Towards the Synthesis of 1‐Deoxy‐1‐nitropiperidinoses

In the course of the first of several attempts to elaborate methods for the synthesis of 1‐nitropiperidinoses, lincosamine was transformed into lactam 6 via hemiacetal 1 , lactone 2 , amide 3 , oxo amide 4 , and its cyclic tautomer 5 . Treatment of the N‐Boc‐protected lactam oxime 9 , obtained from lactam 6 , with brominating agents failed to provide the bromonitroso carbamate 10 . The N‐Boc‐protected lactam 13 derived from 6 was reduced to hemiacetal 14 , but the corresponding N‐Boc‐aminooxime did not tautomerise to the C(1)‐hydroxylamine, and nitrone 17 , a potential precursor of the nitropiperidine 12 , was not formed. Oxidation of the anomeric azide 20 with HOF?MeCN failed to provide the expected nitropiperidine 21 . The phosphinimines 22 derived from 20 did not react with O₃. In the next approach to 1‐nitropiperidinoses, we treated the N‐Boc‐protected hemiacetal 25 , obtained from the known gluconolactam 23 with N‐benzylhydroxylamine. The resulting nitrone 26 exits in equilibrium with the anomeric N‐benzyl‐glycosylhydroxylamine that was oxidized to the anomeric nitrone 28 . Ozonolysis of 28 led to the hemiacetal 25 , resulting from the desired, highly reactive protected nitropiperidinose 29 , that was evidenced by an IR band at 1561 cm^?1. Similarly to the synthesis of nitrone 26 , reaction of the N‐tosyl‐protected hemiacetal 31 with N‐benzylhydroxylamine and oxidation provided the anomeric N‐benzylhydroxylamines 33 via the p‐toluenesulfonamido nitrone 32 . Their oxidation with MnO₂ led to the anomeric nitrone 34 . Ozonolysis of 34 as evidenced by ¹H‐NMR and ReactIR spectroscopy led to the highly reactive nitropiperidinose 35 . Like 29, 35 was transformed during workup, and only the hemiacetal 31 was isolated. The similarly prepared lincosamine‐derived nitrone 17 was subjected to ReactIR‐monitored ozonolysis that evidenced the formation of the protected nitropiperidinose 12 , but only led to the isolation of 14 . The facile transformation of the nitropiperidinoses to hemiacetals is rationalised by heterolysis of the anomeric C,N bond, recombination of the ion pair, and denitrosation of the resulting anomeric nitrite by a nucleophile. Attempts to convert the 1‐deoxy‐1‐nitropiperidinose 35 to uloses 43 by base‐catalysed Michael additions or Henry reactions were unsuccessful.     

A Practical One‐Step Synthesis of 1,2‐Oxazoline Derivatives from Unprotected Sugars and Its Application to Chemoenzymatic β‐N‐Acetylglucosaminidation of Disialo‐oligosaccharide

A facile and practical method for synthesis of sugar oxazolines (=dihydrooxazoles) from the corresponding N‐acetyl‐2‐amino sugars has been developed by using 2‐chloro‐1,3‐dimethyl‐1H‐benzimidazol‐3‐ium chloride (CDMBI) as a dehydrative condensing agent. The intramolecular dehydrative reaction between the 2‐acetamido group and the anomeric OH group of unprotected N‐acetyl‐2‐amino sugars took place smoothly in H₂O, leading to the formation of a 1,2‐oxazoline (=4,5‐dihydrooxazole) moiety in good yield. Since the reaction proceeds in H₂O without using any protecting groups, the resulting oxazolines can be utilized as effective glycosyl donors for the subsequent enzymatic glycosylation. We have successfully demonstrated a highly efficient chemoenzymatic transglycosylation of a disialo‐oligosaccharide moiety to p‐nitrophenyl N‐acetylglucosaminide catalyzed by a mutant endo‐N‐acetylglucosaminidase without isolating disialo‐oligosaccharide oxazoline as synthetic intermediate.     

Improving the Ring‐opening Polymerization of l‐Lactide Using n‐Butyl Lithium with Various Bidentate Ligands

A series of bidentate ligands were examined to improve the catalytic activity of l ‐lactide (LA) polymerization by using n‐butyl lithium and BnOH. For LA polymerization, n‐butyl lithium with tetraisopropyl methylenebis(phosphonate) (L⁸ ) showed the greatest catalytic activity but with poor controllability of the polymer molecular weight. The polydispersity indices (PDIs) could be improved without BnOH addition, but Mn _GPC was much different from the Mn _Cal . ¹H NMR spectra confirmed that the cyclized PLA was obtained, thus implying that active chain‐end mechanisms were operative in LA polymerization.     

Synthesis of hydroxyl‐bearing polyurethanes from naturally occurring myo‐inositol

A route from naturally occurring myo‐inositol to hydroxyl‐bearing polyurethanes has been developed. The diol prepared from the bis‐acetalization of myo‐inositol with 1,1‐dimethoxycyclohexane was reacted with a rigid diisocyanate, 1,3‐bis(isocyanatomethyl)cyclohexane to afford the corresponding polyurethane, of which glass transition temperature (T_g) was quite high as 192 °C. The polyurethane contains side chains inherited from the acetal moieties of the diol monomer and was treated with trifluoroacetic acid to hydrolyze the acetal moieties and afford the target polyurethane functionalized with hydroxyl groups. The presence of many hydroxyl groups in the side chains, which can form hydrogen bonds with each other, resulted in a high T_g, 186 °C. In addition, the hydroxyl groups were reacted with isocyanates to achieve further side‐chain modifications. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 1358–1364     

Sequential Dy(OTf)3‐Catalyzed Solvent‐Free Per‐O‐Acetylation and Regioselective Anomeric De‐O‐Acetylation of Carbohydrates

Dysprosium(III) trifluoromethanesulfonate‐catalyzed per‐O ‐acetylation and regioselective anomeric de‐O ‐acetylation of carbohydrates can be tuned by adjusting the reaction medium. In this study, the per‐O ‐acetylation of unprotected sugars by using a near‐stoichiometric amount of acetic anhydride under solvent‐free conditions resulted in the exclusive formation of acetylated saccharides as anomeric mixtures, whereas anomeric de‐O ‐acetylation in methanol resulted in a moderate‐to‐excellent yield. Reactions with various unprotected monosaccharides or disaccharides followed by a semi‐one‐pot sequential conversion into the corresponding acetylated glycosyl hemiacetal also resulted in high yields. Furthermore, the obtained hemiacetals could be successfully transformed into trichloroimidates after Dy(OTf)₃‐catalyzed glycosylation.     

Microwave‐assisted Synthesis and Its Reversible Li‐storage Properties of Porous Sheet‐like Co3O4

Porous Co₃O₄ nanosheets were designed and fabricated from common Co(NO₃ )₂ solution without any surfactants or templates under microwave radiation conditions. After the microstructures and morphologies were characterized by scanning electron microscope (SEM ), X‐ray powder diffraction (XRD ), transmission electron microscopy (TEM ), and N₂ absorption/desorption isotherms techniques, the obtained Co₃O₄ nanosheets were applied for reversible Li‐storage, displaying larger capacity, better cycling performance and rate capability, i.e., a reversible specific capacity of ca. 800 mAh /g during initial 30 cycles and a reversible capacity of 450 mAh /g at 2C for Co₃O₄ nanosheets, which were almost twice higher than those for Co₃O₄ nanoparticles. The improved cycling stability could be attributed to the remarkable synergistic effects between porous structures and nanosheet‐like morphologies.     

Catalytic application of sulfonic acid‐functionalized titana‐coated magnetic nanoparticles for the preparation of 1,8‐dioxodecahydroacridines and 2,4,6‐triarylpyridines via anomeric‐based oxidation

We have developed green, efficient and powerful protocols for the preparation of 2,4,6‐triarylpyridines and 1,8‐dioxodecahydroacridines in the presence of Fe₃O₄@TiO₂@O₂PO₂(CH₂)₂NHSO₃H as a sulfonic acid‐functionalized titana‐coated magnetic nanoparticle catalyst under mild and solvent‐free reaction conditions. These protocols furnished the desired products in short reaction times with good to high yields (20–40 min and 80–86% in the case of 2,4,6‐triarylpyridines; 15–90 min and 80–93% in the case of 1,8‐dioxodecahydroacridines). The final step of the mechanistic route in the synthesis of 2,4,6‐triarylpyridines proceeds via an anomeric‐based oxidation. Also, the nanomagnetic core–shell catalyst can be recycled and reused in both cases of the scrutinized one‐pot multicomponent reactions with high turnover number and turnover frequency.     

3‐Fluoro‐2,4‐dioxa‐7‐aza‐3‐phosphadecalin 3‐Oxides as Rigid Acetylcholine Mimetics: Conformational Analysis and Direct Evidence of the Anomeric Effect

Conformational analyses of the P(3)‐axially and P(3)‐equatorially F‐substituted (±)‐cis‐ and (±)‐trans‐2,4‐dioxa‐7‐aza‐3‐phosphadecalin 3‐oxides (3‐fluoro‐2,4‐dioxa‐7‐aza‐3‐phosphabicyclo[4.4.0]decane 3‐oxides) were performed. The results are based on independent studies in both solution and the solid state by ¹H‐ and ³¹P‐NMR experiments and computational and X‐ray crystallographic data. As expected, the axial epimers adopt neat double‐chair conformations in solution and in the crystal. Due to the anomeric effect of the electron withdrawing F‐substituent, the 2,4‐dioxa‐3‐phospha moiety in the equatorial epimers adopts a mixture of conformations in solution, mainly chair and twist‐boat; whereas a neat twist‐boat (trans‐isomer) and the unusual envelope conformation (cis‐isomer) were detected in the solid state. This is the first report of a straight visualization of these conformations and the impact of the anomeric effect in such systems.     

2,3,4,6‐Tetra‐O‐acetyl‐α‐d‐glucopyranosyl azide

The Cu^I‐catalysed 1,3‐dipolar cycloaddition of an azide and a terminal alkyne is becoming an increasingly popular tool for synthetic chemists. This is the most representative of the so‐called `click reactions' and it is used to generate 1,4‐disubstituted triazoles in high yield. During studies on such cycloaddition reactions, a reduced reactivity of an α‐glucosyl azide with respect to the corresponding β‐anomer was observed. With the aim of understanding this phenomenon, the structure of the title compound, C₁₄H₁₉N₃O₉, has been determined at 140 K. The glucopyranosyl ring appears in a regular ⁴C₁ chair conformation with all the substituents in equatorial positions, except for the anomeric azide group, which adopts an axial orientation. The observed bond lengths are consistent with a strong anomeric effect, which is reflected in a change in dipolar character and hence reduced reactivity of the α‐glucosyl azide.     

Isothiourea‐based lewis pairs for homopolymerization and copolymerization of 2,2‐dimethyltrimethylene carbonate with ε‐caprolactone and ω‐pentadecalactone

In this study, the homopolymerization of 2,2‐dimethyltrimethylene carbonate (DTC) and its copolymerizations with ε‐caprolactone (CL) were carried out in detail using the isothiourea‐based Lewis pairs comprised 2,3,6,7‐tetrahydro‐5H‐thiazolo(3,2‐a)pyrimidine and magnesium halides (MgX₂) with benzyl alcohol (BnOH) as the initiator. The copolymerization of DTC and CL via one‐pot addition produced randomly sequenced copolymers. On the other hand, a well‐defined linear poly(ε‐caprolactone)–block–poly(2,2‐dimethyltrimethylene carbonate) (PCL‐b‐PDTC) diblock copolymer was prepared by simple sequential ring‐opening polymerization of CL and DTC. In addition, poly(ω‐pentadecalactone)–block–PDTC diblock copolymer was successfully prepared by the same strategy. Moreover, PDTC–poly(ethylene glycol) (PEG)–PDTC triblock copolymer was synthesized in the presence of PEG 2000. The effects of different polymerization conditions on the polymerization reactions have been systematically discussed. The resulting polymers were characterized by the ¹H and ¹³C NMR spectra, gel permeation chromatography (GPC), differential scanning calorimetry (DSC), and matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry (MALDI‐ToF MS). The block copolyester structures were confirmed by the ¹³C NMR spectroscopy and DSC characterizations. These results indicated that the supposed mechanism was a dual catalytic mechanism. The proposed mechanism involved activation of the monomer via coordination to the MgX₂, and the initiator alcohol was deprotonated by base. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 2349–2355     

A Novel High Efficient Catalyst AgBr/CaMoO4 for the Reduction of p‐Nitrophenol

A new composite catalyst AgBr/CaMoO₄ was successfully fabricated by loading AgBr nanoparticles on CaMoO₄ support via a convenient precipitation/deposition method, without any controlling agent and template. The microstructure, chemical composition, and morphologies of the AgBr/CaMoO₄ were characterized by X‐ray diffraction, Fourier transform infrared, X‐ray photoelectron spectroscopy, and scanning electron microscopy. A series of comparative experiments showed that the composite AgBr/CaMoO₄ exhibits higher catalytic activity than pure AgBr or CaMoO₄ for the reduction of p‐nitrophenol (4‐NP). Moreover, the AgBr content greatly impacted the catalytic activity of composite AgBr/CaMoO₄ . The conversion rate of 4‐NP with AgBr/CaMoO₄ ‐5% as catalyst could reach 100% within only 4 min, which might be attributed to more number of available active sites from the highly dispersed AgBr nanoparticles on the surface of CaMoO₄ microspheres. In addition, the composite catalyst AgBr/CaMoO₄ displayed a good structural and cycling stability. The present study might provide a new strategy to design composite materials with excellent catalytic performance.     

Anti‐Inflammatory Activity of a Novel Acetylene Isolated from the Roots of Angelica tenuissima Nakai

Three polyacetylenes, one novel and two known, were isolated from the root of Angelica tenuissima. Using ¹H‐ and ¹³C‐NMR, COSY, HMBC, and HMQC, their structures were found to be (3R,8S)‐heptadeca‐1‐en‐4,6‐diyne‐3,8‐diol ( 1 ), falcarindiol ( 2 ), and oplopandiol ( 3 ). Absolute configurations of compound 1 were established using Mosher's esterification. In addition, the polyacetylenes ( 1 – 3 ) were evaluated for their anti‐inflammatory activity. Compounds 1 and 3 showed potent inhibitory activity against lipopolysaccharide‐induced nitric oxide (NO) production in RAW267.7 macrophage cells with IC₅₀ values of 4.31 and 5.06 μm, respectively. Compound 1 strongly inhibited inducible nitric oxide synthase (iNOS) and cyclooxygenase (COX)‐2 in a concentration‐dependent manner.     

Fe3O4@TiO2@O2PO2(CH2)NHSO3H as a novel nanomagnetic catalyst: Application to the preparation of 2‐amino‐4,6‐diphenylnicotinonitriles via anomeric‐based oxidation

A new, green and reusable nanomagnetic heterogeneous catalyst, namely Fe₃O₄@TiO₂@O₂PO₂(CH₂)NHSO₃H, was synthesized and fully characterized using suitable techniques such as infrared spectroscopy, X‐ray diffraction, scanning and transmission electron microscopies, thermogravimetry, vibrating sample magnetometry and energy‐dispersive X‐ray spectroscopy. The applicability of the constructed heterogeneous core–shell catalyst as a promoter was successfully explored for the synthesis of 2‐amino‐4,6‐diphenylnicotinonitrile derivatives upon the reaction of a good range of aromatic aldehydes, acetophenone derivatives, malononitrile and ammonium acetate. The desired products were obtained with good to high yields in short reaction times under solvent‐free conditions. The suggested mechanism offers an anomeric‐based oxidation route to the products in the final step of the synthetic pathway.     

Producing highly linear polyethylenes by using t‐butyl‐functionalized 2,6‐bis(imino)pyridylchromium(III) chlorides

A new family of t‐butyl substituted chromium(III) chloride complexes ( Cr1 – Cr6 ), bearing 2‐(1‐(2,6‐dibenzhydryl‐4‐t‐butylphenylimino)ethyl)‐6‐(1‐(arylimino)ethyl)pyridine (aryl = 2,6‐Me₂C₆H₃ Cr1 , 2,6‐Et₂C₆H₃ Cr2 , 2,6‐i‐Pr₂C₆H₃ Cr3 , 2,4,6‐Me₃C₆H₂ Cr4 and 2,6‐Et₂‐4‐MeC₆H₂ Cr5 ) or 2,6‐bis(1‐(2,6‐dibenzhydryl‐4‐t‐butylphenylimino)ethyl)pyridine ( Cr6 ), has been synthesized by the reaction of CrCl₃·6H₂O in good yield with the corresponding ligands ( L1 – L6 ), respectively. The molecular structures of Cr2 and Cr6 were characterized by X‐ray diffraction highlighted a distorted octahedral geometry with the coordinated N,N,N ligand and three bonded chlorides around the metal center. On activation with modified methylaluminoxane or triisobutyl aluminum, most of the chromium precatalysts exhibit good activities toward ethylene polymerization and produce linear polyethylenes with high‐molecular weight. In addition, an in‐depth catalytic evaluation of Cr2 was conducted to investigate how cocatalyst type and amount, reaction temperature, and run time affect the catalytic activities and polymer properties. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 1049–1058     

Thermal isomerization of ruthenium hydride compounds containing asymmetric bidentate pyrrole‐imine ligands

A series of ruthenium hydride compounds containing substituted bidentate pyrrole‐imine ligands were synthesized and characterized. Reacting RuHCl(CO)(PPh₃)₃ with one equivalent of [C₄H₃NH(2‐CH=NR)] in ethanol in the presence of KOH gave compounds {RuH(CO)(PPh₃)₂[C₄H₃N(2‐CH=NR)]} where trans‐Py‐Ru‐H 1, R = CH₂CH₂C₆H₉; cis‐Py‐Ru‐H 2, R = Ph‐2‐Me; and cis‐Py‐Ru‐H 3, R = C₆H₁₁. Heating trans‐Py‐Ru‐H 1 in toluene at 70°C for 12 hr resulted a thermal conversion of the trans‐Py‐Ru‐H 1 into its cis form, {RuH(CO)(PPh₃)₂[C₄H₃N(2‐CH=NCH₂CH₂C₆H₉)]} (cis‐Py‐Ru‐H 1) in very high yield. The ¹H NMR spectra of trans‐Py‐Ru‐H 1, cis‐Py‐Ru‐H 2, cis‐Py‐Ru‐H 3, and cis‐Py‐Ru‐H 1 all show a typical triplet at ca. δ–11 for the hydride. The trans and cis form indicate the relative positions of pyrrole ring and hydride. The geometries of trans‐Py‐Ru‐H 1, cis‐Py‐Ru‐H 1, and cis‐Py‐Ru‐H 3 are relatively similar showing typical octahedral geometries with two PPh₃ fragments arranged in trans positions.     

Synthesis of Highly Dispersed Fe3O4 Submicrometer Spheres in a One‐Pot Anion‐induced Solvothermal System

A facile, anion‐induced, one‐pot solvothermal method was successfully developed to prepare two kinds of highly dispersed magnetic Fe₃O₄ submicrometer spheres at 200°C in 12 h. The diameters of the as‐prepared Fe₃O₄ submicrometer spheres are ~500 and ~200 nm, respectively. With the guidance of OAc ⁻ ions, the size and morphology of the Fe₃O₄ spheres could be well controlled. The saturation magnetization of the Fe₃O₄ spheres was measured to be 84 and 74 emu/g, respectively. The assembly of tiny precursor nuclei into the Fe₃O₄ spheres relies on Ostwald ripening. The synthesized Fe₃O₄ submicrometer spheres show good magnetic response, good water solubility, and uniform size.     

Synthesis of a novel and reusable biological urea based acidic nanomagnetic catalyst: Application for the synthesis of 2‐amino‐3‐cyano pyridines via cooperative vinylogous anomeric based oxidation

In the current study, a novel and reusable biological urea based nano magnetic catalyst namely Fe₃O₄@SiO₂@(CH₂)₃‐urea‐benzimidazole sulfonic acid was designed and synthesized. The structure of the titled catalyst was fully characterized using several skills including Fourier transform infrared (FT‐IR) spectroscopy, energy dispersive X‐ray (EDX) analysis, X‐ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermo gravimetric analysis/differential thermal analysis (TG/DTG) and vibrating sample magnetometer (VSM). Then, the catalytic performance of Fe₃O₄@SiO₂@(CH₂)₃‐urea‐benzimidazole sulfonic acid was successfully inspected towards the multicomponent synthesis of 2‐amino‐3‐cyano pyridine derivatives through a vinylogous anomeric based oxidation pathway.     

Fe3O4@SiO2@sulfated boric acid as superparamagnetic and recyclable nanocatalyst‐assisted,one‐pot,pseudo four‐component synthesis of 5‐amino‐2‐aryl‐3H‐chromeno[4,3,2‐de][1,6]naphthyridine‐4‐carbonitrile derivatives

The catalytic performance of the superparamagnetic nanocatalyst Fe₃O₄@SiO₂@Sulfated boric acid as a green, recyclable, and acidic solid catalyst in the synthesis of chromeno[4,3,2‐de][1,6]naphthyridine derivatives has been studied. Chromeno[4,3,2‐de][1,6]naphthyridine derivatives via a pseudo four‐component reaction from aromatic aldehydes (1 mmol), malononitrile (2 mmol), and 2′‐hydroxyacetophenone in the presence of Fe₃O₄@SiO₂@Sulfated boric acid (0.004 g) as a nanocatalyst in 3 mL of water as a green solvent at 80°C has been synthesized. The advantages of this method are higher product yields in shorter reaction times, easy recyclability and reusability of the catalyst, and easy work‐up procedures. The nanocatalyst was reused at least six times. The nanocatalyst retained its stability in the reaction, and after reusability, it was separated easily from the reaction by an external magnet.     

gem‐Difluorocarbadisaccharides: Restoring the exo‐Anomeric Effect

Molecular mimicry is an essential part of the development of drugs and molecular probes. In the chemical glycobiology field, although many glycomimetics have been developed in the past years, it has been considered that many failures in their use are related to the lack of the anomeric effects in these analogues. Additionally, the origin of the anomeric effects is still the subject of virulent scientific debates. Herein, by combining chemical synthesis, NMR methods, and theoretical calculations, we show that it is possible to restore the anomeric effect for an acetal when replacing one of the oxygen atoms by a CF₂ group. This result provides key findings in chemical sciences. On the one hand, it strongly suggests the key relevance of the stereoelectronic component of the anomeric effect. On the other hand, the CF₂ analogue adopts the natural glycoside conformation, which might provide new avenues for sugar‐based drug design.     

Theoretical study on the deglycosylation mechanism of rice BGlu1 β‐glucosidase

It is proposed that the catalysis of GH1 enzymes follows a double‐displacement mechanism involving a glycosylation and a deglycosylation steps. In this article, the deglycosylation step was studied using quantum mechanical/molecular mechanical (QM/MM) approach. The calculation results reveal that the nucleophilic water (Wat1) attacks to the anomeric C₁, and the deglycosylation step experiences a barrier of 21.4 kcal/mol from the glycosyl‐enzyme intermediate to the hydrolysis product, in which an oxocarbenium cation‐like transition state (TS) is formed. At the TS, the covalent glycosyl‐enzyme bond is almost broken (distance of 2.45 Å), and the new covalent bond between the attacking oxygen of the water molecule and C₁ is basically established (length of 2.14 Å). In addition, a short hydrogen bridge is observed between the nucleophilic E386 and the C₂? OH of sugar ring (distance of 1.94 Å) at the TS, which facilitates the ring changing from a chair form to half‐chair form, and stabilizes the oxocarbenium cation‐like TS. © 2013 Wiley Periodicals, Inc.