Asymmetric nitrogen−35 : Structure and properties of l(s)-α-carboxyethyl-3, 3-bis(trifluoromethyl)diaziridine and its derivatives

A second-kind asymmetric transformation involving N-atom inversion has been observed at 20° for 1(S) - α - carboxyethyl - 3,3 - bis(trifluoromethyl)diaziridine 1 and its methyl ester 2. X-Ray data for the diastereomer (1S, 2S, α-S), 1A (which is thermodynamically preferred in the crystalline phase), ¹H NMR spectra of ethyl ester 3-¹⁵N(1) and 3-¹⁵N(2), CD spectra of 1A,B, 2A,B, potassium salt 4A,B and semiempirical calculations (MINDO/3 and INDO) for 1A, show that the stereospecificity of crystallization of the diastereomer A is due to the higher energy of the crystal lattice of the diastereomer (1R, 2R, α-S), 1B because of hindered charge compensation as well as to the hindrance by the CF₃, groups to intermolecular H-bonds. According to semiempirical calculations, the stability of 3,3 - bis(trifluoromethyl) - diaziridines (TFD) to the action ofel w-orbital energies and depolarization of the C-N bonds due to hyperconjugation and the inductive effect of the CF₃,-groups. The steric effect of these groups is the reason of the low configurational stability of TFD compared with the 3,3-dimethyl analogues.     

Gloriosaols A and B, two novel phenolics from Yucca gloriosa: structural characterization and configurational assignment by a combined NMR-quantum mechanical strategy

Gloriosaols A (1) and B (2), two novel phenolic derivatives characterized by unusual spirostructures made up of two C₁₅ units linked via a γ-lactone to a central stilbenic portion were isolated from the roots of Yucca gloriosa. On the basis of an extensive NMR analysis, the same basic structure was established for the two compounds but no further information about their structural difference could be deduced. Thus two hypotheses were formulated: (1) gloriosaols A and B could be atropisomers caused by a restriction of the free rotation around the double bond due to a steric congestion of the bulky phenolic portions; (2) gloriosaols A and B could be two configurational isomers, indicating, in this case, a nonstereoselective biogenetic formation of the stereogenic center C-2. Semi-empirical calculations of the potential energy surfaces on gloriosaols A and B, together with the ¹H NMR spectra recorded at various temperatures, allowed us to unambiguously exclude the hypothesis of two restricted rotational conformers of a single configurational isomer. Finally, quantum mechanical calculations of the geometries and of the ¹H chemical shifts on the gloriasols A and B in combination with the analysis of the ROE data allowed us to deduce a diastereomeric relation between the two compounds and to assess the relative configuration of the two diastereomers.     

Synthesis and conformational analysis of 1,3-azasilinanes

1-Isopropyl-3-methyl-3-phenyl-1,3-azasilinane 1 and 1-isopropyl-3,3-dimethyl-1,3-azasilinane 2 were synthesized and a detailed analysis of their NMR spectra, conformational equilibria and ring inversion processes is presented. Low temperature ¹H/¹³C NMR spectroscopy, iteration of the ¹H NMR spectra and quantum chemical calculations showed slight predominance of the Ph_eqMe_ax over the Ph_axMe_eq conformer of 1 at low temperature. The barrier for the chair to chair interconversion of both compounds was measured to be 8.25 kcal/mol.     

Conformational and configurational diversity of solvent inclusion complexes of some calix[4]pyrroles and their anion recognition properties

Sterically hindered meso-tetramethyl-meso-tetraarylcalix[4]pyrroles 1-4 where aryl is p-fluorophenyl 1, p-chlorophenyl 2, and p-methylphenyl 3, 4 (configurational isomers) are synthesized and purified by the recrystallization technique. They are characterized by IR, ¹H and ¹³C NMR, and mass spectroscopy. Configurational isomers ααββ (3) and αααα (4) of meso-tetramethyl-meso-tetramethylphenylcalix[ 4]pyrroles are assigned by the ¹H NMR studies and confirmed by the X-ray diffraction analysis. The single crystal X-ray diffraction analysis reveals that the ethanol adduct of 1, the acetone adduct of 2 and 3 adopt the 1,2-conformation while the acetone-water adduct of 1 and the acetone adduct of 4 adopt partial cone and cone conformations respectively. The conformational diversity is due to non-covalent interactions among the encapsulated guest, pyrrolic NH protons, and meso- substituents. Anion binding studies (F^–, Cl^–, CH₃COO^–, HSO ₄ ^? ) are carried out through ¹H NMR titrations; the binding constants are evaluated using the EQNMR program, displaying that they are more selective towards fluoride rather than other anions with the 1:1 stoichiometry. The configuration of compounds drastically influences the ion-recognition processes.     

Pseudo-tetrahedral semi-sandwich cycloruthenated compounds: 1H NMR data and DFT-calculations about the racemisation process of the ruthenium atom

The partial substitution of the acetonitrile ligand of compound 1a 〚(η⁶-C₆H₆)Ru(C₆H₄-2-CH₂NMe₂)(NCMe)〛⁺PF₆^– by CD₃OD was observed while running the ¹H NMR spectra of 1a in this solvent, this giving rise to the formation of 1b. In opposition to 1a, the ¹H NMR spectrum of 1b is temperature-dependent, as at T > 40 °C the coalescence of the signals of the –CH₂NMe₂ protons was observed, this being an evidence for the fast racemisation of the Ru centre in 1b at the NMR timescale. DFT-calculations allowed us to envision a likely process for this racemisation. It should take place via the decoordination of the methanol ligand at an early step of the reaction, followed by the inversion of the configuration of the thus-obtained 16 e^– species (2). The transition state (3) for this latter reaction was identified and the total free energy of the racemisation was thus calculated, affording a value close to the activation energy found experimentally by ¹H NMR (∼13 kcal mol^–1 vs ∼15.5 kcal mol^–1, respectively).     

Poly(vinylpyrrolidone): Configurational assignments by one- and two-dimensional NMR spectroscopy

The configurational assignment of poly(vinylpyrrolidone) (PVP) prepared by peroxide-initiated solution polymerization was studied by the combination of one- and two-dimensional NMR spectroscopy. The broad and overlapping ¹H-NMR and ¹³C{¹H}-NMR spectra of PVP were assigned to the configurational triad, pentad (CH, ²CH₂, ³CH₂, and ⁴CH₂ regions), and tetrad (β-CH₂ region) sequences. The configurational assignments of the various carbon resonances were confirmed with the help of two-dimensional experiments such as heteronuclear single quantum correlation (HSQC), heteronuclear single quantum correlation–total correlation spectroscopy (2-D HSQC–TOCSY). The various geminal and vicinal couplings within the configurational sequences were assigned with the help of total correlation spectroscopy (TOCSY low mixing time). The propagation pathway was studied using the ¹³C{¹H}-NMR (carbonyl carbon) and ¹⁵N{¹H}-NMR spectra. The ¹⁵N{¹H} resonance signals were assigned to pentad-level configurational sequences. The results obtained by the analysis of the area under the resonance signals confirmed that poly(vinylpyrrolidone) obeys Bernoullian statistics. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3922–3928, 1999     

Alkaloids of NIRAM,natural dye from Polygonum tinctorium,and their anti-inflammatory activities

Phytochemical investigation of EtOH extract of NIRAM, natural dye from Polygonum tinctorium, resulted in the purification of nine alkaloid compounds (1–9) including four new compounds (1–4). Structures of these new compounds were elucidated by 1D and 2D NMR (¹H and ¹³C NMR, ¹H–¹H COSY, ¹H–¹³C HSQC, ¹H–¹³C HMBC), IR, UV, HR-ESI-MS, and ECD spectra. Isolated compounds (1–9) were tested for their inhibitory effects on nitric oxide (NO) production in lipopolysaccharide (LPS)-activated BV-2 cells. Compounds 1–3, 5, and 7 showed potent NO production inhibitory activities, with IC₅₀ values of 3.88–22.87 μM.     

Synthesis, 1H NMR, 13C NMR spectra and conformational preference of open chain ligands on lipophilic macrocycles

Several open chain ligands (polypodands) 3 and 4 have been synthesized introducing short oligoethylene glycol units (-CH₂CH₂O)_mCH₃, (m = 1,2,) on lipophilic matrices represented by cyclic tetra- 1 and octa-2 oligomers obtained from the base catalyzed reaction of p-butylphenol or p-octylphenol and formaldeyde. ¹H NMR and ¹³C NMR spectral data have been used to establish the conformational freedon of the ligands, which is important for cation binding studies.     

Aufkl?rung der 1H- und 13C-NMR-spektren sowie der kristallstruktur unges?ttigter glycosylphosphonate und konformationsberechnungen an modellen1

By application of a modified LAOCN-3 program a complete elucidation of the ¹H NMR spectra of 2,3-unsaturated glycosyl phosphonates 1–5 could be achieved. The exactly determined ⁿJ(H, H) and novel ⁿJ(C, P) coupling constants are discussed, and permit a conclusive deduction of the conformations. The ¹³C NMR spectra of 1 to 6 can be fully interpreted. By a close inspection of chemical shifts as well as ¹J(C-H) and ⁿJ(C, P) coupling constants the conformational assignment is supported. For all the derivatives the correlations ¹J(C-1,H_e)>¹J(C-1, H_a) and ¹J(C-1, P_e) >¹J(C-1, P_a) can be used for the assignment of anomers. The crystal structure of 1 is in accordance with this assignment of anomers and displays an unexpected conformation. Calculations by MINDO-3 in resembling model compounds serve to elucidate such conformative effects.     

Conformational przferknce of the S→O bond. 1H and 13C NMR studies of the mono-S-oxides of 1,2-, 1,3- and 1,4-dithianes

The ¹H and ¹³C NMR behavior of the monosulfoxides of 1,2-, 1,3-and 1,4-dithianes (1–3) were studied in order to determine the conformational preference of the S→O bond in these heterocycles. From the results of variable temperature, double irradiation, solvent effects and shift reagent experiments, It is concluded that the axial conformers dominate the conformational equilibria of 1 and 3. On the other hand, 2-equatorial is more stable than 2-axial by 0.64 kcal/mol (ΔG°) at -80°, in CD₃OD. This value is essentially identical with the one determined in CHClF₂, and the lack of a solvent effect appears to indicate that dipole/dipole interactions do not control this equilibrium. AΔG_c³ = 11.0 kcal/mol was determined for the inversion process of 2. Complete ¹H and ¹³C NMR assignments for 1–3 are presented.     

Conformational analysis of 3-(substituted benzo[b]furan-2-yl)-γ-aminobutyric acid,new GABAB ligands,by 1H NMR in D2O

The conformations of 3-(substituted benzo[b]furan-2-yl)-GABA (1–4) in solution (D₂O) are estimated from high-resolution (400 MHz) ¹H NMR coupling data. Conformations and populations of conformers are calculated by means of a modified Karplus-like relationship for the vicinal coupling constants and are compared with X-ray crystallographic investigations. ¹H NMR spectral analysis evidences how 1–4 keep also in solution the preferred g⁻ conformation around the C3C4 bond as found in the solid state while a partial rotation is set up around the C2C3 bond.     

Mono- and diprotonation of dihydropyrene, 2,7-di-tert-butyl-dihydropyrene,and their conversion to pyrenium ions; Influence of the radical cation and its potential utility in NMR assignments of the arenium ions of readily oxidizable PAHs

Parent dihydropyrene 1 and 2,7-di-tert-butyldihydropyrene 3 are monoprotonated with FSO₃H/SO₂CIF to give their persistent monoarenium ions 1H ⁺ and 3H ⁺ by the attack of proton at C-3 (peri to the ethano-bridge not at C-1 as previously suggested). Dihydropyrene 3 is diprotonated in FSO₃H.SbF₅ 1∶1 “Magic Acid”^R/SO₂CIF to give the symmetrical dication 3H ₂ ⁺², similar diprotonation of 1 with “Magic Acid”/SO₂CIF or with FSO₃H.SbF₅ (4∶1)/SO₂CIF gave the diprotonated species 1H ₂ ⁺² in a mixture. NMR characteristics of the mono- and dications are discussed. On raising temperature or on prolonged cold storage, 1H ⁺ and 3H ⁺ are converted to their corresponding pyrenium cations (2H ⁺ and 4H ⁺). Formation of 2H ⁺ from 1 is more rapid than conversion of 3 to 4H ⁺. Parent pyrenium cation was independently generated by protonation with FSO₃H/SO₂CIF. When a mixture of 2 and 1 is reacted with FSO₃H/SO₂CIF (dry ice/acetone temperature) only 2H ⁺ is seen in the NMR (concomitant presence of the radical cation 1 ⁺⁺ is inferred from EPR). Similar protonation of a mixture of 6-chlorochrysene 5 and 1 with FSO₃H/SO₂CIF leads to NMR observation of 1H ⁺ (with concomitant presence of 5 ⁺⁺); on raising temperature 1H ⁺ is converted to 2H ⁺. The nature of the paramagnetic radical cation (RC) present in the arenium ion samples influences the position, and resolution of the NMR spectra. This approach may prove useful in NMR studies of large polycyclic aromatic hydrocarbons PAHs where concomitant RC formation greatly diminishes the quality of the NMR spectra.     

Conformational equilibria in N-chloropiperidines

Nitrogen inversion equilibria in the anancomeric piperidines 3–6, 8 and 9 have been studied by variable temperature ¹H NMR in order to determine free energy differences ΔG_e→a⁰ for one class of N-substituted piperidines by an unequivocal method, i.e. direct integration of separate NMR signals for conformers whose interconversion is slow on the NMR timescale at an easily accessible temperature. Using 6 as a model ΔG_e→a⁰ (N-chloropiperidine) has been found to be 5·3±0·1 kJ mol^-1 at 193 K; similarly a study of 10 leads to ΔG_e→a⁰ (N-chloromorpholine) = 4·2±0·1 kJ mol^-1 at 203 K.     

Reduction of iridoid aglycones—III: Reactivity of lamiolgenin towards NaBH4

The reaction which occurs when lamiolgenin 2 is treated with an excess of NaBH₄ is unusually complex owing to an intramolecular aldolic condensation which leads to a bicyclo[3.2.0]heptane derivative 4. The mechanism of this reduction has been investigated by using NaBD₄. Spectral data (IR, ¹H NMR, ¹³ C NMR) of the products are presented.     

Considération sur l'ordre des acidités successives du diacide 7-para carboxy anilino 4-nitrobenzofurazane

On the dissociation constants of successive acidities of the diacid 7-para carboxy anilino-4-nitrobenzofurazane. The first dissociation constant of the 7-para carboxy anilino-4-nitrobenzofurazane noted 4H,COOH, in dimethylsulfoxyde was estimated using an NMR method. Diacid 4H,COOH was prepared by simple reaction of aromatic nucleophilic substitution (S_NAr) and monopotassium salt and was precipitated by chloroform addition to a solution of 4H,COOH in Me₂SO, after neutralisation of an acid function by one equivalent of solid potassium bicarbonate. Initially, a titration NMR ¹H of two acidities of 4H,COOH was carried out in Me₂SO-d₆ by the strong base potassium tert-butoxide. After, we showed that ionization NH/N⁻ is carried out completely before that of function COOH. We could estimate the first dissociation constant (7.5) of 4H,COOH in dimethylsulfoxyde by using the 9-cyano fluorene as a reference compound.     

Crystal structures and physico-chemical properties of two new one-dimensional zinc(II) complexes with sulfide bridging bispyridines

4,4′-Dipyridyl sulfide (L₁) and 4,4′-di(3-methyl)pyridyl (L₂) sulfide coordination compounds of the general formula Zn(L)(X)₂ (L₁=4,4′-dipyridyl sulfide; L₂=4,4′-di(3-methyl)pyridyl sulfide; X=CH₃COO⁻, Cl⁻), have been obtained. The compounds were characterized by single crystal X-ray diffraction, elemental analysis, IR and ¹H NMR. Both compounds are of one-dimensional coordination polymers and crystallize in the orthorhombic systems, while in different space groups with Pnc2 for [ZnL₁(CH₃COO)₂] 1 and Pna2(1) for [ZnL₂Cl₂] 2, respectively. X-ray analysis and ¹H NMR experiments indicate that variation of ligands rather than counter anions, CH₃COO⁻ and Cl⁻, leads to the change in the modes of the dimensionality array, that is, complexes 1 prefers a linear coordination fashion while complexes 2 exhibits a zigzag conformation.     

Titanium complexes containing new dianionic tetradentate [ONNO]-type ligands with benzyl substituents on bridging nitrogen atoms: Syntheses, X-ray structures, and catalytic activities in ring opening polymerization of lactide

Several titanium isopropoxides 1–8 have been prepared by the reaction of Ti(O-i-Pr)₄ with a series of corresponding tetradentate Salan-type [ONNO] ligands with benzyl or methyl substituents on bridging nitrogen atoms. They have been characterized by ¹H NMR, ¹³C{¹H} NMR, and elemental analysis. Solid state structures of compounds 2, 4, 6, and 7 have been determined by X-ray crystallography. X-ray diffraction analysis and ¹H NMR confirmed that these titanium complexes were all monomeric species with a six-coordinated central titanium in their solid and solution structures. Complexes 2, 4, 6, and 8 with benzyl substituents on bridging nitrogens gave PLA with higher molecular weight than compounds 1, 3, 5, and 7 with methyl substituents did.     

A new C21-steroidal glycoside from Cynanchum stauntonii

A new C21-steroidal glycoside with two known compounds were isolated from the root of Cynanchum Stauntonii.Based on thespectral analysis,including MS,1H NMR,13C NMR,DEPT,1H-1H COSY,13C-1H COSY,HMQC and HMBC,their chemicalstructures were determinated as glaucogenin-C 3-O-a-L-cymaropyranosyl-(1→4)-b-D-digitoxopyranosyl-(1→4)-β-D-canaropyranoside(1),stigmasterol(2)and ursolic acid(3).     

Darstellung und eigenschaften von und reaktionen mit metallhaltigen heterocyclen: LXXXII. Cyclocotrimerisierung der P=icr;S-Gruppe mit dem sterisch anspruchsvollen t-Butylpropinoat

The P=icr;S functional group in (η²-PCy₂

S)Mn(CO)₄ (1) undergoes cyclocotrimerization with t-butyl propynoate to give the isomeric compounds 3a und 3b in a 1 : 1 ratio. Oxidation of 3a and 3b with (NH₄)₂[Ce(NO₃)₆] gives thiophene 4. Compounds 3a and 3b were characterized by use of MS spectrometry and IR, ³¹P{¹H}, ¹H, and ¹³C{¹H} NMR spectroscopy.     

Chiral solvating properties of (S)-1-benzyl-6-methylpiperazine-2,5-dione

In CDCl₃ solution, enantiopure (S)-1-benzyl-6-methylpiperazine-2,5-dione (S)-1a formed diastereomeric CO⋯H–N hydrogen-bonded associates with racemic (RS,Z)-1-benzyl-3-[(dimethylamino)methylidene]piperazine-2,5-diones 2a and 2b, (RS)-tert-butyl pyroglutamate (RS)-2c and (RS)-N-benzoylalanine methyl ester (RS)-2d. This resulted in splitting (doubling) of the characteristic signals in the ¹H NMR and ¹³C spectra of racemic compounds 2a–d in the presence of 1 equiv of (S)-1a. The formation of hydrogen-bonded dimers in CDCl₃ solution was studied by ¹H NMR, ¹³C NMR and 2D NMR and confirmed by the intermolecular NOE observed between the hydrogen-bonded amide protons from each of the monomeric units, (S)-1a and 2a–c. On the other hand, a slightly different binding mode was proposed for association of (S)-1a with alaninamide (RS)-2d. Enantiomer compositions of known (weighed) mixtures of both enantiomers of tert-butyl pyroglutamate 2c were re-determined by ¹H NMR in the presence of (S)-1a in CDCl₃. The experimental values were in good agreement with the theoretical values, thus indicating the potential applicability of (S)-1a and related diketopiperazines as chiral solvating agents in NMR spectroscopy.