(5Z)‐4‐Amino‐2‐(4‐hydroxyphenyl)‐1H‐imidazol‐5(2H)‐one oxime 3‐oxide

The title molecule, C₉H₁₀N₄O₃, consists of benzene and imidazole rings which are almost perpendicular to each other. A hydroxyimino group is directly linked to the imidazole ring with a double C=N bond, which is the first example in this type of compound. The double bond may be a good location for the initiation of various reactions with a wide range of potential applications. In the crystal structure, there are π–π interactions between molecules related by a centre of symmetry, with the imidazole and benzene rings almost completely overlapped. The molecules are hydrogen bonded in each direction and form a three‐dimensional hydrogen‐bond network.     

Synthesis of oligomers of trans-(4S,5R)-4-carboxybenzyl 5-methyl oxazolidin-2-one: an approach to new foldamers.

The synthesis of two oligomers containing three and four residues, respectively, of trans-(4S,5R)-4-carboxy 5-methyloxazolidin-2-ones is described. The monomer is obtained by starting from benzyl-N-Boc-(3R)-aminobutanoate, by cyclization into the corresponding trans-(2S,3R)-2-carboxybenzyl-3-methyl-N-Boc-aziridine and rearrangement of the product to trans-(4S,5R)-4-carboxybenzyl-5- methyloxazolidin-2-one, catalyzed by Sn(OTf)2. The oligomers are synthesized by activating the carboxy group as its pentaflourophenyl ester. The trimer and the tetramer are obtained in good yield, and their 1H NMR spectra suggest that these molecules fold in ordered structures, where the C-4 hydrogen of a ring is always close to the carbonyl of the next ring. This result shows that the 4-carboxy-5-substituted-oxazolidin-2-ones are a new class of pseudoprolines which fully control the formation of a Xaai-1-Proi peptide bond in the trans conformation and are complementary to the pseudoprolines obtained from cyclocondensation of cysteine, serine, or threonine and aldehydes or ketones, which strongly favor the Xaai-1-Proi peptide bond in the cis conformation.     

N‐{(1E)‐Amino­[3‐methyl‐5‐(4‐methyl­phenyl)‐4,5‐di­hydro‐1H‐pyrazol‐1‐yl]­methyl­ene}‐1H‐imidazole‐1‐carbox­amide

In the title compound, C₁₆H₁₈N₆O, an N‐carbonyl­imidazole derivative of pyrazoline‐1‐carboximid­amide, the π‐electron density of the N atom in the 1‐position on the pyrazoline ring is delocalized through the amidine moiety and the adjacent carbonyl group. The imidazole ring, though coplanar with the rest of the mol­ecule, is deconjugated. The pyrazoline ring adopts a flat‐envelope conformation, having the substituted phenyl ring oriented perpendicular to the mean plane of the heterocycle. Both of the two potential hydrogen‐bond donors are involved in intramolecular hydrogen‐bonding interactions.     

Efficient and beta-Stereoselective Synthesis of 4(5)-(beta-D-Ribofuranosyl)- and 4(5)-(2-Deoxyribofuranosyl)imidazoles(1)

A synthetic route to 4(5)-(beta-D-ribofuranosyl)imidazole (1), starting from 2,3,5-tri-O-benzyl-D-ribose (5), was developed via a Mitsunobu cyclization. Reaction of 5 with the lithium salt of bis-protected imidazole afforded the corresponding 5-ribosylimidazole 7RS. Hydrolysis of 7RS gave a 1:1 mixture of diol isomers 8R and 8S having an unsubstituted imidazole. Mitsunobu cyclization of the mixture 8RS using N,N,N',N'-tetramethylazodicarboxamide and Bu(3)P exclusively afforded benzylated beta-ribofuranosyl imidazole 9beta in 92% yield, accompanied by alpha-anomer 9alpha, in a ratio of 26.3:1. The configuration of 9beta was established by X-ray crystallography of ethoxycarbonyl derivative 10beta. Reductive debenzylation of 9beta over Pd/C was carried out, and the synthesis of 1 was attained from starting 5 in four steps and 87% overall yield. This synthetic methodology was extended to the synthesis of 4(5)-(2-deoxy-beta-D-ribofuranosyl)imidazole (2). Mitsunobu cyclization of a 1:1 mixture of the corresponding diol isomers 14RS produced 15beta and 15alpha in a ratio of 5.4:1. The synthesis of 2 was attained in a 59% overall yield from the starting 3,5-di-O-benzyl-2-deoxy-D-ribose (12). beta-Stereoselective glycosylation in the key step is discussed and explained by intramolecular hydrogen bonding between an NH in the imidazole and the oxygen functional group in the sugar moiety.     

Synthesis and luminescence properties of anhydrides and N-phenylimides of substituted 4-(5-phenyl-2-oxazolyl)-naphthalic acids

Anhydrides and N-phenylimides of 4-(5-phenyl-2-oxazolyl)naphthalic acids with various substituents in the para position of the phenyl ring were synthesized. Electron-donor substituents, particularly the dimethylamino group, induce an appreciable long-wave shift of the absorption maxima and the luminescence due to their interaction with the carbonyl group of the peri-anhydride grouping. A large Stokesian shift and a high photoluminescence quantum yield are characteristic for the dimethylamino-substituted anhydrides.     

Synthesis and properties of analogs of 5(4)-aminoimidazole-4(5)-carboxamide and purines. 14. Acylation of 5(4)-aminoimidazole derivatives

The acylation of 5(4)-aminoimidazole derivatives was studied. It is shown that acylation by means of carboxylic acid anhydrides and chlorides takes place at the amino group, whereas acylation by means of chlorocarbonic acid esters takes place at the nitrogen atoms of the imidazole ring. Methods for the selective introduction of a carbomethoxy group in the 1, 3, and 5 positions of the 5(4)-aminoimidazole-4(5)-carboxamide molecule were developed.See [1] for communication 13.Deceased.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 247–252, February, 1984.     

Synthesis and Crystal Structure of Ethyl 1-（2-bromoethyl）-3-（4-meth-oxyphenyl）-1H-pyrazole-5-carboxylate

The title compound ethyl 1-(2-bromoethyl)-3-(4-methoxyphenyl)-1H-pyrazole-5-carboxylate 1 has been synthesized and structurally characterized by single-crystal X-ray diffraction.The crystal is of monoclinic(C15H17BrN2O3,Mr = 353.22),space group C21 with a = 24.691(7),b = 6.7678(17),c = 17.884(5) ,β = 97.184(5)o,V = 2965.1(13) 3,Z = 8,Dc = 1.583 g.cm-3,F(000) = 1440,μ = 2.784 mm-1,the final R = 0.0260 and wR = 0.0596 for 2684 observed reflections with I > 2σ(I).All the carbon atoms in the molecule are nearly coplanar except C(15),with a large conjugated system among the carbonyl group,pyrazole ring and the benzene ring.Three non-classical intermolecular hydrogen bonds help to stabilize the crystal lattice.The regioselectivity was rationalized based on the coordination of potassium ion with the N-anion and the carbonyl oxygen atom.     

Vergleich der Produkte aus der Reaktion von Phenylguanidin-Derivaten mit β-Ketoestern bzw. Propiolsäureestern (Synthese von Pyrimidonen)

Comparison of reaction products afforded by phenylguanidine derivatives with β-ketoesters or propiolic esters, respectively (synthesis of pyrimidones). 2-Anilino-imidazolines, when treated with either β-ketoesters or propiolic esters, yield two isomeric groups of pyrimidones. The isomerism is based on different positions of the carbonyl group in the pyrimidone ring. The mass spectra permit an unequivocal assignment of constitution I to the product formed with β-ketoesters and of constitution V to that formed with propiolic esters. Additionally, 2-(2-amino-anilino)-2-imidazoline (XII) when treated with methyl phenylpropiolate yields IX; while treatment with ethyl benzoylacetate yields XIII as an intermediate, which eliminates spontaneously one molecule of water to give the benzimidazole derivative XIV. Phenylguanidines (XV) add propiolic esters in the same way as do imidazoline derivatives. Photochemical cleavage of two carbon atoms with their adherent hydrogen atoms from the imidazole ring of the pyrimidones (V) leads to aminopyrimidine derivatives, e.g. XVI.     

Decomposition of oroidin in DMSO/TFA

Oxidative cyclization of the pyrrole-imidazole alkaloids oroidin and sventrin in DMSO/TFA (1:1) yields oxazolines via nucleophilic attack of the carbonyl oxygen at the alkenyl double bond. Oxidation takes place in the benzylic position of the imidazole ring. On prolonged reaction times, the oxazoline ring is hydrolyzed yielding the corresponding ester of pyrrole-2-carboxylic acid containing a free amino group. Overall, the double bond of oroidin is dioxygenated.     

Spectroscopic characterization of the 1-substituted 3,3-diphenyl-4-(2'-hydroxyphenyl)azetidin-2-ones: application of (13)C NMR, (1)H-(13)C COSY NMR and mass spectroscopy

The article deals with spectroscopic characterization of azetidin-2-ones. The presence of substituents like hydroxyl, fluoro, methoxy and benzhydryl, etc., on the azetidin-2-one ring significantly affects the IR absorption and (13)C NMR frequencies of the carbonyl group present in these compounds. The presence of an ester carbonyl group or too many methine protons in the molecule has been observed to limit the scope of IR and (1)H NMR spectroscopy in unambiguous assignment of the structure. The application of (13)C NMR, 2D NMR ((1)H-(13)C COSY) and mass spectroscopy in characterization of complex azetidin-2-ones is discussed. An application of the latter two techniques is described in deciding unequivocally between an azetidin-2-one ring and chroman-2-one ring structure for the product obtained by treatment of the 1-substituted 3,3-diphenyl-4-[2'-(O-diphenylacyl)hydroxyphenyl]-2-azetidinones with ethanolic sodium hydroxide at room temperature.     

Characterization of highly unusual NH+-O hydrogen bonding to ester ether oxygen atoms through spectroscopic and computational studies

We characterize a highly unusual, charged NH-O hydrogen bond formed within esters of 8-(dimethylamino)naphthalen-1-ol in which an ammonium ion serves as an intramolecular hydrogen bond donor to spatially proximate ester ether oxygen atoms. Infrared spectroscopic analysis of the ester carbonyl frequencies demonstrates significant blue-shifting when ether hydrogen bonding is possible, in stark contrast to the more commonly observed red shift that occurs upon hydrogen bonding to the ester carbonyl oxygen. The intrinsic behavior of the linkage (i.e., in which counterions and solvent effects are eliminated) is provided by vibrational predissociation spectroscopy of the isolated gas-phase cations complexed with weakly bound D(2) molecules.     

Coordination properties of 4(5)-hydroxymethylimidazole and 4(5)-hydroxymethyl-5(4)-methylimidazole towards cobalt(II) ions

Two new complexes of imidazole alcohols, 4-hydroxymethylimidazole (4-CH₂OHim) and 4-hydroxymethyl-5-methylimidazole (4-CH₂OH-5-CH₃im), with cobalt(II) of formula [CoL₂(H₂O)₂](NO₃)₂ were obtained. These compounds were described through single X-ray diffraction studies, spectroscopic (Ir. Far-IR, UV-Vis-NIR) and magnetic measurements. In the present complexes imidazole ligands are bidentate coordinating the heterocyclic ring through pyridine-like nitrogen and the oxygen atom of the hydroxymethyl group (chromophore CoN₂O₄). The shape of Co(II) coordination polyhedra is that of a distorted octahedron, with the equatorial plane defined by the 4-CH₂OHim (or 4-CH₂OH-5-CH₃im) bidentate ligands and two water molecules occupying axial positions (i.e. trans to each other). Formation of successive cobalt(II) complexes with 4-CH₂OH-5-CH₃im in aqueous solution was followed quantitatively by potentiometry.     

Gas-phase structure of protonated histidine and histidine methyl ester: combined experimental mass spectrometry and theoretical ab initio study

Gas-phase H/D exchange experiments with CD3OD and D2O and quantum chemical ab initio G3(MP2) calculations were carried out on protonated histidine and protonated histidine methyl ester in order to elucidate their bonding and structure. The H/D exchange experiments show that both ions have three equivalent fast hydrogens and one appreciably slower exchangeable hydrogen assigned to the protonated amino group participating in a strong intramolecular hydrogen bond (IHB) with the nearest N(sp2) nitrogen of the imidazole fragment and to the distal ring NH-group, respectively. It is taken for granted that the proton exchange in the IHB is much faster than the H/D exchange. Unlike in other protonated amino acids (glycine, proline, phenylalanine, tyrosine, and tryptophan) studied earlier, the exchange rate of the carboxyl group in protonated histidine is slower than that of the amino group. The most stable conformers and the enthalpies of neutral and protonated histidine and its methyl ester are calculated at the G3(MP2) level of theory. It is shown that strong intramolecular hydrogen bonding between the amino group and the imidazole ring nitrogen sites is responsible for the stability and specific properties of the protonated histidine. It is found that the proton fluctuates between the amino and imidazole groups in the protonated form across an almost vanishing barrier. Proton affinity (PA) of histidine calculated by the G3(MP2) method is 233.2 and 232.4 kcal mol(-1) for protonation at the imidazole ring and at the amino group nitrogens, respectively, which is about 3-5 kcal mol(-1) lower than the reported experimental value.     

Crystal structure of 4,5-bis(4-dimethylaminophenyl)-2-(4-nitrophenyl)imidazole.

A nonlinear optical chromophore, 4,5-bis(4-dimethylaminophenyl)-2-(4-nitrophenyl)imidazole, was investigated by X-ray crystallography. The study focused on coplanarity among several aromatic rings, including phenyls and imidazole. Two phenyl rings with NMe2 groups are twisted by 46.39(3) degrees from each other. However, they are twisted by 23.05(5) degrees and 46.84(3) degrees from the imidazole, respectively. These unequal twists were elucidated by different conjugation pathways from the donors to the acceptor. The phenyl ring with the NO2 group is twisted by only 6.76(6) degrees from the imidazole.     

Strong overcrowding in dimethyl 2‐(dimethylamino)terephthalate

The molecular structure of the title compound, C₁₂H₁₅NO₄, has several features related to steric hindrance due to the ester and dimethylamine groups being located ortho with respect to one another. In particular, the carbonyl group of the ester is not coplanar with the ring, the amine N atom is in a pyramidal arrangement [the N atom is 0.2161 (12) Å from the three C atoms to which it is bonded] and the C atom of the adjacent ester group lies 0.3784 (14) Å out of the plane of the aromatic ring. The deformations found in the X‐ray structure have been confirmed by ab initio quantum mechanical calculations.     

Crystal Structure of Ethoxyethyl 3-(2-Chloro-5-pyridyl methylamino)-2-cyano-4-methylpent-2-enoate

1 INTRODUCTION The nature and topography of the herbicide binding site in the reaction center of photosystem Ⅱ (PSⅡ) have been the subject of intense interest for many years. Among several commercially important herbicides with different structures such as atrazine and polypeptide of the PSII reaction center[1], the cyanoacrylates with general structure 1 have proved hightly potent and useful as probes[2, 3] of the receptor because their activities as inhibitors of photosynthetic ele…     

Polyfluorination using IF(5)

The polyfluorination of α-(arylthio)carbonyl compounds was achieved by a successive application of polyfluorination using IF(5), Friedel-Crafts arylation, and desulfurizing fluorination using IF(5). Three to six fluorine atoms were selectively introduced to the carbons located between the aromatic ring and the carbonyl group.     

聚4-甲基-5-乙烯基噻唑键合硅胶柱的选择性研究

 较为系统地研究了聚4甲基5乙烯基噻唑键合硅胶固定相(PMVCAphase)与C18,C8及苯基柱在反相色谱中甲醇水体系下的选择性差别。结果表明,该固定相与常用反相色谱固定相有相似性,显示了一般反相色谱固定相填料的特性;另一方面,又由于其特殊结构,更多地显示了其在反相色谱上的特殊选择性。     

Neutral loss of water from the b ions with histidine at the C-terminus and formation of the c ions involving lysine side chains

Neutral loss of water from the amide bond induced by the His side chain has been reported. The proposed fragmentation pathway is a retro-Ritter reaction catalyzed by the imidazole nitrogen. In our MS/MS study of the neuropeptide GAHKNYLRFamide, we observed that the neutral loss of water from the b(3) ion is abundant. The b(3) ion has a His residue at the C-terminus. As reported previously, in the b ions with His at the C-terminus, the imidazole residue is connected to the carbonyl carbon to form a five-membered ring. Therefore, it is unlikely that the neutral loss of water from the b(3) ion is catalyzed by the imidazole nitrogen. Through MS2 and MS3 studies of a synthetic peptide standard AGHKLL and its chemically labeled and isotope-encoded forms, we discovered that the water loss from the b(3) ion involves the carbonyl group of His, the hydrogen connected to the alpha-carbon of Gly, and the amide hydrogen of His. We also discovered the formation of an unusual c(x) ion in peptides with a Lys or Arg residue at the (x + 1) position of the peptide.     

Methyl 3‐para‐anisyl‐4‐(2‐hydroxy­benzoyl)­isoxazole‐5‐carboxyl­ate

The title compound, C₁₉H₁₅NO₆, contains a planar isoxazole ring. An intramolecular hydrogen bond is formed between the OH group attached to a phenyl ring and a carbonyl O atom.