2D 1H-13C Research Articles

Conformational Aspects of the p-Nitrosophenolate Anion and Related Compounds: NMR Study and ab initio 6-31G Optimizations of Molecular Structures

Abstract The p-nitrosophenolate anion, PNPA (3), represents an excellent example of variable π-electron transfer demanded by a network of different hydrogen bonds. The limiting structures of mono-protonation in the solid state and in solution are either the p-nitrosophenol (1) or the p-quinonoxime (2) molecules. For the systems 1 to 3 and the related compounds 4 to 7 are results of ab initio 6-31G HF MO optimizations of molecular structures presented which are calculated additionally in variously rotated conformations. Solid state 13C-CP/MAS NMR spectra of two PNPA salts 8 and 9 have been recorded at 7.0 Tesla. The protonation of 8 and 9 was studied in solution using a 400 MHz NMR spectrometer recording the variations in 1H and 13C NMR chemical shifts on changing the solvent from DMSO-d6 to D2O in steps of 25%. The 2D 1H-13C correlated spectrum leads to unambigous assignment of NMR signals. From the coalescence temperature of 1H signals of 9 the experimental barrier of rotation in D2O was determined as 16.9 ± 0.1 kcal mol-1. The calculated gas phase rotational barrier for free PNPA is with 26.9 kcal mol-1 much higher, but is lowered by calculations for the Li-salt 6 c to 14.5 kcal mol-1 and to 11.8 kcal mol-1 for the protonated PNP If. The in-plane inversion of PNPA through 3c is calculated to be extremely high with 52.4 kcal mol-1. The effects of rotation of substituents to orthogonal conformations on calculated energies and on intramolecular distances were studied thoroughly.

Geometrical and optical isomers of the nickel(II) complexes of chiral, tetradentate unmixed and mixed schiff bases: CD and NMR spectroscopic studies

Electronic, circular dichroïsm (CD) and NMR spectroscopic studies (1D 1H and 13C, 2D 1H COSY and NOESY, 1H 13C correlation) of several chiral unmixed Schiff base nickel complexes and chiral mixed nickel complexes have been carried out. In such Schiff base complexes, the Cotton effect associated with a given transition reflects the conformation of the chelate five-membered ring of the diamino chain. The entire set of mixed and unmixed NiN 2O 2 ( S) complexes involve a chelate ring adopting, at least preferentially, a λ conformation, with the methyl substituent taking an axial orientation. This result is confirmed by the NMR study of the vicinal coupling constants 3 J HH in the C(H α )(H β )C(H γ )R fragments of the diamino chain. On the contrary, the unmixed NiN 4 ( S) complex and the mixed NiN 3O ( S) complex are clearly different. This change comes from the presence of a 5,5,5- or a 5,5,6-chelate ring arrangement around the metal atoms that leads to a larger CNC angle involving the imine function and, eventually, allows a shift of the methyl substituent towards a more equatorial position. Furthermore, use of 2D 1H 13C NMR correlations allows a straightforward attribution of the entire set of signals. In one case, these results lead to a different assignment from previously published data.

A ferulic acid ester of sucrose and other constituents of Bhesa paniculata

A novel derivative of sucrose, β-(3,6-di- O-feruloyl)-fructofuranosyl- α-(2,3,4,6-tetra- O-acetyl)-glucopy-ranoside, was isolated from the wood of Bhesa paniculata. Its structure was determined by a combination of 2D 1H 1H and 1H 13C correlation NMR spectroscopy. The known compounds, glycerol 1–9′,12′-octadecadienoate, β-sitosterol, (±)-pinoresinol, methyl 3,4-dihydroxybenzoate, 4-hydroxy-3-methoxybenzoic acid, anofinic acid and 2-(1′-methylethenyl)-benzofuran-5-carboxylic acid were also isolated.

The Tetracyclic Lantibiotic Actagardine 1H-NMR and 13C-NMR Assignments and Revised Primary Structure

The primary structure of the peptide lantibiotic actagardine was determined in (2H3)acetonitrile/H2O by homonuclear two- and three-dimensional NMR spectroscopy as well as 2D 1H(13C) correlation spectra at natural abundance. Actagardine was found to be a tetracyclic 19-residue peptide containing one lanthionine and three overlapping beta-methyllanthionine bridges. Sequential resonance assignment and location of the four thioether rings was accomplished by 2D NOESY, 3D NOESY-TOCSY and gradient-enhanced 1H(13C)-HMBC spectra. The C-terminal thioether bridge was shown to be oxidized to a sulfoxide. The NMR data were additionally confirmed by mass spectrometry and Edman degradation after chemical modification, which allowed sequencing of lanthionine and beta-methyllanthionine residues. Our studies clearly show, that the structure of actagardine as previously published by Kettenring et al. (1990) J. Antibiot. 43, 1082-1088 is not correct.

Setosol, a Biologically Active Heptaketide-like Metabolite from thePleiochaeta setosaPhytopathogen

Setosol, a biologically active natural product, was extracted from Pleiochaeta setosa, an organism isolated from volcanic rock in the Canaries. With molecular formula C15H16O5 and a melting point of 139°C, this pale yellow and amorphous compound inhibited the growth of Pyricularia oryzae, Drechslera oryzae, and Gerlachia oryzae. Isolation of the new compound was performed by repeated centrifugal TLC on silica gel, and its structure was established as 2,8-dimethyl-4-methoxy-6,10,11-trihydroxy-benzooxaonin by detailed spectral studies, including COSY, 2D 1H-13C direct chemical shift correlation (XHCORR), 2D 1H-13C correlation via long-range coupling (COLOC), heteronuclear-gated decoupling (GATEDEC), and single-frequency heteronuclear-gated decoupling (SFDEC) NMR techniques, as well as UV, IR, and MS.

NMR determination of EPR hyperfine coupling constants of some 5-(n-alkyl)-1,1,3,3-tetrakis(trideuteriomethyl)isoindolin-2-yloxyls

2D 1H–13C chemical shift correlation spectroscopy has been used to determine some small 1H and 13C EPR hyperfine interaction constants in some 5-(n-alkyl)isoindolin-2-yloxyl radicals. In the methodology used, it was necessary to measure the chemical shifts of both the isoindolines and of the cognate isoindolin-2-yloxyl radicals. The latter n-alkyl-substituted radicals have considerable potential as EPR spin probes in lipid systems.

13C NMR determination of the tautomeric and ionization states of folate in its complexes with Lactobacillus casei dihydrofolate reductase.

13C NMR studies provide a convenient way of obtaining detailed information about tautomeric and ionization states in protein-ligand complexes provided that suitably 13C-labeled molecules are available. In the present study, [4,6,8a-13C]- and [2,4a,7,9-13C]folic acid were synthesized and the 13C NMR spectra of their complexes with Lactobacillus casei dihydrofolate reductase (DHFR) were assigned and analyzed as a function of pH. From these data it was possible to determine the tautomeric and ionization states of the bound folate and to obtain further evidence about the orientation of the pteridine ring in the complexes. In the 13C spectra of the ternary complexes of the 13C-labeled folic acids with DHFR and NADP+, each labeled carbon gave rise to multiple signals, confirming our previous findings that there are three interconverting conformational forms of bound folate (forms I, IIa, and IIb) in the ternary complex (Birdsall et al., 1989b). The 13C spectra of the binary complexes of folate and DHFR also provide direct evidence for the presence of forms IIa and IIb and indirect evidence of some form I at low pH values ( < 5.0). 2D 1H-13C HMQC-NOESY experiments on ternary complexes formed using the [2,4a,7,9-13C]folic acid were used to obtain intermolecular NOEs between the folate H7 proton and protons on the protein, and these provided further characterization of the orientations of the pteridine ring in the different bound forms of folate (form IIb with its pteridine ring in the catalytically active conformation and forms I and IIa with their pteridine rings turned over by 180 degrees).(ABSTRACT TRUNCATED AT 250 WORDS)

Kadsulignan C and D, two novel lignans from Kadsura longipedunculata

Two novel lignans, kadsulignan C (4) and D (5), were isolated from the root bark of Kadsura longipedunculata. Their structures, including absolute configurations, were elucidated by 2D 1H–13C long-range COSY experiments and chemical transformation to the known compound 10. Key words: isolation and structure, absolute configuration, kadsulignan C, kadsulignan D, lignans, Kadsura longipedunculata.

Optically active phosphine oxides: 10 [1]; X-ray structure and conformation of (Sp)- and (Rp)-L-menthyl α-(phenylvinylphosphinyl)acetates

The structures and solid-state stereochemistry of the two P-epimeric compounds (1 and 2) formed in a reaction of butyl phenylvinylphosphinite with (-)-L-menthyl bromoacetate were studied by X-ray crystallography and CP–MAS 13C NMR spectroscopy. The two compounds were also analyzed in solution by means of 2D 1H NMR, 13C NMR, IR, UV, and dipole moment measurement techniques. Compound 1, C20H29O3P, crystallized in the orthorhombic group P 212121 with Z = 4, a = 20.491(2), b = 16.719(1), and c = 5.910(1). Compound 2, C20H29O3P, crystallized in the monoclinic space group P 21 with Z = 2, a = 9.266(1), b = 9.852(1), c = 10.954(1), and β = 95.20(1)°. In the crystals both compounds possess their CCPO fragments in an s-cis array, and have their PO and CO dipoles oriented uniformly in a syn, nearly parallel, fashion. In solution, however, an anti arrangement of these two dipoles is slightly preferred.

Two-dimensional n.m.r. characterization of cycloaliphatic epoxy resins

The cycloaliphatic epoxy resins were studied by various two-dimensional nuclear magnetic resonance (2D n.m.r.) spectroscopies. The 13C n.m.r. spectra of the epoxy resins were assigned by using DEPT and 2D INADEQUATE techniques and the 1H n.m.r. spectra were assigned by using 2D 1H 1H and 1H 13C COSY techniques. Complete characterization of the samples synthesized by the oxidation of cyclohexene derivatives not only revealed the existence of the stereochemical isomers resulting from the structural difference of the oxide rings in the samples but also provided the composition ratio of the isomers.

Synthesis, characterization and in vitro antitumour activity of a series of substituted 2,2‐di‐n‐butyl‐4‐oxo‐benzo‐1,3,2‐dioxastannins

AbstractThe characterization by 1D and/or 2D 1H NMR, 13C NMR, 119Sn NMR, Mössbauer and mass spectrometry of a series of di‐n‐butyltin derivatives of 3‐, 4‐, and 5‐methyl‐, 3‐, 4‐, and 5‐methoxy‐, 4‐ and 5‐amino‐substituted, and 3,5‐diiodo‐salicyclic acids is described. Their NMR spectra suggest that they are present as dimers in CDCl3 solution, like the di‐n‐butyltin derivative of unsubstituted salicyclic acid. This has been confirmed by the observation of mixed dimers. The insoluble derivatives have been characterizerd by solid state cross polarization/magic angle spinning (CP/MAS) 13C and/or 119Sn NMR, Mössbauer and mass spectroscopy. These compounds are characterized in vitro by a lower inhibition dose than cis‐platin or etoposide against a series of five human cell lines.

New Polyhydroxylated Triterpenes from Uncaria tomentosa

Three novel polyhydroxylated triterpenes have been isolated from Uncaria tomentosa. Their structures were established as 1, 2, and 3 by detailed spectral studies including 1H-13C correlations via long range couplings using the INAPT pulse sequence, nOeds, and 2D 1H-13C direct chemical shift correlation (HETCOR) nmr techniques.

13C NMR studies of tautomerism in imidazo[4,5‐c]pyridines

AbstractA detailed analysis of the 13C NMR spectra of the 1‐N‐ and 3‐N‐methyl derivatives of 1H‐2‐(2,4‐dimethoxyphenyl)imidazo[4,5‐c]pyridine, utilizing long‐range couplings and 2D 1H13C correlation experiments, has led to an unambiguous assignment of all carbons. Comparison of these definitive assignments of C‐3a and C‐7a, in particular, with those of the tautomers of 1H‐2‐(2,4‐dimethoxyphenyl)imidazo[4,5‐c]pyridine has permitted confirmation of the predominance of the 1H‐tautomer for the latter. In addition, previous conflicting assignments for 1H‐imidazo[4,5‐c]pyridine and its 3‐N‐methyl derivative are now resolved. Revision of these assignments leads to the conclusion that the 1H‐tautomer of 1H‐imidazo[4,5‐c]pyridine is predominant.

Kadsulignan A and B, two novel lignans from Kadsuracoccinea

Two novel lignans, kadsulignan A (1) and B (2), were isolated from the seeds of Kadsuracoccinea. Their structures were elucidated by 2D1H–13C COSY, 2D1H–13C long-range COSY experiments, and chemical transformation to a known compound (5) using AlCl2H. Keywords: isolation and structures, kadsulignan A, kadsulignan B, Kadsuracoccinea.

New approaches to oligosaccharide sequencing and conformational distribution around the glycosidic bond. One‐ and two‐dimensional 13C{1H} NOE spectroscopy

AbstractBoth negative, indirect heteronuclear NOE and 2D 1H13C relayed incoherent transfer spectroscopy are shown to be useful in oligosaccharide sequencing. The one‐ and two‐dimensional manifestation of the former effect allows the experimental determination of the average carbon–proton distances along the non‐rigid glycosidic bond. However, these preliminary attempts must be further improved for predicting the accurate weights of the preferred conformers.

Stereostructure of auricularic acid, a cleistanthane diterpenoid from Pogostemon auricularis hassk

Auricularic acid, a spasmolytic diterpene, isolated from Pogostemon auricularis has been characterized as cleistanth-13,15-dien-18-oic acid ( 1 ) with the help of high resolution 2D 1H 1H (COSY, NOESY) and 1H 13C (Hetero-COSY) n.m.r. studies.

13C NMR studies of the triterpene 3α-hydroxylup-20(29)-en-23,28-dioic acid and some derivatives

The 13C NMR assignment of the triterpene 3α-hydroxylup-20(29)-en-23,28-dioic acid and some of its derivatives has been carried out. In addition to conventional methods, 2D 1H13C chemical shift correlation, nuclear Overhauser enhancement difference and decoupling difference techniques were used for the assignment.

High resolution nmr and x-ray crystallography data of caudicifolin from Euphorbia acaulis

A diterpene lactone was isolated from the cold petrol (60−80°) extract of rhizomes of Euphorbia acaulis, a plant material used by a tribe of central India for curing various inflammatory disorder. The diterpene, which was observed to be identical to caudicifolin on the basis of its physical constants, was subjected to high resolution NMR spectroscopy and X-ray crystallography examination. This paper reports the salient features of the 2D 1H NMR, 13C NMR and X-ray crystallography data of the compound. 13C NMR assignments were made by the use of proton noise decoupling, SFORD, APT and automatic spectral editing techniques. 1H NMR assignments were made with the aid of a COSY experiment for long range couplings and NOE correlated 2D-experiments. The 1H and 13C NMR spectral assignments have been further corroborated by H/C correlation experimental results.

Two alkaloids from Narcissus requienii

The aerial part of Narcissus requienii (Amaryllidaceae) was found to contain pseudolycorine as the major alkaloid, and two new phenolic bases: 2-O-acetylpseudolycorine and 1-O-acetylpseudolycorine. The present communication reports the complete assignments of the NMR spectra of pseudolycorine, and the structure elucidation of the other comnounds by means of 2D 1H-1H and 1H-13C NMR chemical shift correlation experiments.

Les steganolides B et C, nouveaux lignanes analogues de l'episteganacine, isoles a partir de [formula omitted] hochst. - correlation 13C- 1H de la steganacine, en RMN bidimensionnelle -

Isolation from Steganotaenia araliacea Hochst. (Apiacaeae) and structure determination of Steganolides B and C -two new bisbenzocyclooctadlene lignan lactones having the same skeleton and bearing angeloyl and tigloyl benzylic substituants respectively- were performed with the help of high resolution 1H NMR at 500 MHz. An unambigous 13C assignement of the aliphatic carbones of the available steganacin congener was carried out in using 2D 1H 13C correlation and, skeleton conformation induced by the C 5 benzylic substitution in connection with 13C chemical shift and 1H vicinal coupling was established.