[2+2] Cycloaddition and electrophilic alkynylation reactions of 4-chloro-1,1,1-trifluorobut-3-yn-2-one and alkyl vinyl ethers

Reaction of 4-chloro-1,1,1-trifluorobut-3-yn-2-one with alkyl vinyl ethers leads to the parallel formation of [2+2] cycloaddition and electrophilic alkynylation products, the ratio of which depends on the nature of vinyl ether. Preparative methods for the separation of compounds formed are suggested.     

Sliced linear zone plates for hard X-ray radiation

Linear zone plates for hard (E > 10 keV) X rays are considered. The technology of the plates includes cutting magnetron-sputtered W₅Si₃/Si multilayer coatings. The results of numerical computation suggest that this pair of materials provides a high efficiency in the first and second diffraction orders. It is found experimentally that good multilayer structures consisting of several hundreds of layers can be synthesized on silicon and glass substrates. It is shown that they can be cut by ion etching the multilayer coating through a mask.     

The Isolation,Structure Elucidation and Bioactivity Study of Chilensosides A,A1, B,C, and D,Holostane Triterpene Di-, Tri- and Tetrasulfated Pentaosides from the Sea Cucumber Paracaudina chilensis (Caudinidae,Molpadida)

Five new triterpene (4,4,14-trimethylsterol) di-, tri- and tetrasulfated pentaosides, chilensosides A (1), A₁ (2), B (3), C (4), and D (5) were isolated from the Far-Eastern sea cucumber Paracaudina chilensis. The structures were established on the basis of extensive analysis of 1D and 2D NMR spectra and confirmed by HR-ESI-MS data. The structural variability of the glycosides concerned the pentasaccharide chains. Their architecture was characterized by the upper semi-chain consisting of three sugar units and the bottom semi-chain of two sugars. Carbohydrate chains of compounds 2–5 differed in the quantity and positions of sulfate groups. The interesting structural features of the glycosides were: the presence of two sulfate groups at C-4 and C-6 of the same glucose residue in the upper semi-chain of 1, 2, 4, and 5 and the sulfation at C-3 of terminal glucose residue in the bottom semi-chain of 4 that makes its further elongation impossible. Chilensoside D (5) was the sixth tetrasulfated glycoside found in sea cucumbers. The architecture of the sugar chains of chilensosides A–D (1–5), the positions of sulfation, the quantity of sulfate groups, as well as the aglycone structures, demonstrate their similarity to the glycosides of the representatives of the order Dendrochirotida, confirming the phylogenetic closeness of the orders Molpadida and Dendrochirotida. The cytotoxic activities of the compounds 1–5 against human erythrocytes and some cancer cell lines are presented. Disulfated chilensosides A₁ (2) and B (3) and trisulfated chilensoside C (4) showed significant cytotoxic activity against human cancer cells.