Determination of the geometrical configuration of the polyen chain of monocis C40-carotenoids—I: A 13C NMR study of monocis zeaxanthins and monocis capsorubins

¹³C NMR studies reveal that the polyen chain of neo-zeaxanthin A (2) and that of neo-capsorubin A (5) have 13-cis configuration, while those of neo-zeaxanthin B (3) and neo-capsorubin B (6) have 9-cis geometrical configuration. ¹³C NMR data on the corresponding all-trans carotenoids (1 and 4) are also reported.     

Strukturaufklärung einer neuen diterpensäure aus metasequoia glyptostroboides mit hilfe der 13C-NMR-spektroskopie

In addition to methyl communate (1) the hitherto unknown 3-acetoxylabda-8(20), 13-diene-15-oic acid (3) has been isolated from the autumnal leaves of metasequoia glyptostroboides. Its structure has been determined by ¹³C NMR spectroscopy, aided by the analysis and assignment of the ¹³C NMR spectra of two degradation products as well as of α-onocerine diacetate (13) and of methyl communate (1).     

The chemistry and 13C NMR assignments of oxaline,a novel alkaloid from penicillium oxalicum

Oxaline is the main alkaloid of several strains of Penicillium oxalicum. Structural studies on oxaline (1a) and the assignment of its ¹³C NMR spectrum are described.     

The structure of the products of coupling aryldiazonium salts with phenacylthiocyanates. Correction of literature reports

A variety of coupling products of phenacylthiocyanates 1a—d with aryldiazonium chlorides is reported. The i.r., u.v.¹³C NMR as well as the chemical behaviour of the coupling products clearly reveal that they are hydrazones (7) and not thiadiazol-2-imines (5) as previously reported.     

The synthesis, using microwave irradiation and characterization of novel, metal-free and metallophthalocyanines

The synthesis of novel metal-free (4) and metallophthalocyanines (5, 6, 7 and 8) were prepared by cyclotetramerization of a novel 4-[2-(1-naphthyloxy)ethoxy]phthalonitrile (3). New substitute phthalocyanines showed the enhanced solubility in organic solvents. The new compounds were characterized by a combination of IR, ¹H NMR, ¹³C NMR, UV-Vis and MS spectral data.     

Organoboration of alkynlystannanes: XIX. Stannacyclopentadienes via organoboration of diethylnyldimethylstannane with B-alkyl-9-borabicyclo[3.3.1]nonanes

Tricyclic heterocycles (8) containing a stannacyclopentadiene unit are obtained as the major products (ρ 80%) from the reaction between diethynyldimethylstannane and B-alkyl-9-borabicyclo[3.3.1]nonanes (2). By comparison with the analogous reaction of ethynyltrimethylstannane (1) it is shown that compounds 8 are the kinetically controlled products. Assignments of the structure of 8 and those of some minor products are based on multinuclear NMR spectra (¹H, ¹¹B, ¹³C, ¹¹⁹Sn NMR).     

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.     

Stabilization of the cyclopropenum and cyclopropenone ring systems by ferrocene : A 13C nuclear magnetic resonance study

The ¹³C NMR spectra of diferocenylcyclopropenone (1) and the triferrocenylcyclopropenium (2) and ferrocenyldiphenylcyclopropenium (3) cations in non-acidic media are analyzed with special reference to the information they afford concerning charge distribution in these species. A delocalization of the positive charge into the remote unsubstituted five-membered rings of 2 and 3 is indicated. The role of the metal as a conduit for this effect is suggested.     

Proton NMR criteria for configurational assignment of S-methylthianium cations

Certain ¹H NMR features are reported for several conformationally biased diastereomeric pairs of 6-membered methylsulphonium cations (4–7) the members of each pair differing for the axial or equatorial orientation of the S⁺CH₃ group. The configurational assignment being secured by ¹³C NMR, the scope of a number of ¹H NMR parameters is discussed as criteria for configurational and conformational analysis. Two mobile systems have also been considered, 2 and 9, whose ¹H NMR is consistent with their (independently determined) conformer distribution.     

The structure of tatsinine,a novel c19-diterpenoid alkaloid from delphinium tatsienense franch

A novel C₁₉-diterpenoid alkaloid designated as tatsinine has been isolated from the roots of $\text{Delphinium}$$\text{tataienence}$ and its structure (3) has been derived from ¹H NMR and ¹³C NMR spectroscopic evidence.     

Organoborierung von alkinylstannanen: XV. Synthese von 1,2-dihydro-1,2,5-disilaborepinen

The reaction between 1,2-diethynyl-tetramethyldisilane (1) and two equivalents of diethylaminotrimethylstannane (2) leads to 1,2-bis(trimethylstannylethynyl)-tetramethyldisilane (3). The new alkyne derivative 3 reacts, already at room temperature, with trialkylboranes, R₃B (5) (R = Me, Et), quantitatively to give 1,1,2,2-tetramethyl-3,7-bis(trimethylstannyl)-4,5,6-trialkyl-1,2-dihydro-1,2,5-disilaborepines (6). The reaction is much slower with R = Prⁱ which allows detection of intermediates by NMR spectroscopy. All products are characterized by ¹H, ¹¹B, ¹³C, ²⁹Si and ¹¹⁹Sn NMR data.     

Novel rhodium-1,3-dialkyl-3,4,5,6-tetrahydropyrimidin-2-ylidene complexes as catalysts for arylation of aromatic aldehydes

Six new rhodium-tetrahydropyrimidin-2-ylidene complexes (2a–f) have been prepared and characterized by C, H, N analysis, ¹H NMR and ¹³C NMR. Phenylboronic acid reacts with aldehydes in the presence of a catalytic amount of the new rhodium(I)-carbene complexes, RhCl(COD)(1,3-dialkyl-3,4,5,6-tetrahydropyrimidin-2-ylidene), (2a–f), to give the corresponding secondary aryl alcohols in good yields (72–96%).     

Pseudapenes A–C,sesquiterpenoids from the marine-derived fungus Pseudallescheria apiosperma F52-1

Three sesquiterpenoids pseudapenes A–C (1–3) were isolated from the marine-derived fungus Pseudallescheria apiosperma F52-1. Pseudapene A (1) has an unprecedented 2-methyl-5-methylene-3-(2-methylbut-2-ene)-dicyclo(3, 3, 0)-octane carbon skeleton and pseudapenes B (2) and C (3) possess an unique 2-methyl-4-methylene-2-(2-methylpent-2-ene)-dicyclo(3, 2, 0)-heptane chemical scaffold. Their structures were determined by use of MS and NMR spectroscopic data, and ECD, optical rotation and ¹³C NMR calculations.     

One-pot efficient synthesis of novel fused pentacyclic indolopyridobenzimidazoles and pyridoimidazopyridoindoles from the reaction of pyranoindolones with 1,2-diaminobenzenes and 2,3-diaminopyridines

The synthesis of a number of novel, fully conjugated, planar pentacyclic 5H-indolo[3′,2′:4,5]pyrido[1,2-a][1,3]benzimidazoles (8) and 11H-pyrido[3″,2″:4′,5′]imidazo[1′,2′:1,6]pyrido[3,4-b]indoles (12) by a one-pot reaction of pyranoindolones with substituted o-phenylenediamines or 2,3-diaminopyridines is described. In the case of 2,3-diaminopyridines the reaction proceeds regioselectively affording only regioisomers 12. Structural assignments of the new compounds as well as complete assignment of ¹H and ¹³C NMR signals were based on the analysis of their ¹H and ¹³C NMR (1D and 2D), IR, MS and elemental analysis data. Plausible mechanisms are proposed.     

Enantioselective fluorescent sensors for amino acid derivatives based on BINOL bearing benzoyl unit

The derivatives of BINOL, (S)-1 and (R)-1, and their analogues have been prepared and the structures of these compounds have been characterized by IR, MS, ¹H, and ¹³C NMR spectroscopy and elemental analysis. The enantioselective recognition of these receptors has been studied by fluorescence titration and ¹H NMR spectroscopy. The receptors exhibited different chiral recognition abilities toward some enantiomers of chiral materials and formed 1:1 complexes between host and guest. Receptor (S)-1 or (R)-1 exhibits excellent enantioselective fluorescent recognition abilities toward amino acid derivatives.     

Structure elucidation and vasodilator activity of methoxy flavonols from Calycotome villosa subsp. intermedia

Two flavonols identified as 3,5,7,4′-tetrahydroxy-3′-methoxyflavone (1) and 3,5,7,4′-tetrahydroxy-8-methoxyflavone (2) were isolated from the seeds of Calycotome villosa subsp. intermedia. The structure elucidation of the isolated compounds was performed by the spectroscopic methods (UV, IR, ¹H NMR, ¹³C NMR and MS) and also by a single crystal X-ray analysis in the case of compound (2). Vasodilator activity of compound (2) was demonstrated in isolated rat aorta contracted with high KCl or with noradrenaline.     

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.     

Stibatriptycene

Stibatriptycene (1c) has been synthesized by cyclization of 9-(o-chlorophenyl)-9,10-dihydro-9-stibaanthracene (2c) with an excess of lithium piperidide. The general applicability of this ring closure reaction, first developed for the synthesis of phosphatriptycene (1a) and presumed to proceed by nucleophilic attack of a carbanionic centre on a (slowly generated) benzyne, has further been demonstrated by a new synthesis of the known arsatriptycene (1b) and by the synthesis of stibatriptycene (1c). The structure of 1c was confirmed by IR, ¹H NMR and, in particular, by ¹³C 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.     

Synthesis and crystal structure analysis of 2-(4-fluorobenzyl)-6-phenylimidazo[2,1-b][1,3,4]thiadiazole and its chlorophenyl derivative

Preparations of 2-(4-fluorobenzyl)-6-phenylimidazo[2,1-b][1,3,4]thiadiazole (3a) and its chlorophenyl derivative (3b) are described. Preliminary analysis was done spectroscopically by means of ¹H NMR, ¹³C NMR spectra, mass spectra and elemental analyses. Further the structures were confirmed by X-ray crystal structure analyses. The compound (3a) has crystallized in a triclinic P-1 space group with three independent molecules in the asymmetric unit, while the compound (3b) belongs to P2₁/c space group with one molecule in the asymmetric unit. The molecule (3b) differs from molecule (3a) by the presence of chlorine substituent. Additionally, the imidazo-thiadiazole entity is as usual planar. Intramolecular C–H⋯N hydrogen bonding between the imidazole and the phenyl ring of the molecule can be observed in (3a) & (3b). The molecules of (3a) are linked into two dimensional supramolecular hexagonal hydrogen bonded network sustained by C–H⋯F interaction, while those of (3b) are linked by bifurcated C–H⋯N interactions. Further, the molecular packing of both the compounds is stabilized by π–π stacking interactions between the benzene and imidazo-thiadiazole ring systems.