Unprecedented Structural Features Research Articles

Norstaminane- and isopimarane-type diterpenes of Orthosiphon stamineus from Okinawa

Nine novel highly oxygenated and structurally diverse diterpenes, named norstaminolactone A ( 1 ), norstaminols B and C ( 2 and 3 ), secoorthosiphols A–C ( 4– 6 ) and orthosiphols R–T ( 7– 9 ) have been isolated from the aerial part of Orthosiphon stamineus cultivated in Okinawa Prefecture, Japan. Norstaminolactone A ( 1 ) is the first representative of a biogenetically unusual norstaminane-type diterpene bearing a nitrogen atom. Norstaminol C ( 3 ) possessed a framework presumed to be biosynthesized from the staminane-type diterpene. Secoorthosiphols A–C ( 4– 6 ) possessed an unprecedented structural feature of the opened ring A system, encountered for the first time in isopimarane-type diterpenes. Secoorothosiphol C ( 6 ) also represents the first example of biogenetically unique and unconventional secoisopimarane-type diterpene bearing a cyano group. Norstaminolactone A ( 1 ) showed a potent antiproliferative activity with an IC 50 value of 2.16 μg/mL against highly liver metastatic colon 26-L5 carcinoma cell line.

Au2trien: a dinuclear gold(III) complex with unprecedented structura features.

The X-ray structure of a dinuclear gold(III) complex, Au2trien, shows the presence of two square planar gold(III) centers bridged by a nitrogen donor, in a very unusual fashion.

Secoorthosiphols A–C: three highly oxygenated secoisopimarane-type diterpenes from Orthosiphon stamineus

Three new highly oxygenated 2,3-secoisopimarane-type diterpenes, named secoorthosiphols A ( 1 ), B ( 2 ) and C ( 3 ), have been isolated as extremely minor constituents from the aerial parts of the Orthosiphon stamineus from Okinawa. A unique unprecedented structural feature of such a ring A opened system in newly isolated compounds was encountered for the first time in isopimarane-type diterpenes. Secoorthosiphol C ( 3 ) represents the first example of a biogenetically unique and unconventional secoisopimarane-type diterpene having a cyano group.

A novel acetated 54-member crown-shaped polyoxomolybdate with unprecedented structural features: Na26[{Na(H2O)2}6({μ3-OH)4MoV20MoVI34O164(μ2-CH3COO)4}]·≈120H2O

The EPR silent acetated 54-member crown-shaped polyoxomolybdate Na26[{Na(H2O)2}6( {μ3-OH)4MoV20MoVI 34- O164(μ2-CH3COO)4}] ·≈120H2O (1), constructed from two different but related building blocks in a new mode, is synthesized in high yield by reducing an acidified aqueous solution of Na2MoO4·2H2O and CH3COONa·3H2O.

Structural links between zeolite-type and clathrate hydrate-type materials: strands of small clusters of water molecules interconnect oligomeric silicate [Si8O18(OH)2]6–anions to generate the 3D host structure of the heteronetwork clathrate [DMPI]6[Si8O18(OH)2]·48.5h2O (DMPI = 1,1-dimethylpiperidinium)

The mixed silicate–water host framework, 3∞[{[Si8O18(OH)2]6–}2[H2O]97], of the title compound contains unprecedented and remarkable structural features, e.g. pseudo-hexagonal layer-like subunits with large circular apertures (free diameter ca. 7.9 A) that resemble layer-like structural units of large-pore zeolite-type materials; the preparation and X-ray structure of the heteronetwork clathrate are reported.

New niobium complexes of alkynes. 5. Electronic structure and bonding in the tetranuclear complex of niobium [Nb4OCl8{(PhC)4}2]2-

Electronic structure and bonding in a newly prepared tetranuclear complex of niobium , [Nb 4 OCl 8 {(PhC) 4 } 2 ] 2− , are discussed on the basis of molecular orbital calculations by the Fenske-Hall method. The anion consists of a planar, rectangular Nb 4 group with an oxygen atom at the center, and a C-shaped phC-C(Ph)C(Ph)-CPh chain clasps each short Nb-Nb edge at the middle and lies in a plane perpendicular to the Nb 4 O plane. Our study has been mainly focused on the problems related to the unprecedented structural features of the anion, specifically, the Nb-Nb and Nb-O bonding, and the bonding of the C 4 Ph 4 unit to the metal atoms. The resulting bonding scheme gives a satisfactory account of the structure and is consistent with the assignement of a formal oxidation state of III to the metal atoms and the existence of strong bonds between the close pairs of metal atoms

Three novel spin-labeled crown ethers

The following nitroxide spin-labeled crown ethers have been synthesized: 2,2-(sym-dibenzo-16-crown-5)-4,4-dimethyloxazolidinyl-N-oxyl (1), 2,2-(sym-dibenzo-16-crown-5)-4,4,5,5-tetramethylimidazolinyl-N-oxyl (2), and 3-carboxy-2,2,5,5-tetramethyl-3-pyrrolinyl-l-oxy hydroxy-sym-dibenzo-16-crown-5 ester (3). 1 and 2 are characterized by having the nitroxide near the crown cavity and rigidly bound to a ring carbon atom of the crown. 1-3 have been studied by EPR, and the proton hyperfine splittings have been determined by second harmonic out-of-phase detection. The values obtained for the proton hyperfine splittings of 1 were compared to those determined by ENDOR and found to agree within experimental error. EPR studies of hyperfine splitting constants and Heisenberg spin exchange suggest that these spin-labeled crowns are poor complexing agents for alkali metal cations. The structure of 1 has been determined by x-ray diffraction, and the poor complexing ability of the crown is attributed to an unprecedented structural feature in which the hydrogen atoms of one methylene group of the propylene bridging linkage have turned inward with respect to the cavity of the crown. The proton hyperfine splitting observed for 1 is attributed to protons located at approximately van der Waals distances from the NO group.