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Lagunamides A (1) and B (2) are new cyclic depsipeptides isolated from the marine cyanobacterium Lyngbya majuscula obtained from Pulau Hantu Besar, Singapore. The planar structural characterization of these molecules was achieved by extensive spectroscopic analysis, including 2D NMR experiments. In addition to Marfey’s method and 3JH−H coupling constant values, a modified method based on Mosher’s reagents and analysis using LC-MS was deployed for the determination of the absolute configuration. Lagunamides A and B displayed significant antimalarial properties, with IC₅₀ values of 0.19 and 0.91 μM, respectively, when tested against Plasmodium falciparum. Lagunamides A and B also possessed potent cytotoxic activity against P388 murine leukemia cell lines, with IC₅₀ values of 6.4 and 20.5 nM, respectively. Furthermore, these cyanobacteri...
The title molecule, [Co3(C2H3)(C5H9N)3(CO)6] or [Co3(3-CCH3)(CNtBu)3(CO)6], lies on a threefold rotation axis. The three isonitrile ligands each occupy an equatorial site on each of the three Co atoms. The average Co-Co bond length is 2.4769 (6) Å. The tert-butyl groups are disordered over two orientations, with site occupancies of ca 0.6:0.4.
The title compound, [Mn(C₁₀H₉O₃)(CO)₄], is formed by orthomanganation of 3'-acetoxyacetophenone at the sterically crowded ortho site. The atoms of the benzene and the cyclometallated rings are coplanar to within <0.018 Å, and there are no significant intramolecular interactions between the Mn(CO)₄ group and the adjacent acetoxy group.
The resorcylic acid lactones zearalenone (1), α-zearalenol (2), β-zearalenol (3), α-zearalanol (zeranol) (4), β-zearalanol (taleranol) (5), and zearalanone (6) were converted to their glucuronides on a preparative scale in good yields. Reactions were conducted with bovine uridine 5′-diphosphoglucuronyl transferase (UDPGT) as catalyst and uridine 5′-diphosphoglucuronic acid (UDPGA) as cofactor. The glucuronides were isolated by column chromatography and characterized by NMR spectroscopy and mass spectrometry. Although the principal products were 4-O-glucuronides (i.e., linkage through a phenolic hydroxyl), significant quantities of the 6′-O-glucuronides (i.e., linkage through the aliphatic hydroxyl) of alcohols 2, 4, and 5 were also isolated. In the case of 3, the 2-O-glucuronide was isolated as the minor product. Overall isolated yield...
Marine algal toxins of the okadaic acid group can occur as fatty acid esters in blue mussels, and are commonly determined indirectly by transformation to their parent toxins by alkaline hydrolysis. Some data are available regarding the identity of the fatty acid esters, mainly of palmitic acid (16:0) derivatives of okadaic acid (OA), dinophysistoxin-1 (DTX1) and dinophysistoxin-2 (DTX2). Other fatty acid derivatives have been described, but with limited mass spectral data. In this paper, the mass spectral characterization of the [M H]- and [M+Na]+ ions of 16 fatty acid derivatives of each of OA, DTX1 and DTX2 is presented. The characteristic fragmentation of [M+Na]+ ions of OA analogues provided a useful tool for identifying these, and has not been described previously. In addition, a set of negative ion multiple reaction monitoring (M...
animals and people consuming seafood. Brevetoxin-B2 (5) is a toxic metabolite produced in shellfish exposed to algae that contain brevetoxin-B (1). S-Desoxybrevetoxin-B2 (4) has been proposed as a cometabolite produced during this transformation, and while LC-MS analyses suggest its presence in shellfish, it has not yet been isolated and characterized. Studies on these materials are severely constrained by the difficulty of obtaining and purifying them from natural sources. We have developed a convenient one-pot conversion of commercially available brevetoxin-B (1) into S-desoxybrevetoxin-B2 (4), and a simple method for converting 4 into brevetoxin-B2 (5). Full NMR and mass-spectral characterization of 4 and 5 confirmed their structures and showed that the ratio of diastereoisomers in the synthetic 4 and 5 was similar to that observed ...
Marine algal toxins of the okadaic acid (OA) group can occur as diol esters and sulfated diol esters in algae and as fatty acid esters in shellfish. Several of these ester forms have been identified, but the most common procedure for detecting OA group toxin esters is by measuring the increase in parent toxin after alkaline hydrolysis. Use of this alkaline hydrolysis method led to the discovery of high levels of conjugates of OA and dinophysistoxins-2 (DTX2) in seawater and of OA, DTX1, and DTX2 in blue mussel hepatopancreas (HP) from Flødevigen, Norway, during a bloom of Dinophysis spp. In the water sample, a C8-diol ester, a C9-diol ester, and a previously undescribed C8-triol ester of OA were characterized using HPLC-MS2, -MS3, and -MS4 in combination with various derivatization procedures. Palmitic acid (16:0) ester derivatives of ...
Treatment of Co₃(μ₃-CC≡CR)(μ-dppm)(CO)₇ with O₂ (air) in the presence of [FcH]PF₆ afforded Co₃{μ₃-CC(O)R}(μ-dppm)(CO)₇ by the formal conversion –C≡C– + O–O → >C–O + C≡O. In this way, complexes with R = Ph, Fc, and W(CO)₃Cp, bis-clusters {Co₃(μ-dppm)(CO)₇}₂{μ₃:μ₃-[≡C(O)(C≡C)C≡]}, {Co₃(μ-dppm)(CO)₇}₂{μ₃:μ₃-[≡C(O)(C≡C)xC(O)C≡]} (x = 1, 2), and {Co₃(μ-dppm)(CO)₇}₂{μ₃:μ₃-[≡CC(O)C≡CC₆H4C≡CC(O)C≡]}, and heterometallic bis-clusters {Co₃(μ-dppm)(CO)₇}{μ₃:μ₃-[≡CC(O)C≡CC≡]}{M₃(μ-H)₃(CO)₉} (M = Ru, Os) have been prepared. Single-crystal XRD structure determinations of several products are reported together with that of precursor {Co₃(μ-dppm)(CO)₇}₂{μ₃:μ₃-[≡C(C≡C)₂C₆H₄(C≡C)₂C≡]}.
We have used different computational methods, including B3LYP, CCSD(T)-F12 and CBS-QB3, to study and compare the addition–elimination reaction of the nitrate radical NO₃ with four sulfur-containing species relevant to atmospheric chemistry: hydrogen sulfide (H₂S), dimethyl sulfide [(CH₃)₂S], dimethyl sulfoxide [(CH3)₂SO] and sulfur dioxide (SO₂). We find that the reaction with (CH₃)₂SO to give NO₂ + (CH₃)₂SO₂ has a very low barrier, and is likely to be the dominant oxidation mechanism for (CH₃)₂SO in the atmosphere. In agreement with previous experimental data and computational results, we find that the reaction with H₂S and SO₂ is very slow, and the reaction with (CH₃)₂S is not competitive with the hydrogen abstraction route. The differences in reaction energetics and rates between the four species are explained in terms of stabilizin...
“Etch and coat” methods, potentially useful for large scale production of superhydrophobic surfaces on metals, have been extended by introduction of a thin 20 nm Au interlayer which allowed thiol surface modifiers to be investigated. Fe, Ti and Zn surfaces modified in this way with a polyfluorothiol generally had lower contact angles, θ, than their silane modified equivalents but were more uniform and reproducible. The higher θ values for silanes appear to be associated with an increased effective roughness that is not seen in the thiol coatings, which follow the underlying surface. For Fe, Ti and Zn, θ increased to a maximum with etching time but then decreased significantly. Electron microscopy of samples etched for long times showed fewer grain boundaries, suggesting that the loss of hydrophobicity was related to reduced roughness. ...
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