Über Pterinchemie. 57. Mitteilung. Zur Konfiguration und Konformation von 6,7-Dimethyl-und 5,6,7-Trimethyl-5,6,7,8-tetrahydropterin

Configuration and conformation of 6,7-Dimethyl- and 5,6,7-Trimethyl-5,6,7,8-tetrahydropterines. During the hydrogenation of 6,7-dimethylpterine, cis-6,7-dimethyl-tetrahydropterine is formed. A possible conformation for this substance and for the 5,6,7-trimethyl derivative, which is obtained from it, is discussed, taking the ¹H-NMR. spectra of both tetrahydropterines into consideration.     

Über Pterinchemie 23. Mitteilung [1]. Radikalbildung während der Oxydation von Tetrahydrofolsäure und 5,6,7,8-Tetrahydropterin

EPR. investigations show the existence of one-electron oxidation of 5,6,7,8-tetrahydropterine and tetrahydrofolic acid resulting in unstable cationic radicals of red color which are trapped at liquid nitrogen temperature.     

Über die Elektronenspinresonanzspektren einiger Cu2+-Komplexe in wässeriger Lösung

The e.s.r. spectra of aqueous solutions of Cu²⁺-complexes with a series of methylpyridines (PYR) have been investigated at liquid nitrogen temperature. The experimental data indicate that the formula CU(PYR) holds for the compounds in the frozen solutions. The marked decrease of the copper hyperfine coupling constant for some of the complexes is explained in terms of a distortion of the square planar structure towards a tetrahedral environment of the Cu²⁺. An analogous interpretation of the e.s.r. spectra of some copper containing electron-transfer-oxidases, e.g. ceruloplasmin and laccase, presents a possible explanation of the experimentally observed connections between the spectra and the enzymatic activity of these compounds.     

Über Pterinchemie. 69 Mitteilung [1]. Konformationsanalyse von 5,6,7,8-Tetrahydropteroinsäure und 5,6,7,8-Tetrahydro-L-folsäure

Conformational analysis of 5,6,7,8-tetrahydropteroic acid and 5,6,7,8-tetrahydro-L -folic acid In the 360-MHz-¹H-NMR.-spectrum of (6R, S)-9,9-dideuterio-5, 6, 7, 8-tetrahydropteroic acid (racemic) (XIII) (AMX-System, Fig. 4) and (6R, S)-9,9-dideuterio-5, 6, 7, 8-tetrahydro-L -folic acid (diastereomeric) (XVI) the H_a–C(6) and H_a–C(7) show a vicinal coupling constant of 6,7 Hz and the H_a–C(6) and H_e–C(7) one of 3,2 Hz. The first coupling constant provides evidence for an approximate trans-diaxal arrangement of H_a–C(6) and H_a–C(7), and the second for a gauche conformation of H_a–C(6) and H_e–C(7). The tetrahydropyrazine ring in the racemic 5, 6, 7, 8-tetrahydropteroic acid (III) and in the diastereomeric 5, 6, 7, 8-tetrahydro-L -folic acid (XVII) exists therefore in a half-chair conformation with a pseudoequatorial position of the side chain at C(6) (Fig.5).     

Über Pterinchemie. 64. Mitteilung. Die Kristallstruktur von 6-Methyl-7,8-dihydropterin-monohydrochlorid-monohydrat

The crystal structure of 6-methyl-7,8-dihydropterine-monohydrochloride-monohydrate The crystal structure of the title compound has been determined by X-ray analysis (direct methods) and refined with 990 structure amplitudes to R = 0.025. The crystal system is triclinic, space group P1 , with unit cell dimensions a = 5.859, b = 7.686, c = 12.107, α = 71.84, β = 76.35, γ = 85.80. The molecule is protonated at the N(5)-position and is planar. The atoms H(19) and H(20) are with 0.818 Å above respectively with ?0.705 Å under the plane.     

Über Pterinchemie. 59. Mitteilung [1]. Konformationsanalyse von acylierten 5,6,7,8-Tetrahydropterinen

Conformational Analysis of Acylated 5,6,7,8-Tetrahydropterines The conformation of N(5)-acetates, and of N(5)- and N(8)-trifluoroacetates, respectively, of 6-methyl- and cis-6, 7-dimethyl-tetrahydropterines is studied by ¹H-NMR. spectroscopy. It is shown that the methyl group next to the acylated nitrogen atom is in quasi-axial position.     

Über Pterinchemie. Mitteilung. Die Kristallstruktur von 5,6,7-Trimethyl-5,6,7,8-tetrahydropterindihydrochlorid-monohydrat

The crystal structure of 5,6,7-trimethyl-5,6,7,8-tetrahydropterine-dihydrochloride-monohydrate The crystal structure of the title compound has been determined by X-ray analysis (direct methods) and refined with 947 structure amplitudes to R = 0.026. The crystal system is orthorhombic, space group Pna2₁, with unit cell dimensions a = 14.081, b = 14.623, c = 6.773 Å. The molecule is protonated at the N(1)- and N(5)-position. The tetrahydropyrazine ring exists in a conformation in which C(6) deviates markedly from the mean plane of the other five atoms. The CH₃-groups at N(5) and C(6) possess a trans configuration with a pseudoaxial and an axial conformation respectively. The CH₃-groups at C(6) and C(7) in return possess the cis configuration, whereby the CH₃-group at C(7) occupies an equatorial conformation.     

Cob(I)alamin als Katalysator. 1. Mitteilung. Reduktion von gesättigten Nitrilen in wässeriger Lösung

Co(I)alamin as Catalyst. 1. Communication. Reduction of Saturated Nitriles in Aqueous Solution Using cob(I)alamin as homogeneous catalyst in the presence of aqueous acetic acid saturated nitriles 5a – m are reduced to the corresponding aldehydes 6a – m in good yields. A possible reaction mechanism for this reduction is discussed.     

Die Komplexbildungstendenz des dreiwertigen Antimons in wässeriger Lösung

The formation of the complexes of trivalent antimony ion with the following ligands has been investigated with pH measurements: D -tartaric acid, L -tartaric acid, catechol, catechol-3,5-disulfonic acid, 2,3-dihydroxybenzoic acid, mercaptoacetic acid, rac-thiomalic acid, meso-, rac-dithiotartaric acid, and mercapto-ethanol. Using the determined equilibrium constants, a classification of the ligands with respect to their ability to sequester the cation studied is given. In a discussion in which data of the literature are also included the structure of the tartar emetic, the possibility of a volumetric determination of the antimony, some problems concerning the coordination number, and the structure of the complexes are examined.     

Über Pterinchemie 80. Mitteilung Die Herstellung von (6RS)Tetra- und (6RS)Pentaacetyl-5,6,7,8-tetrahydro-L-bioplerinen

Preparation of (6RS)Tetra- and (6RS)-Pentaacetyl-5,6,7,8-tetrahydro-L-biopterines Boiling of (6RS) l′-O,2′-O,2-N-triacetyl-5,6,7,8-tetrahydro-L-biopterine in acetic anhydride as described in [2], leads to a mixture of the diastereoisomeric (6R)- and (65)-l′-O,2′-O,2-N-,5,8-pentaacetyl-5,6,7,8-L,-biopterines. One of the diastereoisomers can be obtained as pure crystals. It corresponds to the pentaacetate of the natural (6R)- or (6S).,5,6,7,8-tetrahydro-L-biopterine. For the preparation of the earlier described (6RS)- and (6S)-tetraacetyl-tetrahydro-L-biopterines [2] improved conditions are reported.     

Über Pterinchemie. 49. Mitteilung. Eine neue Synthese von 5-Formyl-6, 7-dimethyl-5,6,7,8-tetrahydropterin und 5,6,7-Trimethyl-5,6,7,8-tetrahydropterin

Starting with 5-formyl-6,7-dimethyl-5,6,7,8-tetrahydropterine (II), a new synthesis of 5,6,7-trimethyl-5,6,7,8-tetrahydropterine (III) is described. Thereby the chemical behaviour of the 5-formyl group in II is investigated, in order to enable the unequivocal differentiation between formylation at position 5 and at position 10 in folic and tetrahydrofolic acid derivatives. ¹³C-NMR. spectra of II and III are discussed.     

Über Pterinchemie 51. Mitteilung [1] CNDO-Rechnungen an Pterin, 6,7-Dimethyl-7,8-dihydropterin und 5-Formyl-6, 7-dimethyl-5,6,7,8-tetrahydropterin

The ¹³C-NMR.-spectra of 7,8-dihydropterines and 5,6,7,8-tetrahydropterines show a large difference in the chemical shifts of the 4a- and 8a-sp²-carbon atoms. From the CNDO calculations it is apparent that there is a considerable difference in electron density at C(4a) and C(8a) atoms, which leads to a strong polarity of the C? C-Bond. The electron distribution in the highest occupied molecular orbital (HOMO) is discussed.     

Über Pterinchemie 81. Mitteilung Die Konfiguration an C(6) von natürlichem 5,6,7,8-Tetrahydro-L-biopterin und seinem Pentaacetylderivat

The Configuration at C(6) of Natural 5,6,7,8-Tetrahydro-L-biopterin and of its Pentaacetate The structure of (6.R)-pentaacetyl-5,6,7,8-tetrahydro-L-biopterin, one of two diastereoisomers obtained by catalytic hydrogenation and subsequent acetylation of L-biopterin, has been determined by X-ray diffraction analysis. The space group is P2₁2₁2₁, a=8,053(l), b=14,955(3), c= 21,502 (4) Å. The asymmetric unit contains one molecule of the biopterin derivative and one of ethyl acetate. The R-configuration can be assigned to C(6) by reference to the known configurations of the other asymmetric C-atoms. As hydrolysis of this diastereoisomer yields the natural 5, 6,7,8-tetrahydro-L-biopterin, the latter also possesses the (6 R)-configuration.     

Über Pterinchemie. 61. Mitteilung. Die Kristallstruktur von 5-Formyl-6,7-dimethyl-5,6,7,8-tetrahydropterin

The crystal structure of 5-formyl-6,7-dimethyl-5,6,7,8-tetrahydropterine The crystal structure of the title compound, a tetrahydropterine, has been determined by X-ray analysis (direct method) and refined with 1579 structure amplitudes to R = 0.054. The crystal system is triclinic, space group P1 , with unit cell dimensions a = 7.171, b = 7.255, c = 12.369 Å, α = 100.64, β = 93.32, γ = 98.27°. The tetrahydropyrazine ring exists in a distinctly flattened conformation. The C(13)- and C(14)-CH₃-groups possess a cis-configuration with axial position for C(13)-CH₃ and equatorial for C(14)-CH₃. The carbonyl-group of the N-formyl function has an (E)-configuration.     

Über Pterinchemie. 58. Mitteilung [1]. Sterische Eigenschaften von acylierten 5,6,7,8-Tetrahydropterinen. Rotameren von 5-Trifluoracetyl-tetrahydropterin-Derivaten

Sterochemical Properties of the Acylated 5,6,7,8-Tetrahydropterines. Rotameres of the 5-Trifluoroacetyl-tetrahydropterine Derivatives 6-Methyl- and 6,7-dimethyl-5,6,7,8-tetrahydropterine are acylated with the anhydrides of acetic acid and trifluoroacetic acid. It is shown that the reactivity of the nitrogen otoms increases in the following order: N(3), N(8), N(2′) and N(5). Two rotameres are present in the ¹H-NMR. spectra of the N(5)-trifluoroacetates, but not in those of the N(5)-acetates.     

Über Pterinchemie 75. Mitteilung Synthese von 7-Aminoxanthopterin

Synthesis of 7-Aminoxanthopterin 7-Aminoxanthopterin (II) is obtained in good yield and purity by the transformation of isomer-free xanthopterin-7-carboxylic acid (I) with NH₃ followed by oxidation with MnO₂. The Frontier Orbital Theory contributes to a better understanding of the reaction pathway.     

Über Pterinchemie 18. Mitteilung [1] Monohydro- und Trihydropterin-Radikale

By oxydation of N(5)-methyl-6,7-diphenyl-5,6-dihydro- and N(5)-methyl-6,7-diphenyl-5,6,7,8-tetrahydro-pterine derivatives with perhydrol 8-monohydro- and 6,7,8-trihydro-pteridine radical cations are produced which are sufficiently stable for detection and structural elucidation by ESR. hyperfine analysis. The biological implications of these radicals for pteridine dependent hydroxylation and methyl transfer from 5-methylfolinic acid are discussed.