Behavior of a Metastable Gel of Sodium N‐Stearoyl‐l‐Glutamate/Water System

Gel formation was observed at 25°C in a mono sodium N‐stearoylglutamate (C18GS)/water system by quick cooling (quenching, 15°C/minute), whereas coagel was formed by slow cooling (annealing, 1°C/minute). Two kinds of phase transition temperatures, T_gel (coagel‐gel) and T_c (gel‐liquid crystal or micelle), were detected in the annealing system using a differential scanning calorimeter (DSC). On the other hand, only T_c was observed in the quenching system. Since the phase transition entropies at T_c in both the quenching and annealing systems are similar, both gels are considered to be in the same structure, and the gel observed in the quenching system at low temperature is in the metastable, supercooled state. Judging from the ¹H‐NMR data and microscopic observation, a homogenous gel is formed above 7 wt% of C18GS. With an increase in surfactant concentration, the thixotropic tendency of the gel increases due to the decrease in free‐water. Since it was difficult to show gel formation with the shorter chain homologs, C14GS and C12GS, the hydrocarbon chain length of the surfactant appears to be very important in the formation of a metastable, supercooled gel.     

Synthesis of L‐6‐Chloropyrroloindoline of Chloptosin Cyclohexapeptide

Abstract

Chloptosin is an apoptosis‐inducing dimeric cyclohexapeptide. Enantioselective synthesis of L‐6‐chloropyrroloindoline, as the key chiral synthon of the cyclohexapeptide of chloptosin, was successfully achieved starting from 3‐chloroaniline by utilizing Fischer indole/Schöllkopf protocol and oxidative cyclization of resulting L‐6‐chlorotryptophan.     

Studies Towards the Synthesis of the β‐D‐Xyl‐(1 → 3)‐L‐ara Disaccharide Moiety of OSW‐1 from Ornithogalum saundersiae

Abstract

The OSW‐1 disaccharide having 2‐O‐p‐methoxybenzoyl‐β‐D‐xylopyranosyl‐(1 → 3)‐L‐arabinopyranoside structure was obtained as the benzylated 4‐O‐acetyl derivative 19. Also, the 4,2′‐di‐O‐acetate 18 was synthesized by a short synthetic approach. The arabinose acceptor 15 was obtained in a three step‐one pot sequence from easily available benzyl β‐L‐arabinopyranoside.     

Conformation of Azobenzene‐Modified Poly(α‐L‐Glutamate) (AZOPLGA) in Thin Films: Solid State NMR Studies

Abstract

The conformations of azobenzene‐modified poly(α‐L‐glutamate)s (AZOPLGA) with a different degree of functionalization were examined by solid state ¹³C NMR. The polymer main chain conformations in AZOPLGA powders (precipitated from reaction system) changes from α‐helix to β‐sheet when the degree of functionalization increases from 12% to 56%. In addition, the solvent used for fabricating films plays an important role in organizing AZOPLGA backbones into characteristic conformation. For AZOPLGA56 (AZOPLGA with 56% of functionalization) cast films, the polymer backbones can assume conformations ranging from order state (β‐sheet) to random coil by changing the solvent for fabrication. In contrast, the effect of solvent on the conformation of AZOPLGA23 (AZOPLGA with 23% of functionalization) is not so significant. When compared with AZOPLGA23 powder (precipitated from reaction system), the helical conformation increases for AZOPLGA23 film cast from TFA. However, the fractions of α‐helix and β‐sheet conformation in AZOPLGA23 films (cast from DMF or pyridine) are nearly identical to that of AZOPLGA23 power. Moreover, even though the polymer backbones are random coil in AZOPLGA56 films when cast from TFA, some locally ordered domain can be observed. Lastly, the effect of the azo content appears to play a dominant role over the effect of solvents in directing the conformation of these polymers.     

The Structure of N‐(1‐Deoxy‐β‐D‐fructopyranos‐1‐yl)‐L‐proline Monohydrate (“D‐Fructose‐L‐proline”) and N‐(1,6‐Dideoxy‐α‐L‐fructofuranos‐1‐yl)‐L‐proline (“L‐Rhamnulose‐L‐proline”)

Nano n-propylsulfonated γ-Fe₂O₃ was found to be a highly efficient, reusable heterogeneous catalyst for the conversion of a range of monosaccharides and some of their derivatives to the corresponding O-isopropylidene derivatives in good to excellent yields by refluxing the reaction mixture in dry acetone. The magnetic property of the catalyst enabled its separation from the reaction mixture by a simple process of filtration along with the aid of an external magnet. The efficiency of the catalyst was found to be largely unaffected for at least up to six cycles of reuse, thus proving the new methodology to be environmentally rewarding besides being simple and facile in operation.     

Rapid and Efficient Microwave‐Assisted Synthesis of N‐Carbamoyl‐L‐amino Acids

A rapid and efficient method for the synthesis of N‐carbamoyl‐L‐amino acids is reported. The procedure, involving the reaction between urea and α‐amino acids sodium salts, was performed under microwave conditions using an unmodified domestic microwave oven. A careful study of the operative conditions indicated proline (1d) as the less reactive substrate and phenylglycine (1e) as the more reactive one among all the α‐amino acids tested. Substitution of urea with potassium cyanate produced a low conversion into the corresponding N‐carbamoyl derivative, and a possible explanation of this result is reported.     

Synthesis of the Aliphatic Subunit of the Macrolide LL‐Z 1640‐2 via Vasella Ring Opening of a 6‐Iodo‐4‐deoxy‐D‐mannose

The synthesis of the aliphatic subunit 9 of the macrolide LL‐Z1640‐2 (I), starting from a 4‐deoxy‐D‐mannose derivative 2a, is described. The procedure includes the first successful application of a Vasella ring opening reaction for a 4‐deoxypyranoside. Nucleophilic addition of an alkynyllithium reagent to the aldehyde 4 led to the propargylic alcohol 7, which was converted to the advanced building block 9 in two further steps.     

Dendritic Macroinitiator for the Ring—Opening Polymerization of γ—Benzyl L—Glutamate N—Carboxyanhydride

Much effort has been dedicated to the molecular design and synthesis of model proteins to define protein folding interactions and to develop protein-based materials. Among them, the ring-opening polymerization of -amino acid-N-carboxyanhy- drides (NCAs) has drawn much attention because the resulting artificial polypeptides have wide applications in biotechnology, biomineralization and diagnostics1, 2. It is well known that dendrimers are hyperbranched macromolecules possessing a very high co…     

Application of Dichlorovinyl Xyloside for the Novel Synthesis of 2,3,4‐Tri‐O‐methyl‐D‐xylono‐1,5‐lactone

A novel synthesis of 2,3,4‐tri‐O‐methyl‐D‐xylopyranose, 4, and its oxidation product 2,3,4‐tri‐O‐methyl‐D‐xylono‐1,5‐lactone, 5, are reported. The new synthesis applies a regioselective Wittig‐like reaction of tetra-O-acetyl-D-xylopyranase, 1, with triphenylphosphine and carbon tetrachloride to yield an O‐dichlorovinyl xyloside protected at C‐1, 2. The protecting group facilitates the permethylation of xylose and is removed under the methylation conditions, to yield tetra-O-acetyl-D-xylopyranase, 3. The anomeric methyl group was removed under mildly acidic conditions to give 2,3,4‐tri‐O‐methyl‐D‐xylopyranose, 4, in good yield. Compound 4 was oxidized using pyridinium chlorochromate to give the title compound, 5, in 95% yield.     

New Method for the Synthesis of 2‐Aza‐1,3‐Butadienes

2‐Aza‐1,3‐butadienes have been synthesized from carbonyl compounds and 1,1,1,3,3,3‐hexamethyl‐disilazane in the presence of cobalt‐containing catalysts. The best yields (up to 95%) were achieved in the case of aldehydes branched in the α-position and 2-methylcyclohexanone. In the case of two α,β‐unsaturated ketones, pyridine derivatives were found as the main products.     

Effect of Triton‐X‐100 Solvent in the Micellar Catalysis of the Aquation of Tris(2‐nitroso‐1‐naphtholate) Ferrate (II)

The effect of triton‐X‐100 micelles on the aquation of Fe(C₁₀H₆N₂O)₃ ²⁺ has been investigated with triton‐X‐100 as solvent. In liquid triton‐X‐100, over a range of [H₂O] _T (0.0–3 M), significant rate enhancement factors of 50–150 are observe. Acid inhibits the rate of aquation at fixed [H₂O] _T . A mechanism based on effective solvent participation in a chemical environment similar to that in reversed micelles is proposed in liquid triton‐X‐100 with dispersed water pockets. This mechanism predicts direct H₂O substitution into the coordination sphere of Fe(C₁₀H₆N₂O)₃ ²⁺ in the highly polar water pockets or cavities where the Fe (II) complex molecules are solubilized. Changes in the tumbling rate, structure, and activity of water are suggested to account for the observed changes in the rate of aquation as a function OH [H₂O] _T . All k _ψ–[H₂O] _T profiles are structured and exhibit maxima with k _ψ(max) shifted to progressively higher [H₂O] _T as the fixed concentration [H⁺] _T is increased.     

Two‐dimensional step‐scan FTIR: a tool to unravel the OH‐valency‐range of the spectrum of Cellulose I

This article presents the results of the first application of dynamic mechanical analysis (DMA) coupled with 2D stepscan Fourier transform infrared (FTIR) spectroscopy, to cellulose. It is demonstrated that the broad hydroxyl infrared absorption band between 3700 and 3000cm^–1 in the cellulose infrared spectra could be separated into distinct bands by this dynamic rheooptical investigation using FTIRspectroscopy as detecting system. The responses of the OHgroups to an external perturbation were recorded as inphase and outofphase spectra. The cross correlation of these spectra gave the 2D synchronous and asynchronous plots, which showed clearly separated bands in the OHvibration range and the relation of the OHgroups to each other. It is demonstrated that it is possible to establish relations between the OHbands and the cellulose structure.     

Synthesis and Characterization of Hydroxyl‐Terminated Poly(γ‐benzyl‐L‐glutamate)

In order to provide an active end group of hydroxyl group and improve the hydrophility of poly(γ‐benzyl‐L‐glutamate) (PBLG), ethanolamine (EA) was utilized as the initiator to initiate N‐carboxy‐γ‐benzyl‐L‐glutamate anhydride (Bz‐L‐Glu‐NCA) polymerization. The prepared hydroxyl‐terminated PBLG (HO‐PBLG) was fully characterized by FTIR, ¹H‐NMR, XPS, XRD, DSC, and GPC. The results of FTIR and XRD indicated that the chain conformation of HO‐PBLG predominantly presented α‐helix. The water contact angle was measured to confirm that the hydrophilicity was improved by the introduction of hydroxyl group. Chondrocytes studies showed that the cells attachment efficiency on the HO‐PBLG film was good and the cells grew well.     

Utility of 1‐Chloro‐3,4‐dihydronaphthalene‐2‐carboxaldehyde in the Synthesis of Novel Heterocycles with Pharmaceutical Interest

Ethyl α‐cyano‐β‐(1‐chloro‐3,4‐dihydronaphthalene‐2‐yl) acrylate (2) was prepared by the Knoevenagel condensation of 1 with ethyl cyanoacetate. Compound 2 was used as the key intermediate to prepare Schiff bases (3a, b), benzo[c]acridine (4), naphthyl thiopyrimidine (5), and pyrazolo[2,3‐a]‐benzo[h]quinazoline (6) derivatives through its reaction with hydrazines, p‐ansidine, thiourea, and 3,5‐diamino‐4‐phenylazopyrazole, respectively. Base‐catalyzed cyclocondensation of 1 with hippuric acid gives oxazolone derivative (7). Reaction of compound 7 with aniline gave imidazolone derivative (9). Treatment of compound 1 with different types of diaminopyrazoles gave 6,7‐dihydro‐pyrazolo[2,3‐a]‐benzo[h]quinazoline (10–13) derivatives. The multicomponent reaction of compound 1 with pyrazolone and malononitrile in the presence of ammonium acetate furnished pyrazolo[3,4‐b]‐benzo[h]quinoline (14) while in the presence of piperidine afforded benzo[h]chromeno[2,3‐c]pyrazole derivative 15.     

Practical One‐Pot Procedure for the Synthesis of 1,2,3,4‐Tetrahydroquinolines by the Imino‐Diels‐Alder Reaction

A novel‐one‐pot procedure for the synthesis of tetrahydroquinolines via the imino‐Diels‐Alder reaction is described. This procedure gives better yields and exhibits better versatility for alkene substrates than the existing hemi‐aminal based methodologies.     

Solid‐Phase Synthesis of N‐Aryl‐N′‐Carboalkoxy Guanidines by the Mitsunobu Reaction of Fmoc‐Guanidines

Abstract

A new method for the solid‐phase synthesis of N‐aryl‐N′‐carboalkoxy guanidines is described. Aromatic amines were reacted with Fmoc‐isothiocyanate to provide Fmoc‐thioureas, which were coupled with Rink amide resin to provide the corresponding resin‐bound Fmoc‐guanidines. Subsequent Mitsunobu alkylation with a variety of alcohols delivered N‐aryl‐N′ carboalkoxy guanidines in good to high purity after resin cleavage.     

RAFT Polymerization of Styrene in the Presence of 2‐Nonyl‐benzoimidazole‐1‐carbodithioic Acid Benzyl Ester

A novel dithiocarbamate, 2‐nonyl‐benzoimidazole‐1‐carbodithioic acid benzyl ester ( 1a ), was synthesized and successfully used in RAFT polymerization of styrene in bulk with thermal initiation. The effect of molar ratio of styrene to RAFT agent on the polymerization was investigated. The linear relationship between ln([M]₀/[M]) and polymerization time indicated that the polymerization was first‐order with respect to monomer concentration. The molecular weights increased linearly with monomer conversion and were close to corresponding theoretical values. The molecular weight distributions (M _w /M _n ) kept very narrow (M _w /M _n <1.1) at a wide range of conversions of 14.2% to 73.3%. The obtained polymer had a strong ultraviolet absorption at 329 nm, which indicated that the 1a moiety remained at the end of polymer chain.     

Improved Procedure for the Preparation of cis‐2,4‐Dimethylglutaranhydride

Addition of 2.5 mol% DBU to a mixture of isomeric 2,4‐dimethylglutaric anhydrides in ethyl acetate promotes crystallization‐induced transformation, affording the pure cis‐2,4‐dimethylglutaric anhydride in 87% yield.     

Generalization of the fourth‐order Hylleraas functional for the case of a non‐Hermitian unperturbed Hamiltonian

Generalization of the fourthorder Hylleraas functional form have been performed for the case of nonHermitian operators. Our new formulas are relevant when the Hermitian Born–Oppenheimer Hamiltonian is decomposed into a nonHermitian unperturbed part and also a nonHermitian perturbation. The results can be used to develop BSSEfree intermolecular perturbation theory up to fourthorder.     

One‐Pot Synthesis of 2‐Arylthio‐2‐cyclohexenone Derivatives by the Diels–Alder Reaction of 4‐Arylthio‐3‐hydroxy‐2‐pyrones

The base‐catalyzed Diels–Alder reactions of 4‐arylthio‐3‐hydroxy‐2‐pyrones are reported. Treatment of 4‐arylthio‐3‐hydroxy‐2‐pyrones and dienophiles with triethylamine gave 2‐arylthio‐2‐cyclohexenone derivatives by the Diels–Alder reaction involving a decarboxylation in excellent to reasonable yields.