Maureen F. Mackay

Synthesis and structure of bis(diethyldithiocarbamato)nitridotechnetium(V): a technetium–nitrogen triple bond

The title compound [Tc(S2CNEt2)2N] has been prepared by the reduction of [NH4][TcO4] with hydrazine followed by reaction with Na[S2CNEt2]. The crystal structure of [Tc(S2CNEt2)2N] has been determined by single-crystal X-ray diffraction methods at 17 °C. Crystals are monoclinic, space group P21/c, with a= 14.823(1), b= 9.159(1), c= 12.865(1)A, β= 107.98(1)°, and Z= 4. Diffractometry has provided significant Bragg intensities for 2 152 independent reflections and the structure has been refined by full-matrix least-squares methods to R 0.042. The compound, which is isostructural with the rhenium analogue, consists of discrete [Tc(S2CNEt2)2N] molecules, each containing a terminal N3– group. The technetium atom has a distorted square-pyramidal environment with the nitrogen atom in the apical position and four sulphur atoms forming the base. The TcN bond, which has not been observed before, has a length of 1.604(6)A, and the Tc–S bond distances range between 2.392(2) and 2.405(2)A.

Structure elucidation and absolute configuration of phomopsin a, a hexapeptide mycotoxin produced by phomopsis leptostromiformis

Abstract Phomopsin A, C36H45CIN6O12, the main mycotoxin isolated from cultures of Phomopsis leptostromiformis and the cause of lupinosis disease, is a linear hexapeptide containing 3-hydroxy-L-isoleucine, 3,4-didehydrovaline, N-methyl-3-(3-chloro-4,5-dihydroxyphenyl)serine, E-2,3-didehydroaspartic acid, E-2,3-didehydroisoleucine, and 3,4-didehydro-L-proline. The L-configuration of the indicated amino acids was established by a comparison of the N-trifluoroacetyl n-butylester derivatives of the acid hydrolysis products of phomopsin A with samples prepared from authentic amino acids, using capillary gas chromatography on a chiral stationary phase. The E configuration of the two 2,3-didehydro amino acids is based on the products obtained by catalytic hydrogenation and sodium borohydride reduction of phomopsin A followed by acid hydrolysis (for 2,3-didehydroisoleucine) or by analysis of the coupled 13C n.m.r. spectrum of phomopsin A (for 2,3-didehydroaspartic acid). Evidence is presented which shows that the glycine formed during the acid hydrolysis of phomopsin A is derived from the 3,4-didehydrovaline moiety. The sequence of the amino acids was established by heteronuclear 13C{1H} selective population inversion (SPI) experiments and by fast atom bombardment (f.a.b.) mass spectrometry of phomopsin A and its derivatives. An X-ray crystallographic study of phomopsin A confirmed the amino acid sequence and showed that the linear hexapeptide is modified by an ether bridge in place of the 5-hydroxy group of the N-methyl-3-(3-chloro-4,5-dihydroxyphenyl)serine and the hydroxy group of the 3-hydroxyisoleucine units. In addition, the X-ray study specified the absolute configuration of phomopsin A as 22E, 25E, 3R, 4S, 7S, 10S, 11S, 19S.

Bis (2-thio-5-nitropyridine)-S-di-n-butylstannane (IV): Crystal structure and spectroscopic studies

Abstract X-Ray analysis has defined the crystal structure of the title compound. The crystals are monoclinic and belong to the space group C2/c with cell dimensions, a = 21.731(8), b = 14.141(6), c = 7.648(5) A , β = 100.04(5) and Z = 4. The complex molecule has C2 symmetry; the S and C atoms bonded to the Sn form a distorted tetrahedral arrangement around the latter, with SnS and SnC bond distances of 2.477(3) and 2.162(11)A respectively. There is a short intramolecular contact between the Sn and N in the pyridine ring, of 2.77(1)A. IR and NMR spectral data have been interpreted on the basis of the X-ray structure; mass spectral data is predominantly influenced by strong tin-ligand bonding, reflecting a contribution by the Sn..... N interaction.

Preparation and structure of bis(tetraphenylarsonium) trans-aquatetracyanonitridotechnetate(V) pentahydrate. ESR studies of the [TcN(CN)4(OH2)]2-/[TcNCl4]-system

Abstract The reaction of (AsPh4)[TcNCl4] with KCN and added AsPh4Cl in CH3CN/H2O yields crystals of (AsPh4)2[TcN(CN)4(OH2)]·5H2O (1). The complex crystallises in the monoclinic space group P21/n with a=17.107(5), b=19.965(7), c=15.473(5)A, β= 101.70(2)° and Z=4. Refinement with 3212 data measured with Cu Kα radiation converged at R= 0.065. The geometry of the anion is distorted octahedral with a water molecule coordinated trans to the nitrido ligand (TcOH2, 2.56(1) A). The TcN distance is 1.60(1) A. ESR studies have established the presence of two paramagnetic intermediates in the conversion of [TcN(CN)4(OH2)]2− to [TcNCl]4− in HCl solutions.

Preparation and crystal structures of [AsPh4]4[Tc4N4O2(ox)6] and [AsPh4]2[TcO(ox)2(Hox)]·3H2O: technetium complexes containing quadridentate or unidentate oxalato ligands

The reaction of oxalic acid (H2ox) with [AsPh4][TcNCl4] and [NBu4][TcOCl4] in aqueous acetone yields crystals of [AsPh4]4[Tc4N4O2(ox)6](1) and, after precipitation with AsPh4Cl, [AsPh4]2[TcO(ox)2(Hox)]·3H2O (2) respectively. Complex (1) crystallises in the monoclinic space group P21/n with cell parameters a= 14.433(1), b= 13.229(1), c= 27.020(1)A, β= 92.90(1)°, and Z= 4. Refinement with data measured with Cu-Kα radiation converged at R= 0.069 for 3 076 observed reflections. The anion in (1) is a cyclic tetranuclear complex, [Tc4N4O2(ox)6]4–, with Ci point symmetry. Each technetium(VI) atom is co-ordinated by five oxygen atoms and one nitrogen atom to give a distorted octahedron. In each half of the anion, a quadridentate oxalato ligand forms a bridge between the two octahedra, each of which is also linked to an adjacent octahedron by the corner sharing of an oxo ligand. Two oxygen atoms of a bidentate oxalato ligand and a nitrido nitrogen complete the octahedral co-ordination in each polyhedron. The Tc ⋯ Tc spacings of 3.586(2) and 5.756(3)A preclude any Tc–Tc bonding. The monoclinic crystals of complex (2) belong to the space group P21/c with a= 16.495(3), b= 14.802(2), c= 21.805(4)A, β= 98.76(1)°, and Z= 4. Refinement with 5 099 observed data measured with Mo-Kα radiation converged at R= 0.059. The technetium(V) atom is co-ordinated by six oxygen atoms to give a distorted octahedron. The structure of the anion is unusual in that it contains a protonated unidentate oxalato ligand and that there is no appreciable lengthening of the Tc–O bond trans to the oxo ligand.

The X-ray structure of phomopsin A, a hexapeptide mycotoxin

A crystallographic study of phompsin A, the hexapeptide mycotoxin of Phomopsis leptostromiformis responsible for lupinosis disease in animals, has shown that it is a linear peptide, modified by an ether bridge in place of the hydroxy groups of the N-methyl-3-(3-chloro-4,5-dihydroxyphenyl)-3-hydroxyalanine and 3-hydroxyisoleucine units, and thus containing a 13-membered ring.

SYNTHESIS OF SOME ACRIDONE ALKALOIDS AND RELATED COMPOUNDS

Abstract An efficient Pd/C aromatization of 1,2,3,4,9,10-hexahydroacridine-1,9-diones to 1-hydroxyacridones is reported. The previously reported four-step synthesis of the diones has been extended to give a number of methoxy substituted derivatives and the aromatization reaction, along with hydrobromic acid demethylation, provides a useful route to various methoxy and hydroxy substituted acridones.

Crystal structures of (AsPh4)[TcO(SCOCOS)2] and (AsPh4)2[TcN(SCOCOS)2]. A comparison of the TcVO3+ and TcVN2+ cores in the same coordination environment

Abstract The reaction of potassium dithiooxalate in acetone with (AsPh4)[TcNCl4] in acetonitrile yields crystals of (AsPh4)2[TcN(SCOCOS)2] (1). We now report the X-ray structures of 1 and the oxo analogue (AsPh4)[TcO(SCOCOS)2] (2), both of which contain the technetium atom in the +5 oxidation state and in the same coordination environment. Crystals of 1 and 2 belong to the triclinic space group P 1 with Z=2. Unit cell parameters are: 1, a=14.225(5), b=17.778(2), c=10.993(3) A, α=101.52(2), β= 111.74(2), γ=100.68(2)° and 2, a=12.294(2), b=12.531(2), c=13.071(2) A, α=115.10(1), β= 114.22(1), γ=101.93(1)°. Refinement with data measured with Cu Kα radiation converged at R= 0.055 for 7569 observed data 1 and at R=0.041 for 4739 observed data 2. The technetium atoms in the complex anions are five-coordinate with the four sulphur atoms in the basal position and either the oxygen or nitrogen in the apical position, to give a distorted square-pyramidal environment about each technetium. The TcO and TcN bond lengths are 1.646(4) and 1.613(4) A in 1 and 2 respectively.

cis-Dihydrocatechols as precursors to highly oxygenated troponoids: a fully regiocontrolled synthesis of 3,4-dimethoxy-α-tropolone

The highly oxygenated α-tropolone antibiotic 3,4-dimethoxy-α-tropolone 3 has been synthesized in a fully regiocontrolled manner from commercially available cis-1,2-dihydrocatechol 5. Demethylation of 3,4-dimethoxy-α-tropolone 3 produced the potent antitumour agent 3,4-dihydroxy-α-tropolone 4.

The crystal and molecular structure of (-)-phaseollin

Abstract X-ray analysis has defined the molecular structure of (-)-phaseollin C 20 H 18 O 4 a pterocarpan with lipophilic antifungal activity, isolated from Phaseolus vulgaris L. The orthohombic crystals belong to the space group P2 1 2 1 2 1 with a =6.540(3), b = 12.975(6), c = 19.388(4) A and Z =4. The structure was solved by direct methods from diffractometer data measured with CuKα radiation, and refined to a final R index of 0.083 for the 992 observed terms. The molecular skeleton(I) has a cis B/C ring junction. Viewed down C(6B)-C(7) the conformation is staggered; ring C is envelope whereas ring B is skewed with C(6B) and C(7) lying respectively above and below the plane of the other ring atoms.