Configurational assignment in alkyl‐branched sugars via the geminal C,H coupling constants

The measurement of the magnitude and sign of ²J(C,H) couplings offers a reliable way to determine the absolute configuration at a carbon center in a fixed cyclic system. A decrease of the dihedral angle ? in the O—C_A—C_B—H fragment always leads to a change of the ²J(C_A,H_B) coupling to more negative values, independent of the type and position of substituents at the two carbon centers. The orientations of the two substituents at C‐3 of the epimeric pair 1 and 2 were determined unambiguously through the measurement of the geminal coupling constants between C‐3 and the hydrogen atoms at C‐2 and C‐4. In particular, ²J(C‐3,H‐2ax) with ?1.5 Hz, ? = 174° in 1 and ?6.6 Hz, ? = 47° in 2 , and ²J(C‐3,H‐4) with +1.5 Hz, ? = 175° in 1 and ?4.7 Hz, ? = 49° in 2 showed the greatest differences between the two epimers. Both couplings therefore allow the determination of the absolute configuration at C‐3. It should be noted, however, that the size of the coupling constants can be different for dihedral angles of nearly identical size, when there are different numbers of electronegative substituents on the two coupling pathways, i.e. no O‐substituent at C‐2, but one axial O‐substituent at C‐4. It becomes clear that it is not sufficient to measure the magnitude of ²J coupling constants only, but that the sign of the geminal coupling is needed to identify the absolute configuration at a chiral center. The coupling of C‐3 with H‐2eq is not useful for the determination of the configuration at C‐3, as the similarity of the dihedral angles ? (O—C‐3—C‐2—H‐2eq) (57° in 1 and 70° in 2 ) leads to identical coupling constants (?6.1 Hz) for both epimers. Copyright © 2003 John Wiley & Sons, Ltd.     

1H and 13C spectral assignment of substituted 5H-[1,3]thiazolo[2,3-b]quinazolin-5-one and 12H-[1,3]benzothiazolo[2,3-b] quinazolin-12-one

(1)H and (13)C spectroscopic data for 5H-[1,3]thiazolo[2,3-b]quinazolin-5-one and 12H-[1,3]benzothiazolo[2,3-b]quinazolin-12-one derivatives were fully assigned by combination of one- and two-dimensional experiments (DEPT, HMBC and HMQC). Both heterocyclic systems show similar spectroscopic properties with some remarkable differences.     

1H and 13C spectral assignment of 2(1H)-pyridone derivatives

1H and 13C NMR spectroscopic data for 4-aryl-3,4-dihydro-6-methyl-2(1H)pyridone derivatives were fully assigned by a combination of one- and two- dimensional experiments (DEPT, HMBC, HMQC, COSY, NOE).     

Eremophilane esters of Robinsonecio gerberifolius and their rearranged products. Study of the coupling constants (2)J(H, H), (3)J(H, H) and (4)J(H, H)

In the course of the basic hydrolysis of four eremophilane esters isolated from Robinsonecio gerberifolius, some rearrangements, eliminations, and additions occurred. Five compounds were obtained, three of them not previously described. Additionally, a new sesquiterpene was produced by autooxidation of compound 1. The (1)H and (13)C NMR spectra of these compounds were completely assigned by utilization of HMQC, HMBC, COSY, DEPT, and NOESY techniques. The long-range coupling constants of the peroxide 10 are reported, and all its coupling constants (2)J(H, H), (3)J(H, H), and (4)J(H, H) are calculated at the B3LYP/6-31G(d,p) level of theory. Their magnitude is explained in terms of electronic delocalization and the additivity of stereoelectronic effects.     

Electronic influences on 3J(C,H) coupling constants via -S-, -S(O)- and -SO2-: their determination, calculation and comparison of detection methods

3J(C,H) coupling constants via a sulfur atom in two series of compounds, both including a sulfide, a sulfoxide and a sulfone, were detected experimentally and calculated by quantum mechanical methods. In the first series (1-3) the coupling between a hydrogen, bonded to an sp3 carbon, and an sp2 carbon is treated; the second series (4-6) deals with the coupling between a hydrogen, bonded to an sp3 carbon, and an sp3 carbon. Different pulse sequences (broadband HMBC, SelJres, 1D HSQMBC, J-HMBC-2, selective J-resolved long-range experiment and IMPEACH-MBC) proved to be useful in determining the long-range 3J(C,H) coupling constants. However, the dynamic behaviour of two of the compounds (4 and 6) led to weighted averages of the two coupling constants expected (concerning equatorial and axial positions of the corresponding hydrogens). DFT calculations proved to be useful to calculate not only the 3J(C,H) coupling constants but also the different contributions of FC, PSO, DSO and SD terms; the calculation of the Fermi contact term (FC) was found to be sufficient for the correct estimation of 3J(C,H) coupling constants.     

1H and 13C NMR spectral assignment of alkyl and polyamine-linked bis(2-thioxo-[1,3,5]-thiadiazinan-3-yl) carboxylic acids

The 1H and 13C NMR spectroscopic data for alkyl and polyamine-linked bis(2-thioxo-[1,3,5]thiadiazinan-3-yl) carboxylic acids, prepared from alkyl diamines and N4-(benzyl) spermidine have been fully assigned by combination of one- and two-dimensional experiments (DEPT, HMBC, HMQC, COSY).     

Halogen - metal exchange of 3-substituted 1,2-dibromoarenes: the use of long-range JCH coupling constants to determine regiochemistry

Regioselective halogen/metal exchange reactions were carried out on a series of 3-substituted- 1,2-dibromoarenes. Product mixtures were quenched with CO2 to form the corresponding benzoic acid analogs to facilitate HPLC and NMR analysis. Substitution at the 3-position could readily be assigned on the basis of 2D HMBC long-range correlations, while assignment at the 2-position was not as straightforward. The use of three-bond J(CH) coupling constant measurements, extracted from 1-D 1H coupled 13C experiments, were necessary to render unequivocal regio assignments.     

Cis‐1‐phosphabicyclo[3.3.0]octan

A new approach to 1‐phosphabicyclo[3.3.0]octane compounds starts from the reaction of 4‐chloro‐hepta‐1.6‐diene with Mg in THF. No Grignard rearrangement is observed. The Grignard reagent is converted into 1‐allyl‐3‐butenylphosphonous dichloride followed by reduction with LiAlH₄. Cis‐1‐phosphabicyclo[3.3.0]octane has been prepared by radical‐initiated cyclization of 1‐allyl‐3‐butenylphosphane. The bicyclic phosphane is characterized by analytical data as well as ³¹P and ¹³C NMR measurements and the reactionswith NO, S₈, KSeCN, CH₃I, Ni(CO)₄ and HSO₃F, respectively.     

1H and 13C NMR spectral characterization of some novel 7H-1,2,4-triazolo[3, 4-b] [1,3,4] thiadiazine derivatives

Some novel 1, 2, 4-triazolo[3,4-b][1,3,4]thiadiazines derivatives were synthesized. The complete (1)H and (13)C NMR chemical shift assignments were analyzed on one- and two-dimensional NMR techniques, including DEPT, NOE-DIF, COSY, HMBC, and HSQC.     

Determination of 31P,31P coupling constants in cyclotriphosphazenes and their influence on 1H and 13C NMR spectra of phosphorus substituents

¹H and ¹³C NMR spectra of symmetrically substituted cyclotriphosphazenes exhibit second‐order effects. The influence of the ³¹P,³¹P coupling constants between ring phosphorus atoms on these effects was studied. Some values of this coupling constant between phosphorus bearing identical substituents were measured using ¹³C satellites of the ³¹P signals or by introduction of a chiral substituent on the third phosphorus atom. Copyright © 2003 John Wiley & Sons, Ltd.     

3‐Methylflavones characterization revisited: complete assignment of 1H and 13C NMR data

Ten 3‐methylflavone derivatives were studied. Previously reported NMR data of some derivatives were corrected and/or completed, including the complete assignment of the two known natural derivatives. The complete ¹H and ¹³C NMR assignments were achieved by combination of one‐dimensional and two‐dimensional NMR experiments. Copyright © 2013 John Wiley & Sons, Ltd.     

1H and 13C NMR study of 5-substituted-4- (arylidene)amino-2,4-dihydro-3H-1,2,4-triazole-3-thiones and 6-aryl-3-(D-gluco- pentitol-1-yl)-7H-1,2,4-triazolo[3,4-b] [1,3,4]thiadiazines

Five 5-substituted-4-(arylidene)amino-2,4-dihydro-3H-1, 2,4-triazole-3-thiones (2a-2e) and seven 6-aryl-3-(D-gluco-pentitol-1-yl)-7H-1,2,4-triazolo[3,4-b][1,3,4]thiadiazines (3a-3g) were synthesized. The complete 1H and 13C NMR chemical shift assignments were analyzed on one- and two-dimensional NMR techniques, including DEPT, NOE-DIF, COSY, gHMBC, and gHSQC.     

Selective J‐resolved HMBC,an efficient method for measuring heteronuclear long‐range coupling constants

An efficient pulse sequence for measuring long‐range C? H coupling constants (J_{C? H}) named selective J‐resolved HMBC has been developed by replacing a ¹H 180° pulse with a selective ¹H 180° pulse and the HMBC pulse scheme with the constant time (CT) HMBC employed in the J‐resolved HMBC pulse sequence that we reported previously. The novel pulse sequence providing only long‐range J_{C? H} cross peaks for easy and accurate analysis enables to overcome disadvantages of the previous HMBC‐based pulse sequences (J‐resolved HMBC‐1) along with maintaining high sensitivity. The efficiency of measuring long‐range J_{C? H} using the proposed pulse sequence has been demonstrated in applications to the complicated natural products, portmicin and monazomycin. Copyright © 2009 John Wiley & Sons, Ltd.     

Long-range J(CH) heteronuclear coupling constants in cyclopentane derivatives

Detailed measurements of long-range heteronuclear spin-spin coupling constants, especially (2, 3)J(CH) spin-spin couplings for various cyclopentane derivatives, are reported. The measurements are based on a 2D heteronuclear correlation experiment named G-BIRD(R, X)-CPMG-HSQMBC.     

1H and 13C NMR spectral assignment of androstane derivatives

(1)H and (13)C NMR spectroscopic data for 5alpha-androstanes and halo-5alpha-androstanes with different substituents at positions C-3, C-9, C-11 and C-17 were examined and assigned by a combination of 1D and 2D NMR experiments. The substituent effects on the (13)C chemical shifts were compared with those of epi-androsterone, used as a reference compound. The coupling constants (n)J((19)F,(13)C) were measured for compounds 6, 8, 11 and 14.     

Measurement of long‐range heteronuclear coupling constants using the peak intensity in classical 1D HMBC spectra

In this contribution, we show that the magnitude of heteronuclear long‐range coupling constants can be directly extracted from the classical 1D HMBC spectra, as all multiplet lines of a cross‐peak always and exclusively vanish for the condition Δ = k/ⁿJ_CH. To the best of our knowledge, this feature of the classical HMBC has not yet been noticed and exploited. This condition holds true, irrespective of the magnitude and numbers of additional active and passive homonuclear ⁿJ_HH′ couplings. Alternatively, the ⁿJ_CH value may also be evaluated by fitting the peak's intensity in the individual spectra to its simple sin(πⁿJ_CHΔ)exp(−Δ/T_2eff) dependence. Compared to the previously proposed J‐HMBC sequences that also use the variation of the cross‐peak's intensity for extracting the coupling constants, the classical HMBC pulse sequence is significantly more sensitive.     

Long-range JCH heteronuclear coupling constants in cyclopentane derivatives. Part II

Here we report the detailed measurement of long-range heteronuclear spin-spin coupling constants, especially 2, 3JCH spin-spin couplings for eight different cyclopentane derivatives. These 2, 3JCH constants were shown to be a useful tool in the determination of the relative stereochemistry in these rings. The coupling constant measurements reported here are based on two different experiments: a 2D heteronuclear correlation experiment named G-BIRDR, X-CPMG-HSQMBC and the 2D-coupled gHSQC {1H-13C} experiment     

1H and 13C spectral assignment of 4-aryl-1,4,5,6,7,8-hexahydro-2,7,7,5-oxo-quinolines 3-substituted derivatives

The 1H and 13C NMR spectroscopic data for 4-aryl-1,4,5,6,7,8-hexahydro-2,7,7,5-oxo-quinoline 3-substituted derivatives have been fully assigned by the combination of one- and two dimensional experiments (DEPT, HMBC, HMQC, COSY, NOE).     

Determination of heteronuclear coupling constants from 3D HSQC-TOCSY experiment with optimized random sampling of evolution time space

An application of 3D version of HSQC-TOCSY experiment for the measurement of heteronuclear coupling constants of organic compounds yielding complex spectra is proposed. The approach presented here is based on the optimized random sampling of the evolution time space followed by Multidimensional Fourier Transform (MFT). In this study, we show that the interpretation of omega(3)-(13)C coupled (1)H-(13)C 3D HSQC-TOCSY spectra with E.COSY-type multiplets allows one to evaluate heteronuclear coupling constants of strychnine with high accuracy, whereas the employment of 2D methods is associated with signal overlap and use of conventionally recorded 3D NMR spectra cannot provide accurate results in an overnight experiment.     

Synthesis and structure elucidation of five new pyrimido[5,4-c]quinoline-4(3H)-one derivatives using 1D and 2D NMR spectroscopy

Five new 2-(amino/aroxy)-5-methylpyrimido[5,4-c]quinolin-4(3H)-one derivatives have been designed and synthesized via an aza-Wittig reaction, and the structure elucidation was accomplished using extensive 1D ((1)H, (13)C) and 2D NMR spectroscopic studies (COSY, HSQC and HMBC experiments).