Search results for "stereochemistry"
showing 10 items of 4831 documents
Ethyl 1-acetyl-3-amino-1H-pyrazole-4-carboxylate, a tetragonal structure with Z′ = 4
2006
The title compound, C8H11N3O3, crystallizes with Z' = 4. One pyrazole N atom is substituted and excluded from intermolecular contacts. The amine N, acetyl O and an ester O atom are involved in the formation of nearly planar molecular layers. The layers are perpendicular to the c axis, with an interlayer distance of 3.333 Å. The hydrogen-bonding patterns are similar for each molecule, i.e. intramolecular N-H...O, as well as intermolecular N-H...O and C-H...N(pyrazole), bonds are present.
Rearranged abietane diterpenoids from the root of teucrium polium subsp. vincentinum
1990
Abstract From the root of Teucrium polium subsp. vincentinum (Labiatae) four new rearranged abietane derivatives, teuvincenones A, B, C, and D (1-4, respectively), have been isolated. Two of these compounds, teuvincenones C (3) and D (4), possess a novel hydrocarbon skeleton which contains a cyclopropane ring constituted by the C-3, C-4, and C-18 carbons of the 17(15→16)-abeo-abietane framework. The structures of these diterpenoids were established mainly by spectroscopic means and, in the case of teuvincenones A (1) and C (3), also confirmed by X-ray diffraction analyses.
Herbicidal Derivatives of Aminomethylenebisphosphonic Acid. Part IV. Hydroxyalkylidenebisphosphonates, Iminomethylenebisphosphonates and Ureidomethyl…
2000
Derivatives of aminomethylenebisphosphonic acids constitute a class of promising herbicides. Replacement of the amino group by hydroxyl, ureido, thioureido, or imino moieties leads to compounds of significant herbicidal properties. This indicates that protonated amino function is not a requirement for phytotoxic action of bisphosphonates.
Struktur-Wirkungs-Beziehungen bei Histaminanaloga, 22. Mitt. Absolute Konfiguration und histaminartige Wirkung der enantiomeren α, Nα-Dimethylhistami…
1980
Es werden die Synthesen der enantiomeren α, Nα-Dimethylhistamine (+)—3 und (−)—3, die Ableitung der absoluten Konfiguration sowie die histaminartige Wirksamkeit der Enantiomere am Ileum (H1) und Atrium (H2) des Meerschweinchens beschrieben. Structure-Activity Relationship of Histamine Analogues. XXII: Absolute Configuration and Histamine-like Activity of the Enantiomeric α, Nα-Dimethylhistamines The synthesis of the enantiomeric α, Nα-Dimethylhistamines (+)—3 and (−)—3, the determination of the absolute configuration and the histamine-like activity of the enantiomers on the guinea-pig ileum (H1) and atrium (H2) are reported.
Struktur-Wirkungs-Beziehungen bei Histaminanaloga, 23. Mitt. Absolute Konfiguration und histaminartige Wirkung der enantiomeren α-Chlormethylhistamin…
1981
Es wird die histaminartige Wirksamkeit der enantiomeren α-Chlormethylhistamine (+)-2a und (−)-2a sowie der Nα-Methyl-α-chlormethylhistamine (+)-2b und (−)-2b am Ileum (H1) und Atrium (H2) des Meerschweinchens beschrieben und die absolute Konfiguration der Enantiomere abgeleitet. Structure-Activity Relationships of Histamine Analogues, XXIII: Absolute Configuration and Histamine-like Activity of the Enantiomeric α-Chloromethylhistamines and Nα-Methyl-α-chloromethylhistamines The histamine-like activities of the enantiomeric α-chloromethylhistamines (+)-2a and (−)-2a and of the Nα-methyl-α-chloromethylhistamines (+)-2b and (−)-2b on the guinea pig ileum (H1) and atrium (H2) are reported. The …
Metal Dependence on the Bidirectionality and Reversibility of the Singlet Energy Transfer in Artificial Special Pair-Containing Dyads
2017
International audience; The demetalation of a precursor dyad, 3, built upon a zinc(II)-containing artificial special pair and free-base antenna, leads to a new dyad, 4, for singlet energy transfer composed of cofacial free-base porphyrins (acceptor), [Fb](2) bridged by a 1,4-C6H4 group to a free-base antenna (donor), [Fb]. This dyad exhibits the general structure [M](2)-C6H4-[Fb], where [M](2) = [Fh](2), and completes a series reported earlier, where [M](2) = [Mg](2) (2) and [Zn](2) (3). The latter dyads exhibit a bidirectional energy-transfer process at 298 K for 2 and at 77 K for 3. Interestingly, a very scarce case of cycling process is observed for the zinc-containing dyad at 298 K. The…
Conformational investigation of α,β‐dehydropeptides. XV: N‐acetyl‐α,β‐dehydroamino acid N ′N ′‐dimethylamides: conformational properties from infrare…
2005
The FTIR spectra were analysed in the region of the nu(s)(N-H), AI(C=O) and nu(s)(Calpha=Cbeta) bands for a series of Ac-DeltaXaa-NMe2, where DeltaXaa = DeltaAla, (Z)-DeltaAbu, (Z)-DeltaLeu, (Z)-DeltaPhe and DeltaVal, to determine a predominant solution conformation of these alpha,beta-dehydropeptide-related molecules. Measurements were taken in CCl4, DCM and MeCN solutions. In the same way, spectra of saturated analogues Ac-Xaa-NMe2, where Xaa = Ala, Abu, Leu, Phe and Val, were investigated. To help interpret the spectroscopic results, conformational maps were calculated by the B3LYP/6-31+G** method. Also, the relative energies of all conformers of the dehydro compounds in vacuo as well as…
Crystal structure of the tripeptideN-(benzyloxycarbonyl)glycylglycyl-L-norvaline
2015
The title tripeptide, C17H23N3O6, contains a nonproteinogenic C-terminal amino acid residue, norvaline, which is an isomer of the amino acid valine. Norvaline, unlike valine, has an unbranched side chain. The molecule has a Gly–Gly segment which adopts an extended conformation. The norvaline residue also adopts an extended backbone conformation while its side chain has ag+tconformation. In the crystal lattice, N—H...O and O—H...O hydrogen bonds stabilize the packing. Molecules translated along the crystallographicaaxis associate through an N—H...O hydrogen bond. The remaining three hydrogen bonds are between molecules related by a21screw axis.
Cyclobutane Pyrimidine Photodimerization of DNA/RNA Nucleobases in the Triplet State
2010
The photoinduced formation of cyclobutane pyrimidine dimers in the triplet excited state of the DNA/RNA pyrimidine nucleobases pairs has been studied at the CASPT2 level of theory. A stepwise mechanism through the triplet state of the homodimer is proposed for the pairs of nucleobases cytosine, thymine, and uracil involving a singlet−triplet crossing intermediary structure of biradical character representing the most favorable triplet state conformation of the nucleobases as found in the DNA environment. The efficiency of the mechanism will be modulated by two factors: the effectiveness of the triplet−triplet energy transfer process from a donor photosensitizer molecule, which relates to th…
Copper( ii ) complexes with phosphorylated 1,10-phenanthrolines: from molecules to infinite supramolecular arrays
2016
International audience; The reaction of phosphorylated 1,10-phenanthrolines 3-Pphen, 3,8-Pphen and 4,7-Pphen (3-Pphen = 3-diethoxyphosphorylphenanthroline, 3,8-Pphen = 3,8-bis(diethoxyphosphoryl) phenanthroline, 4,7-Pphen = 4,7-bis(diethoxyphosphoryl) phenanthroline) and hydrated copper(II) nitrate in a 1 : 1 ratio leads to the formation of supramolecular architectures. In the 1D coordination polymer [Cu(3-Pphen)(NO3)(2)](n) (2) the copper atom is coordinated to only one phenanthroline ligand and the coordination sphere is completed by two oxygen atoms of nitrate anions and the oxygen atom of the phosphoryl group from the neighbouring phenanthroline ligand. Complex Cu(3,8-Pphen)(NO3)(2) (3)…