X-ray crystallographic structure of a teixobactin analogue reveals key interactions of the teixobactin pharmacophore.

The X-ray crystallographic structure of a truncated teixobactin analogue reveals hydrogen-bonding and hydrophobic interactions and a cavity that binds a chloride anion. Minimum inhibitory concentration (MIC) assays against Gram-positive bacteria correlate the observed structure with antibiotic activity.

Synthesis of arene-soluble mixed-metal uranium/zirconium complexes using the dizirconium nonaisopropoxide ligand.

The utility of polydentate monoanionic [Zr(2)(O(i)Pr)(9)](-) (dzni) in generating arene-soluble, mixed-metal Zr/U complexes is described. K[Zr(2)(O(i)Pr)(9)] reacts readily with UI(3)(THF)(4) to form [Zr(2)(O(i)Pr)(9)]UI(2)(THF), 1, in >90% yield. The integrity of the [[Zr(2)(O(i)Pr)(9)]U](2+) unit in 1 was examined by the reaction of 1 with K(2)C(8)H(8), which formed the organometallic complex [Zr(2)(O(i)Pr)(9)]U(C(8)H(8)), 2. In contrast, the reaction of K[Zr(2)(O(i)Pr)(9)] with UCl(4) did not form U(IV)-dzni complexes, and only the ligand exchange product, [UCl(2)(O(i)Pr)(2)(DME)](2), 3, was isolated. The effect of the dzni ligand on the electrochemistry and near-infrared spectroscopy of U(III) is also described.

Intramolecular ditryptophan crosslinks enforce two types of antiparallel beta structures.

BACKGROUND: Two types of biaryl crosslinks can be formed with natural protein sidechains: ditryptophan and dityrosine. Biaryl crosslinks have the same topology as disulfide crosslinks, yet little is known about their effect on local peptide structure. RESULTS: Three ditryptophan-linked peptide dimers based on the sequence Ac-Leu-Trp-Ala-COX were prepared. The tripeptide dimer with -CONH(2) termini was too insoluble to study, but the tripeptide dimer with -COOMe termini crystallized from methanol/chloroform as an antiparallel beta-sheet. The tripeptide dimer with a -CONMe(2) termini adopted a slipped antiparallel beta structure in methanol/chloroform. CONCLUSIONS: These results suggest that intermolecular ditryptophan crosslinks that join the middle of peptide chains can confer a preference for antiparallel beta-sheet structure. The effect is most dramatic when both the inside and outside edges of the dimer can form hydrogen bonds as in the crystal structure of dimer 3b.

Synthesis and structure of tris(alkyl- and silyl-tetramethylcyclopentadienyl) complexes of lanthanum.

In efforts to make sterically crowded tris(peralkylcyclopentadienyl) complexes of lanthanum for the exploration of sterically induced reduction chemistry with a diamagnetic system, the synthesis of (C(5)Me(4)R)(3)La complexes has been pursued with R = Me, Et, (i)Pr, and SiMe(3). The complexes were synthesized in four steps: reaction of LaCl(3) with KC(5)Me(4)R to form (C(5)Me(4)R)(2)LaCl(2)K(THF)(2), addition of allylmagnesium chloride to make (C(5)Me(4)R)(2)La(C(3)H(5)), protonolysis with Et(3)NHBPh(4) to make [(C(5)Me(4)R)(2)La][BPh(4)], and finally the replacement of BPh(4)(-) with C(5)Me(4)R(-) using KC(5)Me(4)R to make (C(5)Me(4)R)(3)La. X-ray crystallographic data were obtainable on the (C(5)Me(4)R)(3)La complexes for R = Me, Et, (i)Pr, and SiMe(3). In each complex, the three C(5)Me(4)R ring centroids define a trigonal planar geometry around La. The average La-(ring centroid) distances are 2.64, 2.65, 2.66, and 2.69 A for the Me, Et, (i)Pr, and SiMe(3) structures, respectively, with La-C distances ranging from 2.857 (3) to 3.029 (2) A. Despite the steric crowding, ligand exchange can be observed by NMR spectroscopy.

Metallocyclic receptors with Re(I)/Os(II)-based moieties: molecular photophysics and selective molecular sensing.

New metallocyclic Re(I) and Os(II) complexes with polyphosphane/polyyne spacers, including dimers [(Re(CO)3Cl(C2nP2))2] (n = 1, 1; 2, 2) and tetramers [(Re(CO)3Cl(C2nP2))4] (n = 1, 3; 2, 4, C2P2 = Ph2P-C...C-PPh2, C4P2 = Ph2P-C...C-C...C-PPh2), as well as the mixed-metal [(Re(CO)3Cl)2(Os(bpy)2)2(C2P2)4](PF6)4 (6, bpy = 2,2'-bipyridine) and its precursor [Os(bpy)2(C2P2)2](PF6)2 (5) have been synthesized. Characterization has been carried out using 31P(1H) NMR, FAB/MS, ESI/MS, IR spectroscopy, elemental analysis (EA), and X-ray single crystal structure determination. These new metallocyclic complexes are found to be emissive, with a characteristic ReI-based emission at 505-525 nm (lifetimes of 3.4-6.8 ns) and an Os(II)-based emission at 600-605 nm (lifetimes of 650-675 ns). High quantum yields of 0.25 and 0.17 were observed for 5 and 6, which were representative of the few most emissive species reported with Os(II) centers. Efficient energy transfer from the Re(I) donor to the Os(II) acceptor was also found. In addition, a host-guest study was performed using emissive metallocycle 6, and host-guest binding constants of 775M(-1), 1580M(-1), and 1680M(-1) were obtained for the guests anisole, 1,4-dimethoxybenzene, and 1,3,5-trimethoxybenzene, respectively. The correlation between the guest molecule size, cavity dimension, and the host-guest binding constant is discussed. Furthermore, the relationship between the pi-acceptor ability of the nonchromophoric phosphanes, the energy gap between the ground and excited state, and the nonradiative decay rate constant (knr) is also explored.

The tetramethylpiperidinyl-1-oxide anion (TMPO-) as a ligand in lanthanide chemistry: synthesis of the per(TMPO-) complex [(ONC5H6Me4)2Sm(mu-ONC5H6Me4)]2.

(C5Me5)3Sm reacts with the free radical 2,2,6,6-tetramethylpiperidinyl-1-oxy (TMPO) to form (C5Me5)2 and the per nitroxide [(eta 1-ONC5H6Me4)2Sm(mu-eta 1:eta 2-ONC5H6Me4)]2.

Reactivity of "Eu(OiPr)2" with phenols: formation of linear Eu3, square pyramidal Eu5, cubic Eu8, and capped cubic Eu9 polymetallic europium complexes.

The direct reaction of europium with 2-propanol and phenols has been investigated under a variety of conditions. The reaction of europium metal with 2,6-dimethylphenol and 2,6-diisopropylphenol in 2-propanol at reflux revealed that polymetallic europium complexes could be generated by this method. Hx[Eu8O6(OC6H3Me2-2,6)12(OiPr)8], 1, and H5[Eu5O5(OC6H3iPr2-2,6)6(NCCH3)8], 2, were isolated by recrystallization in the presence of hexanes and acetonitrile, respectively, and characterized by X-ray crystallography. Complex 1 has a cubic arrangement of europium ions with face-bridging mu 4-O donor atoms, edge-bridging mu-O(phenoxide/phenol) ligands, and terminal O(isopropoxide/2-propanol) ligands. Complex 2 is mixed valent and has a square pyramidal europium core with four Eu(II) ions at the basal positions and one Eu(III) ion at the apex. Since these reactions gave complicated mixtures of products from which 1 and 2 could only be obtained in low yields, direct reactions under less forcing reaction conditions were investigated. Europium reacts slowly at room temperature to form arene-soluble divalent [Eu(OiPr)2(THF)x]n, 3. Complex 3 reacts with 2,6-dimethylphenol to form the arene-insoluble complex (H[Eu(OC6H3Me2)2(OiPr)])n, 4. Recrystallization of 4 in the presence of THF results in the crystallographically characterizable divalent trimetallic complex [Eu(OC6H3Me2-2,6)2(THF)2]3, 5, which has an unusual linear metal geometry. In the presence of HOiPr at ambient conditions in the glovebox, crystals of 5 slowly convert to the mixed valent H10[Eu8O8(OC6H3Me2-2,6)10(OiPr)2(THF)6], 6, which was found to have a cubic arrangement of europium atoms similar to 1 by X-ray crystallography. Complex 4, upon heating under vacuum, followed by reaction with THF, forms the arene-soluble divalent complex H18([Eu9O8(OC6H3Me2-2,6)10(THF)7][Eu9O9(OC6H3Me2-2,6)10(THF)6]), 7, which contains two types of capped cubic arrangements of europium ions in the solid state.

Synthesis of arene-soluble mixed-metal Zr/Ce, Zr/Y, and related [[Zr2(OiPr)9]LnX2]n complexes using the dizirconium nonaisopropoxide ligand.

The utility of polydentate monoanionic [Zr2(OiPr)9]- in generating arene-soluble, unsolvated, mixed-metal Zr/Ce and Zr/Y complexes is described. The synthesis of other mixed-metal zirconium lanthanide complexes was also studied to explore the relationship of metal size to structure. Lanthanide trihalides react in THF with KZr2(OiPr)9 to form unsolvated dimers, [[Zr2(OiPr)9]LnCl2]2, with the larger metals, Ln = Ce (1), Ho (2), Y (3), and unsolvated monomers, [Zr2(OiPr)9]LnCl2, with the smaller elements, Ln = Er (4), Yb (5). The synthesis of a monomeric iodide analogue, [Zr2(OiPr)9]TmI2, 6, by reduction of Zr2(OiPr)8(iPrOH)2 with TmI2(DME)3 is also reported. In all of these complexes, the [Zr2(OiPr)9]- subunit is tetradentate. 1-6 are compared with related cyclopentadienyl halide complexes to evaluate the special features of the dizirconium nonaisopropoxide ligand versus cyclopentadienide.

Relative and absolute configuration of aloperine.

The relative and absolute configuration of the title compound, (6R,7R,9R,11S)-16,17-didehydro-9-de-2-piperidinylormosanine, C15H24N2, has been elucidated. Two X-ray structures, one of the free base of the alkaloid and the second of its dihydrochloride monohydrate salt, C15H26N2(2+).2Cl-.H2O, have been determined to unequivocally establish the stereochemistry of aloperine, the parent member of a rare family of lupinine alkaloids.

3-Benzyl-5-phenyl-2-p-tolylthiophene.

The crystal structure of 3-benzyl-5-phenyl-2-p-tolylthiophene, C24H20S, is described. The thiophene ring in the title compound is planar and its structural properties are very similar to those of thiophene. The thiophene ring in compound (1) is planar as are the phenyl rings. The structure of the thiophene ring in compound (1) is very similar to that of thiophene (Bak, Christensen, Hansen-Nygaard & Rastrup-Andersen, 1961; Bak, Christensen, Rastrup-Andersen & Tannenbaum, 1956; Harshbarger & Bauer, 1970). The C-S distances are 1.735 (2) and 1.731 (2) A, respectively, and the C-S-C bond angle is 92.3 (1) degree. The steric repulsion between the p-tolyl ring at C(2) and the benzyl group at the adjacent carbon, C(3), is minimized by the rotation of the p-tolyl group 56.1 degrees from the thiophene plane. The benzene ring at C(5) deviates from the plane of the thiophene ring by 36.9 degrees. In 2,5-bis(4-nitro-phenyl)-3,4-diphenylthiophene (Meester, Maldar, Hosmane & Chu, 1986) the angle between the 4-H nitrophenyl and thiophene rings is 26.6 degrees. The angle between the phenyl and thiophene rings in 2-amino-4-methyl-5-phenylthiophene-3-carboxamide is 54.9 degrees (Joseph, Selladurai, Kannan & Parthasarathi, 1991).

(1Z,3Z)-1,4-diphenyl-1,4-bis(p-tolylmethylthio)-1,3-butadiene.

The crystal structure of (1Z,3Z)-1,4-diphenyl-1,4-bis-(p-tolylmethylthio)-1,3-b utadiene (1), C32H30S2, is described. Compound (1) has an s-trans conformation. The single bond length, C(2)--C(2'), in compound (1) of 1.432 (5) A is shorter than the C(3)--C(4) single bond (1.48 A) in 1,3-butadiene and the double-bond length, C(1)--C(2), of 1.350 (3) A in compound (1) is comparable to that in 1,3-butadiene (1.34 A). The short C--C single and double bonds in (1) may be attributed to delocalization (resonance) over the planar four-atom unit, hybridization changes, the presence of the S atoms, and/or other factors.