Heteronuclear Multiple Bond Connectivity Research Articles

4′,5′‐SUBSTITUTED METHYLANGELICINS: PHOTOCYCLOADDUCTS WITH PYRIMIDINE BASES OF DNA

The isolation and characterization of photocycloadducts with pyrimidine bases from DNA samples irradiated (365 nm) in the presence of four 4',5'-substituted methylangelicins was performed. All these furocoumarins yielded mainly the cis-syn furan-side cycloadduct with thymine. For 4',5'-dimethyl-, 5,4',5'-trimethyl- and 6,4',5'-trimethylangelicin this adduct was accompanied by two pyrone-side adducts (cis-syn and cis-anti), whereas the 4,4',5'-trimethyl derivative gave the furan-side adduct with cytosine. The characterization of the regio- and stereochemistry of the adducts was accomplished by 1H NOE (nuclear Overhauser effect) and 1H-13C HMBC (heteronuclear multiple-bond connectivity) spectroscopies. The formation of different cycloadducts in DNA by the various derivatives highlights the role of the methyl groups in determining the regio- and stereochemistry of the cycloaddition.

Structural study of a cell-wall mannan of Saccharomyces kluyveri IFO 1685 strain. Presence of a branched side chain and beta-1,2-linkage.

Acetolysis of the cell-wall mannan of Saccharomyces kluyveri under mild conditions, gave fragments with 1-6 mannose residues. The structures of mannopentaose and mannohexaose were determined to be [Formula; see text] respectively, by two-dimensional homonuclear Hartmann-Hahn spectroscopy and a sequential NMR assignment method that combines 1H-13C correlated spectroscopy, relayed coherence transfer spectroscopy, 1H-detected heteronuclear multiple-bond connectivity and methylation analysis. The H1 proton chemical shift of a neighboring alpha-1,2-linked mannose unit of the 3-O-substituted structure was shifted upfield by the addition of a mannose unit to the adjacent 3-O-substituted unit by an alpha-1,6 linkage. The characteristic H1--H2-correlated cross-peak of the alpha-1,3-linked mannose unit substituted by a beta-1,2 linkage, beta 1-->2Man alpha 1-->3, in the mannan of S. kluyveri, as also found by two-dimensional homonuclear Hartmann-Hahn spectroscopy in the mannan of Candida guilliermondii, a pathogenic yeast in man.

Complete Assignment of 1H and 13C Nuclear Magnetic Resonance Chemical Shifts of β-1,2-Linked Mannooligosaccharides Isolated from the Phosphomannan of the Pathogenic Yeast Candida albicans NIH B-792 Strain

To confirm correctness of the previous assignment study of H-i protons of β-1,2-linked mannooligosaccharides provided by Shibata et al. (Biochemistry 31, 5680-5686, 1992), anotber type of nonempirical assignment of the H-1 signals of be same oligosaccharides was achieved by adopting a sequential NMR assignment method that combines two-dimensional 1H-13C correlated spectroscopy, two-dimensional 1H-1H correlated spectroscopy, and two-dimensional heteronuclear multiple-bond connectivity. Based on the above results, all of the 1H and most of the 13C signals in each oligosaccharide could also be assigned. The results of the proton assignment study provided sufficient evidence to confirm the correctness of that obtained in the previous H-1 proton assignment study. Furthermore, the existence of a regularity rule between the order of mannose units and its 1H and 13C chemical shifts has been revealed.

Constituents of the Roots of Boerhaavia diffusa L. III. Identification of Ca2+ Channel Antagonistic Compound from the Methanol Extract.

Two known lignans, liriodendrin and syringaresinol mono-beta-D-glucoside, have been isolated from the methanol extract of the roots of Boerhaavia diffusa L. (Nyctaginaceae), and the former compound was found to exhibit a significant calcium (Ca2+) channel antagonistic effect in frog heart single cells using the whole-cell voltage clamp method. Reexamination of the carbon-13 nuclear magnetic resonance (13C-NMR) spectra of these compounds was also carried out by the use of two-dimensional NMR techniques including a 1H-detected heteronuclear multiple bond connectivity (HMBC) experiment, and it was found that the previous signal assignments for C-1' and C-4' have to be revised.

YS-822A, a new polyene macrolide antibiotic. II. Planar structure of YS-822A.

The planar structure of a new polyene macrolide antibiotic, YS-822A, which was isolated from the culture filtrate of a mutant strain H-8 of Streptoverticillium eurocidicum var. asterocidicus S-822, was established as I on the basis of spectroscopic evidences and by comparison spectroscopic data with nystatin A1 (II) and amphotericin A (III), representative polyene macrolide antibiotics. Molecular formula of YS-822A was established as C37H59NO14 (MW 741) by elemental analysis, NMR, and FAB mass spectra. The UV spectrum of YS-822A was very similar to that of nystatin A1, suggesting that YS-822A also has a conjugated all-trans-tetraene moiety. 1H and 13C NMR spectra of YS-822A showed a number of broad and overlapped signals, but the 1H-1H and 13C-1H COSY spectra implied the existence of a mycosamine moiety and several other partial structures. The connectivity of these partial structures was established by extensive 2D NMR experiments, including homonuclear Hartmann-Hahn and heteronuclear multiple-bond connectivity measurements, which led to the determination of the gross planar structure of YS-822A as I.

Constituents of the leaves of Woodfordia fruticosa Kurz. I. Isolation, structure, and proton and carbon-13 nuclear magnetic resonance signal assignments of woodfruticosin (woodfordin C), an inhibitor of deoxyribonucleic acid topoisomerase II.

Woodfruticosin (woodfordin C), a new cyclic dimeric hydrolyzable tannin having an inhibitory activity toward deoxyribonucleic acid (DNA) topoisomerase II, has been isolated from the leaves of Woodfordia fruticosa Kurz (Lythraceae) along with three known flavonol glycosides and three known flavonol glycoside gallates. The structure of wood fruticosin (woodfordin C) was determined by the use of two-dimensional nuclear magnetic resonance (2-D NMR) spectroscopy including heteronuclear multiple quantum coherence (HMQC) and heteronuclear multiple bond connectivity (HMBC) techniques. Detailed analyses of the proton and carbon-13 NMR (1H- and 13C-NMR) spectra of six known flavonoids were performed.

Landomycins, new angucycline antibiotics from Streptomyces sp. I. Structural studies on landomycins A-D.

The chemical structure of the new angucycline antibiotic landomycin A has been elucidated via chemical and spectroscopic methods, in particular by 2D NMR correlation spectroscopy, e.g., 1H, 1H-COSY, 13C, 1H-COSY, correlation spectroscopy via long-range-couplings and heteronuclear multiple bond connectivity spectroscopy sequences. The spectroscopic investigations were carried out principally with the octaacetyl derivative of landomycin A, which is more soluble in organic solvents than landomycin A itself. The structure consists of a new, unusual angucyclinone, landomycinone A, and of six deoxy sugars, four D-olivoses and two L-rhodinoses, which are all assembled in one chain thus forming the sequence (olivose-4----1-olivose-3----1-rhodinose)2. This long sugar chain is bonded as a phenolic glycoside to the aglycone moiety, a unique structural feature among quinone glycoside antibiotics. By comparison with the main component landomycin A, the structures of three minor congeners, namely landomycins B, C and D, could be proposed.

Isolation and structures of citropone-A, -B, and -C from Citrus plants, the first examples of naturally occurring homoacridone alkaloids containing a seven-membered ring system.

The first isolation of the unique homoacridone alkaloids, citropone-A (1), -B (2), and -C (3) from the root or stem bark of some cultivated Citrus plants is described. The structure of citropone-A (1) was established unequivocally by spectrometric and single-crystal X-ray analyses, while citropone-B, which has the same skeleton as 1, was assigned structure 2 by comparison of the 1H- and 13C-nuclear magnetic resonance spectra with those of 1. The structure of citropone-C was proposed as formula 3 on the basis of spectrometric analyses using H-C long-range two-dimensional correlation spectroscopy and heteronuclear multiple bond connectivity spectrometries.

Assignments of the1H- and13C-NMR Spectra of Four Lycopodium Triterpenoids by the Application of a New Two-dimensional Technique, Heteronuclear Multiple Bond Connectivity (HMBC)

The complete assignments of four lycopodium triterpenoids, lycoclavanol, lycoclaninol, 21- epi-serratenediol and serratenediol, were accomplished by the use of a new two-dimensional technique, HMBC (heteronuclear multiple bond connectivity). It appears this technique is extremely powerful for the structural analysis of complicated compounds with many methyl groups.

Assignments of the 1H- and 13C-NMR spectra of four lycopodium triterpenoids by the application of a new two-dimensional technique, heteronuclear multiple bond connectivity(HMBC).

The complete assignments of four lycopodium triterpenoids, lycoclavanol, lycoclaninol, 21- epi-serratenediol and serratenediol, were accomplished by the use of a new two-dimensional technique, HMBC (heteronuclear multiple bond connectivity). It appears this technique is extremely powerful for the structural analysis of complicated compounds with many methyl groups.

Proton and carbon-13 assignments from sensitivity-enhanced detection of heteronuclear multiple-bond connectivity by 2D multiple quantum NMR

Proton and carbon-13 assignments from sensitivity-enhanced detection of heteronuclear multiple-bond connectivity by 2D multiple quantum NMR