(+)- and (-)-2-aminocyclobutane-1-carboxylic acids and their incorporation into highly rigid beta-peptides: stereoselective synthesis and a structural study

[Chemical reaction: See text] Several derivatives of (+)- and (-)-2-aminocyclobutane-1-carboxylic acid, 1, have been prepared through enantiodivergent synthetic sequences. The stereoselective synthesis of free amino acid (+)-1 has been achieved, and this product has been fully characterized for the first time. Stereocontrolled alternative synthetic methodologies have been developed for the preparation of bis(cyclobutane) beta-dipeptides in high yields. Among them, enantio and diastereomers have been synthesized. beta,beta- and beta,delta-Dimers resulting from the coupling of a cyclobutane residue and a linear amino acid have also been prepared. The ability of the cyclobutane ring as a structure-promoting unit both in the monomers and in the dimers has been manifested. The NMR structural study and DFT theoretical calculations evidence the formation of strong intramolecular hydrogen bonds giving rise to cis-fused [4.2.0]octane structural units that confer high rigidity on these molecules both in solution and in the gas phase. The contribution of a cis-trans conformational equilibrium derived from the rotation around the carbamate N-C(O) bond has also been observed, the trans form being the major conformer. In the solid state, this equilibrium does not exist, and moreover, intermolecular hydrogen bonds are present.     

Degradation thermique et etude vibrationnelle de MII(NH4)4(P3O9)2x4H2O(M II=Cu2+, Ni2+, Co2+)

We have studied the thermal behaviour under atmospheric pressure of isotypic tetrahydrate cyclotriphosphates M^II(NH₄)₄(P₃O₉)₂x4H₂O (M ^II=Cu, Ni and Co), between 25 and 1400°C, by X-ray diffraction, thermal analyses (TG and DTA) and infrared spectrometry. This study shows that the series of the compounds M^II(NH₄)₄(P₃O₉)₂x4H₂O (M ^II=Cu, Ni and Co) after elimination of water, in two different stages, and ammonia leads, at 400°C to cyclotetraphosphate M₂ ^IIP₄O₁₂ crystallized and to a thermal residue with a formula H₄P₄O₁₂ which undergoes under a thermal degradation by evolving water and pentoxide phosphorus. The kinetic characteristics of the dehydration and elimination of ammonia have been determinated. The vibrational spectra of Cu(NH₄)₄(P₃O₉)₂x4H₂O were examined and interpreted, in the domain of the valency frequencies, on the basis of the crystalline structure of its isotypic compound Co(NH₄)₄(P₃O₉)₂x4H₂O whose cycle has the site symmetry C₁, of our results of the calculation of the IR frequencies and the successive isotopic substitutions of the equivalent atoms (3P, 3Oi and 6Oe belonging to the P₃Oi₃Oe₆ ring) of the P₃O₉ ³⁻ cycle with high symmetry D_3h. This revised version was published online in August 2006 with corrections to the Cover Date.     

Etude Des Propriétés Physico-Chimiques De ZnRb 4 (P 3 O 9 ) 2 ·6H 2 O

The dehydration of ZnRb 4 (P 3 O 9 ) 2 ·;6H 2 O was investigated, between 25 and 600°;C, by TG-DTA, X-ray diffraction, IR. It leads, between 300 and 500°;C, to a mixture of long chain polyphosphates RbPO 3 and ZnRb 2 (PO 3 ) 4 which stays stable until its melting point. The IR (1400-30 cm m 1 ) and Raman spectra (1400-100 cm m 1 ) of ZnRb 4 (P 3 O 9 ) 2 ·;6H 2 O are reported and assignments of fundamental modes proposed and compared with theoretical results obtained via the MNDO method for P 3 O 9 ring with C s symmetry. (La déshydratation, sous pression atmosphérique, du cyclotriphosphate ZnRb 4 (P 3 O 9 ) 2 ·;6H 2 O, a ét´;e effectuée, entre 25 and 600°;C, par spectrométrie IR, diffraction des rayons X, ATG et ATD. Elle conduit, entre 300 and 500°;C, au mélange de polyphosphates RbPO 3 et ZnRb 2 (PO 3 ) 4 qui reste stable jusqu'à la fusion. Les spectres vibrationnels IR (1400-30 cm m 1 ) et Raman (1400-100 cm m 1 ) du sel étudié ont été interprétés dans le domaine des vibrations de valence et de déformation du cycle P 3 O 9 et comparés avec les résultats des calculs théoriques par la méthode MNDO pour un cycle isolé de symétrie C s .)     

Thermal Dehydration and Vibrational Studies of ZnK4(P3O9)2 · 6H2O

The thermal dehydration of ZnK₄(P₃O₉)₂ · 6H₂O was studied in the range 25–500°C by thermogravimetric analysis (TGA and DSC) and X‐ray diffraction. We found, based on the TGA and DSC scans, the dehydration of this salt takes place in three stages with a loss of the six water molecules. The infrared and Raman spectra of ZnK₄(P₃O₉)₂ · 6H₂O have been recorded and interpreted using a factor group analysis. The internal modes are assigned in terms of POP and PO₂ structural units using experimental and theoretical IR and Raman frequencies.     

Structural basis of pyrazolopyrimidine derivatives as CAMKIIδ kinase inhibitors: insights from 3D QSAR,docking studies and in silico ADMET evaluation

Ca²⁺/calmodulin-dependent protein kinase II (CAMKIIδ) belongs to the serine/threonine kinase family, which is involved in a broad range of cellular events in cell survival and proliferation as well as a number of other signal transduction pathways. Thus, it is regarded a promising target for treatment of cancers. In the present paper, a three-dimensional quantitative structure–activity relationship and molecular docking were applied to investigate a series of new CAMKIIδ inhibitors of pyrazolopyrimidine derivatives. The determination coefficient (R²) and leave-one-out cross-validation coefficient (Q²) of CoMSIA model are 0.676 and 0.956, respectively. The predictive ability of this model was evaluated by the external validation using a test set of eight compounds with a predicted determination coefficient \(R^{ 2}_{\text{test}}\) of 0.80, besides the mean absolute error of the test set was 0.328 log units. Docking results are in concordance with CoMSIA contour maps, gave the information for interactive mode exploration. Based on those satisfactory results, newly designed molecules were predicted with highly potent CAMKIIδ inhibitory activity, additionally, they have showed promising results in the preliminary in silico ADMET evaluations. This study could expand our understanding of pyrazolopyrimidine derivatives as inhibitors of CAMKIIδ and would be of great help in lead optimization for early drug discovery of highly potent CAMKIIδ inhibitors.     

Theoretical Study of Copper Acetonitrile Effects on Parr Functions Indices and Regioselectivity Using Density Functional Theory (DFT)

Russian Journal of Physical Chemistry A - Copper-catalyzed azide–alkyne cycloaddition (CuAAC) is a straightforward way for making covalent connections between building blocks containing...     

Ab Initio Study of Endo/Exo and Diastereofacial Selectivities in Diels-Alder Reactions between Chiral Butenolides and Cyclopentadiene

Diels-Alder reactions of cyclopentadiene with crotonolactone and beta-angelica lactone have been studied using ab initio methods at the MP3/6-31G//RHF/3-21G and MP2/6-31G//RHF/6-31G levels. The transition states corresponding to the formation of different stereoisomers and diastereoisomers have been located. The results obtained show that the correct endo/exo selectivity is only obtained when polarization functions are included in the basis set. However, syn/antiselectivity is correctly described at all levels of calculation.     

Charge carriers in P - doped polyacetylene,optical study

The dielectric properties of p-doped polyacetylene are investigated in the infrared and far infrared region. The behaviour of the dielectric function is discussed on the basis of two kinds of carriers: free and pinned carriers. A metallic state is characterized for doping level higher than 0.03 charge per C-H unit. The effective mass of carriers is shown to be close to the free electron mass.     

Préparation Chimique,Caracterisation Cristallographique,Etudes Thermique et Vibrationnelle du Cyclotriphosphate Hexahydraté de Manganèse et de Tetra-Argent,MnAg 4 (P 3 O 9 ) 2 .6H 2 O

The cyclotriphosphate hexahydrate of manganese and silver, MnAg 4 (P 3 O 9 ) 2 .6H 2 O, was prepared by Boullé's process. MnAg 4 (P 3 O 9 ) 2 .6H 2 O crystallizes in the triclinic system, P-1, Z = 1 and its structure was determined by Rietveld's method. The refinement of 54 parameters by this method, using 1752 independent reflections leads to Rw p = 0.098, R p = 0.065 and R B = 0.033 on the basis of its isotype NiAg 4 (P 3 O 9 ) 2 .6H 2 O. The unit cell parameters of this salt are the following a = 8.824(1)Å, b = 8.485(1)Å, c = 6.609(1)Å, f = 90.30(1)°;, g = 92.89(1)°; and n = 107.28(1)°;. The thermal behavior of this new compound was studied, between 25 and 600°;C, under atmospheric pressure by infrared spectrometry, X-ray diffraction, thermal analyses TGA and DTA coupled. This study allows us the identification and the crystallographic characterization of a new phase, MnAg 2 (PO 3 ) 4 isotype of ZnRb 2 (PO 3 ) 4 , obtained between 350 and 450°;C, mixed with the long-chain polyphosphate of silver AgPO 3 . The kinetic characteristics of the dehydration of MnAg 4 (P 3 O 9 ) 2 .6H 2 O and the thermal phenomena accompanying this dehydration were determined and discussed on the basis of the proposed crystalline structure. The vibrational spectrum of the, MnAg 4 (P 3 O 9 ) 2 .6H 2 O, was examined and interpreted in the domain of the stretching vibrations of the P 3 O 9 rings, on the basis of the proposed crystalline structure and in the light of the calculation of the thirty fundamental IR frequencies for the idealized D 3h symmetry.     

Computation of the infrared active modes in single-walled boron nitride nanotube bundles

In this work, the infrared active modes are computed for homogeneous bundles of single-walled boron nitride nanotubes (BBNNTs), using the so-called spectral moments method. The dependence of the wavenumber on these modes in terms of diameters, lengths, and numbers of tubes, is investigated. To this end, use is made of a Lennard-Jones potential for describing the van der Waals interactions between tubes in a bundle. We find that, for a finite homogeneous bundle, additional modes appear as a specific signature. Finally, these results are useful for the interpretation of the experimental infrared spectra of BBNNTs.