Total assignment of 1H and 13C NMR spectra of three triterpene saponins from roots of Silene vulgaris (Moench) Garcke

The assignments of ¹H and ¹³C NMR spectra for three new triterpene saponins from Silene vulgaris (gypsogenin 3‐O‐glucuronide, quillaic acid 3‐O‐glucuronide, and gypsogenin 3‐O‐glycoside) are reported. In addition to 1D NMR methods, 2D NMR techniques (COSY, HSQC, HMBC, and HSQC‐TOCSY) were used for the assignments. Copyright © 2002 John Wiley & Sons, Ltd.     

Unequivocal total assignment of 13C and 1H NMR spectra of some pyrido[1,2‐a]pyrimidine derivatives by 2D‐NMR

We report the total assignments of the ¹³C and ¹H NMR spectra of some 4‐methyl‐2‐oxo‐(2H)‐pyrido[1,2‐a]pyrimidine and 2‐methyl‐4‐oxo‐(4H)‐pyrido[1,2‐a]pyrimidine derivatives. The products were characterized by ¹H and ¹³C NMR and reported data for similar compounds. No comparative data for the two sets of isomeric compounds with respect to ¹³C and ¹H NMR have been reported to date. We made some detailed studies of the 2D NMR spectra of these compounds and observed that assignments made for non‐protonated carbon atoms by us and those reported in the literature for similar compounds need correction. The revised assignments were made on the basis of heteronuclear single quantum correlation (HSQC) and heteronuclear multiple bond correlation (HMBC) techniques. Copyright © 2003 John Wiley & Sons, Ltd.     

Complete 1H NMR spectral analysis of ten chemical markers of Ginkgo biloba

The complete and unambiguous ¹H NMR assignments of ten marker constituents of Ginkgo biloba are described. The comprehensive ¹H NMR profiles (fingerprints) of ginkgolide A, ginkgolide B, ginkgolide C, ginkgolide J, bilobalide, quercetin, kaempferol, isorhamnetin, isoquercetin, and rutin in DMSO‐d₆ were obtained through the examination of 1D ¹H NMR and 2D ¹H,¹H‐COSY data, in combination with ¹H iterative full spin analysis (HiFSA). The computational analysis of discrete spin systems allowed a detailed characterization of all the ¹H NMR signals in terms of chemical shifts (δ_H) and spin‐spin coupling constants (J_HH), regardless of signal overlap and higher order coupling effects. The capability of the HiFSA‐generated ¹H fingerprints to reproduce experimental ¹H NMR spectra at different field strengths was also evaluated. As a result of this analysis, a revised set of ¹H NMR parameters for all ten phytoconstituents was assembled. Furthermore, precise ¹H NMR assignments of the sugar moieties of isoquercetin and rutin are reported for the first time. Copyright © 2012 John Wiley & Sons, Ltd.     

An Approach to NMR Assignment of Intrinsically Disordered Proteins

An efficient approach to NMR assignments in intrinsically disordered proteins is presented, making use of the good dispersion of cross peaks observed in [¹⁵N,¹³C′]‐ and [¹³C′,¹H^N]‐correlation spectra. The method involves the simultaneous collection of {3D (H)NCO(CAN)H and 3D (HACA)CON(CA)HA} spectra for backbone assignments via sequential H^N and H^α correlations and {3D (H)NCO(CACS)HS and 3D (HS)CS(CA)CO(N)H} spectra for side‐chain ¹H and ¹³C assignments, employing sequential ¹H data acquisitions with direct detection of both the amide and aliphatic protons. The efficacy of the approach for obtaining resonance assignments with complete backbone and side‐chain chemical shifts is demonstrated experimentally for the 61‐residue [¹³C,¹⁵N]‐labelled peptide of a voltage‐gated potassium channel protein of the Kv1.4 channel subunit. The general applicability of the approach for the characterisation of moderately sized globular proteins is also demonstrated.     

A Novel Synthesis of the Macrocyclic Spermidine Alkaloid (+)‐(S)‐Dihydroperiphylline

A novel, short, and highly stereoselective synthesis of the macrocyclic spermidine alkaloid (+)‐(S)‐dihydroperiphylline ( 15 ) is described. The key synthetic steps were the stereoselective addition of the chiral amine 1 to the cinnamate 2 and cyclization of the bis[toluene‐4‐sulfonamide] precursor 12 in the presence of Cs₂CO₃ as a template. Unambiguous assignments of the signals in both the ¹H‐ and ¹³C‐NMR spectra of 15 were achieved by 2D NMR spectra.     

Proton high‐field NMR study of tomato juice

A detailed analysis of the proton high‐field (600 MHz) NMR spectra of tomato juice and pulp is reported for the first time. A combination of J‐resolved, COSY, TOCSY, DOSY, ¹H–¹³C HSQC and ¹H–¹³C HMBC 2D sequences was used to assign each spin system and to separate the components of the complex patterns in the 1D overlapped proton spectra. To obtain resolved proton spectra of tomato pulps the high‐resolution magic angle spinning technique was used; a comparison with the liquid‐state NMR spectra of the corresponding juices was accomplished. On the basis of the assignments made, the chemical composition of tomato juices from two cultivars (Red Setter and Ciliegino) was determined. Copyright © 2003 John Wiley & Sons, Ltd.     

Multinuclear NMR studies and ab initio structure calculations of hindered phencyclone diels‐alder adducts from symmetrical cyclic dienophiles: Cyclohexene,vinylene carbonate,vinylene trithiocarbonate and two N‐aryl maleimides

A series of hindered Diels‐Alder adducts have been prepared from phencyclone, 1 , with various unusual symmetrical cyclic dienophiles, including cyclohexene, 2a ; vinylene carbonate, 2b ; vinylene trithiocarbonate, 2c ; and the N‐aryl maleimides: N‐(4‐dimethylamino‐3,5‐dinitrophenyl)maleimide (“Tuppy's maleimide”), 2d ; and N‐[3,5‐bis(trifluoromethyl)phenyl]maleimide, 2e . The highly hindered adducts, 3a‐e , respectively, were extensively characterized by one‐ and two‐dimensional NMR methods, observing proton, carbon‐13 and fluorine‐19. High resolution COSY45 spectra permitted rigorous proton NMR assignments. The 2D heteronuclear C‐H chemical shift correlation spectra (HETCOR, XHCORR) were obtained for adducts 3a‐d , allowing specific assignments for protonated carbons. Corrections to earlier proton NMR assignments for the vinylene carbonate adduct are given; results of the gated decoupling ¹³C NMR experiment for this adduct supported endo adduct stereochemistry. Relative proton chemical shifts for bridgehead phenyls of adduct 3c appeared anomalous relative to other adducts, suggesting possible special anisotropic interactions (with endocyclic sulfur or other anisotropic groups in the product) due to the unusual calculated orientation of the phenyls. The unsubstituted bridgehead phenyls in all adducts were shown to exhibit slow exchange limit (SEL) ¹H and ¹³C spectra on the NMR timescales at ambient temperatures (7 tesla) showing slow rotations about the C(sp³)‐C(aryl sp²) bonds. The rapid rotation of the N‐aryl rings of the maleimide adducts was indicated by fast exchange limit spectra, suggesting that ortho substitution of the N‐aryl ring may be necessary to slow this rotation to the SEL regime. Ab initio geometry optimizations at the Hartree‐Fock level were carried out for each adduct, with the 6‐31G* basis sets. Appreciable geometry differences were seen in calculated structures, and significant NMR chemical shift differences were experimentally observed, depending on the nature of the groups attached to the (Z)‐HC=CH moiety of the dienophiles.     

NMR analysis of 6‐(2′,3′‐dihydro‐1′H‐inden‐1′‐yl)‐1H‐indene

¹H, ¹³C and two‐dimensional NMR analyses were applied to determine the NMR parameters of 6‐(2′,3′‐dihydro‐1′H‐inden‐1′‐yl)‐1H‐indene. The measurements were accomplished with 0.5 mg of the substance, this quantity being sufficient to determine the chemical shifts of all the H and C atoms, and also the appropriate coupling constants and to give the complete NMR resonance assignments of the molecule. The predicted patterns of the four different H atoms of the methylene groups of the indane structural element coincided completely with the complex patterns in the NMR spectra. Copyright © 2002 John Wiley & Sons, Ltd.     

Complete assignment of 1H and 13C NMR data for nine protopanaxatriol glycosides

Nine protopanaxatriol glycosides isolated from mild acid hydrolysis products of crude root saponins of Panax notoginseng were identified as 20(R)‐ginsenoside‐Rh1, 20(S)‐ginsenoside‐Rh1, ginsenoside‐Rg1, ‐Re and ‐Rg2, notoginsenoside‐R2 and ‐R1, a mixture of 25‐hydroxy‐20(S)‐ginsenoside‐Rh1 and its C‐20 (R) epimer, ginsenoside‐Rh4. The complete assignments of the ¹H and ¹³C NMR chemical shifts for these glycosides were obtained by means of 2D NMR techniques, including ¹H–¹H COSY, ROESY, HMQC, HMBC and HMQC‐TOCSY spectra. The glycosylation shift effect of protopanaxatriol and the differences in chemical shifts between 20(R)‐ and 20(S)‐protopanaxatriol isomers are also discussed. Except for ginsenoside‐Re and ‐Rg2, complete NMR assignments of the other seven glycosides are reported for the first time. Copyright © 2002 John Wiley & Sons, Ltd.     

Structural determination of aspericins A?C,new furan and pyran derivates from the marine‐derived fungus Rhizopus sp. 2‐PDA‐61, by 1D and 2D NMR spectroscopy

Three new furan and pyran derivatives named aspericins A? C (1–3), as well as a known asperic acid (4), have been isolated from the marine‐derived fungus Rhizopus sp. 2‐PDA‐61. The complete ¹H and ¹³C NMR assignments for the new compounds were carried out using ¹H, ¹³C, DEPT, COSY, HMQC, HMBC, and NOESY NMR experiments. Compounds 1–3 were evaluated for their cytotoxic activities on P388, A549, HL‐60, and BEL‐7420 cell lines by the MTT and SRB methods. Copyright © 2009 John Wiley & Sons, Ltd.     

An Efficient Labelling Approach to Harness Backbone and Side‐Chain Protons in 1H‐Detected Solid‐State NMR Spectroscopy

¹H‐detection can greatly improve spectral sensitivity in biological solid‐state NMR (ssNMR), thus allowing the study of larger and more complex proteins. However, the general requirement to perdeuterate proteins critically curtails the potential of ¹H‐detection by the loss of aliphatic side‐chain protons, which are important probes for protein structure and function. Introduced herein is a labelling scheme for ¹H‐detected ssNMR, and it gives high quality spectra for both side‐chain and backbone protons, and allows quantitative assignments and aids in probing interresidual contacts. Excellent ¹H resolution in membrane proteins is obtained, the topology and dynamics of an ion channel were studied. This labelling scheme will open new avenues for the study of challenging proteins by ssNMR.     

Complete assignments of 1H and 13C NMR data for two new sesquiterpenes from Cyperus rotundus L.

Two new sesquiterpenes, epi‐guaidiol A (1) and sugebiol (3), together with four known sesquiterpenes, guaidiol A(2), sugetriol triacetate (4), cyperenoic acid (5), and cyperotundone (6) were isolated from the rhizomes of Cyperus rotundus L. Their structures were identified by MS and NMR experiments, and the complete assignments of ¹H and ¹³C NMR data for two new sesquiterpenes were obtained by the aid of two‐dimensional (2D) NMR techniques, including HSQC, HMBC, ¹H‐¹HCOSY and nuclear overhauser enhancement spectroscopy(NOESY). Copyright © 2009 John Wiley & Sons, Ltd.     

Micromelosides A–D,four new coumarins from the stem bark of Micromelum falcatum

Four new coumarins, micromelosides A–D, together with four known coumarins were isolated from the stem bark of Micromelum falcatum. The complete assignments of the ¹H and ¹³C NMR chemical shifts for these new compounds were achieved by means of 1D and 2D NMR techniques, including ¹H‐¹H COSY, HSQC, HMBC and NOE difference. Copyright © 2009 John Wiley & Sons, Ltd.     

Comprehensive 2D NMR analysis: Acrylonitrile/ethyl methacrylate copolymers synthesized by ATRP at ambient temperature

Copolymerization of acrylonitrile and ethyl methacrylate using atom transfer radical polymerization (ATRP) at ambient temperature was carried out under optimized reaction conditions using 2‐bromopropionitrile as initiator and CuBr/2,2′‐bipyridine as the catalyst system. The copolymer composition, obtained from ¹H NMR spectra, were used to determine the monomer reactivity ratios (r_A = 0.68 and r_E = 1.75) involved in ATRP. Two‐dimensional NMR (heteronuclear single quantum correlation and total correlated spectroscopy) experiments were employed to resolve the highly overlapping and complex ¹H and ¹³C{¹H} NMR spectra of copolymers. The complete spectral assignments of the quaternary carbons viz. carbonyl and nitrile carbons were done with the help of heteronuclear multiple bond correlation spectra. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2955–2971, 2006     

Total assignment of NMR spectral lines of synthesized mono‐ and diacyl derivatives of diosgenyl saponins

Identification was made of a series of synthesized mono‐ and diacyl derivatives of diosgenyl saponins at various positions of the sugars. The complete assignments of ¹H and ¹³C NMR spectral lines were achieved by careful analysis of their homo‐ and heteronuclear two‐dimensional NMR spectra. Copyright © 2002 John Wiley & Sons, Ltd.     

Complete assignments of the 1H and 13C NMR spectra of five rearranged abietane diterpenoids

An NMR study of five highly functionalized and rearranged abietane diterpenoids is described. In addition to 1D NMR methods, including 1D NOESY spectra, 2D shift‐correlated experiments [¹H, ¹³C‐gHSQC‐¹J (C,H) and ¹H, ¹³C‐gHMBC‐ⁿJ (C,H) (n = 2 and 3)] were used for the complete and unambiguous ¹H and ¹³C chemical shift assignments of these substances. Copyright © 2002 John Wiley & Sons, Ltd.     

Identification and quantification of cis and trans isomers in aminophenyl double‐decker silsesquioxanes using 1H–29Si gHMBC NMR

Cis and trans isomers of a series of double‐decker silsesquioxanes (DDSQ) were characterized by two‐dimensional NMR techniques. The ¹H NMR spectra of these species have not previously been assigned to a degree that allows for quantification. Thus, ¹H–²⁹Si HMBC correlations were applied to facilitate ¹H spectral assignment and also to confirm previous ²⁹Si assignments for this class of silsesquioxanes. With the ability to identify all the pertinent resonances of the ¹H NMR spectrum, ²⁹Si NMR is no longer required for quantification and required only for characterization. This not only saves time and material but also provides a more accurate quantification, thus allowing for the ratio of cis and trans isomers present in each compound to be determined. A more accurate measure of the cis/trans ratio enables the investigation of its influence on the physical and chemical properties of DDSQ nanostructured materials. Copyright © 2013 John Wiley & Sons, Ltd.     

A new stereoisomer of stemmadenine alkaloid from Tabernaemontana heyneana

A new alkaloid, 15‐β‐stemmadenine, was isolated from the fruits of Tabernaemontana heyneana Wall. from the ethanolic extract. The complete ¹H and ¹³C NMR assignments of the compound were carried out using COSY, HMQC and HMBC. Stereochemistry at C‐15 and C‐16 was established using ROESY and temperature‐dependent ¹H NMR studies. Copyright © 2002 John Wiley & Sons, Ltd.     

Natural product synthesis with unnatural results: Characterization of a novel fused imidazolidinone tetrahydropyrroloindole ring system by long‐range 1H‐15N 2D‐NMR

Synthetic efforts towards the indole alkaloid natural product roquefortine C resulted in the formation of an unknown intermediate. Elucidation of the structure of this molecule relied on the use of long‐range ¹H‐¹⁵N 2D‐NMR. Computational predictions were used to facilitate the location of weak responses in long‐range ¹H‐¹³C HMBC spectra. These methods provided conclusive evidence that this compound possessed a novel tetracycle. The complete ¹²H, ¹³C, and ¹⁵N chemical shift assignments of this unique fused imidazolidinone tetrahydropyrroloindole derivative are reported.     

One‐pot Green Synthesis of Pyrrole Derivatives Catalyzed by Nano Sulfated Zirconia as a Solid Acid Catalyst

A new and efficient method for the preparation of N‐substituted pyrroles from one‐pot Paal‐Knorr condensation has been accomplished using nano‐crystalline sulfated zirconia (SZ) as the catalyst in ethanol at moderate temperature. This new protocol has the advantages of easy availability, stability, reusability and eco‐friendliness of the catalyst, high to excellent yields, simple experimental and work‐up procedure. The synthesized compounds were confirmed through spectral characterization using IR, ¹H NMR, ¹³C NMR and mass spectra.