Juris Popelis

Synthesis, structure and cytotoxicity of 3-C, N, S, Se substituted benzo[b]selenophene derivatives

Synthesis, molecular structure and cytotoxic activity of a series of 3-C, N, S, Se substituted benzo[b]selenophene derivatives on human fibrosarcoma HT-1080, mouse hepatoma MG-22A, and mouse fibroblasts 3T3 cell lines are described. The correlation between compound LD(50) 3T3 fibroblast cell line and HT-1080 morphology was shown.

1-Fluorogermatrane—germatrane with the shortest intramolecular N → Ge bond

Abstract 1-Hydroxygermatrane readily reacts with boron trifluoride etherate in acetonitrile to give 1-fluorogermatrane in good yield. The length of the N → Ge donor-acceptor bond equals 2.011(9) A, which is the shortest among all studied for germatranes.

The conformations of n-substituted 2,2-diaryl-1,3-dioxa-6-aza-2-silacyclooctanes in solution

Abstract 1 H, 13 C and 29 Si NMR data obtained for 2,2-diaryl-1,3-dioxa-6-aza-2-silacyclooctanes Ar 2 Si(OCH 2 CH 2 ) 2 NR indicate the occurrence in solution of an equilibrium between the conformations boat-boat/af chair-chair which are determined by the presence or absence of a transannular N → Si bond. The equilibrium is greatly affected by the electronic and steric effects of the N-and Si-substituents.

Efficient regioselective one-pot synthesis of partially hydrogenated thiazolo[3,2-a]pyridines

Abstract 7 H -Thiazolo[3,2- a ]pyridin-3(2 H )-ones, 7 H -thiazolo[3,2- a ]pyridin-3(2 H )-imines, and 3-hydroxy-3-methyl(phenyl)-2,3-dihydro-7 H -thiazolo[3,2- a ]pyridines have been obtained in good yields by a one-pot synthesis.

Fluoride Ion mediated Reactions of Trimethylsilylacetylene with Carbonyl Compounds and Terminal Acetylenes.

Abstract Fluoride-ion-mediated reaction of trimethylsilylacetylene with carbonyl compounds has been thoroughly studied. The products of addition to the CO bond were obtained in 15–66% yield, their subsequent silylation and addition to the second molecule of the carbonyl compound being observed. It has been found that terminal aryl and hetaryl acetylenes undergo silylation in a two-phase-system Me 3 SiCCH/CsF/18-crown-6 to afford aryl(hetaryl) trimethylsilylacetylenes with up to 100% yields. Combining these two reactions, a novel one-pot fluoride-ion-mediated method for the synthesis of 1-trimethylsiloxy-3-aryl(hetaryl)-2-propynes from trimethylsilylacetylene, terminal aryl or hetaryl acetylenes and carbonyl compounds has been elaborated.

Silyl isoxazolines-2: synthesis, structure and properties

Abstract Silyl isoxazolines have been synthesized by [2 + 3] cycloaddition reaction of nitrile oxides and silylnitronates to vinyl- and allylsilanes. The direction of the cycloaddition reaction of nitrile oxides to trialkoxyvinylsilanes has been shown to depend on the nature of the substituents on silicon and on the method used to generate the nitrile oxides. The addition of silyl esters of aci-nitromethane to triethoxyvinylsilane gives both 5-silyl and 4-silyl isomers. The structures of silyl isoxazolines are discussed.

Synthesis and cytotoxicity of silicon and germanium containing pyridine oxime O-ethers.

Silicon and germanium containing pyridine aldoxime, ketoxime and amidoxime O-ethers have been prepared using phase transfer catalytic systems oxime alkyl halide solid KOH 18-crown-6 benzene and oxime alkyl halide solid K2CO3 or Cs2CO3 18-crown-6 toluene. Cytotoxic activity of silicon and germanium containing pyridine oxime O-ethers was tested in vitro on two monolayer tumor cell lines: MG- 22A (mouse hepatoma) and HT-1080 (human fibrosarcoma). O-[3-Yriethylsilylpropyl]- and O-[3-(1-methyl- 1-silacyclopentyl)propyl] oximes of pyridine aldehydes and ketones exhibit high cytotoxicity. Presence of methyl group in the pyridine ring considerably decreased activity of amidoxime O-ethers. Oxime ethers containing two elements are essentially inactive. For 2-acetylpyridine oxime ethers the activity increases in order of alkyl substituents: Et3GeCH2CH2SiMe2CH2 < Et3SiCH2CH2CH2 < (CH2)4SiCH2CH2CH2. Cytotoxicity of ketoxime O-ethers is considerably lower in comparison with aldoxime O-ethers.

ADDITION OF NITRILE OXIDES TO GERMYL-SUBSTITUTED ETHYLENES

The reactions of [2+3] cycloaddition of nitrile oxides to mono- and 1,2-disubstituted germylalkenes proceed regioselectively and resulted 5-Ge-substituted isoxazolines-2 from triethylvinyl- and triethylallylgermane and 4-Ge-isomers from β -triorganylgermylstyrene and ethyl triorganylgermylacrylates. In the latter case the reaction occurs stereospecifically: Z -germylalkenes give cis - , while E -germylalkenes yield trans -4,5-substituted isoxazolines. The structure of products obtained was determined by 1 H-NMR spectroscopy and for 11a confirmed by single-crystal X-ray analysis.

Bithienylsilanes: unexpected structure and reactivity

Bithienyl)hydrosilanes were prepared by reaction of bithienyl lithium with chlorodimethylsilane, dichloromethylsilane and trichlorosilane. It was shown that 5-(2,2%-bithienyl)dimethylsilane possesses higher reactivity in the hydrosilylation reaction of monosubstituted acetylene derivatives compared with (2-thienyl)dimethylsilane. The elongation of the p-conjugated chain leads to increasing selectivity of the hydrosilylation reaction. An unusual structure for bis(5-(2,2%-bithienyl))methylsilane has been established by X-ray analysis.

Alkylation of Aryl and Hetaryl Ketoximes with Alkyl Iodides Prepared In Situ from Alkyl Chlorides Under Phase Transfer Catalysis Conditions

Abstract Two simple one-pot phase transfer catalytic methods for the preparation of ketoxime O-ethers from the corresponding ketoximes and alkyl iodides prepared in situ from alkyl chlorides were developed. The corresponding aryl and hetaryl ketoxime O-ethers were obtained in 15–83% yields.