1H, 13C and 15N NMR spectra of ciprofloxacin

1H NMR assignment, including the values of delta(H) and J(H,H) for the cyclopropane moiety, and 13C NMR and 15N NMR spectral data for ciprofloxacin are presented.     

1H, 13C and 15N NMR assignments of phenazopyridine derivatives

Phenazopyridine hydrochloride (1), a drug in clinical use for many decades, and some derivatives were studied by one- and two-dimensional (1)H, (13)C and (15)N NMR methodology. The assignments, combined with DFT calculations, reveal that the preferred protonation site of the drug is the pyridine ring nitrogen atom. The chemoselective acetylation of phenazopyridine (2) and its influence on the polarization of the azo nitrogen atoms were evidenced by the (15)N NMR spectra. Molecular calculations of the phenazopyridines 2-4 show that the pyridine and phenyl groups are oriented in an antiperiplanar conformation with intramolecular hydrogen bonding between the N-b atom and the C-2 amino group preserving the E-azo stereochemistry.     

1H, 13C and 15N NMR spectroscopy and tautomerism of nitrobenzotriazoles

Benzotriazole nitro derivatives were prepared by nitration of the corresponding benzotriazoles and by methylation or cyclization of appropriate nitro‐1,2‐phenylenediamines. Structures and tautomerism of the nitrobenzotriazoles were studied by multinuclear ¹H, ¹³C, ¹⁵N, and 2D NMR spectroscopy and quantum chemistry. Copyright © 2008 John Wiley & Sons, Ltd.     

1H, 13C,and 15N NMR spectra of some pyridazine derivatives

¹H, ¹³C, and ¹⁵N NMR chemical shifts for pyridazines 4–22 were measured using 1D and 2D NMR spectroscopic methods including ¹H? ¹H gDQCOSY, ¹H? ¹³C gHMQC, ¹H? ¹³C gHMBC, and ¹H? ¹⁵N CIGAR–HMBC experiments. Copyright © 2010 John Wiley & Sons, Ltd.     

1H, 13C and 15N NMR spectral assignments for new triazapentalene derivatives

Mesomeric heteropentalene betaines are conjugated fused polyheterocyclic structures that represent interesting intermediates for organic synthesis. Five such structures, containing at least four nitrogen atoms and various substituents, have been characterized by ¹H, ¹³C and ¹⁵N NMR. We report, apparently for the first time, nitrogen NMR data and coupling information on such systems. Inter‐ring long‐range correlations across five bonds with ¹⁵N (⁵J_HN) and up to seven bonds with ¹³C (⁶J_HC and ⁷J_HC) were observed in HSQC experiments. The incorporation of an electron‐withdrawing substituent such as NO₂ was observed to cause an increase in the magnitude of the remote couplings and deshielding of nearby protons, carbons and on all nitrogen atoms of the structure, including remote ones situated on other cycles. Copyright © 2009 John Wiley & Sons, Ltd.     

1H, 13C and 15N NMR spectra of [1,2-15N2]pyrazole derivatives

The chemical shifts and coupling constants of [1,2-¹⁵N₂]pyrazole, 2-(1-[1,2- ¹⁵N₂]pyrazolyl)-2-[l,3-²H₆]propanol, 1-nitro[1,2¹⁵N₂] and 3-nitro[1,2-¹⁵N₂]pyrazole are reported.     

Derivatives of pyrazinecarboxylic acid: 1H, 13C and 15N NMR spectroscopic investigations

NMR spectroscopic studies are undertaken with derivatives of 2‐pyrazinecarboxylic acid. Complete and unambiguous assignment of chemical shifts (¹H, ¹³C, ¹⁵N) and coupling constants (¹H,¹H; ¹³C,¹H; ¹⁵N,¹H) is achieved by combined application of various 1D and 2D NMR spectroscopic techniques. Unequivocal mapping of ¹³C,¹H spin coupling constants is accomplished by 2D (δ,J) long‐range INEPT spectra with selective excitation. Phenomena such as the tautomerism of 3‐hydroxy‐2‐pyrazinecarboxylic acid are discussed. Copyright © 2009 John Wiley & Sons, Ltd.     

1H, 13C and 15N NMR observations on the protonation of 1- and 3-deazapurine

Using ¹H, ¹³C and ¹⁵N NMR it has been concluded that 3-deazarpurine protonates exclusively at N-1 with a pK of about 5.6. The base exhibits rapid tautomerism with proportions of 70:30, with the N–7-H tautomer in the majority. The salt exists predominantly as the N-7-H tautomer. 1-Deazapurine protonates essentially in a 1:1 ratio at N-3 and at the imidazole ring, with a pK of about 3.1. This base also exhibits rapid tautomerism with proportions of 30:70, this time with the N-9-H in the majority. The salt also exists in a tautomcric mixture with approximately equal proportions. One form has N-3 and N-9 bearing hydrogens and the other has N-7 and N-9 bearing hydrogens.     

1H, 13C and 15N NMR study of vinyltetrazolium salts and processes of their synthesis

The ¹H, ¹³C and ¹⁵N NMR spectra of several N- and C-vinyltetrazolium salts have been recorded and the observed chemical shifts together with the data of quantum-chemical calculations have been used for evaluation of electronic structure of the investigated substances and selectivity of the exhaustive alkylation of 1,5- and 2,5-substituted tetrazoles.     

Complete 1H, 13C and 15N NMR assignment of tirapazamine and related 1,2,4-benzotriazine N-oxides

1H, 13C and 15N NMR measurements (1D and 2D including 1H--15N gs-HMBC) have been carried out on 3-amino-1, 2,4-benzotriazine and a series of N-oxides and complete assignments established. N-Oxidation at any position resulted in large upfield shifts of the corresponding N-1 and N-2 resonances and downfield shifts for N-4 with the exception of the 3-amino-1,2,4-benzotriazine 1-oxide in which a small upfield shift of N-4 was observed. Density functional GIAO calculations of the 15N and 13C chemical shifts [B3LYP/6-31G(d)//B3LYP/6-311+G(2d,p)] gave good agreement with experimental values confirming the assignments. The combination of 13C and 15N NMR provides an unambiguous method for assigning the 1H and 13C resonances of N-oxides of 1,2,4-benzotriazines.     

13C,15N]2-Acetamido-2-deoxy-D-aldohexoses and their methyl glycosides: synthesis and NMR investigations of J-couplings involving 1H, 13C, and 15N

[reaction: see text] A series of 2-amino-2-deoxy-D-[1-13C]aldohexoses and their methyl glycosides was prepared with use of a simplified cyanohydrin reduction route. Four d-aldopentosylamines (arabino, lyxo, ribo, xylo) were prepared from the corresponding D-aldopentoses by reaction with NH3(g) in MeOH solvent, isolated in solid form, and characterized by 13C and 1H NMR. Hydrolysis of beta-D-xylopyranosylamine was studied using 13C-labeled substrates to establish optimal solution conditions for cyanohydrin formation. Major hydrolytic intermediates were observed and identified by time-lapse 1D and 2D NMR analyses of reaction mixtures. The aldopentosylamines were subsequently employed in cyanohydrin reduction reactions with K13CN to yield C2-epimeric [1-13C]2-aminosugars, which were separated by chromatography on ion-exchange columns. N-Acetylation and methyl glycosidation followed by chromatography gave pure 2-acetamido-2-deoxy-D-[1-13C]aldohexopyranosides. J(CH) and J(CC) spin-spin coupling constants involving the labeled anomeric carbon were measured and compared to those observed previously in methyl D-[1-13C]aldohexopyranosides. In parallel studies, theoretical J-couplings were calculated in model N-acetylated aldopyranosides using density functional theory (DFT) to predict the effect of OH vs NHCOCH(3) substitution at C2 on J(CH) and J(CC) values in aldopyranosyl rings. The synthetic method was also modified to accommodate (15)N- and (13)C-labeling within the N-acetyl side-chain, and some J-couplings involving 1H, 13C, and 15N atoms in 2-[1,2-13C2;15N]acetamido-2-deoxy-D-[1-13C]glucose were measured and interpreted.     

1H, 13C, 15N and 19F NMR study of acetylation products of heterocyclic thiosemicarbazones

Novel 2-acetylamino-4-acetyl-5-aryl(heteryl)-1,3,4-thiadiazolines, 2-acetylamino-5-aryl(heteryl)-1,3,4-thiadiazoles, and some of their salts were prepared and studied by multinuclear 1H, 13C, 15N, 19F and 2D NMR spectroscopy. The acetylation of thiosemicarbazones is accompanied by ring closure to form the corresponding 1,3,4-thiadiazolines and 1,3,4-thiadiazoles. 15N NMR spectroscopy is a unique method for the identification of thiadiazole pyridinium salts.     

NMR studies in the heterocyclic series XXIV—1H, 13C and 15N study of 15N labelled indazoles

The ¹⁵N chemical shifts and ¹H? ¹⁵N and ¹³C? ¹⁵N coupling constants of nine monolabelled indazoles were measured and assigned. The experimental values are discussed in terms of the indazolic and iso-indazolic structures, and compared with literature data for other related heterocycles. All the results are consistent with an N-1(H) tautomeric structure for indazole in DMSO-d₆.     

Ring-substituted benzohydroxamic acids: 1H, 13C and 15N NMR spectra and NH-OH proton exchange

NMR spectra (1H, 13C, 15N) of para- and meta-substituted benzohydroxamic acids were studied in dry dimethyl sulfoxide solutions. The 13C chemical shifts were very close to those found by cross-polarization magic angle spinning in solids, the hydroxamic (not hydroximic) structure of which is unambiguous. The hydroxamic structure of these acids in DMSO solutions was proved independently by their 15N chemical shifts. The 15N and 1H chemical shifts of the NH-OH fragment showed excellent mutual dependences and dependences on the nature of the ring substituent. According to these dependences and ab initio energy calculations, all the acids assume the same Z conformation. Proton exchange between hydroxamic OH and NH groups in DMSO proceeded by both intra- and intermolecular exchange and the rates did not exhibit any simple relationship to the substituent constants.     

1H, 13C and 15N NMR assignments for N6‐isopentenyladenosine/inosine analogues

The complete ¹H, ¹³C and ¹⁵N NMR signals assignments of some new isopentenyladenosine analogues were achieved using one‐ and two‐dimensional experiments (gs‐NOESY, gs‐HMQC and gs‐HMBC). Copyright © 2010 John Wiley & Sons, Ltd.     

1H, 13C and 15N NMR spectral assignments of adenosine derivatives with different amino substituents at C6-position

The complete (1)H, (13)C and (15)N NMR signals assignment of adenosine derivatives differently substituted at C(6)-position was achieved using one- and two-dimensional experiments (gs-COSY, gs-NOESY, gs-HSQC and gs-HMBC).     

1H and 13C chemical shifts for acridines: Part XIX. N,N'-diacylproflavine derivatives

The 1H and 13C NMR resonances of 15 N,N'-diacylproflavines were assigned completely and unequivocally using a concerted application of one- and two-dimensional experiments (DEPT, gs-COSY, gs-HMQC and gs-HMBC).     

Synthesis,1H,13C,14N,and15N NMR spectra,and cathodic behavior of N-chloro-1,2,4-triazoles

Syntheses are reported for N-chloro-1,2,4-triazoles and the NMR spectra of these compounds were studied. An investigation was also carried out on a platinum electrode in 0.1 N Bu₄ClO₄ in acetonitrile. The reduction proceeds with the transfer of two electrons and the formation of triazole and chloride ions. The half-wave potentials of the reduction of N-chlorotriazoles correlates well with the pK_a values of the corresponding NH-acids. The electrochemical reduction of N-chlorotriazoles is accompanied by the reaction of N-chlorotriazole with the chloride ion formed on the cathode, which leads to the NH form of 1,2,4-triazole through a series of chemical steps.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 12, pp. 2814–2821, December, 1990.     

13C and 15N NMR spectra of 4-substituted-1-dimethylphosphonopiperazines

¹³C and ¹⁵N NMR chemical shifts and ¹³C-³¹P and ¹⁵N-³¹P coupling contants are reported for a series of ten 4-substituted-1-dimethylphosphonopiperazines.     

CN-HMBC: a powerful NMR technique for the simultaneous detection of long-range 1H,13C and 1H,15N connectivities

[structure: see text] A new one-shot NMR experiment (CN-HMBC) is proposed for the simultaneous acquisition of 2D 1H,13C and 1H,15N HMBC spectra. Important sensitivity enhancements (up to 41% simultaneously for both 13C and 15N) or time savings (about 50%) can be achieved when compared to the separate acquisition of individual HMBC spectra. The experiment is highly recommended for the complete structural analysis and simultaneous chemical shift assignments of protonated and nonprotonated 13C and 15N resonances in nitrogen-containing organic compounds.