Structural and spectral assignment of a new diterpenoid isolated from Ballota undulata and a complete (1)H and (13)C NMR data assignment for three other structurally related compounds

The structure of 3beta-hydroxyballotinone, a new labdane diterpenoid isolated from Ballota undulata, has been established by NMR spectroscopic studies. In addition, complete and unambiguous assignments of the (1)H and (13)C NMR spectra of three other already known labdanes (ballotinone, ballonigrin and ballonigrinone) isolated from the same source have been achieved. The assignments are based on 2D shift-correlated (1)H--(1)H COSY, (1)H--(13)C gHSQC [(1)J(C,H)] and (1)H--(13)C gHMBC [(n)J(C,H) (n = 2 and 3)], and NOE experiments.     

Complete 1H and 13C assignments of (21R) and (21S) diastereomers of argatroban

The complete 1H and 13C NMR assignments are reported for the antithrombotic (21R)- and (21S)-argatroban by 1D and 2D NMR experiments (HSQC, HMBC, NOESY and 1H--1H COSY). Some well-resolved signals could be used for an accurate measurement of the diastereomeric composition of argatroban.     

NMR study of 5-substituted pyrazolo[3,4-c]pyridine derivatives

Substituted pyrazolopyridines are potent inhibitors of phosphodiesterases and cyclin-dependent kinases. In this study, NMR was used to investigate the potential N1-H and N2-H tautomerism of 5-substituted pyrazolo[3,4-c]pyridine derivatives. Six compounds were fully characterized by using (1)H, (13)C, and (15)N chemical shifts and indirect (1)H--(13)C and (1)H--(15)N coupling constants. The (1)H NMR spectra were measured over a broad range of temperatures. All of the compounds were shown to exist predominantly in the N1-H tautomeric form. Complementary quantum-chemical calculations of the chemical shieldings and indirect spin-spin couplings support the structural conclusions drawn.     

Full NMR analysis of annomontine, methoxy- annomontine and N-hydroxyannomontine pyrimidine-beta-carboline alkaloids

Using modern NMR techniques, including 1H--13C and 1H--15N heteronuclear correlation experiments, the complete and unambiguous 1H, 13C, and 15N NMR chemical shift assignments of annomontine, methoxyannomontine, and N-hydroxyannomontine pyrimidine-beta-carboline alkaloids were performed. All 1H--1H scalar coupling constants and signal multiplicities were determined, and all nOe observations were also included.     

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.     

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.     

Complete NMR data assignments for novel pterocarpans from Harpalyce brasiliana

A NMR study of two new pterocarpans isolated from the roots of Harpalyce brasiliana is described. In addition to 1D NMR, 2D shift-correlated NMR pulse sequences ((1)H-(1)H-COSY, HSQC and HMBC) were used to establish the structures, and unambiguously perform the (1)H and (13)C chemical shift assignments.     

Application of unsymmetrical indirect covariance NMR methods to the computation of the (13)C <--> (15)N HSQC-IMPEACH and (13)C <--> (15)N HMBC-IMPEACH correlation spectra

Utilization of long-range (1)H--(15)N heteronuclear chemical shift correlation has continually grown in importance since the first applications were reported in 1995. More recently, indirect covariance NMR methods have been introduced followed by the development of unsymmetrical indirect covariance processing methods. The latter technique has been shown to allow the calculation of hyphenated 2D NMR data matrices from more readily acquired nonhyphenated 2D NMR spectra. We recently reported the use of unsymmetrical indirect covariance processing to combine (1)H--(13)C GHSQC and (1)H--(15)N GHMBC long-range spectra to yield a (13)C--(15)N HSQC-HMBC chemical shift correlation spectrum that could not be acquired in a reasonable period of time without resorting to (15)N-labeled molecules. We now report the unsymmetrical indirect covariance processing of (1)H--(13)C GHMBC and (1)H--(15)N IMPEACH spectra to afford a (13)C--(15)N HMBC-IMPEACH spectrum that has the potential to span as many as six to eight bonds. Correlations for carbon resonances long-range coupled to a protonated carbon in the (1)H--(13)C HMBC spectrum are transferred via the long-range (1)H--(15)N coupling pathway in the (1)H--(15)N IMPEACH spectrum to afford a much broader range of correlation possibilities in the (13)C--(15)N HMBC-IMPEACH correlation spectrum. The indole alkaloid vincamine is used as a model compound to illustrate the application of the method.     

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).     

Complete and unambiguous assignments of 1H and 13C chemical shifts of new arylamino derivatives of ortho-naphthofuranquinones

Six new nor-beta-lapachones have been synthesized from reaction of 3-bromo-nor-beta-lapachone with arylamines. These derivatives have potent anticancer properties against several cell lines. Here, we report complete unambiguous assignments of (1)H and (13)C chemical shifts of the new compounds. The assignments were made using a combination of one- and two-dimensional NMR techniques ((1)H, (13)C, (1)H-(1)H COSY, (1)H-(13)C HSQC, and (1)H-(13)C HMBC).     

Predicting the NMR spectra of nucleotides by DFT calculations: cyclic uridine monophosphate

We present an experimental and quantum chemical NMR study of the mononucleotide cyclic uridine monophosphate in water. Spectral parameters ((1)H and (13)C chemical shifts and (1)H--(1)H, (13)C--(1)H, (31)P--(13)C and (31)P--(1)H spin-spin coupling constants) have been carefully obtained experimentally and calculated using DFT methods including the solvent effect and the conformational flexibility of the solute. This study confirms that the (1)H and (13)C spectra of polar, flexible molecules in aqueous solution can be predicted with a high level of accuracy, comparable to that obtained for less complex systems.     

Complete 1H and 13C NMR assignments of three new polyhydroxylated sterols from the South China Sea gorgonian Subergorgia suberosa

Three new polyhydroxylated sterols, 3beta,6alpha,11,20beta,24-pentahydroxy- 9,11-seco-5alpha-24-ethylcholest-7,28-diene-9-one (1), 3-(1',2'-ethandiol)-24- methylcholest-8(9),22E-diene-3beta,5alpha,6alpha,7alpha,11alpha-pentaol (2), 24-methylcholest-7,22 E-diene-3beta,5alpha,6beta,25-tetraol (3) together with five known sterols, were isolated from the EtOH/CH2Cl2 extract of the South China Sea gorgonian Subergorgia suberosa. 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 HSQC, HMBC, 1H--1H COSY, and NOESY spectra.     

Complete 1H and 13C data assignments of two new guaianolides isolated from Ainsliaea fragrans

Two new guaianolides, 8alpha-hydroxy-11alpha,13-dihydroglucozaluzanin C and 11alpha,13-dihydroglucozaluzanin C, were isolated from Ainsliaea fragrans, along with two known guaianolides, 8alpha-hydroxy-11alpha,13-dihydrozaluzanin C and glucozaluzanin C. The structures of the new compounds were unambiguously established by HR-ESI-MS, one-dimensional (1D) (DEPT), two-dimensional (2D) ((1)H-(1)H COSY, HSQC, HMBC, ROESY) NMR experiments and by comparison with structurally related compounds. The known compounds were identified by comparison of spectral data with published references. Some NMR data of the known compounds were reported for the first time.     

1H, 13C and 15N NMR coordination shifts in gold(III), cobalt(III), rhodium(III) chloride complexes with pyridine, 2,2'-bipyridine and 1,10-phenanthroline

Au(III), Co(III) and Rh(III) chloride complexes with pyridine (py), 2,2'-bipyridine (bpy) and 1,10-phenanthroline (phen) of the general formulae [M1LCl3], trans-[M2L4Cl2]+, mer-[M2L3Cl3], [M1(LL)Cl2]+, cis-[M2(LL)2Cl2]+, where M1=Au; M2=Co, Rh; L=py; LL=bpy, phen, were studied by 1H--13C HMBC and 1H--15N HMQC/HSQC. The 1H, 13C and 15N coordination shifts (the latter from ca-78 to ca-107 ppm) are discussed in relation to the type of metal, electron configuration, coordination sphere geometry and the type of ligand. The 13C and 15N chemical shifts were also calculated by quantum-chemical NMR methods, which reproduced well the experimental tendencies concerning the coordination sphere geometry and the ligand type.     

Structure determination of baeckeins C and D from the roots of Baeckea frutescens

Baeckeins C (compound 1) and D (compound 2), a pair of new diastereomeric biflavonoids, were isolated from the roots of Baeckea frutescens. Their structures were elucidated on the basis of spectroscopic analysis, including HR-ESI-MS and one- and two-dimensional NMR spectra ((1)H and (13)C NMR, HSQC, HMBC, and ROESY). The absolute configurations of the 2,3-epoxide moiety for compounds 1 and 2 were determined by circular dichroism spectrometry combined with quantum chemical calculations.     

1H and 13C NMR assignments for four triterpenoid saponins from Albizziae cortex

Four triterpenoid saponins were isolated from Albizziae cortex, and a complete assignment of their (1)H and (13)C NMR spectra was carried out using 1D and 2D NMR ((1)H-(1)H COSY, HSQC, HMBC, and HSQC-TOCSY) methods. Their (1)H NMR assignments were reported for the first time and some of their (13)C NMR spectral data reported in literature were corrected.     

Reaction of alkyn-1-yl(diorganyl)silanes with 1-boraadamantane: Si-H-B bridges confirmed by the molecular structure in the solid state and in solution

1-Boraadamantane 1 was treated with alkyn-1-ylsilanes 2 containing one or two Si[bond]H functions. Under mild conditions, the reaction gave 4-methylene-3-borahomoadamantane derivatives 4 quantitatively and selectively by 1,1-organoboration. An electron deficient Si-H-B bridge was present in the product. The analogous reaction of 1 with an alkyn-1-yl-disilane 3 gave the corresponding alkene derivative 5, however, without the Si-H-B bridge. Evidence for the Si-H-B bridge in 4 was given by IR data, an extensive set of NMR spectroscopical data ((1)H, (11)B, (13)C, (29)Si NMR) including various unusual isotope effects on chemical shifts and coupling constants, as well as from the molecular structure of one example, 4 e, in the solid state. The precursor of 4 e, alkyne 2 e, Ph(2)Si(H)C[triple bond]CSi(H)Ph(2), was also studied by X-ray analysis.     

Complete assignments of 1H and 13C NMR data for rings A,B-seco limonoids from the seed of Aphanamixis polystachya

Seven rings A,B-seco limonoids 1-7 were isolated from the EtOH extract of the seed of Aphanamixis polystachya. Their structures were identified as rohituka-7 (1), dregeana-1 (2), rohituka-15 (3), Tr-B (4), rohituka-3 (5), rohituka-5 (6), and rohituka-14 (7) by MS and NMR spectroscopy. The complete assignment of proton and carbon signals was achieved by 1D and 2D NMR experiments including DEPT, HSQC, 1H--1H COSY, HMBC, and NOESY.     

NMR assignments and X-ray diffraction spectra for two unusual kaurene diterpenes from Erythroxylum barbatum

The structural characterization of two new, unusual kaurene diterpenes isolated from roots of Erythroxylum barbatum is described. 1D NMR and several 2D shift-correlated NMR pulse sequences (1H,1H-COSY, HMQC, HMBC and NOESY) were used for structure elucidation and the unambiguous 1H and 13C chemical shifts assignments. Single crystal X-ray diffraction analysis was also used to confirm the final relative configuration of the compounds possessing the C-20 methyl and the CH2-15 methylene groups in cis-orientation.     

Solution structures and behavior of trans-RuH(eta(1)-BH(4)) (binap)(1,2-diamine) complexes

The solution structures of a number of trans-RuH(eta(1)-BH(4))[(S)-tolbinap](1,2-diamine) precatalysts [TolBINAP = 2,2'-bis(di-4-tolylphosphino)-1,1'-binaphthyl; 1,2-diamine==(S,S)- or (R,R)-1,2-diphenylethylenediamine (DPEN), ethylenediamine (EN), and (S)-1,1-di(4-anisyl)-2-isopropylethylenediamine (DAIPEN)] have been determined using 2D NMR ((1)H--(1)H DQF-COSY, (1)H--(13)C HMQC, (1)H--(31)P HSQC, and (1)H--(15)N HSQC), and a double-pulsed field-gradient spin-echo (DPFGSE) NOE technique. All the octahedral Ru complexes adopt a trans configuration with respect to the BH(4) and hydride ligands. Amine protons of trans-RuH(eta(1)-BH(4))[(S)-tolbinap](1,2-diamine) complexes undergo H/D exchange in (CD(3))(2)CDOD. This inherent high acidity, coupled with the lability and chemical properties of the BH(4) ligand, allows for precatalyst activation without the need for an added base, in contrast to trans-RuCl(2)[(S)-tolbinap](1,2-diamine) precatalysts, which require a strong base for generation of a catalytic species. The H/BH(4) complex in a 2-propanol solution is converted to catalytically active [trans-RuH{(S)-tolbinap}{(S,S)-dpen}(ROH)](+) [(RO)(ROH)(n)](-) (R = (CH(3))(2)CH), a loosely associated ion pair of the discrete (solvated) cationic fragment and anionic species.