An enantioselective approach to bis-α-amino acids

Synthesis and applications of symmetric amino acid derivatives

Symmetric α-amino acid derivatives can be used for the synthesis of intermolecularly linked peptides such as dimer-type peptides, and modified peptides in which two amino acids are intramolecularly linked. They are also synthetic intermediates for the total synthesis of natural products and functional molecules. These symmetric amino acid derivatives must be prepared based on organic synthesis. It is necessary to develop an optimal synthetic strategy for constructing the target symmetric amino acid derivative. In this review, we will introduce strategies for synthesizing symmetric amino acid derivatives. Additionally, selected applications of these amino acids in the life sciences will be described.

Polysulfone nanofiltration membranes enriched with functionalized graphene oxide for dye removal from wastewater

Composite-nanofiltration membranes based on polysulfone (PSU) and functionalized graphene oxide (f-GO) were prepared for dye removal from aqueous media. Graphene oxide (GO) was introduced to enhance the performance of these membranes. GO was functionalized using an aminated heterocyclic compound, namely 6-amino-4-(4-nitrophenyl)-3-methyl-4-phenyl-4,7-dihydro-1H-pyrazolo-[3,4-b]pyridine-5carbonitrile. The f-GO was incorporated into the PSU membrane matrix in different weight ratios (0.25, 0.5, 1, 2 and 4 wt %). Characterizing the produced membranes with scanning electron microscope, Fourier Transform Infrared - Attenuated Total Reflectance (FTIR-ATR) and X-ray diffraction indicated the well dispersion of f-GO in the membrane matrix. The obtained membranes were applied to remove Congo red and methylene blue, as typical anionic and cationic dyes respectively from water. The modified membranes showed superior efficiency in terms of water flux and dye rejection upon being compared with the control membrane. The composite membranes loaded with f-GO exhibited promising dye removal efficiency for both dyes.

Catalytic Asymmetric Hydrogenation of Dehydroamino Acid Esters with Biscarbamate Protection and Its Application to the Synthesis of xCT Inhibitors

Catalytic asymmetric hydrogenation of dehydroamino acid esters with biscarbamate protection was examined for the first time to prepare optically active amino acids. The new method was successfully applied to the synthesis of new cystine-glutamate exchanger inhibitors.

Recent advances in asymmetric phase-transfer catalysis

The use of chiral nonracemic onium salts and crown ethers as effective phase-transfer catalysts have been studied intensively primarily for enantioselective carbon-carbon or carbon-heteroatom bond-forming reactions under mild biphasic conditions. An essential issue for optimal asymmetric catalysis is the rational design of catalysts for targeted reaction, which allows generation of a well-defined chiral ion pair that reacts with electrophiles in a highly efficient and stereoselective manner. This concept, together with the synthetic versatility of phase-transfer catalysis, provides a reliable and general strategy for the practical asymmetric synthesis of highly valuable organic compounds.

Synthesis of bis-armed amino acid derivatives via the alkylation of ethyl isocyanoacetate and the Suzuki–Miyaura cross-coupling reaction

Two synthetic routes to bis-armed-alpha-amino acid derivatives are described. The first route involves alkylation of dibromo derivatives with ethyl isocyanoacetate under phase-transfer catalysis (PTC) conditions. The second route uses a palladium-mediated Suzuki-Miyaura cross-coupling reaction between a DL-4-boronophenylalanine derivative and aromatic diiodo (or dibromo) compounds.

Efficient synthesis of 2-aminoindane-2-carboxylic acid via dialkylation of nucleophilic glycine equivalent

An efficient, easy to scale-up method for preparing 2-aminoindane-2-carboxylic acid via two-step alkylation of a Ni(II)-complex of glycine Schiff base with 2-[N-(alpha-picolyl)amino]benzophenone (PAAP) (2b) with o-dibromoxylylene (3) is reported. The first step, monoalkylation of 2b with 3, conducted under phase-transfer conditions, gave the corresponding complex 6 in excellent chemical yield (97.2%). Without any purification the intermediate 6 was cyclized under homogeneous conditions (DMF, NaO-t-Bu) to give the product 7 in high chemical yield (93.1%). Decomposition of prepared 7 afforded the target amino acid 2-aminoindane-2-carboxylic acid (1) in 97.9% yield, along with recovery of ligand 8, which was converted back to the starting glycine complex 2b. Operationally convenient experimental procedures, mild reaction conditions, as well as high chemical and volume yields render the method practical for preparing amino acid 1 and its analogues.