Crystal structure and conformation of 8-(2-hydroxyethylamino) and 8-(pyrrolidin-1-yl) adenosines

In the course of investigation of 8-alkylamino substituted adenosines, the title compounds were synthesized as potential partial agonists for adenosine receptors. The structure determination of these compounds was carried out with the X-ray crystallography study. Crystals of 8-(2-hydroxyethylamino)adenosine are monoclinic, space group P 2(1); a = 7.0422(2), b = 11.2635(3), c = 8.9215(2) A, beta = 92.261(1) degrees, V = 707.10(3) A3, Z = 2; R-factor is 0.0339. The nucleoside is characterized by the anti conformation; the ribose ring has the C(2')-endo conformation and gauche-gauche form across C(4')-C(5') bond. The molecular structure is stabilized by intramolecular hydrogen bond of N-HO type. Crystals of 8-(pyrrolidin-1-yl)adenosine are monoclinic, space group C 2; a = 19.271(1), b = 7.3572(4), c = 11.0465(7) A, beta = 103.254(2), V = 1524.4(2) degrees A3, Z = 4; R-factor is 0.0498. In this compound, there is syn conformation of the nucleoside; the ribose has the C(2')-endo conformation and gauche -gauche form across C(4')- C(5') bond. The molecular structure is stabilized by intramolecular hydrogen bond of O-HN type. For both compounds, the branching net of intermolecular hydrogen bonds occur in the crystal structures.     

The structure and antiviral activity of ribavirin analogs. III. Molecular and crystal structure of 1-(2-hydroxyethoxymethyl)-1,2,4-triazole-carboxamide

The crystal and molecular structure of a ribavirin acyclic analogue, 1-(2-hydroxyethoxymethyl)-1,2,4-triazole-3-carboxamide, has been determined by X-ray diffraction method. The space group is P1, unit cell parameters: a = 5,237, b = 6,960, c = 11,483 A, alpha = 93,89, beta = 97,43, gamma = 94,26 degrees; Z = 2. The structure was solved by the direct method and refined by least-squares procedure to R = 3.7%. Two molecular conformers statistically coexist in the unit cell, differing in the hydroxyethoxymethyl group conformation. Trans-conformation about O4'-C4' bond and gauche about C4'-C5' bond are observed in both molecules. C1'-O4' bond is approximately perpendicular to the aglicon.     

The structure and antiviral activity of ribavirin analogs. I. Molecular and crystal structure of 1-(2-hydroxyethoxymethyl)-1,2,4-triazole-5-carboxamide

The crystal and molecular structures of the antiviral compound 1-(2-hydroxyethoxymethyl)-1,2,4-triazole-5-carboxamide has been determined by the X-ray diffraction method. The space group is P2i/c, unit cell parameters a = 4,381, b = 18,679, c = 10,776 A, beta = 107,40 degrees, Z = 4. The structure was solved by the direct method and refined by a full-matrix least-squares procedure to R = 4.9%. Two planar groups of atoms can be distinguished in the molecule. The first group involves the atoms of triazole ring, C6, and C1', the second one contains C5, C6, O6 and N6 atoms. The angle between these planes is 5.6 degrees. The carboxyamide group is rotated by 180 degrees in comparison with this group in ribavirin. That is why the intramolecular hydrogen bond C1'-H1'. 1...O6 can form. Torsion angle O5'-C5'-C4'-O4' is 73.9 degrees and it corresponds to gauche-rotamer. The conformation about O4'-C4' bond is trans. The C1'-C4' bond is approximately perpendicular to the aglycone.     

The structure and antiviral activity of ribavirin analogs. II. Molecular and crystal structure of 1-(1,5-dihydroxy-3-oxapent-2-yl)-1,2,4-triazole-5-carboxamide

X-ray structure of the title compound, an antiviral agent moderately active towards Herpes simplex virus type 1, has been determined. The space group is P2i/n, unit cell parameters: a = 10,119, b = 7,529, c = 13,585 A, beta = 107,82 degrees, Z = 4. The structure was solved by the direct method and refined by least-squares procedure to R = 2.9%. The gauche-conformation about C4'-C5' bond and trans-conformation about O4'-C4' bond are realized in the molecule. The carboxyamide group at the C5 atom of triazol cycle provides a steric opportunity for the intramolecular hydrogen bond C1'-H1'...O6 formation.     

Variability in the backbone conformation of cyclic pentapeptides. Crystal structure of cyclic(Gly-L-Pro-D-Phe-Gly-L-Ala)

All the peptide bonds in cyclic(Gly-L-Pro-D-Phe-Gly-L-Ala) are in the trans conformation; however, the peptide bond C'5-N1 is twisted by 19 degrees from planarity (omega 5 = -161 degrees). A Type II beta-turn encompasses the L-Pro-D-Phe residues. Carbonyl oxygens O2, O4 and O5 are directed to the same side of the average plane through the backbone ring and they form hydrogen bonds with N3, N5 and N1, respectively, in adjacent molecules in a stacked column where the adjacent molecules are related by one translational unit. The conformation of the backbone is different from that established in other molecules with the DLDDL chirality sequence. The P21 cell contains two molecules of C21H26N5O5 with a = 4.836(2) A, b = 18.346(8) A, c = 12.464(5) A and beta = 100.05(4) degrees. The R factor for 1382 data with [F0[ greater than 1 sigma is 7.0%.     

Synthesis, crystal structure, and molecular conformation of peptide N-Boc-L-Pro-dehydro-Phe-L-Gly-OH

The peptide N-Boc-L-Pro-dehydro-Phe-L-Gly-OH was synthesized by the usual workup procedure and finally coupling the N-Boc-L-Pro-dehydro-Phe to glycine. The peptide crystallizes in monoclinic space group P2(1) with a = 8.951(4) A, b = 5.677(6) A, c = 21.192(11) A, beta = 96.97(4) degrees, V = 1069(1) A3, Z = 2, dm = 1.295(5) Mgm-3, and dc = 1.297(4) Mgm-3. The structure was determined by direct methods using SHELXS86. The structure was refined by the block-diagonal least-squares procedure to an R value of 0.074 for 1002 observed reflections. The C alpha 2-C beta 2 distance of 1.33(2) A is an appropriate double bond length. The angle C alpha 2-C beta 2-C gamma 2 is 133(1) degrees. The peptide backbone torsion angles are theta 1 = -167(1) degrees, omega 0 = 179(1) degrees, phi 1 = -48(1) degrees, psi 1 = 137(1) degrees, omega 1 = 175(1) degrees, phi 2 = 65(2) degrees, psi 2 = 15(2) degrees, omega 2 = -179(1) degrees, and phi 3 = -166(1) degrees. These values show that the Boc group has a trans-trans conformation while the peptide backbone adopts a beta-turn II conformation, which is stabilized by an intramolecular hydrogen bond of length of 3.05(1) A. The structures of dehydro-Phe containing peptides suggest that the dehydro-Phe promotes the beta-turn II conformation. The five-membered pyrrolidine ring of the Pro residue adopts an ideal C gamma-exo conformation with torsion angles chi 1(1) = -24(1) degrees, chi 2(1) = 34(1) degrees, chi 3(1) = -30(1) degrees, chi 4(1) = 15(1) degrees, and theta 0(1) = 6(1) degrees. The side-chain torsion angles in dehydro-Phe are chi 1(2) = -1(2) degrees, chi 2,1(2) = -176(1) degrees, and chi 2,2(2) = 8(2) degrees. The plane of C alpha 2-C beta 2-C gamma 2 is rotated with respect to the plane of the phenyl ring at 7(1) degrees, which indicates that the atoms of the side chain of dehydro-Phe are essentially coplanar. The molecules form a 2(1) screw axis related hydrogen-bonded rows along the b axis.     

A purine nucleoside unequivocally constrained in the syn form. Crystal structure and conformation of 8-(alpha-hydroxyisopropyl)-adenosine

Crystals of 8-(alpha-hydroxyisopropyl)-adenosine dihydrate, C13H19N5O5.2H2O, belong to the monoclinic space group P21. Cell dimensions are a = 8.259 (1), b = 11.117 (2), c = 9.663 (1) A, beta = 109.65 (2) degrees. Intensity data were collected on a four-circle diffractometer and the structure was solved by direct methods. Block diagonal least-squares refinement led to R = 0.031 for 1467 reflections. The glycosyl torsion angle chiCN is 241.4 degrees, corresponding to a syn conformation. The conformation of the exocyclic C(4')-C(5') bond is gauche-gauche and the sugar pucker is C(2') endo. It is considered that the bulky, tetrahedral, neutral 8-substituent, with an effective van der Waals radius of 3.5--4.0 A, provides an adenosine analogue which should exhibit the syn conformation about the glycosidic bond in solution as well as in solid state, irrespective of the nature of the sugar pucker. It should therefore be suitable for studies of interactions with enzyme systems requiring the anti conformation of the nucleoside or nucleotide.     

The structure of 2-methoxy-5-(2',3',4'-trimethoxyphenyl)tropone, an effective analog of colchicine

-Methoxy-5-(2',3',4'-trimethoxyphenyl) tropone is an active analog of colchicine, a mitotic spindle inhibitor, which is missing the middle "B" ring. This compound crystallizes in the triclinic system, space group P1, with Z = 2; a = 10.135(2), b = 10.166 (4), and c = 7.863(2) A; alpha = 82.15(3), beta = 103.49(3), and gamma = 107.16(2); degrees and V = 750.7(4) A. The structure was solved by direct methods and refined by full-matrix least-squares to a final R = 0.063, using 2503 observed reflections and 271 parameters. Despite the absence of the middle ring, the conformation of the molecule is similar to that of colchicine, isocolchicine , and their derivatives. The troponoid ring is dissimilar to the phenyl ring in that it is not aromatic and does have alternating short and long bond lengths. The dihedral angle between the least-squares planes of the two rings is -57.4 degrees. Van der Waals surface representations of the analog and colchicine are presented to demonstrate the similarity and differences of these two molecules . The structural information of the analog is consistent with the interpretation of thermodynamic parameters which govern the interactions between brain tubulin and the analog.     

Crystal structure of the topoisomerase II poison 9-amino-[N-(2-dimethylamino)ethyl]acridine-4-carboxamide bound to the DNA hexanucleotide d(CGTACG)2.

The structure of the complex formed between d(CGTACG)(2) and the antitumor agent 9-amino-[N-(2-dimethylamino)ethyl]acridine-4-carboxamide has been solved to a resolution of 1.6 A using X-ray crystallography. The complex crystallized in space group P6(4) with unit cell dimensions a = b = 30.2 A and c = 39.7 A, alpha = beta = 90 degrees, gamma = 120 degrees. The asymmetric unit contains a single strand of DNA, 1. 5 drug molecules, and 29 water molecules. The final structure has an overall R factor of 19.3%. A drug molecule intercalates between each of the CpG dinucleotide steps with its side chain lying in the major groove, and the protonated dimethylamino group partially occupies positions close to ( approximately 3.0 A) the N7 and O6 atoms of guanine G2. A water molecule forms bridging hydrogen bonds between the 4-carboxamide NH and the phosphate group of the same guanine. Sugar rings adopt the C2'-endo conformation except for cytosine C1 which moves to C3'-endo, thereby preventing steric collision between its C2' methylene group and the intercalated acridine ring. The intercalation cavity is opened by rotations of the main chain torsion angles alpha and gamma at guanines G2 and G6. Intercalation perturbs helix winding throughout the hexanucleotide compared to B-DNA, steps 1 and 2 being unwound by 8 degrees and 12 degrees, respectively, whereas the central TpA step is overwound by 17 degrees. An additional drug molecule, lying with the 2-fold axis in the plane of the acridine ring, is located at the end of each DNA helix, linking it to the next duplex to form a continuously stacked structure. The protonated N,N-dimethylamino group of this "end-stacked" drug hydrogen bonds to the N7 atom of guanine G6. In both drug molecules, the 4-carboxamide group is internally hydrogen bonded to the protonated N-10 atom of the acridine ring. The structure of the intercalated complex enables a rationalization of the known structure-activity relationships for inhibition of topoisomerase II activity, cytotoxicity, and DNA-binding kinetics for 9-aminoacridine-4-carboxamides.     

8-Chloroguanosine: solid-state and solution conformations and their biological implications

The three-dimensional structure of 8-chloroguanosine dihydrate was determined by X-ray crystallography. The crystals belong to the orthorhombic space group P2(1)2(1)2(1), and the cell dimensions are a = 4.871 (1) A, b = 12.040 (1) A, and c = 24.506 (1) A. The structure was determined by direct methods, and least-squares refinement, which included all hydrogen atoms, converged at R = 0.031 for 1599 observed reflections. The conformation about the glycosidic bond is syn with chi CN = -131.1 degrees. The ribose ring has a C(2')-endo/C-(1')-exo (2T1) pucker, and the gauche+ conformation of the -CH2OH side chain is stabilized by an intramolecular O-(5')-H...N(3) hydrogen bond. Conformational analysis by means of 1H NMR spectroscopy showed that, in dimethyl sulfoxide, the sugar ring exhibits a marked preference for the C(2')-endo conformation (approximately 70%) and a conformation about the glycosidic bond predominantly syn (approximately 90%), hence similar to that in the solid state. However, the conformation of the exocyclic 5'-CH2OH group exhibits only a moderate preference for the gauche+ rotamer (approximately 40%), presumably due to the inability to form the intramolecular hydrogen bond to N(3) in a polar medium. The conformational features are examined in relation to the behavior of 8-substituted purine nucleosides in several enzymatic systems, with due account taken of the steric bulk and electronegativities of the 8-substituents.     

Structural and conformational properties of (Z)-beta-(1-naphthyl)- dehydroalanine residue

To understand how chemical structure of beta-substituted alpha, beta-dehydroalanine (particularly size and pi conjugation of beta substituent) affects conformational property, x-ray crystallographic analysis was performed on Boc-Ala-Delta(Z) Nap-Val-OMe [Boc: t-butoxycarbonyl; Delta(Z) Nap: (Z)-beta-(1-naphthyl)dehydroalanine; OMe: methoxy] having the naphthyl group as a bulky beta substituent. Single crystals were grown by slow evaporation from an ethanol solution in the triclinic space group P1 with a = 9.528 (3) A, b = 12.410(4) A, c = 5.975(2) A, alpha = 96.77(3) degrees, beta = 102. 81(2) degrees, gamma = 88.74(3) degrees, V = 684.1(4) A3, and Z = 1. Phase determination was carried out by a direct method (SHELEXS), and the final structure was refined to R = 8.1% and R(w) = 9.0% for 1964 observed reflections. The bond lengths and bond angles of the Delta(Z)Nap residue, characterized by a sp(2) hybridized C(alpha) atom, did not differ from those of other dehydroresidues such as Delta(Z) Phe, Delta(Z) Leu, and DeltaVal essentially. The peptide backbone took a type II beta-turn conformation involving an intramolecular hydrogen bond between CO(Boc) and NH(Val), similar to di- or tripeptides containing a Delta(Z) Phe or Delta(Z) Leu residue in the second positions. Here the naphthyl group was found to be nonplanar [chi(2) = 55(1) degrees ] relative to the C(alpha)==C(beta)==C(gamma) plane. The nonplanarity was supported by conformational energy calculation. The molecular packing was stabilized by two kinds of intermolecular hydrogen bonds and van der Waals interactions. Naphthyl groups were arranged in a partially overlapped face-to-face orientation with a center-to-center distance of 5.97 A. For additional information, peptide Boc-(Ala-Delta(Z) Nap-Leu)(2)-OMe was synthesized and its solution conformation was investigated by (1)H-NMR spectroscopy. The hexapeptide showed the tendency to form a 3(10)-helical conformation in solution essentially. Conformational properties of Delta(Z) Nap residue, characterized by a type II beta-turn and 3(10)-helix, were supported by a conformational energy contour map of the Delta(Z)Nap residue.     

Crystal and molecular structure of methyl O-alpha-D-manno-pyranosyl-(1----2)-alpha-D-mannopyranoside

The crystal and molecular structure of a synthetic mannosyl disaccharide, methyl O-alpha-D-mannopyranosyl-(1----2)-alpha-D-mannopyranoside, has been determined from X-ray diffractometer data by direct methods by use of the Multan programs. The crystals are monoclinic, space group P2 with unit cell dimensions, a 8.086(1), b 9.775(1), c 9.975(2) A, beta 104.58(1) degrees, Z 2, and Dm 1.54 g/cm3. The structure was refined to an R-value of 0.033 for 1359 reflections measured with CuK alpha radiation. The mannopyranose units have the chair conformations 4C(D) with C-5' and C-2' deviating from the best plane through the other four atoms of the ring by -0.68 and +0.53 A in the nonreducing group, and C-3 and O-5 deviating from the mean plane through the other four atoms by +0.57 and -0.66 A, respectively, in the "potentially" reducing residue. The ring-to-ring conformation can be described as (phi, psi) = (-64.5, 105.5 degrees). The conformation across the C-5--C-6 bond is gauche-gauche in both the sugars. The crystal structure is stabilized by a network of intermolecular O-H...O hydrogen bonds.     

Synthesis, characterization and cytotoxicity of new platinum(IV) axial carboxylate complexes: crystal structure of potential antitumor agent [PtIV(trans-1R,2R-diaminocyclohexane)trans(acetate)2Cl2

A series of new platinum(IV) complexes of the type [PtIV(DACH)trans(L)2Cl2] (where DACH = trans-1R,2R-diaminocyclohexane, and L = acetate, propionate, butyrate, valerate, hexanoate, or heptanoate) bearing the carboxylate groups in the axial positions have been synthesized and characterized by elemental analysis, IR, and 195Pt NMR spectroscopy. The crystal structure of the analogue [PtIV(DACH)trans(acetate)2Cl2] was determined by single crystal X-ray diffraction method. There were two crystallographically independent molecules, both of which lie on crystallographic two-fold axes. The bond lengths and bond angles of both the molecules were the same within the experimental error. The compound crystallizes in the monoclinic space group C2, with a = 11.180(2) A, b = 14.736(3) A, c = 10.644(2) A, beta = 112.38(3) degrees, Z = 4 and R = 0.0336, based upon a total of 1648 collected reflections. In this complex, the platinum had a slightly distorted octahedron geometry owing to the presence of a geometrically strained five-member ring. The two adjacent corners of the platinum plane were occupied by the two amino nitrogens of DACH, whereas the other two equatorial positions were occupied by two chloride ions. The remaining two axial positions were occupied by the oxygens of acetate ligands. The DACH ring was in a chair configuration. An intricate network of intermolecular hydrogen bonds held the crystal lattice together. These analogues were evaluated in vitro and demonstrated cytotoxic activity against the human ovarian 2008 tumor cell line (IC50 = 0.001-0.06 microM). Structure-activity study revealed that activity was highest for the analogue where L = butyrate.     

Synthesis, crystal structure, and molecular conformation of N-Boc-L-Phe-dehydro-Leu-L-Val-OCH3

The peptide N-Boc-L-Phe-dehydro-Leu-L-Val-OCH3 was synthesized by the usual workup procedure and finally by coupling the N-Boc-L-Phe-dehydro-Leu-OH to valine methyl ester. It was crystallized from its solution in methanol-water mixture at 4 degrees C. The crystals belong to the triclinic space group P1 with a = 5.972(5) A, b = 9.455(6) A, c = 13.101(6) A, alpha = 103.00(4) degrees, beta = 97.14(5) degrees, gamma = 102.86(5) degrees, V = 690.8(8) A, Z = 1, dm = 1.179(5) Mg m-3 and dc = 1.177(5) Mg m-3. The structure was determined by direct methods using SHELXS86. It was refined by block-diagonal least-squares procedure to an R value of 0.060 for 1674 observed reflections. The C alpha 2-C beta 2 distance of 1.323(9) A in dehydro-Leu is an appropriate double bond length. The bond angle C alpha-C beta-C gamma in the dehydro-Leu residue is 129.4(8) degrees. The peptide backbone torsion angles are theta 1 = -168.6(6) degrees, omega 0 = 170.0(6) degrees, phi 1 = -44.5(9) degrees, psi 1 = 134.5(6) degrees, omega 1 = 177.3(6) degrees, phi 2 = 54.5(9) degrees, psi 2 = 31.1(10) degrees, omega 2 = 171.7(6) degrees, phi 3 = 51.9(8) degrees, psi T3 = 139.0(6) degrees, theta T = -175.7(6) degrees. These values show that the backbone adopts a beta-turn II conformation. As a result of beta-turn, an intramolecular hydrogen bond is formed between the oxygen of the ith residue and NH of the (i + 3)th residue at a distance of 3.134(6) A.(ABSTRACT TRUNCATED AT 250 WORDS)     

Shapes of carcinogenic benz[a]anthracenes: the crystal and molecular structure of 1-methylbenz[a]anthracene.

The crystal structure of 1-methylbenz[a]lanthracene, which is weakly carcinogenic, has been determined by application of direct methods to single-crystal X-ray diffractometric data and refined by least squares to R = 0.09 over 845 independent reflections. Crystals are monoclinic, space group P2(1), with a = 8.491(2), b = 7.138(2), c = 10.500(2)ABEta = 95.06(01), Z = 2. As in other benz[a]anthracenes, the K-region bond C(5)-C(6) is short [1.34(1)A]. The distinctive bay geometry, with a methyl group opposite to a hydrogen, H(12), peri to another hydrogen, H(11), has a long bond C(13)--C(18) = 1.47(1)A in the bay, and the angular benz-ring is inclined at 16.5 degrees to the mean plane of the anthracene fragment. The methyl carbon atom is 0.79 A out of the mean molecular plane (or 0.19 A out of the plane of the benz-ring) and the 1.50 A long C(1)-methyl bond makes angles of 117 degrees and 125 degrees at C(1).     

Investigation on the complex of diperoxovanadate with 2-(2'-pyridyl)-imidazole

A novel diperoxovanadate complex NH4[OV(O2)2{2-(2'-pyridyl)-imidazole}] x 4H2O was synthesized in aqueous solution under physiological conditions. The solution structure of the complex was characterized by multinuclear (1H, 13C, 14N, and 51V) as well as multi-dimensional (DOSY and C-H COSY) NMR techniques in the interaction system of NH4VO3/H2O2/2-(2'-pyridyl)-imidazole at room temperature. The crystal structure of the complex was determined at 173K by single-crystal X-ray diffraction method. It belongs to the monoclinic space group P21/c with a = 13.048(4), b = 6.984(2), c = 17.814(5) A, beta = 104.695(5), V = 1570.3(8) A3 and Z = 4. The crystal is composed of ammonium ions, {2-(2'-pyridyl)-imidazole}oxodiperoxovanadate(V) ions, and water molecules, which are held together by ionic and hydrogen bond forces. The metal atom in the complex is seven-coordinated with a distorted pentagonal bipyramidal geometry. It is the first mononuclear diperoxovanadate complex with a N, N'-chelating biheteroaromatic ligand and its 51V chemical shift is at the highest field among the known mononuclear diperoxovanadate(V) complexes.     

Structure and conformation of 1-beta-D-ribo furanosyl pyridin-2-one-5-carboxamide: an anti-inflammatory agent

The pyrimidine nucleoside, 1-beta-D-ribofuranosyl pyridine-2-one-5-carboxamide, is an anti inflammatory agent used in the treatment of adjuvant-induced arthritis. It is the 2-one isomer of 1-beta-D-ribofuranosyl pyridine-4-one 5-carboxamide, an unusual nucleoside isolated from the urine of patients with chronic myelogenic leukemia and an important cancer marker. Crystals of 1-beta-D-ribofuranosyl pyridine-2-one-5-carboxamide are monoclinic, space group C2, with the cell dimensions a = 31.7920(13), b = 4.6872 (3), c = 16.1838(11), beta = 93.071(3) degrees , V = 2408.2(2) A(3), D(calc) = 1.496 mg/m(3) and Z = 8 (two molecules in the asymmetric unit). The structure was obtained by the application of direct methods to diffractometric data and refined to a final R value of 0.050 for 1669 reflections with I >or= 3sigma. The nucleoside exhibits an anti conformation across the glycosidic bond (chi(CN) = -15.5 degrees , -18.9 degrees ), a C3 '-endo C2 '-exo [(3)(2)T] ribose pucker and g(+) across the C(4 ')-C(5 ') exocyclic bond. The amino group of the carboxamide group is distal from the 2-one and lacks the intramolecular hydrogen bonding found in the related 2-one molecule. Nuclear magnetic resonance studies shows also an anti conformation across the glycosidic bond but the solution conformation of the furanose ring is not the same as that found in the solid state.     

Coordination modes of the novel bifunctional nitrogen ligands 8-(2-pyridyl)quinoline and 8-(6-methyl-2-pyridyl)quinoline towards palladium and platinum. X-ray crystal structures of (8-(2-pyridyl)quinoline)Pd(Me)Cl, (8-(2-pyridyl)quinoline)-Pd(C(O)Me)Cl and (8-(2-pyridyl)quinoline)Pd(PEt3)Cl2

The coordination chemistry of the new bidentate nitrogen ligands 8-(2-pyridyl)quinoline (8-PQ) and 8-(6-methyl-2-pyridyl)quinoline (Me-8-PQ) towards palladium and platinum has been studied. Several (NN)Pd(R)Cl and (NN)Pd(alkene) complexes have been synthesized. The complex (8-PQ)Pd(Me)Cl has been characterised by a single crystal X-ray determination (crystal data triclinic space group

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). A fast CO insertion occurs into the palladium-carbon bond of the complexes (NN)Pd(Me)Cl providing the (NN)Pd(C(O)Me)Cl complexes. For (8-PQ)Pd(C(O)Me)Cl an X-ray structure determination has been carried out (crystal data: monoclinic space group P2₁/c with a=9.084(4), B=10.179(3), C=16.400(3) Å, β=95.59(2)°, V=1509.2(9) ų, R=0.043, Z=4). Unexpected in both molecular structures is the large dihedral angle between the plane of the bidentate nitrogen ligand and the coordination plane of the palladium. Both bidentate coordinating ligands 8-PQ and Me-8-PQ show a relatively large bite angle. A monodentate coordination mode has been observed for the complexes (NN)M(PEt₃)Cl₂ (M=Pd, Pt), as the pyridyl group of the ligand is coordinated to the metal while the quinoline group is dissociated from the metal, which is shown in the X-ray structure determination for the complex (8-PQ)Pd(PEt₃)Cl₂ (crystal data: monoclinic space group P2₁/a with A=15.736(2), B=7.782(1), C=18.255(3) Å, β=102.98(1)°, V=2178.3(6) ų, R=0.062, Z=4).     

Crystal structure of sodium isosaccharate, NaC6H11O6 x H2O

Sodium isosaccharate, NaC(6)H(11)O(6).H(2)O (Na-ISA), has been synthesized, and its crystal structure solved by single-crystal X-ray diffraction methods. Na-ISA crystallizes in the monoclinic space group P2(1) (#4) with cell parameters a = 9.2267(11) A, b = 5.0765(6) A, c = 9.7435(11) A, beta = 103.304(2) degrees, V = 444.13(9) A(3), Z = 2. The structure was refined by full-matrix least-squares on F2 yielding final R-values (all data) R1 = 0.0361 and Rw2 = 0.0935. The structure of Na-ISA consists of (C(6)H(11)O(6))(-) anions arranged in layers parallel to the bc plane. An extended network of O-H...O hydrogen bonds links the (ISA)(-) anions and the crystal water molecules. Each sodium atom is coordinated by four oxygen atoms belonging to four different (ISA)(-) anions and by one water molecule. The resulting NaO(5) polyhedra are linked by sharing common corners in zig-zag chains running parallel to the b-axis.     

Molecular structure of cyclo[-(D-Val-L-Hyi-L-Val-D-Hyi)2-] revealed by x-ray analysis.

The crystal structure of a synthetic analogue of valinomycin, cyclo[-(D-Val-L-Hyi-L-Val-D-Hyi)2-] (octa-meso-valinomycin) (I) (C40H68N4O12.1.5.C4H8O2, M(r) = 937.01 + 88.10), has been determined. Crystals grown from dioxane are monoclinic, space group P2(1)/a, with cell parameters a = 21.487 (8), b = 16.836 (5), c = 16.089 (4) A, beta = 111.70 (4), and Z = 4. The atomic coordinates for nonhydrogen atoms were refined in the anisotropic thermal motion approximation. H atom positions were included in the structure factor calculations at their geometrically expected positions. Values of the standard and weighted R factors after refinement are 0.11 and 0.13, respectively. The conformation of the depsipeptide crystallized from dioxane is different from that crystallized from chloroform (II). The molecule adopts a rectangular shape with two type IV beta-turns containing a hydrogen bond and possesses pseudorotational symmetry. The side chains are located on the molecular periphery. The orientation of the carbonyl groups of the molecule is not conducive for efficient metal-ion coordination and in the observed conformation cannot behave as an ionophore. In the crystal the molecules form infinite chains parallel to the c axis, and are stabilized by two intermolecular hydrogen bonds that are shorter and have better geometry than the intramolecular hydrogen bonds. A phi/psi plot for dodecadepsipeptides with a (DLLD)3 sequence has well-defined areas for Val and Hyi residues only in cases when the crystals have been grown from nonpolar or medium-polar solvents. The phi/psi plot for octadepsipeptides crystallized from chloroform (II) shows this behavior also.(ABSTRACT TRUNCATED AT 250 WORDS)