Hermann Kalchhauser

NMR spectra of nitrogen‐containing compounds. Correlations between experimental and GIAO calculated data

Correlations between experimentally determined chemical shifts (15N, 13C, 1H in CDCl3 and DMSO solutions) and GIAO‐calculated isotropic shielding constants, δexpt = a + bσcalcd, are reported that were obtained from a series of nitrogen‐containing heterocycles (5‐, 6‐, 5+6‐, 6+6‐ and 6+6+6‐membered rings). Based on HF, MP2 and B3LYP optimized geometries [6–31G(d,p) basis set], GIAO calculations were performed at the HF, BLYP, and B3LYP levels of theory [6–311++G(d,p) basis set]. The performance of theoretical NMR calculations and the resulting eligibility for routine practical use were assessed from correlation coefficients and from standard deviations of the theoretically predicted shifts. Depending on the experimental conditions and on computational levels, linear regressions between experimental and theoretical data resulted in standard deviations of about 6–12 ppm for all nitrogens, 5–8 ppm for aromatic nitrogens, 1–2 ppm for aromatic carbons and 0.1–0.15 ppm for aromatic hydrogens. Several points that influence the accuracy of theoretically predicted chemical shifts are discussed. Copyright

Isolation and structure determination of two new macrocyclic biaryl ethers fromGaruga gamblei

Two new macrocyclic biaryl ethers have been isolated from the bark ofGaruga gamblei King (Burseraceae). The structure of the compounds has been established by NMR spectroscopy.ZusammenfassungAus der Rinde vonGaruga gamblei King (Burseraceae) wurden zwei neue makrocyclische Biarylether isoliert. Die Struktur der Verbindungen wurde mittels NMR-Spektroskopie bestimmt.

The conformation of cyclo[l-pro-l-leu-l-val-(gly)thz-(gly)thz], a dolastatin 3 analog, in the crystalline and solution states

Abstract Cyclo[L-Pro-L-Leu-L-Val-(gly)Thz-(gly)Thz], (1), has been prepared in high yield using pentafluorophenol in the ring closure reaction. This dolastatin 3 analog has been subjected to crystal structure analysis (space-group P65, a = b = 34.897(9), c = 24.611(10)A, asymmetric unit contents:(C26H35N7O5S2)4·(C7H8)7·(CH30H)4, ϱcalc = 1.202gcm-3.) and solution (CDCl3 and DMSO-d6) studies using 1H- and 13C-NMR techniques. The molecule has been found to adopt a clearly preferred conformation both in the crystal and in solution. The conformation contains a cis (gly)Thz-Pro peptide bond and two intramolecular hydrogen bonds, one from Leu-NH to a thiazole endocyclic nitrogen atom and the other from a (gly)Thz-NH to the Leu-C=O. The results of this study not only demonstrate that the conformation of (1) is very similar in the crystal and solution, but also provide conclusive evidence that the conformation proposed by Bernier, et al 4. earlier is incorrect. The crystal packing demonstrates that (1) is a very hydrophobic cyclopeptide with a tendency to self associate. In the crystal (1) associates via systematic hydrogen bonding to form a network of interlocking hydrophobic tubes filled with toluene molecules. The solvent molecules migrate out of the crystals on exposure to air resulting in fragmentation.

Anwendung von 2D-NMR-Techniken zur Analyse komplexer Spektren. Maleopimarsäuremethylester

A combination of 2D-NMR-techniques including 2D-J-resolved spectroscopy, SECSY and1H-13C-shift correlation is used to assign the1H- and13C-spectrum of Maleopimaric acid methylester [17,19-Dinoratis-15-ene-4,13,14-tricarboxylic acid 4-methylester, 16-(1-methylethyl)cyclic-13,14-anhydrid (4α, 8α, 12α)] (1).

Asymmetric Allylic Substitution Reactions with a Xylophos-Pd Catalyst

Summary. The chiral diphosphine ligand xylophos (1) was tested as an auxiliary in palladium catalyzed allylic substitution reactions. Whereas its activity was found to be generally good only in the case of 1,3-diphenylprop-2-en-1-yl acetate, a fair level of asymmetric induction was achieved with sodium dimethyl malonate (83%ee) and benzylamine (66%ee) as nucleophiles.

Allylic hydroxylation of vitamin D with Mercury (II)trifluoroacetate

Abstract Treatment of vitamin D with Hg(OCOCF 3 ) 2 results in formation of the isovitamin D derivative 2 , which can be converted into C-1 hydroxylated 5E vitamin D derivatives.

2D-NMR of natural products part III homo- and heteronuclear NMR-spectroscopy of a cyclic tetrapeptide related to chylamydocin

Abstract 2D-1H-13C-shift correlation enables full assignment of the 13C- and proton-spectrum of the Chlamydocin derivate 1 . The conformation of 1 in CDCl3 is discussed.

Synthesis and conformational behaviour of ditosyldiaza[2.2]orthometacyclophanes

SummaryThe N,N′-ditosyl-diaza[2.2]orthometacyclophanes5a, b were synthesized from N,N-ditosyl-metaphenylenediamine by reaction with (Z)-1,4-dichlorobutene and 1,2-bis-bromomethylbenzene, respectively. Low temperature NMR studies showed that the compound5b exists as a 1:1 mixture of chair and boat form of the strained (E,Z)-diazanonadiene ring. At room temperature all corresponding resonances are averaged on the NMR time scale (including all four ethylene bridge protons). Going to lower temperatures, in a first step the methylene bridge inversion is frozen (giving twoexo H and twoendo H, ΔG≠ ca. 52kJmol−1). In a second step the chair and boat form can be observed separately (ΔG≠ ca. 43.5 kJ mol−1 for the chair/boat flip). The assignments were confirmed by 2D NMR experiments.ZusammenfassungDie N,N′-Ditosyl-diaza[2.2]orthometacyclophane5a, b wurden aus N,N-Ditosylmetaphenylendiamin durch Umsetzung mit (Z)-1,4-Dichlorbuten bzw. 1,2-Bisbrommethylbenzol gewonnen. Tieftemperatur-NMR-Untersuchungen ergaben, daß5b als 1:1 Mischung einer Sessel- und einer Bootkonformation des gespanntenE,Z-Diazanonadienringes vorliegt. Bei Raumtemperatur ist die zugehörige Ringinversion schnell in der NMR-Zeitskala, die entsprechenden Protonen in beiden Konformeren, auch die aller CH2-Brückenprotonen, ergeben gemittelte Signale. Bei tiefen Temperaturen wird zunächst die Inversion der Methylenbrücken eingefroren (Signale für zweiexo- und zweiendo-CH2-Protonen werden erhalten, ΔG≠ ca. 52 kJ mol−1). Bei weiterer Temperatursenkung können nach Einfrieren eines zweiten dynamischen Prozesses Sessel- und Bootkonformer anhand von getrennten Signalsätzen identifiziert werden (die freie Aktivierungsenthalpie für den zugehörigen Sessel-Boot-Flip beträgt ΔG≠ ca. 43.5 kJ mol−1). Die Zuordnung der1H- und13C-NMR-Resonanzen wurde mit Hilfe von zweidimensionalen NMR-Experimenten gesichert.

cis-trans-Isomerisation of the proline-peptide-bond in a cyclic tetrapeptide related to chlamydocin

Saturation transfer NMR experiments have been used to study the thermodynamic characteristics of the interconversion of two solute conformations of the chlamydocin derivative2 inDMSO-d6.ZusammenfassungDurch Sättigungstransferexperimente wurde die Kinetik der Isomerisierung mittels NMR-Spektroskopie untersucht. Die thermodynamischen Größen der Reaktion wurden bestimmt.

Intramolecular interactions II

A weak intramolecular interaction has been found between anN,N-dimethylbarbituric acid ring and an aromatic system connected by an aliphatic chain, and has been studied by UV-VIS and NMR spectroscopy. ΔH and ΔS values have been determined from the temperature dependence of chemical shifts.ZusammenfassungEine schwache intramolekulare Wechselwirkung zwischenN,N-Dimethylbarbitursäure und einem mit ihr über eine aliphatische Kette verbundenen aromatischen Ring wurde mittels UV-VIS- und NMR-Spektroskopie untersucht. Aus der Temperaturabhängigkeit der chemischen Verschiebung wurden die thermodynamischen Daten der Wechselwirkung bestimmt.