Arborescent polypeptides from γ‐benzyl l‐glutamic acid

The synthesis of arborescent polymers with poly(γ‐benzyl L‐glutamate) (PBG) side chains was achieved through successive grafting reactions. The linear PBG building blocks were produced by the ring‐opening polymerization of γ‐benzyl L‐glutamic acid N‐carboxyanhydride initiated with n‐hexylamine. The polymerization conditions were optimized to minimize the loss of amino chain termini in the reaction. Acidolysis of a fraction of the benzyl groups on a linear PBG substrate and coupling with linear PBG using a carbodiimide/hydroxybenzotriazole promoter system yielded a comb‐branched or generation zero (G0) arborescent PBG. Further partial deprotection and grafting cycles led to arborescent PBG of generations G1 to G3. The solvent used in the coupling reaction had a dramatic influence on the yield of graft polymers of generations G1 and above, dimethylsulfoxide being preferable to N,N‐dimethylformamide. This grafting onto scheme yielded well‐defined (M_w/M_n ≤ 1.06), high molecular weight arborescent PBG in a few reaction cycles, with number‐average molecular weights and branching functionalities reaching over 10⁶ and 290, respectively, for the G3 polymer. α‐Helix to coiled conformation transitions were observed from N,N‐dimethylformamide to dimethyl sulfoxide solutions, even for the highly branched polymers. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 5270–5279     

3,6‐Bis­(4‐hydroxy­benzyl)­piperazine‐2,5‐dione

In the title compound, C₁₈H₁₆N₂O₄, the piperidine ring adopts a chair conformation, lying on an inversion centre. The 4‐hydroxy­benzyl groups are in quasi‐axial positions. A two‐dimensional network is formed through N—H?O and O—H?O intermolecular hydrogen bonds and C—H?O interactions.     

Ethyl 2‐form­amido‐2‐(4‐iodo­benzyl)‐3‐(4‐iodo­phenyl)­propionate and ethyl 2‐(3‐bromo­benzyl)‐3‐(3‐bromo­phenyl)‐2‐form­amidopropionate

The title compounds, C₁₉H₁₉I₂NO₃ and C₁₉H₁₉Br₂NO₃, are derivatives of α‐amino­isobutyric acid with halogen substituents at the para and meta positions, respectively. The ethoxycarbonyl and formamide side chains attached to the C_α atom of the mol­ecule adopt extended and folded conformations, respectively. The crystal structures are stabilized by N—H⃛O, C—H⃛O, C—Br⃛O and C—I⃛O interactions.     

Three 1,2,4‐triazole derivatives containing subtituted benzyl and benzyl­amino groups

The title compounds, 4‐benzyl­amino‐3‐(4‐methyl­benzyl)‐1H‐1,2,4‐triazol‐5(4H)‐one, C₁₇H₁₈N₄O, (I), 3‐(4‐methyl­benzyl)‐4‐(4‐methyl­benzyl­amino)‐1H‐1,2,4‐tri­azol‐5(4H)‐one, C₁₈H₂₀N₄O, (II), and 3‐(4‐chloro­benzyl)‐4‐(4‐methyl­benzyl­amino)‐1H‐1,2,4‐triazol‐5(4H)‐one, C₁₇H₁₇ClN₄O, (III), were obtained from the corresponding Schiff base in the presence of diglyme and NaBH₄. Each compound contains a 1,2,4‐triazole ring and two benzene rings, which are essentially planar. The molecules are linked by a combination of intermolecular N—H⋯O and N—H⋯N hydrogen bonds. Additionally, there is a weak π–π stacking interaction in (I), involving the benzene ring of the amino­benzyl group and the partially aromatic 1,2,4‐triazole moiety, with a centroid–centroid distance of 3.7397 (10) Å.     

Self‐Assembly of Poly(γ‐benzyl L‐glutamate)‐graft‐Poly(ethylene glycol) and Its Mixtures with Poly(γ‐benzyl L‐glutamate) Homopolymer

Summary: Self‐association behaviors of poly(γ‐benzyl L ‐glutamate)‐graft‐poly(ethylene glycol) (PBLG‐graft‐PEG) and its mixtures with PBLG homopolymer in aqueous media were investigated by fluorescence spectroscopy, transmission electron microscopy (TEM), and nuclear magnetic resonance (NMR) spectroscopy. It was revealed that PBLG‐graft‐PEG could self‐assemble to form polymeric micelles with a core‐shell structure in the shape of spindle. The introduction of PBLG homopolymer not only decreases the critical micelle concentration, but also changes the morphology of the micelles.

The excitation fluorescence spectra of pyrene as a function of concentrations for the mixture of PBLG‐graft‐PEG with PBLG and a TEM image of the formed micelles.     

2,4‐Bis(α,α‐di­methyl­benzyl)­phenol

The structure of the title compound, 2,4‐bis(1‐methyl‐1‐phenylethyl)phenol, C₂₄H₂₆O, was found to have a torsion angle of 129.95 (13)° for the C—C bond that connects the benzyl carbon to the phenol ring ortho to the OH group. A value of ～50° was expected from molecular mechanics calculations. Intermolecular interactions, in particular O—H?O and edge–face π bonding, may contribute to this discrepancy. Intramolecular O—H?π bonding is also observed.     

Microwave‐accelerated synthesis of benzyl 3,5‐dimethyl‐pyrrole‐2‐carboxylate

Benzyl 3,5‐dimethyl‐pyrrole‐2‐carboxylate, a very useful pyrrole in porphyrin and dipyrromethene synthesis, can be synthesized via the Knorr‐type reaction, but in low yield. Alternative routes to benzyl 3,5‐dimethyl‐pyrrole‐2‐carboxylate have been developed involving the trans‐esterification of ethyl 3,5‐dimethyl‐pyrrole‐2‐carboxylate and the de‐acetylation of benzyl 4‐acetyl‐3,5‐dimethyl‐2‐carboxylate, both precursors being easily obtained using the Knorr reaction. These traditional methods involve treatment of the known products with a strong basic solution or heating for extended periods which often lead to decomposition. The use of microwave energy to promote these two reactions proves to be an extremely efficient way to obtain benzyl 3,5‐dimethyl‐pyrrole‐2‐carboxylate quickly, in high yield, and in excellent purity with no need for recrystallization. Of particular note is the use of catalytic sodium methoxide in benzyl alcohol, rather than stoichiometric amounts of sodium benzoxide, to effect benzylation.     

Microstructural characterization of terpolymers of leucine, β‐benzyl aspartate,and valine

Three different characterization methods—¹³C NMR spectroscopy, a terminal terpolymerization model, and a probability analysis based on the Poisson distribution—were used to determine the microstructure of random terpolymers. The methods were used to determine the amino acid sequence distribution of random terpolymers prepared from the polymerization of N‐carboxyanhydrides that contained L ‐leucine, β‐benzyl‐L ‐aspartate, and L ‐valine. Poly(L ‐leucine‐L ‐aspartic acid‐L ‐valine) [poly(LDV)] was designed as a target specific substrate for the α₄β₁ integrin that recognizes the tripeptide sequence leucine‐aspartic acid‐valine (LDV). The presence of the tripeptide sequence LDV within the polymer was determined to be eight LDV triad sequences on average in terpolymers of approximately 100 kDa. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4328–4337, 2006     

Combined experimental and computational modeling studies on 3,5‐dimethyl‐pyrazole‐1‐carbodithioic acid benzyl ester

The title compound, 3,5‐Dimethyl‐pyrazole‐1‐carbodithioic acid benzyl ester, has been synthesized and structurally characterized by X‐ray single crystal diffraction, elemental analysis, IR spectra, and UV‐Vis spectrum. The crystal belongs to orthorhombic, space group P212121, with a = 5.3829(15), b = 11.193(3), c = 21.824(6) Å, V = 1315.0(6) ų, and Z = 4. The molecules are connected via intermolecular C–H···N hydrogen bonds into 1D infinite chains. The crystal structure is consolidated by the intramolecular C–H···S hydrogen bonds. Furthermore, Density functional theory (DFT) calculations of the structure, stabilities, orbital energies, composition characteristics of some frontier molecular orbitals and Mulliken charge distributions of the title compound were performed by means of Gaussian 03W package and taking B3LYP/6‐31G(d) basis set. The time‐dependent DFT (TD‐DFT) calculations have been employed to calculate the electronic spectrum of the title compound, and the UV‐Vis spectra has been discussed on this basis. The results show that DFT method at B3LYP/6‐31G(d) level can well reproduce the structure of the title compound. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012     

An unexpected transformation of benzyl carbamates into α-azidobenzeneacetamides

Successive treatment of benzyl carbamates 5 (Z-protected secondary amines) with lithium diisopropylamide (LDA), diphenyl phosphorochloridate (DPPC1), and NaN 3 yielded the corresponding ã-azidobenzeneacetamides 6 in 45–50% yield (Schemes 2 and 3). In the case of Z-protected diisopropylamine 5b , the phosphate 7 was isolated as a minor product. A reaction mechanism for this unexpected transformation is proposed in Scheme 4, the key step being the ring closure of a benzylic anion to give an oxirane intermediate B. In cursory experiments, it was demonstrated that ã-azidobenzeneacetamides 6 can be used as 2-phenylglycine synthons in the formation of dipeptides by using a phosphine-mediated coupling (Scheme 5).     

1‐(1H‐Indol‐3‐ylcarbonyl)‐N‐(4‐methoxy­benzyl)formamide

In the title compound, C₁₈H₁₆N₂O₃, the indole ring is planar and the two adjacent carbonyl groups are mutually trans oriented with a torsion angle of 144.8 (3)°. The single C—C bond linking the two carbonyl functionalities is 1.539 (4) Å. Mol­ecules are linked into a two‐dimensional network by inter­molecular N—H⋯O hydrogen bonds.     

Stereospecific polymerization of benzyl α-(alkoxymethyl) acrylates

α-(Alkoxymethyl) acrylates, such as methyl α-(phenoxymethyl) acrylate, benzyl α-(methoxymethyl)acrylate (BMMA), benzyl α-(benzyloxymethyl)acrylate, and benzyl α-(tert-butoxymethyl)acrylate, were synthesized, and their polymerizability and the stereoregularity of the polymers obtained by radical and anionic methods were investigated. The radically obtained polymers were found to be atactic by ¹³C- and ¹H-NMR analyses, but the polymers obtained with lithium reagents in toluene at −78°C were highly isotactic. Further, it is noteworthy that isotactic polymers were also produced with lithium reagents even in tetrahydrofuran. Effects of polymerization temperature and counter cation on stereoregularity were clearly observed in the polymerization of BMMA, and a potassium reagent afforded an almost atactic polymer. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 721–726, 1997     

Phase behaviour of poly-(λ-benzyl-L-glutamate) in benzyl alcohol

Polarized optical microscopy has been used to investigate phase transitions in the poly-(λ-benzyl-L-glutamate) benzyl alcohol system and these have been compared with the predictions of Flory. All of the samples studied form gels at room temperature. The behaviour of the lowest concentration studied, 5 per cent by volume, shows transitions in the optical microscope compatible with the Flory phase diagram, becoming isotropic at elevated temperatures. Gels of higher concentrations exhibit bulk phase separation into an isotropic liquid phase and an anisotropic phase at room temperature, also in accord with the Flory predictions; the texture of the anisotropic phase varies with concentration. At higher temperatures these concentrations exhibit two coexistent anisotropic phases.     

α'β-Elimination and wittig rearrangement of the carbanion from benzyl cyclooctyl ether

Beside the Wittig rearrangement and the migration of the cyclooctyl radical to the para position, the title carbanion gives rise to an elimination in a syn process.     

Preparation of benzyl acetate using polyaniline salts as catalysts ‐ Part II

Polyaniline salts were prepared by oxidizing aniline in presence of acid using benzoyl peroxide as an oxidizing agent. Polyaniline salt was used as catalyst for the esterification reaction of phenyl acetic acid with methanol. The process is being reported for the first time. Preparation of catalyst, recovery and reusability of the catalyst were found to be good. Copyright © 2004 John Wiley & Sons, Ltd.