (and those for other gambierones) should be reversed. In an effort to better understand the C-4 stereochemical and periodate reaction characteristics of gambierones (C-4 is an epimerizable hemiacetal carbon), additional NMR data was acquired in D6-DMSO. Unexpectedly, progressive conversion of 44-MeGAM to a long-term stable ring-A furanoid analogue was observed. A subsequent series of microscale stability trials identified several solvents that affected the solution-stability of 44-MeGAM, and these findings should be taken into consideration during isolation, handling, storage and bioassay evaluations of gambierones in future studies.

Introduction of a Chiral Biphenanthrene-Diol Unit to Achieve Circularly Polarized Thermally Activated Delayed Fluorescence.

Circularly polarized luminescence (CPL) materials are promising candidates for future display technology. However, such highly efficient emitters suffer from the issues of difficult chiral separation and low photoluminescence quantum yield (PLQY). In this work, the chiral 4,4'-biphenanthrene-3,3'-diol (BIPOL) unit was introduced into a thermally activated delayed fluorescence (TADF) framework for the first time. We presented two series of enantiomers, R/S-o-DCzBPNCN and R/S-p-DCzBPNCN, and the synthesis of enantiopure BIPOL can be prepared via normal column chromatography. Notably, o-DCzBPNCN showed narrow singlet-triplet gap of 0.05 eV, efficient TADF, and high PLQYs of 82 % in doped films. In addition, R/S-o-DCzBPNCN exhibited high luminescence dissymmetry factor (gPL ) values of -1.94×10-2 /+1.91×10-2 in doped films. The strategy of BIPOL introduction offers a new approach to organic emitters with stereospecific synthesis, TADF, and chiroptical properties.

Metal ion-manipulated afterglow on rhodamine 6G derivative-doped room-temperature phosphorescent PVA films.

The long-lived room-temperature phosphorescence (RTP) originating from thiophene boronate polyvinyl alcohol (PVA) has enabled the creation of metal-ion-responsive RTP films doped with spirolactam ring-containing rhodamine 6G (1). In this study, RTP-active PVA films, namely, TDB@PVA and ATB@PVA, were prepared through boronate esterification of thiophene-2,5-diboronic acid (TDB) and 5-acetylthiophene-2-boronic acid (ATB) with the diol units of PVA. The delayed emission properties were evaluated, revealing an emission band at 477nm with a turquoise afterglow for TDB@PVA and at 510nm with a green afterglow for ATB@PVA after UV light irradiation ceased. The photophysical properties were assessed using TD-DFT and DFT calculations at the B3LYP/cc-pVDZ level. N-(rhodamine-6G)lactam dye with a salicylimine unit (1) was doped into the RTP-based PVA films, producing a multicolored afterglow upon the addition of metal ions. This phenomenon is explained by a triplet-to-singlet Förster-type resonance energy transfer process from the cross-linked thiophene boronate in PVA to the metal-ion-activated colored form of 1. This photophysical feature finds applicability in encryption techniques. Notably, the reversible metal-ligand coordination of 1 in the PVA system enabled a write/erase information process.

Regiospecific Synthesis of a Reprocessable Galactan-Mimic via Topochemical Polymerization

We synthesized a designed monomer with azide and alkyne units that mimic α-d-galactose for topochemical azide-alkyne cycloaddition polymerization to produce a cross-linkable galactan-mimic. The monomer molecules pre-organize in the crystals in a linear head-to-tail fashion, with the reactive units properly aligned for topochemical reaction. When the monomer crystals are heated, they undergo regiospecific topochemical azide-alkyne cycloaddition polymerization, resulting in a galactan-mimic with two vicinal diol units per repeating unit. We covalently cross-linked this galactan-mimic using bis-dioxaborolane as the dynamic covalent cross-linker. When compared to the parent galactan-mimic, the mesoporous cross-linked polymer had a sevenfold increase in porosity, a 200-fold increase in particle size, and higher thermal stability. We demonstrated that by varying the temperature, the extent of cross-linking and thus particle size can be reversibly tuned. Our findings show that topochemical polymerization can be used to create polymers with improved properties from monomers derived from naturally available feedstock materials.

Stepwise photoassisted decomposition of carbohydrates to H2

Stepwise photoassisted decomposition of carbohydrates to H2

N-Fluoroalkylated Morpholinos - a New Class of Nucleoside Analogues.

The first concise and efficient synthesis of some fluorine-containing morpholino nucleosides has been developed. One synthetic strategy was based on the oxidative ring cleavage of the vicinal diol unit of uridine, cytidine adenosine and guanosine derivatives, followed by cyclisation of the dialdehyde intermediates by double reductive amination with fluorinated primary amines to obtain various N-fluoroalkylated morpholinos. Another approach involved cyclisation of the diformyl intermediates with ammonia source, followed by dithiocarbamate formation and desulfurization-fluorination with diethylaminosulfur trifluoride yielding the corresponding morpholine-based nucleoside analogues with a N-CF3 element in their structure.

Expansion and Compression of a Helicate with Central Diol Units as Stereocontrolling Moieties

The dicatechol ester ligand 2-H4 forms the compressed helicate Li4[(2)3 Ti2] which upon removal of the internally bound lithium cations expands. In the compressed form, the chiral diol units control the stereochemistry of the complex which is lost upon expansion of the system.

BINOL as a chiral element in mechanically interlocked molecules.

In this minireview we present the use of the axially chiral 1,1'-binaphthyl-2,2'-diol (BINOL) unit as a stereogenic element in mechanically interlocked molecules (MIMs). We describe the synthesis and properties of such BINOL-based chiral MIMs, together with their use in further diastereoselective modifications, their application in asymmetric catalysis, and their use in stereoselective chemosensing. Given the growing importance of mechanically interlocked molecules and the key advantages of the privileged chiral BINOL backbone, we believe that this research area will continue to grow and deliver many useful applications in the future.

Renewable Furfural-Based Polyesters Bearing Sulfur-Bridged Difuran Moieties with High Oxygen Barrier Properties

With the goal of achieving high barrier with bio-based materials, for example, for packaging applications, a series of novel furfural-based polyesters bearing sulfide-bridged difuran dicarboxylic acid units with high oxygen barrier properties were synthesized and characterized. For the novel poly(alkylene sulfanediyldifuranoate)s, a 11.2–1.9× higher barrier improvement factor compared to amorphous poly(ethylene terephthalate) was observed which places the novel polyesters in the top class among previously reported 2,5-furandicarboxylic acid (FDCA) and 2,2′-bifuran-based polyesters. Titanium-catalyzed polycondensation reactions between the novel synthesized monomer, dimethyl 5,5′-sulfanediyldi(furan-2-carboxylate), and four different diols, ethylene glycol, 1,3-propanediol, 1,4-butanediol, and 1,5-pentanediol, afforded difuran polyesters with high intrinsic viscosities (0.76–0.90 dL/g). These polyesters had good thermal stability, decomposing at 342–363 and 328–570 °C under nitrogen and air, respectively, which allowed processing them into free-standing films via melt-pressing. In tensile testing of the film specimens, tensile moduli in the range of 0.4–2.6 GPa were recorded, with higher values observed for the polyesters with shorter diol units. Interestingly, besides the low oxygen permeability, the renewable sulfide-bridged furan monomer also endowed the polyesters with slight UV shielding effect, with cutoff wavelengths of ca. 350 nm, in contrast to FDCA-based polyesters, which lack significant UV light absorption at over 300 nm.

An enzyme-free monosaccharide fuel cell using bio-mimetically hemin-intercalated polydopamine as anode and cathode catalysts

A hemin-intercalated 5,6-indolequinone-containing polydopamine hybrid (H-PDA) is co-assembled onto carbon-based electrodes by layer-by-layer electrodeposition methods for monosaccharide fuel cells with neutral aqueous electrolytes bio-inspired by quinohemoproteins. Hemin can promote dopamine (DA) electro-polymerization to achieve H-PDA that show synergistically enhanced electrocatalysis to the oxidation of three monosaccharides by oxygen upon incorporation of ascorbate (AA) or nicotinamide adenine dinucleotide (NADH). The electrocatalytic oxidation rate of glucose (Glc) on H-PDA is larger than that of mannose (Man) and galactose (Gal) ascribed to bi-dentate interactions of diol units at C2/C3 (Man) or C3/C4 (Gal) sites with PDA. On the other hand, the modification of H-PDA onto carbon nanotubes can increase largely the oxygen reduction rate and make the onset potential shifted positively, representing oxygen reduction reactions enhanced by non-enzyme and non-precious metal electrocatalysts. The simultaneous use of H-PDA as anode and cathode catalysts can improve remarkably single-compartment or two-compartment glucose fuel cell performance, leading to a 4.3-fold or 13.0-fold increase in the maximum power density. This study provides new insights into the selective oxidation of monosaccharides by oxygen in fuel cell under approximately neutral conditions using bio-mimetic electrocatalysts.

Selective synthesis of glyceryl monolaurate intensified by boric acid based deep eutectic solvent

Glyceryl monolaurate (GML), as one of widely used industrial chemicals, can be synthesized via Fischer esterification of lauric acid (LA) and glycerol (GL). In this work, we screened boric acid-based deep eutectic solvent (DES) formed from tetrapropylammonium bromide (TPAB) and boric acid to intensify the selective Fischer esterification through conductor-like screening model for realistic solvents (COSMO-RS) theory. The solid liquid equilibrium (SLE) phase behavior, hydrogen bond formation process, and thermal stability of the DES were characterized by differential scanning calorimetry (DSC), Fourier transform infrared spectrometry (FT-IR), and thermogravimetric analyzer (TGA). The results verified that equimolar TPAB and boric acid formed DES [TPAB:B(OH)3] with the lowest freezing point and very good thermal stability could efficiently intensify the Fischer esterification of GL and LA to GML. The hydrogen bond accepter TPAB of the DES made the esterification system homogeneous, which promoted the selective esterification process. In addition, the hydrogen bond donor B(OH)3 of the [TPAB:B(OH)3] combined with diol unit of GL to cyclic boric esters and led to a special selective space effect, which also improved the selectivity to GML. Thus, the esterification intensified of GL and LA by 20 wt% DES achieved GML selectivity of 85.7 % and yield of 76.4 % under the optimal reaction conditions. The esterification kinetics suggested the reaction followed pseudo-second-order model and the reaction activation energy was 33.98 kJ mol−1, similar to and/or lower than those reported works. Furthermore, DES and unreacted glycerol were readily recovered and reused through temperature controlled gravity-based separation due to the ability of homogeneity under reaction conditions and splitting phase behavior during the DES recovery. The results can expand the boric acid-based DESs for other potential intensification applications.

Enantioselective Total Synthesis of (+)-EBC-23, a Potent Anticancer Agent from the Australian Rainforest.

We describe here an enantioselective synthesis of (+)-EBC-23, a potent anticancer agent from the Australian rainforest. Our convergent synthesis features a [3+2] dipolar cycloaddition of an olefin-bearing 1,3-syn diol unit and an oxime segment containing 1,2-syn diol functionality as the key step. The segments were synthesized in a highly enantioselective manner using Noyori asymmetric hydrogenation of a β-keto ester and Sharpless asymmetric dihydroxylation of an α,β-unsaturated ester. Cycloaddition provided isoxazoline derivative which upon hydrogenolysis furnished the β-hydroxy ketone expediently. A one-pot, acid-catalyzed reaction removed the isopropylidene group, promoted spirocyclization, constructed the complex spiroketal lactone core, and furnished EBC-23 and its C11 epimer. The C11 epimer was also converted to EBC-23 by chemoselective oxidation and reduction sequence. The present synthesis provides convenient access to this family of natural products in an efficient manner.

Poly(1,4-butylene -co-1,4-cyclohexanedimethylene 2,5-furandicarboxylate) copolyester: Potential bio-based engineering plastic

Poly(1,4-butylene-co-1,4-cyclohexanedimethylene 2,5-furandicarboxylate) (PBCFs) was synthesized from bio-based 2,5-furandicarboxylic acid (FDCA), 1,4-butanediol (BDO) and 1,4-cyclohexanedimethanol (CHDM). The GPC showed that the number average molecular weight (Mn) of PBCFs were in the range of 38400–44200 g/mol and the average molecular weight (Mw) varied from 83,000 to 94,800 g/mol with the polydispersity index of 2.22–2.33. The chemical structures, compositions and sequence distributions of PBCFs were confirmed by 1H NMR and 13C NMR. Their thermal properties and crystallization behavior were investigated by Differential Scanning Calorimeter (DSC). Results showed that the glass transition temperature (Tg) and melting temperature (Tm) of poly(butylene 2,5-furandicarboxylate) (PBF) were increased from 38 and 171.8 °C to 65.8 and 211.7 °C for PBCF-68, respectively. Furthermore, the strength and modulus were increased from 44 and 950 MPa for PBF to 69 and 1360 MPa for PBCF-68 with the mole percentage of CHDM units of 68% in diol units. PBCFs demonstrated much better thermo-mechanical properties when compared with those of PBF, which might be used as the bio-based engineering plastic or excellent packaging materials with high transparency and good gas barrier properties.

Total Synthesis of (−)‐Lepadin F based on a Stereoselective Diels–Alder Reaction Controlled by a Ketolactone‐type Dienophile

An efficient approach to the type III lepadin alkaloids (lepadins F and G) has been developed through a key Diels-Alder reaction, in which a novel ketolactone-type dienophile with chiral diol unit is employed to generate the desirable all-cis-trisubstituted cyclohexene with excellent regio- and stereoselectivity control. The subsequent selective sulfonylation of the diol unit followed by SN 2 cyclization under hydrogenation conditions could construct the substituted piperidine ring. By using this approach, (-)-lepadin F is synthesized from ethyl l-lactate for the first time.

Spiroconjugated Donor-σ-Acceptor Charge-Transfer Dyes: Effect of the π-Subsystems on the Optoelectronic Properties.

Charge-transfer-based materials with intramolecular donor-acceptor structures are attractive for technological applications. Herein, a series of donor-σ-acceptor dyes has been prepared in a modular approach. The design of these intramolecular charge-transfer dyes is based on the concept of spiroconjugation, which leads to unique materials with special optical properties. The optical transitions are based on intramolecular charge transfer, as shown by solvatochromic measurements and density functional theory (DFT) calculations. Crystallographic, computational, electrochemical, and optical studies were performed to clarify the effect of different perpendicular π-moieties on the optoelectronic properties. Our molecular tuning allowed for the synthesis of molecules exhibiting strong visible-range absorption. The compounds are not fluorescent due to structural changes in the excited state, as revealed by DFT calculations. Finally, our study describes enantiomerically pure spiroconjugated absorber molecules using 1,1'-binaphthyl-2,2'-diol (BINOL) units on the donor part.

Relation between the corrosion resistance and the chemical structure of hybrid sol-gel coatings with interlinked inorganic-organic network

Organic-inorganic hybrid coatings have been prepared by a sol-gel route from 3-glycidoxypropyltrimethoxysilane (GPTMS) and tetraethoxysilane (TEOS) with triethylenetetramine (TETA) added in the sol formulation. The main goal of this research was to evaluate how the chemical structure of the GPTMS/TEOS/TETA hybrid coatings influences the corrosion of mild steel. The presence of TETA as an epoxy opening agent offers the possibility to form interconnected epoxy-amine and silica networks. It was found by means of 29Si HRMAS NMR spectroscopy that TETA acted as an efficient basic catalyst for the condensation of GPTMS and TEOS. This accelerates the gelation and gives limited shelf life to GPTMS/TEOS/TETA sols. Structural characterization of the cured hybrid coatings was performed using 13C and 29Si Solid State NMR spectroscopies. The results show that the epoxy amine reaction is the principal epoxide ring opening reaction. The slow formation of diol units with sols prepared with an excess of epoxy groups has also been observed. It was found that the polymerization of the organic network hindered the polymerization of the siloxane network. As a result, the film based on an epoxy rich off-stoichiometric formulation had a higher Persoz hardness value compared to the stoichiometric film.The corrosion behavior of the coatings in neutral chloride solution was studied through electrochemical impedance spectroscopy (EIS). The results revealed that barrier properties have been improved by the addition of TETA to sol-gel films. The films based on epoxy rich off-stoichiometric formulation and those base on stoichiometric formulation resulted in similar barrier properties but a higher resistance to interfacial delamination was observed for the epoxy rich off-stoichiometric films. The relationship between the film structure and its corrosion behavior was discussed.

Adsorption of Fibrinogen and Fibronectin on Elastomeric Poly(butylene succinate) Copolyesters

Proteins adsorbed onto biomaterial surfaces facilitate cell-material interactions, including adhesion and migration. Of particular importance are provisional matrix components, fibrinogen (Fg) and fibronectin (Fn), which play an important role in the wound-healing process. Here, to assess the potential of a series of elastomeric poly(butylene succinate) (PBS) copolymers for soft tissue engineering and regenerative medicine applications, we examined the adsorption of Fg and Fn. We prepared spin-coated thin films of the poly(butylene succinate) homopolymer and a series of elastomeric poly(butylene succinate) copolymers with butylene succinate (PBS, hard segment) to succinate-dimer linoleic diol unit (dilinoleic succinate (DLS), soft segments) weight ratios of 70:30, 60:40, and 50:50. X-ray diffraction was used to assess crystallinity, whereas the obtained thin films were characterized using a quartz crystal microbalance with dissipation monitoring (QCM-D) and atomic force microscopy. Protein adsorption was assessed using QCM-D, followed by data analysis using viscoelastic modeling. On all three copolymers, we observed robust adsorption of both key provisional matrix proteins. Importantly, for both proteins, viscoelastic modeling determined that the adlayers were 30-40 nm thick and had low shear modulus values (<25 kPa), thus indicating soft orientations (end-on for Fg) or conformations (open for Fn) of the hydrated proteins. Overall, our results are very encouraging, as they predict excellent cell adhesion and migration, key features enabling tissue integration of potential PBS-DLS scaffolds.

Thermotropic Liquid Crystalline Polymers with Various Alkoxy Side Groups: Thermal Properties and Molecular Dynamics.

Two series of thermotropic liquid-crystalline polymers (TLCPs) were synthesized by reacting various dialkoxy terephthalate units with hydroquinone (HQ) and 2,6-naphthalene diol (Naph). The dialkoxy terephthalate moieties used in this study include 2,5-diethoxyterephthalate, 2,5-dibutoxyterephthalate, and 2,5-dihexyloxy-terephthalate. All the TLCPs synthesized in this study formed nematic phases. The molecular motions according to the length of the dialkoxy side groups in the TLCPs were evaluated by 13C cross-polarization/magic angle spinning nuclear magnetic resonance spectroscopy. The thermal properties and molecular dynamics of the TLCPs are found to be affected by the length of the dialkoxy side group and the aromatic diol unit in the main chain. Further, the thermal behaviors, liquid crystalline mesophases, and degree of crystallinity of the two series of TLCPs, i.e., HQ- and Naph-TLCPs, are compared.

Catalytic asymmetric synthesis of stereoisomers of 1-C-n-butyl-LABs for the SAR study of α-glucosidase inhibition

We achieved synthesis of seven stereoisomers of 1-C-n-butyl-L-iminofuranose derivatives using catalytic asymmetric alkylation and Negishi coupling as key reactions. The synthetic strategy based on these key reactions was quite useful, since both α- and β-iminofuranoses could be obtained by switching the chirality of the ligand employed for the AAA reaction. The common intermediates for α- and β-isomers were subjected to further manipulations to install a diol unit at C2 and C3 to give the desired stereoisomers of L-iminofuranose derivatives. We achieved the preparation of all stereoisomers of 1-C-n-butyl-L-iminofuranose derivatives, with the exception of β-lyxo type iminofuranose. It is noteworthy that a synthetic route for many stereoisomers of iminofuranose derivatives was developed. Unfortunately, none of the L-iminofuranoses obtained showed inhibitory activity against the α-glycosidases examined—e.g., maltase, sucrase, and isomaltase.

Effect of dihalides on the polymer linkages in the Cs2CO3-promoted polycondensation of 1 atm carbon dioxide and diols

Synthesis of biodegradable polycarbonates directly from carbon dioxide and diols has seen renewed interest. In the present report, the effect of a series of organic dihalides (CH2X2 and (CHX)2, where X = Cl, Br, and I) in the Cs2CO3-promoted copolymerization of 1 atm CO2 with diols has been studied. Structural analysis of the resultant polymers/oligomers by spectroscopic techniques reveals that a variety of main chain linkages can be obtained, depending on the dihalides used. Specifically, the methylene units from dibromomethane (DBM) are incorporated into the products as carbonate and ether linkages, and the methylene units from diiodomethane (DIM) are incorporated mainly as the ether linkage and without much CO2 incorporation. In comparison, all dihaloethanes examined lead to clean formation of alternating polycarbonates incorporating both the ethylene units from dihaloethanes and the diol units, and the halide is identified as the end group. The mechanistic pathways and the relative activity of the key intermediates are discussed in light of these results.