Elena B. Nikolaenkova

Effect of intramolecular hydrogen bond on the azide-tetrazole equilibrium of 5-(2′-hydroxyphenyl)tetrazolo[1,5-a]pyrimidine,-tetrazolo[1,5-c]pyrimidme, -tetrazolo[1,5-c]quinazoline, and 7-(2′-hydroxyphenyl)tetrazolo[1,5-c]pyrimidine

The intramolecular hydrogen bond between the phenolic hydroxyl and the pyrimidine nitrogen atom in the title compounds exerts a destabilizing effect on the tetrazole ring and shifts the azide-tetrazole equilibrium toward the azide form, especially in the case of tetrazolo[c]pyrimidine and -[c]quinazoline. It has been found that the introduction of a methoxy group into theortho-position of the phenyl fragment stabilizes the tetrazole tautomer more efficiently than introduction of this group into thepara-position.

Synthesis of 2-Aroyl(Hetaroyl)-1-Hydroxy- Imidazoles by the Interaction of Alkyl-Aromatic α-Hydroxyaminooximes with Aryl(Hetaryl)Glyoxals

The interaction of alkylaromatic and alkylheteroaromatic α-hydroxyaminooximes with aryl(hetaryl)-glyoxals hydrates produced a new series of 2-aroyl(hetaroyl)-5-aryl(hetaryl)-1-hydroxy-4-methylimid-azoles. The X-ray structural data for 2-benzoyl-5-(4-fluorophenyl)-1-hydroxy-4-methylimidazole are presented.

Synthesis of 2- and 4-chloropyrimidines with hydroxyphenyl substituents by the interaction of Vilsmeier-Haack reagents with (hydroxyphenyl)dihydropyrimidin-2- and -4-ones

The reaction of 2- and 4-hydroxypyrimidines containingortho- andpara-hydroxyphenyl substituents with Vilsmeier-Haack reagents generatedin situ from DMF and SOCl2 or POCl3 results in the chemoselective replacement of the heterocyclic hydroxyl group by chlorine and formylation of the phenolic hydroxyl group. Aryl formates are hydrolyzed under the conditions of their isolation to give the corresponding phenols, especially if the pyrimidyl fragment isortho to the formyloxy group.

Copper(II) complex with 6-(3,5-dimethyl-1H-pyrazol-1-yl)-2-(pyridin-2-yl)pyrimidin-4-amine: synthesis, crystal structure, and electronic spectroscopy

A copper(II) complex with 6-(3,5-dimethyl-1H-pyrazol-1-yl)-2-(pyridin-2-yl)pyrimidin-4-amine (L), [CuLCl2], has been synthesized. This compound is formed irrespective of the Cu : L molar ratio (Cu : L = 1 : 1, 2 : 1, and 20 : 1) in the MeOH/H2O/DMF mixture as a single product. ESI-MS data demonstrate that the additional amount of CuCl2 above the Cu : L = 1 : 1 molar ratio, is effectively solvated, and high-nuclearity species are formed in trace amounts in the solution. The complex adopts a distorted square-pyramidal geometry with two chlorides and three nitrogen atoms from L. The electronic spectrum of the complex contains a broad band with a maximum at 12,820 cm−1 within the region characteristic for square-pyramidal chromophores CuA5 (A = Cl, N). Due to Cu ··· Cl contacts, the molecules of [CuLCl2] form the dinuclear [CuLCl2]2 unit. Surprisingly, the NH2-group participates in the formation of NH ··· Cl hydrogen bonds instead of the formation of (NH ··· N3(pyrimidine))2 synthon, which is common for N-heteroaromatic compounds containing the NH2-group in the α-position to aza-atom. These hydrogen bonds together with Cu ··· Cl contacts result in the formation of a 3-D-structure.

2,6-Disubstituted 4-azidopyrimidines: synthesis, kinetic and thermodynamic studies of azide-tetrazole rearrangement by NMR spectroscopy

Thermodynamic and kinetic parameters of the tautomeric tetrazole-azide rearrangement for a series of 2,6-disubstituted 4-azidopyrimidines are determined by NOESY/EXSY and DNMR: ΔH = 15—28 kJ mol–1; ΔS = 47—65 J mol–1 К–1; Еa = 93—117 kJ mol–1; lgA = 15.1—18.9. They are dependent on electronic properties of the substituents and the polarity of solvent.

Synthesis of nucleosides containing a photolabile 2-(2-nitrophenyl)propoxycarbonyl group

At present, DNA biochips are widely used in medicine as diagnostic systems [1, 2]. Oligonucleotide biochips are often obtained with the aid of photolabile protecting groups [3–7]. The latter should be stable under the conditions of oligonucleotide synthesis but should be readily removed by photolysis without involving the protected moiety. A widely used photolabile protecting group is the o-nitrobenzyl group [3, 8–10]. The goal of the present work was to extend the series of nucleosides protected by the photolabile 2-(2-nitrophenyl)propoxycarbonyl group and containing readily removable protecting groups in the aromatic heteroring, which can subsequently be used in the design of oligonucleotide biochips. We have synthesized previously unknown nucleosides 4–7. Compounds 4 and 5 were obtained by acylation of 2′-deoxyguanosine and 2′-deoxyadenosine with phenoxyacetyl chlorides 1 and 2, respectively. Nucleosides 6 and 7 protected by photolabile 2-(2-nitrophenyl)propoxycarbonyl groups were synthesized by treatment of compounds 4 and 5, respectively, with 2-(2-nitrophenyl)propyl chloroformate (3) which was prepared as described in [10]. Compounds 6 and 7 were isolated as mixtures of diastereoisomers. ISSN 1070-4280, Russian Journal of Organic Chemistry, 2015, Vol. 51, No. 1, pp. 141–144.

Excitation-Wavelength-Dependent Emission and Delayed Fluorescence in a Proton-Transfer System

Manipulating the relaxation pathways of excited states and understanding mechanisms of photochemical reactions present important challenges in chemistry. Here we report a unique zinc(II) complex exhibiting unprecedented interplay between the excitation-wavelength-dependent emission, thermally activated delayed fluorescence (TADF) and excited state intramolecular proton transfer (ESIPT). The ESIPT process in the complex is favoured by a short intramolecular OH⋅⋅⋅N hydrogen bond. Synergy between the excitation-wavelength-dependent emission and ESIPT arises due to heavy zinc atom favouring intersystem crossing (isc). Reverse intersystem crossing (risc) and TADF are favoured by a narrow singlet-triplet gap, ΔEST ≈10 kJ mol-1 . These results provide the first insight into how a proton-transfer system can be modified to show a synergy between the excitation-wavelength-dependent emission, ESIPT and TADF. This strategy offers new perspectives for designing ESIPT and TADF emitters exhibiting tunable excitation-wavelength-dependent luminescence.

Synthesis of 2-(3,4,5-trimethoxybenzoyl)-4(5)-phenyl-1H-imidazole

The condensation of (2E)-N-hydroxy-2-hydroxyimino-2-phenylethanamine with 3,4,5-trimethoxyphenylglyoxal afforded (1-hydroxy-5-phenyl-1H-imidazol-2-yl)phenylmethanone which reacted with trimethyl phosphite or chloroacetone to give 2-(3,4,5-trimethoxybenzoyl)-4(5)-phenyl-1H-imidazole.

Photogenerator of trichloroacetic acid as a promising detritylation agent for oligonucleotide microarray synthesis

Abstract[[4-(4-Methoxyphenyl)-2,6-dinitro-phenyl](phenyl)methyl]-2,2,2-trichloroacetate, which generates trichloroacetic acid when irradiated with light of 405 nm wavelength, has been studied as a detritylation agent in the oligonucleotide microarray synthesis. This agent was shown to be suitable for the deprotection of the 4,4′-dimethoxytrityl group during the solid phase oligonucleotide synthesis.

Synthesis of 4-(4-methoxyphenyl)-2,6-dinitrobenzaldehyde

Photoacid generators capable of undergoing decomposition under irradiation with visible light are very important for efficient oligonucleotide microarray fabrication. In this case, there are no detrimental effect of UV irradiation on growing oligonucleotide chain and related side reactions leading to degradation of targeted oligonucleotides [1, 2]. An important intermediate product in the synthesis of photoacids necessary for the preparation of oligonucleotide bioarrays is 4-(4-methoxyphenyl)-2,6-dinitrobenzaldehyde, which was previously synthesized by oxidation of 2-bromomethyl-5(4-methoxyphenyl)-1,3-dinitrobenzene (I) with bis(tetrabutylammonium) dichromate on prolonged heating in boiling chloroform; however, the yield of II was as poor as 23% [2]. The goal of the present work was to develop a procedure which could be the most convenient for the preparation of 4-(4-methoxyphenyl)2,6-dinitrobenzaldehyde. The transformation of benzyl halides into the corresponding aldehydes is widely used in synthetic organic chemistry [3–5]. Benzyl halides can be converted into aldehydes via oxidation according to Kornblum [4]. However, the Kornblum oxidation of benzyl bromide I in DMSO in the presence of NaHCO3 (Scheme 1) gave a mixture of aldehyde II and alcohol III at a ratio of ~2 : 1 (cf. [6]). By oxidation of that mixture with pyridinium chlorochromate (PCC) in methylene chloride we succeeded in obtaining aldehyde II in 90% yield. Variation of the reaction conditions made it possible to synthesize alcohol III in 94% yield from compound I, and the subsequent oxidation of III with PCC quantitatively afforded aldehyde II. In addition, benzyl halides can be converted into aldehydes according to Krohnke [5]. The reaction of pyridinium salt IV with N,N-dimethyl-4-nitrosoaniline hydrochloride and subsequent hydrolysis of Schiff ISSN 1070-4280, Russian Journal of Organic Chemistry, 2013, Vol. 49, No. 7, pp. 1089–1091.