Synthesis and structural studies of homooligomers of geminally disubstituted β(2,2)-amino acids with carbohydrate side chain

A new class of geminally disubstituted C-linked carbo-β(2,2)-amino acids (β(2,2)-Caa) were prepared from d-glucose. The structures of homooligomeric di-, tetra-, and hexapeptides prepared from (S)-β(2,2)-Caa were studied with NMR (in CDCl(3)), CD, and Molecular Dynamics calculations. These β(2,2)-peptides have shown the presence of stable 6-membered (6-mr) NH(i)···CO(i) intra-residue H-bonded (C(6)) strands. It was found that the strand structures realized in these systems were additionally stabilized by the electrostatic interaction arising due to the proximity of amide proton (NH(i)) to the oxygen of the preceding methoxy group (O(Me)(i-1)) at the C3 carbon of the carbohydrate ring. The new β(2,2)-Caa residues with additional support to H-bonding considerably expand the domain of foldamers.     

Synthesis of novel non-proteinogenic α-amino acids with charged imidazolium fragment in the side chain

Zwitterionic imidazolium and benzimidazolium salts bearing chiral amino acid moiety were synthesized using chiral Ni^II complexes. Different N-derivatives of the synthesized enantiomerically pure amino acids were prepared; their zwitterionic structures were confirmed by X-ray analysis.     

Synthesis and structural characterization of homochiral homo-oligomers of parent cis- and trans-furanoid-β-amino acids

The synthesis of homochiral homo-oligomers of cis- and trans-3-aminotetrahydrofuran-2-carboxylic acids (parent cis- and trans-furanoid-β-amino acids, referred to as "cis-/trans-FAA") has been carried out to understand their secondary structures and their dependence on the ring heteroatom. The oligomers of two diastereomers have been shown to have a distinct left-handed helicity. The cis-FAA homo-oligomers show a 14-helix structure, in contrast to the homo-oligomers of cis-ACPC, which adopt a sheet like structure. The trans-FAA homo-oligomers were found to adopt a 12-helix structure, the same trend found in trans-ACPC homo-oligomers. With the help of ab initio calculations, the structural features of cis-ACPC and cis-FAA hexamers were compared. We believe that the more compact packing of the cis-FAA hexapeptide should be due to a more favorable interaction between the ring and the backbone amide hydrogen.     

Catalytic asymmetric synthesis of the docetaxel (Taxotere) side chain: organocatalytic highly enantioselective synthesis of esterification-ready α-hydroxy-β-amino acids

A highly enantioselective catalytic route to protected β-amino-α-hydroxy acids, such as the side chain of Taxotere, is presented. The organocatalytic asymmetric reactions between unmodified protected α-oxyaldehydes and N-Boc-protected aryl imines give the corresponding compound with up to >19:1 dr and 99-99% ee.     

New pentacoordinated Schiff-base diorganotin(IV) complexes derived from nonpolar side chain α-amino acids

In this work we report the synthesis and spectroscopic characterization of twenty new pentacoordinated diorganotin(IV) compounds. These compounds have been prepared in good yields by multicomponent reactions (MCRs) of α-amino acids (isoleucine, leucine, methionine, phenylalanine and aminophenylacetic acid), 2,4-dihydroxybenzaldehyde, 2-hydroxy-4-methoxybenzaldehyde and either di-n-butyltin(IV) oxide or diphenyltin(IV) oxide. All compounds were characterized by IR spectroscopy, ¹H, ¹¹⁹Sn and ¹³C NMR spectroscopy and mass spectrometry. Each compound has a coordinative N→Sn bond and shows the expected ¹¹⁹Sn NMR chemical shift indicative of a pentacoordinated or hexacoordinated tin atom in CDCl₃ and DMSO-d₆, respectively. These compounds were also tested in tumoral cell lines, HeLa, HCT-15 and MCF-7, in order to evaluate the antiproliferative activity and to obtain the medial inhibitory concentrations (IC₅₀) values.     

Reduction ofβ-amino acids with lithium aluminum hydrids

Summary Some-amino acids were reduced to the corresponding amino alcohols with the aid of lithium aluminum hydride.Deceased.     

Complexes of copper(II) with sugar α-amino acids as ligands

Summary Complexes of Cu^II with 2-(benzylamino)-2-deoxy-d-glycero-d-talo heptonic acid (BnMa) and 2-(benzylamino)-2-deoxy-d-glycero-l-gluco heptonic acid (BnGa) were prepared and characterized by elemental analysis, thermal data, i.r., electronic and e.s.r. spectra, magnetic susceptibility measurements, and X-ray powder diffraction. The metal:ligand stoichiometry of these complexes is 12 and coordination around Cu^II seems to be octahedral, with the ligands bound through the N atom of the amino group and O atoms of the bridging carboxylate group.     

Deracemisation of α-amino acids—(R)- and (S)-phenylalanine from the same enantiomer of a homochiral auxiliary

Chiral auxiliary (3S)-N,N′-bis-(p-methoxybenzyl)-3-isopropylpiperazine-2,5-dione 1 was employed for the synthesis of both enantiomers of phenylalanine using a regioselective deprotonation/stereoselective reprotonation strategy. Modification of this approach enables the efficient deracemisation of (±)-phenylalanine.     

β-Strand mimetics: formation of bend-strands in oligomers of enantiomeric β-amino acids

Oligomers comprising of enantiomeric cis-oxo-β-norbornene amino acid [2R,3S] and [2S,3R] residues at alternate positions were synthesized and characterized by extensive NMR and MD studies, which showed robust bend-strand secondary structures.     

Reaction of 1-(R-Sulfonyl)indoles with N,N-Dibenzyl-β-amino Alcohols

The reaction of 1-(methylsulfonyl)- and 1-(phenylsulfonyl)indoles with N,N-dibenzylamino alcohols leads to the formation of a mixture of isomeric 1-(-aminoethyl)indoles.     

The influence of side substituents in α-amino acids on their sorption by a cation-exchange membrane

The isotherms of sorption of ornithine, lysine, arginine, and histidine by an MK-40 membrane were obtained by the method of variable concentrations. The influence of the geometric parameters of side groups in the basic amino acids and pH on the degree of their absorption by the membrane was studied. The formation of doubly charged amino acid cations in the membrane phase when membranes in the H⁺ form were used was substantiated IR spectroscopically. The distribution coefficient was found to depend linearly on the size of amino acid side groups. The dependence of interphase surface tension at the membrane-solution interface on the degree of membrane filling was indicative of the formation of sorbate associates in the membrane phase.     

Investigation of complexes of zinc(II) and cadmium(II)DI-n-butyldithiocarbamates with 2,2′-bipyridyl

A new mixed-ligand complex, Cd(S₂CN(C₄H₉)_{2 2})₂(2,2′-Bipy), was synthesized. A polycrystal X-ray diffraction analysis was performed (DRON-3M and DRON-UM1 diffractometers, CuK_α radiation, Ni filter) and the crystal structure was determined [Enraf-Nonius CAD-4 automatic diffractometer, MoK_α radiation, 2440 nonzero independent reflections, 153 refined structural parameters, R is 0.11 for I>2σ(I)]. Crystal data for C₂₈H₄₄CdN₄S₄ : a = 28.716(4), b = 6.848(6), c = 17.188(2) Å, space group Pcca, V-3380.2(7) ų, Z = 4, M = 679.42, dcaU.= 1.335 g/cm3. The structure consists of monomeric molecules in which the cadmium atom has a distorted octahedral environment. The polycrystal diffraction analysis revealed that the complex is isostructural with the defined complex Zn(S₂CN(C₄Hg)₂)₂(2,2′-Bipy). A crystal-chemical search on metal dialkyldithiocarbamates in the Cambridge Structural Database was accomplished and isostructural pairs of Zn and Cd metal complexes were found.     

Preparation of α-alkyl-β-amino acids via β-alanine Ni(II) complex

A new β-amino acrylic acid Ni(II) complex has been developed and used for the synthesis of α-alkyl-β-amino acids via alkylation with alkyl halides under operationally convenient conditions. The pivotal α-alkylated intermediate can be converted into the corresponding α-alkyl-β-amino acids via two steps with a wide range of substituents.     

Synthesis of (R)-(-)-γ-amino β-hydroxy Butyric Acid (GABOB)

An efficient enantiospecific synthesis of a neuromodulator, antiepileplic and hypotensive drug (R)-(-)-γ-amino-β-hydroxybutyric acid (1) starting from (+) tartaric acid is described.     

Complexes of Cu(II) with 2,2′-dipyridyl and some malonic acids

The stability constants of ternary complexes containing copper(II), 2,2′-dipyridyl and a set of mono- and di-substituted malonic acids, were obtained by potentiometric titrations. The results are discussed in terms of substituent influences upon the chelation of the malonic dianions to the system Cu(dip). It is suggested that the electronic and geometric characteristics of the strongest ligand, govern the coordination of the second one.     

Enantioselective synthesis of β-amino acids. Part 10: Preparation of novel α,α- and β,β-disubstituted β-amino acids from (S)-asparagine

Perhydropyrimidinone (S)-1 is alkylated with very high diastereoselectivity to give trans products (2S,5R)-3, (2S,5R)–4 and (2S,5R)-5. Dialkylation of (S)-1 also proceeds with complete stereoselectivity to afford adducts (2S,5R)-6, (2S,5S)-6, (2S,5R)-7 and (2S,5S)-7. Hydrolysis (6N HCl, 100°C) of monoalkylated derivative (2S,5R)-3 gives enantiopure α-substituted β-amino acid (R)-8. Hydrolysis of dialkylated adducts 6 and 7 affords enantiopure α,α-disubstituted β-amino acids (R)- or (S)-9 and (R)- or (S)-10. Related iminoester (2S,6S)-2 is alkylated with complete diastereoselectivity to give products (2S,6S)-11–13 whose hydrolysis under relatively mild conditions (2N CF₃CO₂H, CH₃OH, 100°C) affords enantiopure N-benzoylated β,β-disubstituted β-amino acid esters (S)-14–16, with intact double bonds in the olefinic substituents.