Organic conductors with BiIII and SbIII chloride-based anions

New layered organic conductors, (BEDT-TTF)4(BiCl5)1 7 (1), δ-(BEDT-TTF)2BiCl5 (2), and δ-(BEDT-TTF)6Sb3Cl12 (3), were obtained (BEDT-TTF is bis(ethylenedithio)tetrathia-fulvalene). In the crystal structures of 1—3, organic radical cation layers are composed of di-merized stacks. The dimers are formed by BEDT-TTF radical cations rotated through angle ω relative to each other, which results in twisted stacks, giving rise to so-called twisted overlap mode in the layers. These layers alternate with non-conductive inorganic layers consisting of chains in which the Cl, Bi, and Sb sites are partially occupied. This indicates discontinuities in the chains of anions, and, apparently, the absence of continuous polymer chains in the crystal structure. According to measurements of the temperature dependence of the electrical resistance, the compounds are semiconductors.

     

First structural characterization of binary AsIII and SbIII azides

The highly explosive molecules As(N(3))(3) and Sb(N(3))(3) were obtained in pure form by the reactions of the corresponding fluorides with (CH(3))(3)SiN(3) in SO(2) and purification by sublimation. The crystal structures and (14)N NMR, infrared, and Raman spectra were determined, and the results compared to ab initio second-order perturbation theory calculations. Whereas Sb(N(3))(3) possesses a propeller-shaped, pyramidal structure with perfect C(3) symmetry, the As(N(3))(3) molecule is significantly distorted from C(3) symmetry due to crystal packing effects.     

Heteropolymolybdates of phosphate,phosphonate, and phosphite functionalized by glycine

The novel, functionalized heteropolymolybdates [RPMo(6)O(21)(O(2)CCH(2)NH(3))(3)](2)(-) (R = OH, CH(3), C(2)H(5), H) have been synthesized and characterized by IR, (31)P NMR spectroscopy, and elemental analysis. Single-crystal X-ray analysis was carried out on K(2)[HOPMo(6)O(21)(O(2)CCH(2)NH(3))(3)].8.5H(2)O, which crystallizes in the orthorhombic system, space group Pnma, with a = 14.118(2) A, b = 20.660(3) A, c = 12.191(2) A, and Z = 4; K(2)[H(3)CPMo(6)O(21)(O(2)CCH(2)NH(3))(3)].8.5H(2)O, which crystallizes in the orthorhombic system, space group Pnma, with a = 14.1643(6) A, b = 20.8658(8) A, c = 12.2235(5) A, and Z = 4; and K(2)[HPMo(6)O(21)(O(2)CCH(2)NH(3))(3)].8H(2)O, which crystallizes in the orthorhombic system, space group Pnma, with a = 14.092(3) A, b = 20.696(2) A, c = 12.199(4) A, and Z = 4. We also report on the synthesis and characterization of the isostructural derivative K(2)[H(5)C(2)PMo(6)O(21)(O(2)CCH(2)NH(3))(3)]. The four title polyanions consist of an RP (R = OH, CH(3), C(2)H(5), H) hetero group surrounded by a ring of six MoO(6) octahedra sharing edges and corners alternatingly. Three glycine molecules are each bound to two edge-sharing Mo centers via their carboxylate functionality on the same side of the ring. The central phosphorus atom is located slightly above the plane of the six molybdenums, and its terminal R group is on the same side of the ring as the glycines. NMR studies show that the solid state structures of the title compounds are preserved in solution.     

Recognition of amino acids by functionalized calixarenes

The calixarenic receptors exhibit remarkable host-guest properties towards biologically relevant guests. Aspects of complex formation reactions between both native and derivatized amino acids, di-and tripeptides with calixarenic (chiral or not) receptors are summarized in this critical review. Thus, the discussions emphasize the parameters that affect the molecular binding selectivity and efficiency of functionalized calix[n]arenes towards these substrates. A brief survey on their application in separation of amino acids is also considered (123 references).     

Synthesis of functionalized guanidino amino acids

We report the synthesis of guanidino amino acids (GuAA), which are structurally related to Arg and resemble a dipeptide consisting of alpha- and gamma-amino acid with a guanidinium group in the main chain. The compounds are available with different protecting groups in gram amounts and are intended as synthetic building blocks for the construction of synthetic oxoanion or peptide receptors. Tyr, Trp or dansyl-functionalized Lys can be introduced as the alpha-amino acid part, which leads to luminescent GuAAs. The compounds signal carboxylate binding in MeOH, DMSO and buffered water by change of the emission intensity. The property may find use in the construction of chemosensors.     

A facile transformation of amino acids to functionalized coumarins

The synthesis of novel chiral coumarins functionalized with proteinogenic amino acid side chains via N-protected γ-amino-β-keto esters and their incorporation into the cell permeable HIV-1 TAT peptide through the modified solid phase peptide synthesis are described.     

Tetraalkylammonium amino acids as functionalized ionic liquids of low viscosity

Four of nine tetraalkylammonium-based amino-acid ionic liquids prepared in this work show lower viscosities than all amino acid-based ionic liquids found in the literature and their reversible CO(2) absorption approaches 0.5 mol per mol ionic liquid.     

Isostructural hybrid iodometalate(III)/triiodide salts with perovskite-like packing: comparison of physical properties for SbIII and BiIII complexes

Reactions of Sb₂O₃ or Bi₂O₃, 1,2-bis(4-pyridyl)ethane (bpe) and diiodine in concentrated HI resulted in isostructural salts (H₂bpe)₂[MI₆](I₃) [M = Sb (1), Bi (2)] featuring perovskite-like arrangement of anions in crystal packing. Physical properties, including UV-Vis and Raman spectra, as well as thermal stability, were investigated and compared for this pair of complexes; the optical band gaps for 1 and 2 are 1.32 and 1.57 eV, respectively.     

A highly enantioselective amino acid-catalyzed route to functionalized alpha-amino acids

The development of syntheses providing enantiomerically pure alpha-amino acids has intrigued generations of chemists and been the subject of intense research. This report describes a general approach to functionalized alpha-amino acids based on catalytic asymmetric synthesis. Proline catalyzed Mannich-type reactions of N-PMP-protected alpha-imino ethyl glyoxylate with a variety of unmodified ketones to provide functionalized alpha-amino acids in high yields with excellent regio-, diastereo-, and enantioselectivities. Study of seven examples yielded six with product ee values of > or = 99%. In reactions involving ketone donors where diastereoisomeric products could be formed, two adjacent stereogenic centers were created simultaneously upon carbon-carbon bond formation with complete syn-stereocontrol. Significantly, this methodology utilizes readily available and rather inexpensive starting materials, does not require any preactivation of substrates or metal ion assistance, and can be carried out on a gram scale under operationally simple reaction conditions. The keto-functionality present in the products provides a particularly attractive site for versatile modifications. This study compliments and extends our bioorganic approach to asymmetric synthesis to a versatile synthon class. Given that we have shown that a variety of optically active amino acids can be synthesized with proline catalysis, where an L-amino acid begets other L-amino acids, our results may stimulate thoughts concerning prebiotic syntheses of optically active amino acids based on this route.     

Asymmetric synthesis of functionalized aza-cyclic amino acids with quaternary stereocenters by a phase-transfer-catalyzed alkylation strategy

[Reaction: see text] Practical asymmetric synthesis of functionalized aza-cyclic alpha-amino acid derivatives possessing quaternary stereocenters has been achieved by the phase-transfer-catalyzed alkylation of 2 or 3 using chiral quaternary ammonium bromide 1 as catalyst. Subsequent reduction and alkylation of the 3-keto carbonyl moiety of 4 proceeded with complete diastereochemical control to afford the corresponding beta-hydroxy aza-cyclic alpha-amino acid derivatives having stereochemically defined consecutive quaternary carbon centers.     

Synthesis of alkynes and alkynyl iodides bearing a protected amino alcohol moiety as functionalized amino acids precursors

Amino acid precursors in protected amino alcohol form are important synthons that can be used as building-blocks for the hemisynthesis of non-natural amino acids. Serine can be used as a common starting material for the synthesis of such compounds differently protected. Particularly, protected amino alcohols bearing an ethynyl and/or an iodoethynyl group can be used in cross-couplings, in 1,3-dipolar cycloadditions and/or in Nozaki-Hiyama-Kishi type reactions. We thus demonstrated that the efficiently protected amino alcohols derived from serine can be coupled to a sugar derivative by an indium mediated alkynylation reaction. The conditions of this coupling are compatible with such functionalized derivatives and allow envisaging an access to C-glycosylated amino acids.     

Silyl-substituted amino acids: new routes to the construction of selectively functionalized peptidomimetics

[reaction: see text]. Silylated amino acids have been incorporated into peptides and then converted into N-acyliminium ions with the use of an anodic oxidation reaction. The result is a method for selectively incorporating conformational constraints or external nucleophiles within the peptide.     

Abc amino acids: design, synthesis, and properties of new photoelastic amino acids

Photoisomerizable amino acids provide a direct avenue to the experimental manipulation of bioactive polypeptides, potentially allowing real-time, remote control of biological systems and enabling useful applications in nanobiotechnology. Herein, we report a new class of photoisomerizable amino acids intended to cause pronounced expansion and contraction in the polypeptide backbone, i.e., to be photoelastic. These compounds, termed Abc amino acids, employ a photoisomerizable azobiphenyl chromophore to control the relative disposition of aminomethyl and carboxyl substituents. Molecular modeling of nine Abc isomers led to the identification of one with particularly attractive properties, including the ability to induce contractions up to 13 A in the backbone upon trans --> cis photoisomerization. This isomer, designated mpAbc, has substituents at meta and para positions on the inner (azo-linked) and outer rings, respectively. An efficient synthesis of Fmoc-protected mpAbc was executed in which the biaryl components were formed via Suzuki couplings and the azo linkage was formed via amine/nitroso condensation; protected forms of three other Abc isomers were prepared similarly. An undecapeptide incorporating mpAbc was synthesized by conventional solid-phase methods and displayed characteristic azobenzene photochemical behavior with optimal conversion to the cis isomer at 360 nm and a thermal cis --> trans half-life of 100 min at 80 degrees C.     

Alkylated sugar amino acids: a new entry toward highly functionalized dipeptide isosters

[reaction: see text] Novel highly functionalized dipeptide isosters are synthesized via a diastereoselective alkyl/arylation protocol of a glucose-derived (R)-tert-butanesulfinylimine. One of these novel sugar amino acid derivatives, a D-Ala-Ser/Thr isostere, was applied in a peptide synthesis protocol to afford a cyclic tetramer.     

Empirical and ab initio calculations of thermochemical parameters of amino acids: IV. Non-Typical amino acids: Hydroxyamino acids, thioamino acids, and heterocyclic amino(imino) acids

Using a set of computational methods we calculated the basic thermochemical characteristics of the fifteen non-typical L-??-amino acids of hydroxyaminocarboxylic and thioaminomonocarboxylic series, and of some heterocyclic amino(imino)carboxylic acids.     

Photolysis of diacyl peroxides: a radical-based approach for the synthesis of functionalized amino acids

[reaction: see text] Photolysis of the amino acid derived symmetrical and unsymmetrical diacyl peroxides at 254 nm at low temperature (-78 to -196 degrees C) generates various bis(amino acids) in a concise manner and with orthogonal protection. The methodology was applied to the synthesis of (4R)-5-propyl-L-leucine (PrLeu), a component of HUN-7293.     

The phosphorylation of carboxylic acids and amino acids by diseryl pyrophosphates

Summary 1. From the reaction of chymotrypsin with the NPE of CBZ-L- and CBZ-D-valine the enzyme-substrate compounds CBZ-L-valylchymotrypsin and CBZ-D-valylchymotrypsin have been isolated. The methyl esters of benzoyl-D-phenylalanine and of benzoyl-L-valine also form enzyme-substrate compounds with chymotrypsin, although to a smaller extent. The methyl ester of benzoyl-D-valine does not react with chymotrypsin.2. Conditions for the isolation of a water-soluble enzyme-substrate compound have been found.Khimiya Prirodnykh Soedinenii, Vol. 2, No. 2, pp. 134–138, 1966Given at the First All-Union Biochemical Congress, 25 January 1964 (Leningrad).