Independent Generation and Time‐Resolved Detection of 2′‐Deoxyguanosin‐N2‐yl Radicals

Guanine radicals are important reactive intermediates in DNA damage. Hydroxyl radical (HO^.) has long been believed to react with 2′‐deoxyguanosine (dG) generating 2′‐deoxyguanosin‐N1‐yl radical (dG(N1‐H)^.) via addition to the nucleobase π‐system and subsequent dehydration. This basic tenet was challenged by an alternative mechanism, in which the major reaction of HO^. with dG was proposed to involve hydrogen atom abstraction from the N2‐amine. The 2′‐deoxyguanosin‐N2‐yl radical (dG(N2‐H)^.) formed was proposed to rapidly tautomerize to dG(N1‐H)^.. We report the first independent generation of dG(N2‐H)^. in high yield via photolysis of 1 . dG(N2‐H)^. is directly observed upon nanosecond laser flash photolysis (LFP) of 1 . The absorption spectrum of dG(N2‐H)^. is corroborated by DFT studies, and anti‐ and syn‐dG(N2‐H)^. are resolved for the first time. The LFP experiments showed no evidence for tautomerization of dG(N2‐H)^. to dG(N1‐H)^. within hundreds of microseconds. This observation suggests that the generation of dG(N1‐H)^. via dG(N2‐H)^. following hydrogen atom abstraction from dG is unlikely to be a major pathway when HO^. reacts with dG.     

Synthesis and NMR characteristics of N‐acetyl‐4‐nitro,N‐acetyl‐5‐nitro,N‐acetyl‐6‐nitro and N‐acetyl‐7‐nitrotryptophan methyl esters

N‐acetyl‐4‐nitrotryptophan methyl ester (2), N‐acetyl‐5‐nitrotryptophan methyl ester (3), N‐acetyl‐6‐nitrotryptophan methyl ester (4) and N‐acetyl‐7‐nitrotryptophan methyl ester (5) were synthesized through a modified malonic ester reaction of the appropriate nitrogramine analogs followed by methylation with BF₃‐methanol. Assignments of the ¹H and ¹³C NMR chemical shifts were made using a combination of ¹H–¹H COSY, ¹H–¹³C HETCOR and ¹H–¹³C selective INEPT experiments. Copyright © 2008 Crown in the right of Canada. Published by John Wiley & Sons, Ltd     

Complete assignment of NMR data of 22 phenyl‐1H‐pyrazoles' derivatives

Complete assignment of ¹H and ¹³C NMR chemical shifts and J(¹H/¹H and ¹H/¹⁹F) coupling constants for 22 1‐phenyl‐1H‐pyrazoles' derivates were performed using the concerted application of ¹H 1D and ¹H, ¹³C 2D gs‐HSQC and gs‐HMBC experiments. All 1‐phenyl‐1H‐pyrazoles' derivatives were synthesized as described by Finar and co‐workers. The formylated 1‐phenyl‐1H‐pyrazoles' derivatives were performed under Duff's conditions. Copyright © 2011 John Wiley & Sons, Ltd.     

Synthesis of isotopomers of <Emphasis Type="SmallCaps">l</Emphasis>-DOPA and dopamine labeled with hydrogen isotopes in the side chain

The enzymatic synthesis of three isotopomers of l-DOPA labeled with deuterium and tritium at α carbon atom was elaborated. These compounds were converted into [(1S)-²H]–, [(1S)- ³H]–, and doubly labeled [(1S)-²H/³H]-dopamines using enzyme tyrosine decarboxylase. Doubly labeled (1R) isotopologue, i.e., [(1R)-²H/³H]-dopamine, was afforded by enzymatic decarboxylation of authentic l-DOPA carried out in deuteriated and tritiated incubation medium.     

One‐ and two‐dimensional NMR characterization of N‐vinyl‐2‐pyrrolidone/methyl acrylate copolymers

N‐vinyl‐2‐pyrrolidone/methyl acrylate (V/M) copolymers were prepared by free‐radical bulk polymerization using benzoyl peroxide as an initiator. The copolymer composition of these copolymers was calculated from ¹H NMR spectra. The radical reactivity ratios for N‐vinyl‐2‐pyrrolidone (V) and methyl acrylate (M) were r_V = 0.09, r_M = 0.44. These reactivity ratios for the copolymerization of V and M were determined using the Kelen–Tudos and nonlinear least‐squares error‐in‐variable methods. The ¹³C{¹H} and ¹H NMR spectra of these copolymers overlapped and were complex. The complete spectral assignment of the ¹³C and ¹H NMR spectra were done with distortionless enhancement by polarization transfer and two dimensional ¹³C‐¹H heteronuclear single quantum correlation spectroscopic experiments. The two‐dimensional ¹H‐¹H homonuclear total correlation spectroscopic NMR spectrum showed the various bond interactions, thus inferring the possible structure of the copolymers. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2225–2236, 2002     

One‐ and two‐dimensional NMR characterization of N‐vinyl‐2‐pyrrolidone/methyl acrylate copolymers

N‐vinyl‐2‐pyrrolidone/methyl acrylate (V/M) copolymers were prepared by free‐radical bulk polymerization using benzoyl peroxide as an initiator. The copolymer composition of these copolymers was calculated from ¹H NMR spectra. The radical reactivity ratios for N‐vinyl‐2‐pyrrolidone (V) and methyl acrylate (M) were r_V = 0.09, r_M = 0.44. These reactivity ratios for the copolymerization of V and M were determined using the Kelen–Tudos and nonlinear least‐squares error‐in‐variable methods. The ¹³C{¹H} and ¹H NMR spectra of these copolymers overlapped and were complex. The complete spectral assignment of the ¹³C and ¹H NMR spectra were done with distortionless enhancement by polarization transfer and two dimensional ¹³C‐¹H heteronuclear single quantum correlation spectroscopic experiments. The two‐dimensional ¹H‐¹H homonuclear total correlation spectroscopic NMR spectrum showed the various bond interactions, thus inferring the possible structure of the copolymers. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2225–2236, 2002     

Pyrimidine and Pyrazole Linked Azetidin‐2‐ones: Entry to Novel Class of β‐Lactam Heterocycles

A novel series of pyrimidine/pyrazole linked β‐lactams have been synthesized in excellent yields using a simple and efficient methodology involving conjunction of different heterocyclic substrates. All the new products were characterized on the basis of various spectroscopic techniques viz. FT‐IR, ¹H NMR, ¹³C NMR, elemental analysis (CHN), ¹H‐¹H correlation spectroscopy (¹H‐¹H COSY) and mass spectrometry (EIMS) in representative cases. Furthermore, theoretical calculations have also been performed on representative compounds and the results were compared with Cefuroxime axetil (a broad spectrum antibacterial agent). The phenomenon of tautomerism was also observed which was confirmed by different NMR experiments (D₂O exchange study and ¹H‐¹H correlation spectroscopy).     

The Studies of Structure of 2N‐(3‐phenyl‐allyl‐)(5‐phenyl‐[1,3,4] Thiadiazol‐2‐yl) Amine in Solution

2N‐(3‐phenyl‐allyl‐)(5‐phenyl‐[1,3,4] thiadiazol‐2‐yl) amine was studied by means of the ¹H, ¹³C, ¹⁵N NMR spectroscopy and DFT calculations. On the basis of the one‐dimensional ¹H, ¹³C, ¹⁵N‐NMR and two‐dimensional ¹H‐¹³C HMQC, ¹H‐¹³C HMBC, ¹H‐¹⁵N HMQC, ¹H¹H NOESY, ¹H¹H COSY correlation spectra the amine‐type and the imine‐type tautomers have been determined in the solution. Variety of structural forms including: biradical, ionic–biradical, and ionic structures of the amine‐type a and of the imine‐type b , c tautomers exist in the solution. According to the DFT computations the differences in the total energy between a and b , a and c , and b and c tautomers are equal to 1.5 kJ/mol, 1.2 kJ/mol, and 0.3 kJ/mol, respectively.     

Stacking Structure of Confined 1‐Butanol in SBA‐15 Investigated by Solid‐State NMR Spectroscopy

Understanding the complex thermodynamic behavior of confined amphiphilic molecules in biological or mesoporous hosts requires detailed knowledge of the stacking structures. Here, we present detailed solid‐state NMR spectroscopic investigations on 1‐butanol molecules confined in the hydrophilic mesoporous SBA‐15 host. A range of NMR spectroscopic measurements comprising of ¹H spin–lattice (T₁), spin–spin (T₂) relaxation, ¹³C cross‐polarization (CP), and ¹H,¹H two‐dimensional nuclear Overhauser enhancement spectroscopy (¹H,¹H 2D NOESY) with the magic angle spinning (MAS) technique as well as static wide‐line ²H NMR spectra have been used to investigate the dynamics and to observe the stacking structure of confined 1‐butanol in SBA‐15. The results suggest that not only the molecular reorientation but also the exchange motions of confined molecules of 1‐butanol are extremely restricted in the confined space of the SBA‐15 pores. The dynamics of the confined molecules of 1‐butanol imply that the ¹H,¹H 2D NOESY should be an appropriate technique to observe the stacking structure of confined amphiphilc molecules. This study is the first to observe that a significant part of confined 1‐butanol molecules are orientated as tilted bilayered structures on the surface of the host SBA‐15 pores in a time‐average state by solid‐state NMR spectroscopy with the ¹H,¹H 2D NOESY technique.     

Synthesis and Characterization of trans‐PdII Trimethylsilylchalcogenolates

The trans‐bis(trimethylsilyl)chalcogenolate palladium complexes, trans‐[Pd(ESiMe₃)₂(PnBu₃)₂] [E = S ( 1 ) and Se ( 2 )] were synthesized in good yields and high purity by reacting trans‐[PdCl₂(PBu₃)₂] with LiESiMe₃ (E = S, Se), respectively. These complexes were characterized by ¹H, ¹³C{¹H}, ³¹P{¹H} (and ⁷⁷Se{¹H}) NMR spectroscopy and single‐crystal X‐ray analysis. The reaction of 2 with propionyl chloride led to the formation of trans‐[Pd(SeC(O)CH₂CH₃)₂(PnBu₃)₂] ( 3 ), a trans‐bis(selenocarboxylato) palladium complex and thus established a new method for the formation of this type of complex. Complex 3 was characterized by ¹H, ¹³C{¹H}, ³¹P{¹H} and ⁷⁷Se{¹H} NMR spectroscopy and a single‐crystal X‐ray structure analysis.     

Characterization of the complex formation of 1,6‐anhydro‐β‐maltotriose with potassium using 1H and 39K NMR spectroscopy

The ¹H and ³⁹K longitudinal relaxation times (T₁) and ¹H diffusion coefficients were measured to investigate the complex formation of 1,6‐anhydro‐β‐maltotriose and potassium ions. Although the ¹H‐T₁ values of H3′, H5′, H1″ and H4″ decreased in the presence of potassium ions, ¹H chemical shifts and ¹H diffusion coefficients did not show significant changes. The long‐range coupling constants of ³J_C?H around the glycosyl bonds did not show significant changes either. In the measurements of ³⁹K spectra, the ³⁹K signal obviously broadened and the ³⁹K‐T₁ values decreased in the presence of 1,6‐anhydro‐β‐maltotriose, indicating the complex formation of 1,6‐anhydro‐β‐maltotriose and potassium ions. These results indicate that the conformation and molecular volume were unaffected in the complex formation. Copyright © 2009 John Wiley & Sons, Ltd.     

1H and 13C NMR spectral characterization of some antimalarial in vitro 2,4‐diamino‐10‐methylpyrimido[4,5‐b]‐5‐quinolone derivatives

We report the ¹H NMR and ¹³C NMR chemical shifts and J(H,H), J(H,F) and J(C,F) coupling constants of 13 2,4‐diamino‐10‐methylpyrimido[4,5‐b]‐5‐quinolone derivatives, some of them with moderate activity against Plasmodium falciparum in vitro. They were characterized and assigned on the basis of ¹H, ¹³C and ¹³C–¹H (short‐ and long‐range) correlated spectra. Copyright © 2002 John Wiley & Sons, Ltd.     

Real‐Time Band‐Selective Homonuclear Proton Decoupling for Improving Sensitivity and Resolution in Phase‐Sensitive J‐Resolved Spectroscopy

Real‐time band‐selective homonuclear ¹H decoupling during data acquisition of z‐filtered J‐resolved spectroscopy produces ¹H‐decoupled ¹H NMR spectra and leads to sensitivity enhancement and improved resolution, and thus aids the measurement of J couplings and residual dipolar couplings in crowded regions of ¹H NMR spectrum. High quality spectra from peptides, organic molecules, and also from enantiomers dissolved in weakly aligned chiral media are reported.     

Heterocyclic analogs of xanthiones: 5,6‐fused 3‐methyl‐1‐phenylpyrano[2,3‐c]pyrazol‐4(1H) thiones—synthesis and NMR (1H, 13C, 15N) data

Various [5,6]pyrano[2,3‐c]pyrazol‐4(1H)‐thiones were synthesized in high yields by treatment of the corresponding [5,6]pyrano[2,3‐c]pyrazol‐4(1H)‐ones with Lawesson's reagent. Detailed NMR spectroscopic studies were undertaken of the title compounds. Complete and unambiguous assignment of chemical shifts (¹H, ¹³C, ¹⁵N) and coupling constants (¹H,¹H; ¹³C,¹H) was achieved by the combined application of various one‐ and two‐dimensional (1D and 2D) NMR spectroscopic techniques. Unequivocal mapping of most ¹³C,¹H spin coupling constants is accomplished by 2D (δ, J) long‐range INEPT spectra with selective excitation. Copyright © 2010 John Wiley & Sons, Ltd.     

2‐(4‐methylpyridin‐2‐yl)‐1H‐benzimidazole derivatives. Part II,lH nmr characterization

A selected series of 2‐(4‐methylpyridin‐2‐yl)‐1H‐benzimidazole derivatives, bases and cyclic mono‐ and bis‐salts, were synthesized. Complete ^'1H nmr characterization is reported. Ambiguous assignments were solved using ¹H‐¹H NOESY analysis. Significant ir and ¹H nmr data are presented concerning: i) tautomeric equilibrium of imidazole hydrogen; ii) hydrogen bonds; iii) conformational inversion of partially saturated rings.     

Tris[3‐hydroxy‐2(1 H)‐pyridinonato]‐Komplexe von Al3+, Cr3+ und Fe3+ – Kristall‐ und Molekülstrukturen von 3‐Hydroxy‐2(1 H)‐pyridinon und Tris[3‐hydroxy‐2(1 H)‐pyridinonato]chrom(III)

Tris[3‐hydroxy‐2(1 H)‐pyridinonato] Complexes of Al³⁺, Cr³⁺, and Fe³⁺ – Crystal and Molecular Structures of 3‐Hydroxy‐2(1 H)‐pyridinone and Tris[3‐hydroxy‐2(1 H)‐pyridinonato]chromium(III) Tris[3‐hydroxy‐2(1 H)‐pyridinonato] complexes of Al³⁺, Cr³⁺ and Fe³⁺ are obtained by reactions of 3‐hydroxy‐2(1 H)pyridinone with the hydrates of AlCl₃, CrCl₃ or Fe(NO₃) in aqueous alkaline solutions as polycrystalline precipitates. The compounds are isotypic. X‐ray structure determinations were performed on single crystals of the uncoordinated 3‐hydroxy‐2(1 H)‐pyridinone ( 1 ) (orthorhombic, space group P2₁2₁2₁, a = 405.4(1), b = 683.0(1), c = 1770.3(3) pm, Z = 4) and of the chromium compound 3 (rhombohedral with hexagonal setting, space group R3c, a = 978.1(1), c = 2954.0(1) pm, Z = 6).     

Structure elucidation of [1,3]oxazolo[4,5‐e][2,1]benzisoxazole and naphtho[1,2‐d][1,3]‐ and phenanthro[9,10‐d]oxazoles using gradient selected gHMBC,gHMQC and gHMQC‐TOCSY NMR techniques

Structure elucidation of compounds in the benzisoxazole series ( 1 – 6 ) and naphtho[1,2‐d][1,3]‐ ( 7 – 10 ) and phenanthro[9,10‐d][1,3]oxazole ( 11 – 14 ) series was accomplished using extensive 2D NMR spectroscopic studies including ¹H–¹H COSY, long‐ range ¹H–¹H COSY, ¹H–¹³C COSY, gHMQC, gHMBC and gHMQC‐TOCSY experiments. The distinction between oxazole and isoxazole rings was made on the basis of the magnitude of heteronuclear one‐bond ¹J_{C2, H2} (or ¹J_{C3, H3}) coupling constants. Complete analysis of the ¹H NMR spectra of 11 – 14 was achieved by iterative calculations. Gradient selected gHMQC‐TOCSY spectra of phenanthro[9,10‐d][1,3]oxazoles 11 – 14 were obtained at different mixing times (12, 24, 36, 48 and 80 ms) to identify the spin system where the protons of phenanthrene ring at H‐5, H‐6 and at H‐9 and H‐7 and H‐8 were highly overlapping. Copyright © 2003 John Wiley & Sons, Ltd.     

H‐transfer reaction during decomposition of N‐(2‐methylpropyl)‐ N‐(1‐diethylphosphono‐2,2‐dimethylpropyl)‐N‐oxyl (SG1)‐based alkoxyamines

Thermal decomposition of four tertiary N‐(2‐methylpropyl)‐N‐(1‐diethylphosphono‐2,2‐dimethylpropyl)‐N‐oxyl (SG1)‐based alkoxyamines (SG1‐C(Me)₂‐C(O)‐OR, R = Me, tBu, Et, H) has been studied at different experimental conditions using ¹H and ³¹P NMR spectroscopies. This experiment represents the initiating step of methyl methacrylate polymerization. It has been shown that H‐transfer reaction occurs during the decomposition of three alkoxyamines in highly degassed solution, whereas no products of H‐transfer are detected during decomposition of SG1‐MAMA alkoxyamine. The value of the rate constant of H‐transfer for alkoxyamines 1 (SG1‐C(Me)₂‐C(O)‐OMe) and 2 ( SG1‐C(Me)₂‐C(O)‐OtBu) has been estimated as 1.7 × 10³ M^?1s^?1. The high influence of oxygen on decomposition mechanism is found. In particular, in poorly degassed solutions, nearly quantitative formation of oxidation product has been observed, whereas at residual pressure of 10^?5 mbar, the main products originate from H‐atom transfer reaction. The acidity of the reaction medium affects the decomposition mechanism suppressing the H‐atom transfer. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

首次合成来源于鼠李属植物中的两个新颖的蒽环鼠李糖苷，2’, 3’-Di-O-acetylfrangulin A 和 Prinoidin

首次全合成来源于鼠李属植物中的两个天然产物2’, 3’-di-O-acetylfrangulin A (1) 和 prinoidin (2),它们对KB细胞表现出较好的细胞毒活性。通过1H NMR, 13C NMR, 1H-1H COSY, HMQC 和 HMBC确证了两个化合物的结构。     

Constantes de couplage vicinales à travers deux hétéroatomes: III—Calculs théoriques et mesures expérimentales dans les hydrazides enrichies en 15N

Different calculations, among them those utilizing the finite perturbation theory with INDO wave functions, have been effected to calculate the value of the ³J(¹H ? N? N? ¹H ) coupling constant in hydrazides as a function of the dihedral angle. Experimental coupling constants have been compared with calculated ones in order to determine the conformation around the N? N bond. The first example of a ²J(¹H ? N? ¹⁵N ) coupling is described.