A chemoenzymatic route to the (+)-form of the amaryllidaceae alkaloid narseronine

The enzymatically derived and enantiopure cis-1,2-dihydrocatechol 1 has been converted, over 14 one-pot operations, into the (+)-form of the alkaloid narseronine (2). The present study, which complements earlier work that established a route from metabolite 1 to enantiomer (–)-2, involves an N-bromosuccinimide/tri-n-butyltin hydride-mediated cyclisation reaction to construct the unsaturated B-ring lactone of the target compound.We thank the Australian Research Council and the Institute of Advanced Studies for generous financial support

Structures of New Alkaloids from Rain Forest Trees Galbulimima belgraveana and Galbulimima baccata in Papua New Guinea, Indonesia, and Northern Australia

Following on our 60-year research on the chemical constituents of the rain forest trees Galbulimima belgraveana and Galbulimima baccata, we report the isolation of seven new alkaloids: GB14 (14), GB22 (15), GB25 (16), GB21 (17), GB23 (18), GB24 (19), and GB26 (20). Their structures were elucidated by a combination of spectroscopic analyses and single-crystal X-ray crystallography, as well as structure degradation and interconversion. The newly isolated alkaloids are precursors or derivatives of the known family members from our early studies and could be intermediates in the biosynthesis of the Galbulimima alkaloids. Therefore, the present study has expanded the range of structures in this family of alkaloids and provided some missing links in the biosynthetic sequences.This study was supported by the Fundamental Research Funds for the Central Universities, Chin

Thioxoethenylidene (CCS) as a bridging ligand

The reaction of [Mo(≡CBr)(CO)2(Tp*)] (Tp* = hydrotris(3,5-dimethylpyrazol-1-yl)borate) with [Fe2(μ-SLi)2(CO)6] affords, inter alia, the unsymmetrical binuclear thioxoethenylidene complex [Mo2(μ,σ(C):η2(C′S)-CCS)(CO)4(Tp*)2], which may be more directly obtained from [Mo(≡CBr)(CO)2(Tp*)] and Li2S. The reaction presumably proceeds via the intermediacy of the bis(alkylidynyl)thioether complex S{C≡Mo(CO)2(Tp*)}2, which was, however, not directly observed but explored computationally and found to lie 78.6 kJ mol–1 higher in energy than the final thioxoethenylidene product. Computational interrogation of the molecules [M2(μ-C2S)(CO)2(Tp*)2] (M = Mo, W, Re, Os) reveals three plausible coordination modes for a thioxoethenylidene bridge which involve a progressive strengthening of the C–C bond and weakening of the M–C and M–S bonds, as might be expected from simple effective atomic number considerations.This work was supported by the Australian Research Council (DP130102598 and DP110101611)

Synthesis, structure characterization, DNA binding, and cleavage properties of mononuclear and tetranuclear cluster of copper(II) complexes

Two copper(II) complexes, cluster 1, and mononuclear 2, have been synthesized by reacting acetylacetone and benzohydrazide (1:1 ratio for 1 and 1:2 ratio for 2) with CuCl2 in a methanol solution. In 2, which is a new complex, the ligand acts as a tetradentate which binds the metal ion via two amide-O atoms and two imine-N atoms providing an N2O2 squa-re-planar around the copper(II) ion. The absorption spectra data evidence strongly suggested that the two copper(II) compounds could interact with CT-DNA (intrinsic binding constant, Kb = 0.45 × 10⁴ M⁻¹ for 1 and Kb = 2.39 × 10⁴ M⁻¹ for 2). The super coiled plasmid pBR322 DNA cleavage ability was studied with 1 and 2 in the presence and absence of H₂O₂ as an oxidant. In both the absence and the presence of an oxidizing agent, complex 2 exhibited no nuclease activity. However, even in the absence of an oxidant, complex 1 exhibited significant DNA cleavage activity.The authors are grateful to the Yazd University and the Australian National University for partial support of this work

gem-Dibromocyclopropanes and enzymatically derived cis-1,2-dihydrocatechols as building blocks in alkaloid synthesis

The application of the title building blocks, the 6,6-dibromobicyclo[3.1.0]hexanes and the cis-1,2-dihydrocatechols, to the total synthesis of crinine and lycorinine alkaloids is described.We thank the Australian Research Council and the Institute of Advanced Studies for generous financial support

New methods for the synthesis of certain alkaloids and terpenoids

The use of ring-fused gem-dihalocyclopropanes, Au(I)-catalyzed cyclization reactions, and chemoenzymatic techniques in the synthesis of natural products is described.We thank the Australian Research Council for generous financial support through the provision of various grants

First detection of phase-dependent colliding wind X-ray emission outside the Milky Way

After having reported the detection of X-rays emitted by the peculiar system HD5980, we assess here the origin of this high-energy emission from additional X-ray observations obtained with XMM-Newton. This research provides the first detection of apparently periodic X-ray emission from hot gas produced by the collision of winds in an evolved massive binary outside the Milky Way. It also provides the first X-ray monitoring of a Luminous Blue Variable only years after its eruption and shows that the dominant source of the X-rays is not associated with the ejecta.Comment: 13 pages, 3 figures and 1 table, accepted for publication in ApJ (letters

Gold- and Silver-Catalysed Cyclisation Reactions of β-Amino Allenes

Herein we report the formation of pyrrolines and tetrahydropyridines from the cyclisation reactions of β-amino allenes by both AuI and AgI catalysts in yields ranging from 5 to 70 %. AuI catalysts favour a 5-endo-dig cyclisation before rapid rearrangement to the 5-exo-dig product, while AgI favours a 6-endo-trig cyclisation. We also report the first known Ag2O catalysed cyclisation reaction of an allene which occurred in good yield (61 %)

Slopes To Prevent Trapping of Bubbles in Microfluidic Channels

The idea of designing a microfluidic channel to slope upward along the direction of flow of the liquid in the channel has been conceived to help prevent trapping of gas bubbles in the channel. In the original application that gave rise to this idea, the microfluidic channels are parts of micro-capillary electrophoresis (microCE) devices undergoing development for use on Mars in detecting compounds indicative of life. It is necessary to prevent trapping of gas bubbles in these devices because uninterrupted liquid pathways are essential for sustaining the electrical conduction and flows that are essential for CE. The idea is also applicable to microfluidic devices that may be developed for similar terrestrial microCE biotechnological applications or other terrestrial applications in which trapping of bubbles in microfluidic channels cannot be tolerated. A typical microCE device in the original application includes, among other things, multiple layers of borosilicate float glass wafers. Microfluidic channels are formed in the wafers, typically by use of wet chemical etching. The figure presents a simplified cross section of part of such a device in which the CE channel is formed in the lowermost wafer (denoted the channel wafer) and, according to the present innovation, slopes upward into a via hole in another wafer (denoted the manifold wafer) lying immediately above the channel wafer. Another feature of the present innovation is that the via hole in the manifold wafer is made to taper to a wider opening at the top to further reduce the tendency to trap bubbles. At the time of reporting the information for this article, an effort to identify an optimum technique for forming the slope and the taper was in progress. Of the techniques considered thus far, the one considered to be most promising is precision milling by use of femtosecond laser pulses. Other similar techniques that may work equally well are precision milling using a focused ion beam, or a small diamond-tipped drill bit

6-Hydroxy-5,6-seco-stemocurtisine: a novel seco-stemocurtisine-type alkaloid

A novel seco-stemocurtisine-type alkaloid, 6-hydroxy-5,6-seco-stemocurtisine was isolated from the aerial parts of Stemona curtisii (Stemonaceae) collected from Trang Province in Thailand. The unprecedented 5,6-seco-pyrido[1,2-a] azepine structure was elucidated by 2D NMR analysis and a single crystal X-ray crystallographic analysis. (C) 2013 Phytochemical Society of Europe