Long-range COSY Research Articles

Conformational Assignments of Thujopsene and Related Compounds

Conformational analysis suggests that thujopsene (1) can exist as 2 possible conformations, steroidal and nonsteroidal. The conformation of 1 has been investigated using a NMR spectroscopic method. Analyses of the 1H NMR, ROESY, and long-range 1H-1H COSY spectra indicate that 1 exists in a steroidal conformation. Although the conformations of related compounds 2 and 3 were originally assigned as nonsteroidal, careful reexamination of the published NMR data indicates that both compounds exist in a steroidal conformation.

Technical and practical aspects of 19F NMR‐based screening: toward sensitive high‐throughput screening with rapid deconvolution

The technical and practical aspects of (19) F NMR-based screening against a macromolecular target are analyzed in detail. A novel method utilizing the relaxation of (19) F homonuclear double quantum coherence is proposed for performing NMR-based binding assays in a direct- or competition-mode format. A combined strategy based on (19) F NMR chemical shift prediction, 2D (19) F NMR DOSY, and 2D (19) F-(1) H NMR long-range COSY experiments is presented for the deconvolution of complex mixtures of fluorinated molecules generated by either addition of single compounds or by chemical synthesis. The approaches presented here allow the screening of complex mixtures, even in the case where the exact composition is not known, and the rapid identification of the binders contained in the mixtures.

NMR studies of the conformation of the natural sweetener rebaudioside A

Rebaudioside A is a natural sweetener from Stevia rebaudiana in which four β-d-glucopyranose units are attached to the aglycone steviol. Its 1H and 13C NMR spectra in pyridine-d5 were assigned using 1D and 2D methods. Constrained molecular dynamics of solvated rebaudioside using NMR constraints derived from ROESY cross peaks yielded the orientation of the β-d-glucopyranose units. Hydrogen bonding was examined using the temperature coefficients of the hydroxyl chemical shifts, ROESY and long-range COSY spectra, and proton–proton coupling constants.

The Observation of the C–H···O Hydrogen Bond in Trisialic Acid Lactone and Its Implications for Cooperative Lactonization

AbstractThe C–H···O hydrogen bond in trisialic acid lactones has been examined by using long‐range COSY (LRCOSY) and ab initio calculations. From an analysis of the LRCOSY spectra, 3J correlations of BH9ax/AH8 and CH9ax/BH8 confirmed the existence of hydrogen‐bond connections of x+1C9–x+1H9ax···xO8. The theoretical bond energy of the hydrogen bond was estimated to be 1.0 or 1.6 kcal/mol by using two models. The acid‐catalyzed cooperative lactonization of oligosialic acids can be understood in terms of the additional C–H···O stabilization in the lactone product. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

One-bond and long-range coupling constants of substituted 2-cyanopyridines. GIAO/DFT calculations of proton and carbon chemical shifts and coupling constants

The magnitude of one bond and long-range coupling constants ( n J HH and n J CH) in isomeric cyanopyridines-( 1, 2, 3), methyl-( 4, 5, 6, 7), 3-ethyl-( 8), chloro-( 9), 3-bromo-( 10), acetyl-( 11, 12), 5-ethoxycarbonyl-( 13) and 4-(4′-pyridyl)-( 14) derivatives of 2-cyanopyridines were determined in CDCl 3. The Density Functional Theory/Gauge Including Atomic Orbitals (GIAO/DFT) calculation was employed for the estimation of proton or carbon chemical shifts and coupling constants ( n J HH and n J CH) and the calculated NMR data compared with the experimental NMR data. The experimental values of n J HH and n J CH in derivatives of 2-cyanopyridines 1– 14 are discussed with respect to the corresponding data in previously reported compounds and compared with values obtained from GIAO/DFT calculations and iterative simulation using gNMR software. Assignments of proton and carbon chemical shifts were achieved using one- and two-dimensional NMR techniques, such as 1D NOE difference, COSY, long-range COSY, gHMBC and gHMQC.

Multinuclear NMR Studies of Palladium(II) Dihalide Complexes of Dibutyl {α-[4-(Phenyldiazenyl)anilino]benzyl}phosphonate

The 1H, 13C, 15N and 31P NMR studies of two types of palladium(II) dihalide complexes of dibutyl {α-[4-(phenyldiazenyl)anilino]benzyl}phosphonate (L) are reported: those with the monodentate trans-bonded ligands through the azo nitrogen, trans-Pd(L)2X2 (X = Cl, Br), and a cyclopalladated binuclear complex in which chloride ions bridge two metal centers, [Pd(L-H)(μ-Cl)]2. The 15N-enriched organophosphorus compound and its palladium(II) complexes were also prepared to enable unambiguous determination of the nitrogen ligation site by 15N NMR. The NMR analysis was accomplished by one- and two-dimensional homo- and heteronuclear experiments including 1H-1H COSY, long-range 1H-1H COSY, NOESY, 1H-13C COSY, long-range 1H-13C COSY, HMQC and HMBC. With the mononuclear complexes, the formation of isomeric species was observed, which are interpreted as rotational isomers caused by restricted rotation around the metal-ligand bond.

Research in the chemistry of diterpenoid alkaloids

Abstract

NMR and AM1 Quantum Chemical Study of the Regioselectivity of the Reaction of 2-Hydroxyethyl Methacrylate with 3-Nitrophthalic Anhydride

The reaction of 2-hydroxyethyl methacrylate with 3-nitrophthalic anhydride catalyzed with triethylamine results in the 3 : 1 mixture of two possible monoesters, the more populated one being that with the ester group in ortho position to the nitro group. The isomers were identified and quantified by 1H and 13C 1D and 2D techniques including APT, INEPT, superselective long-range (SSLR) INEPT, SSLR HHCR, COSY, NOESY, HETCOR and COLOC. Theoretical analysis was done on the model reaction of methanol with the anhydride using semiempirical AM1 quantum chemical calculations. The results indicate that the relative regioselectivity of the reaction is due to both the electron distribution in the anhydride molecule and hydrogen bonding in the stages immediately preceding the transition state.

Hypoestenone: a fusicoccane diterpene ketone from Hypoestes forskalei

The aerial parts of Hypoestes forskalei yielded a new fusicoccane diterpene ketone, named hypoestenone. Its structural assignment was based on chemical derivatization and 1H and 13C NMR spectroscopic studies, mainly 2D NMR experiments, including long-range COSY and HETCOR correlations. X-Ray crystallographic analysis established the complete structure and relative stereochemistry of the epoxide of hypoestenone.

Matteuorienate A and B, two new and potent aldose reductase inhibitors from Matteuccia orientalis (Hook.) Trev.

Matteuorienate A and B, two new C-methyl flavanone derivatives, were isolated from the Matteuccia orientalis (Hook.) Trev. (Aspidiaceae), and their structures were determined by the use of spectroscopic methods including 2D-NMR (1H-1H COSY, 1H-13C COSY and 1H-13C long-range COSY) experiments and chemical methods. Both the compounds were found to be very strong inhibitors of aldose reductase among the natural products.

Synthesis and conformational analysis of nitropolycyclic fluoranthenes

Nitroarenes are ubiquitous environmental pollutants some of which exhibit mutagenic and tumorigenic activities. The first systematic investigation of the nitration reactions of the polycyclic fluoranthenes, a major clans of nonalternant polyarenes, is described. The specific hydrocarbons studied were benz[e]acephenanthrylene (1), benz[a]aceanthrylene (2), indeno[1,2,3-cd]pyrene (3), indeno[1,2,3-hi]chrysene (4), dibenz[a,e]aceanthrylene (5), dibenz[a,j]aceanthrylene (6), and dibenz[e,k]acephenanthrylene (7). The nitration of all hydrocarbons, except 1, proceeded with remarkable regioselectivity to provide a single mononitro product. In the cane of 1, 17% of a second mononitro isomer was isolated. The structure of the resulting mononitrofluoranthenes (8-15) were fully characterized by analysis of their high-resolution COSY, long-range COSY, and NOESY NMR spectra and by comparison with the spectra of the parent hydrocarbons. The observed nitration sites of the polycyclic fluoranthenes were in excellent agreement with theorical predictions made by the DEWAR-PI method based on the relative energies of the Wheland intermediates for substitutions at variuos ring positions. The availability of the complete 1 H chemical shift assignments of the nitropolycyclic fluoranthenes, together with those of the parent hydrocarbons and their UV-visible spectral data, enabled the molecular conformations of the nitro groups to be probed

Sequence and solution conformation of the 20-residue peptaibols, saturnisporins SA II and SA IV.

Saturnisporins SA II and SA IV are the major components of the 20-residue peptaibol mixture isolated from a culture of the fungus Trichoderma saturnisporum. These peptides exhibit antibiotic activity against Staphylococcus aureus. Their sequences were derived from unequivocal methodology implying the combined use of positive ion FAB mass spectrometry and NMR: the majority of the sequences result from mass spectrometry fragmentations and the location of isomeric residues arises either from analysis of ROESY cross-peaks between contiguous amide protons or from heteronuclear 2J or 3J 1H-13C couplings detected in long-range 1H-13C COSY experiments. The sequence specific 1H and 13C NMR assignments are described. Saturnisporins SA II and SA IV exhibit similar secondary structures, as deduced from their ROESY patterns and 3JNHC alpha H coupling constant values, together with amide hydrogen-deuterium exchange rates and temperature coefficients of amide and carbonyl groups. An overall alpha-helical structure is proposed, maintaining two regions of distortion to this regular structure; i) the N-terminal part, which contains 3(10) and mixed alpha-3(10) turns, and ii) the Aib10-Val15 region, including a Pro residue which accommodates a bend stabilized by two 3(10) H-bonds.

Structure of acrignine-A, the first naturally occurring acridonolignoid from Citrus plants.

The chemical structure of acrignine-A (1), an acridone alkaloid carrying lignan moiety, from roots of Citrus plants (Rutaceae) have been elucidated by spectrometric studies using 1H-13C long-range COSY and NOE experiments. The structure was confirmed by single crystal X-ray analysis. This is the first example of an acridonolignoid isolated from natural sources.

Spectroscopic elucidation of glycobismines, first naturally occurring binary acridone alkaloids containing a carbon–carbon linkage

The structures of glycobismine-A 1, -B 4 and -C 4′, novel binary acridone alkaloids, from Glycosmis citrifolia(Willd.) Lindl. (Rutaceae) have been elucidated by spectroscopic studies using 1H-13C long-range COSY and/or HMBC experiments. In a preliminary communication we reported the structure of glycobismine-A 1 as the first naturally occurring binary acridone alkaloid having a carbon–carbon linkage. This paper deals with the complete and detailed spectroscopic structural elucidation of compound 1 and the structures of two additional new binary acridone alkaloids, glycobismine-B 4 and -C 4′.

Structures of Tetra-O-demethylcolchicine, -isocolchicine, and 10-O-Demethylcolchicine Derivatives.

During the exhaustive demethylation of both colchicine and isocolchicine analogs, tetra-O-demethyl derivatives with identical structures were produced. Spectral examination ( 1 H- 13 C long-range COSY nuclear magnetic resonance) of these analogs (5-8) indicated that isocolchicine-type tautomerism is predominant in tetra-O-demethylcolchicine derivatives. Similarly, structures of 10-O-demethylcolchicine derivatives were revised to be an isocolchicine-type shown by formulae (9) and (10)

Palbinone, a novel terpenoid from Paeonia albiflora; potent inhibitory activity on 3 alpha-hydroxysteroid dehydrogenase.

Palbinone, a novel terpenoid isolated from the roots of Paeonia albiflora, showed a strong inhibitory activity on the reduced form of nicotinamide adenine dinucleotide phosphate (NADPH)-linked 3 alpha-hydroxysteroid dehydrogenase (3 alpha-HSD) of rat liver cytosol. The structures of palbinone and a known compound, paeonilactone-B isolated from the active fraction of this plant were determined by the use of 2D NMR techniques (1H-1H COSY, 1H-13C COSY, 1H-13C long-range COSY, and HMBC).

C-Nucleosides. 19. Synthesis of 7- and 8-Substituted 4-[1-(b-D-Ribofuranosyl)oxo]-1,3-dihydro-2H-1,5-benzodiazepin-2-one

The synthesis of 7- and 8-substituted 4-[1-(2,3,5-tri-O-benzoyl-β-D-ribofuranosyl)oxo]-1,3-dihydro-2H-1,5-benzodiazepin-2-one from furanone glycoside is described. Treatment of 1,2-diamino-4-substituted benzenes with 1 gave a mixture of 7- and 8-substituted 4-[1-(2,3,5-tri-O-benzoyl-β-D-ribofuranosyl)oxo]-1,3,4,5-tetrahydro-2H-1,5-benzodiazepin-2-one. Dehydrogenation of 3a-d with DDQ and a trace of PTSA afforded 7- and 8-substituted 4-[1-(2,3,5-tri-O-benzoyl-β-D-ribofuranosyl)oxo]-1,3-dihydro-2H-1,5-benzodizepin-2-ones. The position of the substituent in compounds was confirmed by 1 H- 13 C long-range COSY and NOE experiments with the corresponding N 1 -methyl derivatives. Deprotection of compounds with methanolic sodium hydroxide afforded 4g-k

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.

Structure and Contents of Main Coloring Constituents in the Calyces of Hibiscus sabdariffa and Commercial Roselle Color

A main coloring constituent in dry calyces of Hibiscus sabdariffa was not delphinidin-primveroside, but delphinidin-sambubioside, whose structure was clearly identified as delphinidin 3-[O-β-D-xylopyranosyl-(1→2)-β-D-glucopyranoside] (1) by spectroscopic methods (i. e. H-H longrange COSY NMR and NOESY NMR). On quantitative analysis by high performance liquid chromatography, the contents of 1 in the water extract and a commercial roselle color were 1.1 and 0.3%, respectively. Since 1 seemed to represent the color of the water extract, 1 might be used as a guide compound for standardization of commercial roselle colors.

ChemInform Abstract: Spectrometric Elucidation of Acrimarines, the First Naturally Occurring Acridone‐Coumarin Dimers.

AbstractThe novel yellow alkaloids acrimarine‐A (Ia), ‐B (Ib), ‐C (IIa), ‐D (IIb), ‐E (IIIa), ‐F (IIIb) and ‐G (IV) are isolated from Citrus funadoko.