Extending the possibility of an N-Troc-protected sialic acid donor toward variant sialo-glycoside synthesis

The potential of an N-Troc-protected sialic acid donor, equipped with phenylsulfenyl functionality as a leaving group, has been explored. As a result, the entitled donor was proven to be highly reactive and to have broad applicability toward the synthesis of variant sialo-glycans, which have N-glycolyl, de-N-acetyl, 1,5-lactam and 8-O-sulfo sialic acid analogs.     

Kinetics study of the photopolymerisation of donor/acceptor pairs using the differential photocalorimetric technique and the relation of the kinetics data to hydrogels formation

The differential photocalorimetric technique was used to study the rates of photopolymerisation initiated by donor/acceptor pairs with N-vinylpyrrolidinone (NVP) as the donor, and the acceptors were a series of N-hydroxy alkylmaleimides including N-hydroxymethyl maleimide (HMMI), N-(2-hydroxy) ethylmaleimide (HEMI), N-(3-hydroxy) propylmaleimide (HPrMI) and N-(5-hydroxy) pentylmaleimide (HPMI). HPMI/NVP system displays the highest rate of polymerisation followed by HMMI/NVP and then HPrMI/NVP, with HEMI/NVP giving the lowest rate.These donor/acceptor pair systems were subsequently used to initiate the polymerisation of NVP under the influence of UV radiation. With the exception of the HEMI/NVP system, the other three systems produced polymers with characteristics pertaining to that of hydrogel. A previously proposed mechanism (Proceedings of the RadTech Asia ’01 Conference, Kunming, China, 2001, pp. 182–201) was used to explain such phenomenon.     

Pyrazine-N,N′-dioxide/tetracyanoethylene electron donor-acceptor bonding and the effect of donor steric demand and symmetry on the cocrystal assembly

The synthesis of a sterically hindered pyrazine dioxide electron donor (2,5-diethyl-3,6-dimethylpyrazine-N,N′-dioxide) and its cocrystallization with tetracyanoethylene (TCNE) are reported. The resulting DA assembly in the cocrystal is compared to that observed for a smaller pyrazine-N-oxide donor. Increased steric demand and lower donor symmetry yield a new, more complex two-dimensional DA assembly with slightly longer DA bonds and higher TCNE content in the cocrystal.     

Syntheses and characterization of Cu,Ni and Zn binding capability of histidinehydroxamic acid derivatives

Two histidinehydroxamic acid derivatives (N-methyl-histidinehydroxamic acid, N-Me-Hisha and Z-histidinehydroxamic acid, Z-Hisha) have been synthesized and their complexation with Cu²⁺-, Ni²⁺- and Zn²⁺-ions has been studied by using pH-potentiometric, UV–Vis, CD, ¹H NMR, EPR and ESI-MS methods. Both of the two new derivatives contain one donor atom less compared to the histidinehydroxamic acid (Hisha). In the case of N-Me-Hisha the hydroxamate-N as donor is eliminated, while the coordination of the amino-N of Z-Hisha is not possible at all.     

Synthesis of N,N-Ac,Boc laurylthio sialoside and its application to O-sialylation

The combination of the 5-N-tert-butoxycarbonyl (Boc) group of laurylthio sialoside and cyclopentyl methyl ether (CPME) as a solvent enhanced the reactivity and α-selectivity of the sialyl donor during sialylation. Selective deprotection of the N-Boc group of sialoside, including an acid-sensitive isopropylidene function, was successfully achieved by Yb(OTf)₃-SiO₂. Transformation of N,N-Ac,Boc into an N-acetylglycolyl group of sialoglycoside was easily performed via selective N-deacylation of the mixed Ac-N-Boc carbamate, subsequent Boc group removal, and acylation.     

Sialylation reactions with N,N-dibenzylthiosialoside donor

A new sialyl donor, N,N-dibenzyl-protected p-toluenethiosialoside, was synthesized and its sialylation reaction was investigated. This reaction proceeded in a preactivation manner and preferred to provide β-anomeric coupling products. The β-selectivity was rationalized based on the assumption that N,N-dibenzylamino group could serve as an oriented group to activate the hydroxyl group of acceptor from β-face.     

Synthesis of glycosaminoglycan oligosaccharides. Part 5: Synthesis of a putative heparan sulfate tetrasaccharide antigen involved in prion diseases

The synthesis of the putative prion-associated heparan sulfate tetrasaccharide containing two d-glucuronic acid units is reported. Key to the synthesis were the differentiation of the N-acetylated and N-unsubstituted glucosamine units, the high-yielding glucosylation at O-4 of an N-acetyl-d-glucosamine derivative and the α-selective glycosylation of the 4′-OH group of a β-d-GlcpA-(1→4)-d-GlcpNAc disaccharide building block with a disaccharide thioglycoside donor.     

Use of Stille-type cross-coupling as a route to oligopyridylimines

The new tin reagents, 2-(n-Bu₃Sn)-6-{C(R)OCH₂CH₂O}-C₅H₃N, (R=H a, Me b), have been employed in Stille-type cross-coupling reactions with a range of oligopyridylbromides generating, following a facile deprotection step, a series of formyl- and acetyl-functionalised oligopyridines. Condensation reactions with 2,6-diisopropylaniline has allowed access to families of novel sterically bulky multidentate N,N,N,N (tetradentate), N,N,N,N,N (pentadentate), N,N,N,N,N,N (sexidentate) and N,N,N,N,N,N,N (heptadentate) nitrogen donor ligands. This work represents a straightforward and rapid synthetic route for the preparation of oligopyridylimines, which are expected to act as useful components for the self-assembly of polymetallic complexes.     

A general method for regioselective Heck arylation of electron-rich N-acyl-N-vinylamine with aryl halides

A highly efficient protocol for the Pd-catalyzed regioselective Heck arylation of the electron-rich olefin N-acyl-N-vinylamine with aryl halides has been developed. In the presence of hydrogen-bond donor [H₂NiPr₂][BF₄] as an additive, this proceeds smoothly in isopropanol to afford exclusively the branched products in high yields.     

Synthesis and magnetic properties of new binuclear Cu(II) complexes with tridentate azomethine ligands

New binuclear copper complexes of tridentate azomethine ligands with various combinations of N, O, and S donor centers were prepared by various procedures, including template synthesis. The magnetochemical data obtained for the range 2-300 K suggest the occurrence of antiferromagnetic coupling in most of these chelates. The only exception is the complex containing N-tosyl and N-ethyl donor fragments, in which the ferromagnetic exchange is observed.     

Synthesis, properties, and molecular structure of nitro-substituted N-methyl-N-nitroanilines

Ten mono-, di-, and trinitro derivatives of N-methyl-N-nitroaniline were synthesized and studied by spectral, electrooptical, and quantum-chemical methods. Three of these derivatives, N-methyl-N,2,3-trinitroaniline, N-methyl-N,2,5-trinitroaniline, N-methyl-N,3,5-trinitroaniline, were also examined by the X-ray diffraction method. The N-nitroamino group in their molecules is almost planar, the N⁷-N⁸ bond is shortened, and the N⁸ atom is characterized by a strong deficit of electron density. The dihedral angle between the planes of the N-nitroamino group and the benzene ring is 56°–92°, which makes conjugation between these fragments impossible. The N-nitroamino group in the examined compounds acts as a weak electron donor with respect to the nitro groups in the aromatic ring; the mechanism of this effect is inductive.     

Enhancement of visible light-induced gelation of photocurable gelatin by addition of polymeric amine

We evaluated the effect of an electron donor on photogelation of photocurable gelatin, which is gelatin partially derivatized with eosin (eosin–gelatin). As an electron donor, ascorbic acid, 2-(N,N-dimethylamino)ethyl methacrylate (DMAEMA), and three kinds of radical polymerized amines such as poly(N,N-dimethylacrylamide-co-2-(N,N-dimethylamino)ethyl methacrylate) (poly(DMAAm-co-DMAEMA)), poly(N,N-dimethylacrylamide-co-3-(N,N-dimethylamino)propyl acrylamide) (poly(DMAAm-co-DMAPAAm)), and poly(3-(N,N-dimethylamino)propyl acrylamide) (polyDMAPAAm) were examined. Upon photo irradiation at the wavelength ranging from 400 to 520 nm with low illumination intensity (7.7 × 10³ lx), no gel was obtained from 20 wt.% of a viscous aqueous solution of the eosin–gelatin even by adding with ascorbic acid. Whereas in the presence of monomeric amine (DMAEMA, 3.0 wt.%), gel formation occurred by radical recombination between eosin groups incorporated into the gelatin. When the polymeric amines were added to the eosin–gelatin solution, gelation was markedly enhanced due to cross-linking of gelatins through polymeric amines in addition to direct bonding between gelatins. An increase in amine unit content in the polymeric amines resulted in increased gel yield and reduced swelling degree of water. In the presence of polyDMAPAAm, almost all gelatins were converted relatively rigid hydrogel. Application for a topical hemostatic glue was preliminary performed in rat injured model. A rat liver injured in laparotomy was coated with the aqueous eosin–gelatin solution containing polyDMAPAAm. Upon irradiation, the solution was immediately converted to a swollen gel, which was tightly adhered to the liver tissue and concomitantly hemostasis was completed with little tissue damage.     

Ruthenium-catalyzed reduction of N-alkoxy- and N-hydroxyamides

A ruthenium-catalyzed reduction of N-alkoxy- and N-hydroxyamides was found to afford corresponding amides in good to high yields. A simple RuCl₃/Zn-Cu/alcohol system, without the addition of any other ligands, exhibited a high catalytic activity, and therefore the present reaction does not require a stoichiometric amount of metals or metal complexes as reductants. When β-substituted-α,β-unsaturated N-methoxyamides were employed as substrates, concurrent hydrogenation of the olefin moiety proceeded slowly with deprotection of the methoxy group. In the reduction of N-hydroxyamides, the alcoholic solvent was found to function as a hydrogen donor.     

Synthesis and Antimicrobial Activity of a Pyridine Complex of (Acetato)[5,10,15,20-tetrakis(<Emphasis Type="Italic">N</Emphasis>-methylpyridin- 4-yl)porphinato]manganese(III) Tetratosylate

Aiming at preparation of new biologically active donor?acceptor complexes, a water-soluble manganese(III) complex with 5,10,15,20-tetrakis(N-methylpyridin-4-yl)porphine tetratosylate was synthesized and its reaction with pyridine was studied by spectrophotometry using the molar ratio method. In water a 1: 1 donor?acceptor complex with pyridine is formed. The chemical structure of the compounds was established by spectral methods. (Acetato)[5,10,15,20-tetrakis(N-methylpyridin-4-yl)porphinato]manganese(III) tetratosylate and especially its donor?acceptor complex with pyridine showed an antifungal activity against Candida albicans.     

Syntheses,crystal structure and chromotropic properties of dinuclear copper(II) complexes of tertiary diamine with hydroxo bridge

Dinuclear copper(II) complex with the general formula [(diamine)Cu(OH)]₂(ClO₄)₂, where diamine stands for N,N-dialkyl,N′-benzyl-ethylenediamine, were prepared. The complexes were characterized by elemental analysis, spectroscopic, conductance measurements, and X-ray structural analysis. The complexes are soluble in various organic solvents and show positive solvatochromism. Thermochromism was also observed particularly in strong donor solvents.     

Syntheses of N-aryl-protected glucosamines and their stereoselectivity in chemical glycosylations

N-Aryl-protecting groups were introduced in glucosamines to achieve β-selective glycosylation. Various N-aryl aminosugars were synthesized via Buchwald–Hartwig reaction. Glycosylation using glycosyl trichloroacetimidates of N-aryl aminosugars smoothly proceeded in the presence of trimethylsilyl trifluoromethanesulfonate. Use of a glycosyl donor comprising an electron-donating 2,4-dimethoxyphenyl (DMP) group led to the glycosylation proceeding with high β selectivity. This stereoselectivity seemed to be derived from the formation of an aziridine intermediate. The DMP-protecting group can be removed immediately by using ammonium hexanitratocerate (IV).     

Photophysics of 4-N,N-dimethylamino cinnamaldehyde in AOT reverse micelles and exploration of its position and orientation

An attempt has been made in this Letter to locate the position and orientation of 4-N,N-dimethylamino cinnamaldehyde (DMACA) inside sodium bis(2-ethylhexyl) sulfosuccinate (AOT)–n-heptane reverse micelle based on change in photophysical properties of DMACA compared to that in n-heptane. It has been proposed that the possibility of finding the donor moiety inside the small water pool of reverse micelle is maximum while the acceptor group straddles in the remaining part of the reverse micelle. The micropolarity in the vicinity of the donor moiety has been computed in terms of dielectric constant with varying water pool size.     

Effects of side-chains ofN-acetylamino acids on the structures of their triphenyltin(IV) complexes

Triphenyltin(IV) complexes ofN-acetylglycine,N-acetyl-L-leucine,N-acetyl-L-asparagine andN-acetyl-L-tyrosine were prepared by two methods and characterized by means of different spectroscopic methods (FTIR, multinuclear,¹H,¹³C and¹¹⁹Sn NMR and¹¹⁹Sn Mössbauer). The spectroscopic data indicated that theN-acetylglycine complex adopts a trigonal-bipyramidal structure in which the monodentate carboxylate and the amide-C=O group are bound to the same organotin(IV) moiety. The other three complexes are linear oligomers in which the planar Ph₃Sn(IV) is coordinated axially by a monodentate carboxylate and an amide-C=O from two different ligands. At theC-terminal end of the oligomer chain there is a tetracoordinated tin(IV) with a monodentate carboxylate as donor group.     

N-benzyl-N-[(E)-2-phenylethenyl]trifluoromethanesulfonamide

In the search for an approach to N-vinyltriflamides with a free NH group TfNHCH=CHR (Tf = CF₃SO₂) N-(benzyl)-N-(2-bromo-2-phenylethenyl)triflamide TfN(Bn)CH=CHPh was synthesized through bromination-dehydrobromination of N-(benzyl)-N-(2-phenylethyl)triflamide. At removing the benzyl protecttion by the action of trifluoromethanesulfonic acid benzyl alcohol separated; however instead of the target N-styryltriflamide unexpectedly the product of its hydrogenation was obtained, N-(2-phenylethyl)triflamide. Obviously, the benzyl alcohol was the hydrogen donor, and the easy hydrogenation was facilitated by the high electrophilicity of the double bond in N-styryltriflamide because of strong electron-acceptor effect of the triflyl group.     

Crown-ether annelated dithiadiazafulvalenes

The synthetic approaches towards crown-ether annelated dithiadiazafulvalenes (DTDAF) are described. As evidenced by electrochemistry, the reaction of N,N′-bridged-bisthiazolium salts in basic medium favors the formation of the DTDAF via an intramolecular coupling while the reaction of N,N′-bridged-bisthiazoline selone with trivalent phosphorus derivative leads to the donor core via an intermolecular coupling. The complexation of various metal cations on these crown-ether annelated DTDAF is investigated by electrochemistry.