Antineoplastic diterpene-benzoate macrolides from the Fijian red alga Callophycus serratus

[structures: see text] Three diterpene-benzoate natural products, with novel carbon skeletons and an unusual proposed biosynthesis, were isolated from extracts of the Fijian red alga Callophycus serratus and identified by a combination of X-ray crystallographic, NMR, and mass spectral analyses. Bromophycolide A (1) displayed cytotoxicity against several human tumor cell lines via specific apoptotic cell death. This represents the first discovery of natural products incorporating a diterpene and benzoate skeleton into a macrolide system.     

FLUORESCENCE ENERGY TRANSFER BETWEEN DIMETHYLDIAZAPEROPYRENIUM DICATION AND ETHIDIUM INTERCALATED IN POLY d(A-T)

Dimethyldiazaperopyrenium is one of the largest known DNA intercalators. Fluorescence energy transfer occurred between dimethyldiazaperopyrenium (donor) and ethidium (acceptor) when these dyes were bound to a double-stranded polynucleotide such as poly d(A-T). The addition of increasing amounts of ethidium bromide led to a marked shortening of the fluorescence lifetime of the donor, whereas the excited state of the acceptor was progressively populated via energy transfer from the donor. Critical Förster distance between these two chromophores was calculated to be 3.8 nm. The observed transfer efficiency was lower than that calculated on the basis of this critical distance and a statistical distribution of bound drugs. These results are discussed taking into account the conformational change induced by intercalation of dimethyldiazaperopyrenium in the double-stranded polynucleotide.     

Stability and structure in alpha- and beta-Keggin Heteropolytungstates, [X(n)(+)W12O40)](8-n)(-), X = p-block cation

beta-[SiW(12)O(40)](4)(-) (C(3)(v) symmetry) is sufficiently higher in energy than its alpha-isomer analogue that effectively complete conversion to alpha-[SiW(12)O(40)](4)(-) (T(d)) is observed. By contrast, beta- and alpha-[AlW(12)O(40)](5)(-) (beta- and alpha-1; C(3)(v) and T(d), respectively) are sufficiently close in energy that both isomers are readily seen in (27)Al NMR spectra of equilibrated (alpha-beta) mixtures. Recently published DFT calculations ascribe the stability of beta-1 to an electronic effect of the large, electron-donating [AlO(4)](5)(-) (T(d)) moiety encapsulated within the polarizable, fixed-diameter beta-W(12)O(36) (C(3)(v)) shell. Hence, no unique structural distortion of beta-1 is needed or invoked to explain its unprecedented stability. The results of these DFT calculations are confirmed by detailed comparison of the X-ray crystal structure of beta-1 (beta-Cs(4.5)K(0.5)[Al(III)W(12)O(40)].7.5H(2)O; orthorhombic, space group Pmc2(1), a = 16.0441(10) A, b = 13.2270(8) A, c = 20.5919(13) A, Z = 4 (T = 100(2) K)) with previously reported structures of alpha-1, alpha- and beta-[SiW(12)O(40)](4)(-), and beta(1)-[SiMoW(11)O(40)](4)(-).     

Carbenoid reactions of 2-halomethyl-4,6-dimethyl-s-triazines

Reactions of lithium, sodium, and potassium salts of 2,4,6-trimethyl-s-triazine (1) with 2-halomethyl-4,6-dimethyl-s-triazine (2) (X = Cl, Br) in glyme have been studied and found to give 1,2-bis(4,6-dimethyl-s-triazin-2-yl)ethane (3), 1,2-bis(4,6-dimethyl-s-triazin-2-yl)ethene (5), 1,2,3-tris(4,6-dimethyl-s-triazin-2-yl)cyclopropane (6), 1,2,3-tris(4,6-dimethyl-s-triazin-2-yl)propane (7), and 1,2,3,4-tetrakis(4,6-dimethyl-s-triazin-2-yl)butane (8). It is proposed that product 3 is formed primarily via an S(N)2 reaction, whereas the remaining products are formed primarily via carbenoid reactions that are enumerated.     

Sono-electroanalysis of copper: enhanced detection and determination in the presence of surfactants

Surfactant adsorption has been shown to have a passivating effect on the electrode surface during anodic stripping voltammetric measurements. In the present work the feasibility of sono-anodic stripping analysis for the determination of copper in aqueous media contaminated with surfactant has been studied at an unmodified bare glassy carbon electrode. We illustrate the deleterious effect of three common surfactants, sodium dodecyl sulfate (SDS), dodecyl pyridinium chloride (DPC) and Triton-X 100 (TX-100) on conventional electroanalysis. The analogous sono-electroanalytical response was investigated for each surfactant at ultrasound intensities above and below the cavitation threshold. The enhancement in the stripping signal observed is attributed to the increased mass transport due to acoustic streaming and above the cavitation threshold the intensity of cavitational events is significantly increased leading to shearing of adsorbed surfactant molecules from the surface. As a result accurate analyses for SDS concentrations up to 100 ppm are possible, with analytical signals visible in solutions of SDS and TX-100 of 1000 ppm. Analysis is reported in high concentration of surfactant with use of sono-solvent double extraction. The power of this technique is clearly illustrated by the ability to obtain accurate measurements of copper concentration from starting solutions containing 1000 ppm SDS or TX-100. This was also exemplified by analysis of the low concentration 0.3 microM Cu(II) solution giving a percentage recovery of 94% in the presence of 1000 ppm SDS or TX-100.     

Synthesis and reactivity of(\mu - H)(\mu _3 - \eta ^2 - H_2 )_4 )Os_3 (CO)_9 : An unusually reactive triosmium cluster

The synthesis of $(\mu - H)(\mu - \eta ^2 - H_2 )_4 )Os_3 (CO)_{10} $ (4) from piperidine and Os₃(CO)₁₀(CH₃CN)₂ and its solid state structure are reported. The room temperature reactions of the decarbonylation product of4, $(\mu - H)(\mu _3 - \eta ^2 - H_2 )_4 )Os_3 (CO)_9 $ (3), with P(C₆H₅)₃, CNCH₃, HCl and H₂ are reported. Overall, the products obtained closely resemble those obtained from the analogous, $(\mu - H)(\mu _3 - \eta ^2 - H_2 )_3 )Os_3 (CO)_9 $ (1). The isomerizations of the phosphine addition products $(\mu - H)(\mu - \eta ^2 - H_2 )_n )Os_3 (CO)_9 P(C_6 H_5 )_3 $ (n = 3,6a;n = 4,5a) have been studied by¹H-NMR techniques and the initial rearrangement was shown to be an intramolecular process. Slower conversion to the complex $(\mu - H)(\mu _3 - \eta ^2 - H_2 )_4 )Os_3 (CO)_8 P(C_6 H_5 )_3 $ (8) was observed and the solid state structure of this product is reported and compared with a related compound containing an ethyl,n-propylμ ₃-imidoyl ligand. Compound4 crystallizes in the triclinic space group Pl (#2) withZ= 2, and unit cell parametersa = 9.294(3) Å,b = 15.758(5) Å,c = 7.406(2) Å,a = 81.10(2)°,β=76.47(2)°,y =74.88(2)°, andV =1013(l) ų. Least-squares refinement of 2677 reflections gave a final discrepancy factor ofR = 0.054 (R _w = 0.066). Compound8 crystallizes in the space group C2/c with unit cell parametersa = 24.818(3) Å,b = 16.389(3) Å,c = 18.111(3) Å,β= 120.94(2)°,V = 6318(4) ų, andZ = 8. Least squares refinement of 3439 reflections gave a final discrepancy factor ofR = 0.039 (R _w =0.047).