Wolfgang von Philipsborn

Nostocyclamide M: a cyanobacterial cyclic peptide with allelopathic activity from Nostoc 31.

A cyclic peptide containing thiazole and oxazole moieties was isolated from Nostoc 31 and its structure determined by chemical degradation detailed NMR and mass spectroscopic analyses. The compound is stereochemically pure and closely related to nostocyclamide in which D-valine is replaced by D-methionine. Therefore, it differs from tenuecyclamide C reported to contain L-methionine. It shows allelopathic activity against Anabaena 7120, but is inactive against grazers.

A correlation between 13C and 59Co NMR data and the catalytic activity of organocobalt complexes in the synthesis of pyridine derivatives

Abstract The correlation between the 13 C and 59 Co NMR spectra of substituted cyclopentadienylcobalt complexes and their catalytic properties in the synthesis of pyridine derivatives is examined. Since the correlations can be expressed as linear relationships, a direct screening of potential catalysts by NMR is possible.

β-Turns induced in bradykinin by (S)-α-methylproline

The ability or (S)‐α‐methylproline(α‐MePro) to stabilise reverse‐turn conformations in the peptide hormone bradykinin (BK = Arg1‐Pro2‐Pro3‐Gly4I‐Phe5‐Ser6‐Pro7‐Phe8‐Arg9) has been investigated. Two BK analogues containing α‐MePro at position 3 or position 7 were synthesised and their conformations in aqueous solution investigated by NMR spectroscopy. Whereas BK is largely disordered on the NMR time scale both analogues showed ROE connectivities in 2D‐ROESY spectra indicative of reverse‐turn conformations at both Pro2‐Phe5 and Ser6‐Arg9, whose formation appears to be cooperative. Some potential applications of α‐MePro as a reverse‐turn mimetic in the construction of synthetic peptide libraries is discussed.

Structure, conformation, and stereoelectronics of 1,4,5,8-tetraazadecalins. Chemical, multinuclear NMR and molecular mechanics studies

Abstract We present a multidisciplinary investigation of some known and new 1,4,5,8-tetraazadecalin (TAD) derivatives. Their structure, static and dynamic conformational analysis, isomerization pathways and relative stabilities were studied using 1H-, 13C-, and 15N-NMR techniques. Molecular mechanics calculations were carried out using the MM2 force field and an earlier modified version for NCN containing systems. The peculiar stereoelectronic features of the CNCNC moieties in the TAD systems are emphasized.

Steric effects in organometallic compounds. A 103Rh NMR study of alkylrhodoximes

Three series of alkylrhodoximes [Rh(Hdmg)2RL] (Hdmg = monoanion of dimethylglyoxime) (L  H2O, R  Me, Et, nPr, nBu, iBu, neoPent; L  py, R  Me, Et, nPr, iPr, nBu, iBu, sBu, tBu, neoPent, adam, CH2Cl, CH2 CH3; L  PPh3, R  Me, Et, nPr, iPr, nBu, iBu, tBu, neoPent, adam) were prepared and characterized by 1H, 13C and 31P NMR spectra; several of the reported compounds are new. The rhodium-103 chemical shifts were measured by (1H, 103Rh)-2D inverse correlation for the complexes with L  H2O and py and by (31P, 103Rh)-{1H}-2D inverse correlation for those with L  PPh3. Rh shielding decreases in the order Et > Me > nBu > i > sBu > neoPent > tBu. Discussion of the shift dependence on the various alkyl parameters allows us to conclude that, in these compounds the R ligand affects rhodium shielding mainly through distortions of the coordination site due to its bulk. The 1J[Rh,P] values reflect the rhodium-phosphine binding interaction.

Coherence pathways and “inverse” spectroscopy of InSm spin systems☆

Abstract An extension of the well-known “inverse” correlation experiment to InSm spin systems is described. A notation for heteronuclear coherences which is useful for designing phase cycles and for interpreting spectra is suggested. Applications to an A2X2 spin system (A = 31P, X = 103Rh) are presented. It is shown how the appearance of the 2D correlation spectra depends upon pulse-sequence parameters and phase cycling.

Steric Influences on the 103Rh NMR Chemical Shifts of Rhodium(III) Half‐Sandwich Complexes

Rhodium‐103 and phosphorus‐31 chemical shifts and Rh,P coupling constants are reported for 59 rhodium complexes of the types RhCp*X2(PR3) (Cp* = C5Me5; X = Cl, Br, I; PR3 = PMe3, PiPr3, PnBu3, PPh3, PMePh2, PMe2Ph), RhCp*X(PR3)Ph (X = Cl, Br, I, PR3 = PMe3, PMe2Ph, PMePh2, PPh3), RhCp*Br(PR3)(aryl), and of miscellaneous mono‐ and dinuclear types. Rhodium shielding generally decreases as the steric requirement of the phosphine increases and a number of linear correlations with the Tolman cone angle of the phosphine ligand are reported. Variable para substitution on the aryl ligand has little effect on rhodium shielding.

Glycosylmanganese pentacarbonyl complexes: an organomanganese-based approach to the synthesis of C-glycosyl derivatives

Abstract Preparation, structure and reactions of glycosylmanganese pentacarbonyl complexes are discussed. Anomerically pure complexes of pyranosyl and furanosyl complexes were prepared in excellent yield. The conformations of the anomeric glucosyl and mannosyl complexes were derived from detailed analysis of their 1D and 2D 1H- and 13C-NMR spectra including NOE data. The complexes are further characterized by 55Mn-NMR chemical shifts and 55Mn, 13C one-bond coupling constants. These compounds undergo various migratory insertion reactions resulting in formation of C-glycosyl derivatives. Applications of this technology to the synthesis of C-glycosyl and C-aryl glycosidic systems are discussed.

13C NMR spectroscopy XI. 4H-indenediiron pentacarbonyl complexes

Abstract The preparation of 4 H -indenediiron pentacarbonyl complexes from 1 H -indenes and diiron enneacarbonyl in hexane solution is described. The structures of the binuclear complexes are based upon spectroscopic analyses, particularly upon 1 H and 13 C NMR data. At room temperature the carbonyl groups of the Fe(CO) 3 and Fe(CO) 2 moieties exhibit very different exchange rates without internuclear scrambling.

57Fe, 13C Coupling Constants from Inverse Detection Experiments at Natural Isotope Abundance

The possibility of measuring 57Fe, 13C coupling constants and 13C/12C isotope effects on 57Fe nuclei by ‘pseudo‐triple’ and ‘pseudo‐quadruple’ resonance experiments using (1H, 57Fe), (1H, 57Fe)‐{31P} and (31P, 13C)‐{13C,1H} HMQC inverse correlations with Ψ‐BIRD or bi‐selective pulses is demonstrated. 57Fe, 1H coupling constants in the range of 1–2 Hz were used for the polarization transfer, 1J and 2J 57Fe, 13C coupling constants, their relative signs, and isotopic shifts 1Δ13/12C(57Fe) were determined for the first time in (cyclopentadienyl)iron complexes with 57Fe and 13C in natural isotope abundance.