Rafael Tamazyan

Two-dimensionally modulated structure of the rare-earth polysulfide GdS2−x (x = 0.18 ≃ 13/72)

The crystal structure of GdS2−x is determined by single-crystal X-ray diffraction as a 144-fold superstructure of the ZrSSi structure type. The superstructure is described as a two-dimensional, commensurately modulated structure with the superspace group P4/n(αβ½)(00)(ss) and with α = 1/4 and β = 1/3. Structure refinements within the classical approach, employing the 144-fold supercell, fail because most of the superlattice reflections have zero intensities within the experimental resolution. Within the superspace approach the absent superlattice reflections are systematically classified as higher-order satellite reflections. Accordingly, the superspace approach has been used to refine the structure model comprising the basic structure positions and the amplitudes of the modulation functions of the three crystallographically independent atoms. The quality of fit to the diffraction data and the values of the refined parameters are independent of the assumption on the true symmetry (incommensurate or a 12 × 12 × 2, I-centred superlattice with different symmetries). Arguments of structural plausibility then suggest that the true structure is a superstructure with space group I\bar{4}, corresponding to sections of superspace given by (t1, t2) equal to [(4n − 1)/48, (4m − 3)/48] or [(4n − 3)/48, (4m − 1)/48] (n and m are integers). Analysis of the structure, employing both superspace techniques (t plots) and the supercell structure model all show that the superstructure corresponds to an ordering of vacancies and an orientational ordering of S_2^{2-} dimers within the square layers of the S2 atoms.

1-Substituted derivatives of 2-phenylpyrrolidine-2-carboxamide.

The structures of two potential anti-human immunodeficiency virus type 1 (HIV-1) non-nucleoside reverse transcriptase inhibitors (NNRTI), namely 1-(2-chlorobenzoyl)-2-phenylpyrrolidine-2-carboxamide, C(18)H(17)ClN(2)O(2), and 1-(2-furoyl)-2-phenylpyrrolidine-2-carboxamide, C(16)H(16)N(2)O(3), have been investigated by X-ray diffraction and the butterfly-like conformation established in each case. The pyrrolidine ring has the same half-chair conformation in both structures.

1-Substituted derivatives of 2-aryl-5-oxopyrrolidine-2-carboxylic acid

The structures of two potential anti-human immunodeficiency virus type 1 (HIV-1) non-nucleoside reverse transcriptase inhibitors (NNRTI), namely 1-benzyl-5-oxo-2-phenylpyrrolidine-2-carboxamide, C(18)H(18)N(2)O(2), (III), and 2-(4-isopropoxyphenyl)-5-oxo-1-(4-tolyl)pyrrolidine-2-carbonitrile, C(21)H(22)N(2)O(2), (IV), have been investigated by X-ray diffraction, confirming the butterfly-like conformation of both compounds. The pyrrolidine ring is in an envelope conformation in (III) and a half-chair conformation in (IV). Two intermolecular N[bond]H...O hydrogen bonds are present in the crystal structure of (III), with N...O distances of 2.995 (2) and 2.927 (2) A.

1,2,5-Substituted derivatives of 2-phenylpyrrolidine.

The structures of the potential anti-human-immunodeficiency virus type 1 (HIV-1) non-nucleoside reverse transcriptase inhibitors (NNRTI) 1-tert-butoxycarbonyl-2-phenylpyrrolidine-2-carboxylic acid, C(16)H(21)NO(4), (I), and 2-ammoniomethyl-1-benzyl-5-oxo-2-phenylpyrrolidine chloride, C(18)H(21)N(2)O(+).Cl(-), (II), have been investigated by X-ray diffraction. The investigations confirm a butterfly-like conformation for both compounds. In (I), the pyrrolidine ring has a marked half-chair conformation, while it has a weakly pronounced envelope conformation in (II). Intermolecular hydrogen bonds, viz. O-H.O in (I), and N-H.O and N-H.Cl in (II), build infinite chains in both structures. Rotational disorder of the three methyl groups is observed in (I).

Synthesis of new derivatives of 5-(3,4-dihydro-2Н-pyrrol-5-yl)-pyrimidine

By one-stage condensation of 6-(arylamino)pyrimidine-2,4(1Н,3Н)-diones with pyrrolidin-2-one new potential antiviral compounds were obtained, analogs of pyrrolinylpyrimidine containing structural fragments of known drugs AZT and HEPT used in treating HIV-infections.

One-step synthesis of pyrido[2,3-d]pyrimidines, amides, and benzoxazolylethylpyrimidine by condensation of substituted 3-(2-phenylpyrimidin-5-yl)propanoic acids with aromatic amines in polyphosphoric acid

Depending on the reactant structure, reactions of substituted 3-(2-phenylpyrimidin-5-yl)propanoic acids with 2-aminopyridine, p-toluidine, and 2-aminophenol in polyphosphoric acid afforded the corresponding N-(pyridin-2-yl)propanamides, 5-[2-(benzoxazol-2-yl)ethyl]pyrimidine, and pyrido[2,3-d]pyrimidinones.

1-Benzyl-6-phenyl­imino-5-(pyrrol-2-yl­idene)hexa­hydro­pyrimidine-2,4-dione

In the title compound, C21H20N4O2, a potential anti-human immunodeficiency virus type 1 (HIV-1) non-nucleoside reverse transcriptase inhibitor, the pyrrolidine ring adopts an envelope conformation, while the hydrogenated pyrimidine ring adopts a weakly expressed twist conformation. The molecules are connected into infinite chains via N—H⋯O hydrogen bonds.

1-(4-Bromo­benzo­yl)-2-phenyl­pyrrolidine-2-carboxamide

In the title compound, C18H17BrN2O2, which is a potential human immunodeficiency virus type 1 (HIV-1) non-nucleoside reverse transcriptase inhibitor, the pyrrolidine ring exhibits an envelope conformation. In the crystal structure, intermolecular N—H⋯O hydrogen bonds [N⋯O = 2.861 (3) Å] link the molecules into centrosymmetric dimers.

Novel route for the transformation of a pyrimidine ring using hydrazides

It has been shown from X-ray structural analytical data that the reaction of 2-ethoxycarbonylmethyl-1,4,6-trimethylpyrimidinium iodide with carboxylic acid hydrazides gives pyrazolo[1,5-a]pyrimidine derivatives and not the isomeric triazolo[4,3-a]pyridines previously reported. This novel and previously unreported rearrangement of 1,2-dialkylpyrimidinium salts occurs via recyclization of the pyrimidine ring with inclusion of a fragment of the nucleophilic reagent into the transformation product.

Synthesis and Structure of 5,5-Disubstituted N -[4-Methyl-3-phenylfuran-2(5 H )-ylidene]- N′ -phenylthioureas

The reaction of 5,5-disubstituted 4-methyl-3-phenyl-2,5-dihydrofuran-2-imines with phenyl isothiocyanate afforded N-[5,5-disubstituted-4-methyl-3-phenylfuran-2(5H)-ylidene]-N′-phenylthioureas.