Martin Feigel

Phenyl rotation in diphenylether and diphenylmethane calculated with ab initio methods

Abstract Diphenylether 1 and diphenylmethane 2 are calculated as chiral C 2 symmetrical minimum structures ( 1A and 2A ) by HF/6-31G(d), MP2/6-31G(d), BLYP/6-31G(d) and B3LYP/6-31G(d) ab initio and density functional computations. The complete torsional energy surface for the rotation of the phenyl rings in 1 and 2 is given (HF/6-31G(d)). The phenyl rings in diphenylether rotate preferably via a C s symmetrical transition state 1C . The energy barrier for the process is very low (e.g. 0.30 kcal mol −1 at the MP2 level). Diphenylmethane uses two transition states of low energy for ring flipping, 2B and 2C having C 2 v and C s symmetry (0.51 and 0.49 kcal mol −1 above 2A at the MP2 calculations). The central COC and CCH 2 C bending angles in 1 and 2 , respectively, are strongly correlated with the dihedral angles of the ring torsion.

Crystal Structure of a Peptide-Steroid Macrocycle—Intramolecular Attraction between Steroids and Peptidicβ(I) Turns

Two molecules of the steroid lithocholic acid and two dipeptides (Phe-Phe) make up the macrocycle 1, in which the two steroidal surfaces approach each other so that the peptide parts fold into β(I) turns. Thus, the structure of a cyclic steroid-peptide compound was determined in the solid state for the first time. The structure of 1 is stabilized in the crystal through intra- and intermolecular hydrogen bonds as well as through π stacking of the side-chain phenyl rings of Phe(i+1).

IS THE PARALLEL OR ANTIPARALLEL BETA -SHEET MORE STABLE? A SEMIEMPIRICAL STUDY

The geometry and energy of parallel and antiparallel peptidic β-sheets have been calculated using AM1. β-Sheets composed of two peptide chains of up to 11 amino acid residues (Ala and Gly) and the dimers of cyclooctapeptides are used as model systems. The enthalpic difference between the parallel and the antiparallel arrangement is calculated to be very small, as it is found experimentally for the cyclic systems. The coordinates of the calculated structure of the cyclooctapeptide dimer 1 (cyclo-D,L-(Ala)8) have an rms deviation of only 0.223 Å to the coordinates of the corresponding cyclopeptide obtained by X-ray analysis.

Kristallstruktur eines Steroid-Peptid-Makrocyclus – intramolekulare Anziehung zwischen Steroiden sowie peptidische β(I)-Schleifen

Aus zwei Molekulen des Steroids Lithocholsaure und zwei Dipeptiden (Phe-Phe) ist der Makrocyclus 1 aufgebaut, in dem sich die beiden Steroidoberflachen so annahern, das die Peptidteile β(I)-Schleifen bilden. Damit gelingt es erstmals, die Struktur einer cyclischen Peptid-Steroid-Verbindung im Festkorper zu bestimmen. Stabilisiert wird die Struktur von 1 im Kristall durch intra- und intermolekulare Wasserstoffbruckenbindungen sowie durch π-Stapelung der Seitenkettenphenylringe von Phe(i+1).

Konformation von Anthranilsäurepeptiden, 3 [1]: Konformationen kleiner Anthranilsäure-Prolinpeptide im Kristall, in Lösung und eine semiempirische (AM 1) Beschreibung der Prolin-Ramachandran-Hyperflächen / Conformation of Anthranilic Acid Peptides, 3 [1]: Conformation of Small Anthranilic-Acid-Proline-Peptides in Crystal, in Solution and a Semi-empirical (AM 1) Description of the Proline-Ramachandran Maps

Starting from tert-Butyloxycarbonyl(BOC)-Anthranilic-Acid(Abz) (1), BOC-Abz-Proline-Methyl-Ester (2) is synthesized. The crystal structure of both compounds are discussed. The conformational features of the crystal structures of 2 are compared with the conformation in solution. The whole conformational area (Φ and Ψ) of the amino acid part of 2 was investigated with the semi-empirical quantummechanical method AM 1, in order to check the general availability of the influence of ester functions to depsipeptide conformations. Cyclo-anthranoyl-prolinyl (3), which had already been described in the literature, forms crystals with a high density. Two independent molecules are found in the crystal structure; these molecules have very similar conformations.

(R)-Di-tert-butyl 1,1′-binaphthyl-2,2′-dicarboxyl­ate

The crystal structure of the title compound, C30H30O4, comprises two crystallographically independent half-molecules which are completed by crystallographic twofold symmetry. The dihedral angles between the naphthalene ring planes are 85.83 (3) and 83.69 (3)° for the two molecules. The atoms of the tert-butyl group of one molecule are disordered over two sets of sites with occupancies of 0.60:0.40. The crystal packing is achieved via π–π stacking interactions between the naphthyl groups of adjacent molecules, with a separation of 3.790 (1) Å between the centroids of the rings.

Konformation von Anthranilsäurepeptiden: Kristallstruktur von tert-Butyloxycarbonyl-Anthranilsäure-Glycinmethylester und semiempirische (AM 1) Beschreibung der Ramachandran-Hyperfläche / Conformation of Anthranilic Acid Peptides: Crystal Structure of tert-Butyloxycarbonyl-Anthranilic-Acid-Glycin-Methyl-Ester and Semi-Empirical (AM 1) Description of the Ramachandran Map

Two different molecules are observed in the asymmetric unit of the crystal structure of tert-butyloxycarbonyl-anthranilic-acid-glycin-methyl-ester (1). The whole conformational area (φ and ψ) of the amino acid part of 1 was investigated with the semi-empirical quantenmechanical method AM 1. The structures of 1 in the crystal are well described by the calculations. Rules are derived for the conformational space of peptides containing esters and anthranilic acids.

Complexation of Organic Dyes by Peptides Built of Lysine and Glutamic Acid Amides

Abstract Two amide libraries, Fmoc-[Lys(aci)]4-Gly-resin (1) (aci = 2-naphthylcarbonyl, 1-adamantylcarbonyl and benzyloxycarbonyl) and Fmoc-[δ-Glu(α-amidei)]4-Gly-resin (2) (amidei = morpholineamide, piperidineamide, (N´-phenyl)-piperazineamide), have been synthesized from the corresponding Fmoc-protected amino acid derivatives. Beads of the libraries complex organic dyes (crystal violet and Sudan black) differently according to the sequence of residues in 1 or 2. The results are considered a step towards artificial receptors for small organic molecules build from linear oligoamides.

2,2′-Dimethylbiphenyl-6,6′-dicarboxylic acid enforces two attached valine molecules to form up a chiral host lattice

Crystals of (R)-valyl 2,2′-dimethylbiphenyl-6,6′-dicarboxylate 3 and (S)-valyl 2,2′-dimethylbiphenyl-6,6′-dicarboxylate 4 are stabilised by a network of inter- and intra-molecular hydrogen bonds; together with the space requirement of the biphenyl core, structures result which contain cavities filled by THF (3) or EtOH molecules engaged in hydrogen bridging (4).