Amino Acid Based Epoxy-Poly(Ester Amide)s—A New Class of Functional Biodegradable Polymers: Synthesis and Chemical Transformations

A new class of biodegradable functional polymers – epoxy-poly(ester amide)s (EPEAs), was synthesized for the first time on the basis of naturally occurring α-amino acids, fatty diols and cis- and trans-epoxysuccinic acids. The syntheses were conducted via both solution Active Polycondensation and Interfacial Polycondensation using, accordingly, either activated di-p-nitrophenyl esters or dichlorides of cis- and trans-epoxysuccinic acids as bis-electrophilic monomers. Di-p-toluenesulfonic acid salts of bis-(L-phenylalanine)-1,6-hexylene and bis-(L-leucine)-1,6-hexylene diesters were used in both cases as bis-nucleophilic counter-partners. High-molecular-weight polymers (M_w up to 67.000) with desirable material properties were obtained via solution polycondensation using di-p-nitrophenyl-trans-epoxy succinate. The EPEAs were chemically modified further under mild conditions: oxirane groups along the backbone were reacted with both nucleophilic and electrophilic reagents, and also subjected to thermal and chemical curing. The macromolecular transformations of EPEAs substantially broaden material properties and, hence, the potential to apply amino acid-based biodegradable poly(ester amide)s as absorbable drug carriers and surgical devices.     

The Simple Synthesis of Chiral Polyazaoxacoronands Derived from α-Amino Acids

Abstract

Bisamidation of oxaloyl chloride using L-amino acid methyl ester hydrochlorides afforded chiral diesters. The following reactions of diesters with 2,2-(ethylene-dioxy)diethylamine, afforded tetramides possessing C₂ symmetry. Coupling of N-hydroxysuccinimide ester of N-benzyloxycarbonyl-L-alanine with 1,5-diamino-3-oxapentane, followed by cleavage of protecting groups, afforded an optically active diamine, which was transformed consequently into tetramide via the reaction with diglycolic acid dimethyl ester under high pressure conditions.     

1H-NMR Study on Inclusion Modes of 2-Chloronaphthalene and α-Cyclodextrin in D2

Abstract

With a 1:1 and a 2:1 host-guest stoichiometry, α-cyclodextrin (α-CD) forms inclusion complexes with 2-chloronaphthalene. From simulations concerning observed chemical-shift differences (Δδ_obs) of proton signals of 2-chloronaphthalene, intrinsic Δδ values are estimated for all the guest protons in the 1:1 and 2:1 inclusion complexes. The intrinsic Δδ values indicate that α-CD first binds to a part of a naphthalene ring bearing a C1 atom to form the 1:1 inclusion complex. In the 1:1 and 2:1 inclusion complexes, the symmetry axes of α-CD are tilted approximately 30° relative to a naphthalene longitudinal axis. In the 2:1 inclusion complex, the association through hydrogen bonding most likely occurs between two α-CD molecules whose symmetry axes are laterally shifted.     

One pot synthesis of unsymmetrical dihydropyridines by green,catalyst free and environmentally benign protocol

Abstract

A facile and ecofriendly synthesis of β-enamino esters is reported by reaction of both aliphatic and aromatic amines with β-keto esters by refluxing in ethanol in absence of any catalyst. Addition of α,β-unsaturated aldehydes to the reaction mixture leads to the formation of unsymmetrical dihydropyridine derivatives which generally are metal free hydrogen sources for asymmetric reduction reactions.     

A novel amperometric biosensor based on a co-crosslinked l-lysine-α-oxidase/overoxidized polypyrrole bilayer for the highly selective determination of l-lysine

An amperometric biosensor for the determination of l-lysine based on l-lysine-α-oxidase immobilized by co-crosslinking on a platinum electrode previously modified by an overoxidized polypyrrole film is described. The optimization of experimental parameters, such as pH and flow rate, permitted to minimize significantly substrate interferences even using a low specific, commercial enzyme. The relevant biases introduced in the measurement of lysine were just about 1% for l-arginine, l-histidine and l-ornithine, roughly 4% for l-phenylalanine and l-tyrosine. The developed approach allowed linear lysine responses from 0.02 mM up to 2 mM with a sensitivity of 41 nA/(mM × mm²) and a detection limit of 4 μM (S/N = 3). No appreciable loss in lysine sensitivity was observed up to about 40 days. Allowing polypyrrole layer to remove interference from electroactive compounds, the present method revealed suitable to detect l-lysine in a pharmaceutical and cheese sample, showing a good agreement with the expected values.     

The Reaction of 1-Nitro-4-(4-nitrophenylsulfonylmethyl)benzene with α,β-Unsaturated Esters

Under solid-liquid PTC conditions, treatment of 1-nitro-4-(4-nitrophenylsulfonyl-methyl)benzene(1) with α,β -unsaturated esters (2a-h) at 35–75°C gave tandem addition-rearrangement products(3a-h). While at higher temperature(75°C), addition-rearrangement-addition products (4a-b) were obtained when acrylates were used. Finally a possible mechanism is proposed.     

An Efficient Procedure for the Preparation of 3′-Acetyl-2′,3′-dihydrobenzothiazoles by Ring Contraction of 2′,3′-Dihydro-1,5-Benzothiazepines Under Acetylating Conditions

Reaction of 2-benzoyl-6-hydroxy-3-methyl-5-(2′-substituted-2′,3′-dihydro-1,5-benzothiazein-4′-yl) benzofurans (4a-f) with a mixture of acetic anhydride and pyridine afforded 6-acetoxy-2-benzoyl-3-methyl-5-(3′-acetyl-2′-substitutedstyryl-2′,3′-dihydrobenzothiazole-2′-yl) benzofurans (5a-f) as sole products in good yields. A reaction mechanism for the ring contraction is proposed. All the compounds (5a-f) were screened for their antifeedant activity by the “Non-Choice test method” using 6 h prestarved fourth instar larvae of Spodoptera litura F. Compounds 5a, 5c and 5d exhibited highest antifeedant activity.     

Ionic Liquid–Catalyzed Internal Redox Esterification Reaction

The internal redox esterification of α,β-unsaturated aldehydes and alcohols was carried out using different ionic liquids (ILs) as catalysts and reaction solvents. The basic ionic liquid, 1-butyl-3-methylimidazolium acetate ([bmim]OAc), exhibited the best activity for this reaction. The influences of the amount of ionic liquid catalyst and reaction time on yield of saturated ester have been investigated. The results showed that ionic liquid anions have a crucial effect on the redox esterification of α,β-unsaturated aldehydes and alcohols. The nucleophilic carbenes generated in situ from the ionic liquid cation were believed to be actual active species for this reactions.     

Synthesis of Dimedone-Annelated Heterocycles: Regioselective Heterocyclization of 2-(Cyclohex-2′-enyl)-5,5-dimethyl-3-hydroxy cyclohex-2-enone

Abstract

2-(Cyclohex-2′-enyl)-5,5-dimethyl-3-hydroxycyclohex-2-enone undergoes regioselective heterocyclization to give bridged heterocycles 5a,b and 7 on treatment with pyridine hydrotribromide or hexamethylenetetramine hydrotribromide (1 h); or elemental bromine (7 h); N-iodosuccinimide in acetonitrile at 0–5°C (1 h) and conc. H₂SO₄ at 0–5°C (2 h), respectively.