Ljuba Iovkova-Berends

Novel stannatranes of the type N(CH2CMe2O)3SnX (X = OR, SR, OC(O)R, SP(S)Ph2, halogen). Synthesis, molecular structures, and electrochemical properties.

The syntheses of the stannatrane derivatives of the type N(CH(2)CMe(2)O)(3)SnX (1, X = Ot-Bu; 2, X = Oi-Pr; 3, X = 2,6-Me(2)C(6)H(3)O; 4, X = p-t-BuC(6)H(4)O; 5, X = p-NO(2)C(6)H(4)O; 6, X = p-FC(6)H(4)O; 7, X = p-PPh(2)C(6)H(4)O; 8, X = p-MeC(6)H(4)S; 9, X = o-NH(2)C(6)H(4)O; 10, X = OCPh(2)CH(2)NMe(2); 11, X = Ph(2)P(S)S; 12, X = p-t-BuC(6)H(4)C(O)O; 13, X = Cl; 14, X = Br; 15, X = I; 16, X = p-N(CH(2)CMe(2)O)(3)SnOSiMe(2)C(6)H(4)SiMe(2)O) are reported. The compounds are characterized by X-ray diffraction analyses (3-8, 11-16), multinuclear NMR spectroscopy, (13)C CP MAS (14) and (119)Sn CP MAS NMR (13, 14) spectroscopy, mass spectrometry and osmometric molecular weight determination (13). Electrochemical measurements show that anodic oxidation of the stannatranes 4 and 8 occurs via electrochemically reversible electron transfer resulting in the corresponding cation radicals. The latter were detected by cyclic voltammetry (CV) and real-time electron paramagnetic resonance spectroscopy (EPR). DFT calculations were performed to compare the stannatranes 4, 8, and 13 with the corresponding cation radicals 4(+•), 8(+•), and 13(+•), respectively.

t-Bu2SiF-derivatized D2-receptor ligands: the first SiFA-containing small molecule radiotracers for target-specific PET-imaging.

The synthesis, radiolabeling and in vitro evaluation of new silicon-fluoride acceptor (SiFA) derivatized D2-receptor ligands is reported. The SiFA-technology simplifies the introduction of fluorine-18 into target specific biomolecules for Positron-Emission-Tomography (PET). However, one of the remaining challenges, especially for small molecules such as receptor-ligands, is the bulkiness of the SiFA-moiety. We therefore synthesized four Fallypride SiFA-conjugates derivatized either directly at the benzoic acid ring system (SiFA-DMFP, SiFA-FP, SiFA-DDMFP) or at the butyl-side chain (SiFA-M-FP) and tested their receptor affinities. We found D2-receptor affinities for all compounds in the nanomolar range (Ki(SiFA-DMFP) = 13.6 nM, Ki(SiFA-FP) = 33.0 nM, Ki(SiFA-DDMFP) = 62.7 nM and Ki(SiFA-M-FP) = 4.21 nM). The radiofluorination showed highest yields when 10 nmol of the precursors were reacted with [18F]fluoride/TBAHCO3 in acetonitrile. After a reversed phased cartridge purification the desired products could be isolated as an injectable solution after only 10 min synthesis time with radiochemical yields (RCY) of more than 40% in the case of SiFA-DMFP resulting in specific activities >41 GBq/µmol (>1,100 Ci/mmol). Furthermore, the radiolabeled products were shown to be stable in the injectable solutions, as well as in human plasma, for at least 90 min.

N-Aryl-substituted 5-aza-2,8-dioxasilabicyclo[3.3.01.5]octanes: syntheses, molecular structures, DFT calculations and cyclovoltammetric studies

Abstract The reaction of the silanes X2SiCl2 (X=H, Cl) with the dilithium salts of N-phenyldiethanolamine (1) and N-4-fluorophenyl-di-(2-dimethylpropan-2-ol)amine (2), respectively, gave the novel 5-aza-2,8-dioxasilabicyclo[3.3.01.5]octanes RN(CH2CR′2O)2SiX2 (3, R=Ph, R′=X=H; 4, R=Ph, R′=H, X=Cl; 5, R=4-FC6H4, R′=Me, X=H). These compounds were characterized by multinuclear NMR spectroscopy and single crystal X-ray diffraction analysis (1–4). The molecular structures of the dialkanolamines 1 and 2 are characterized by intra- and intermolecular O-H ··· O(H) hydrogen bridges giving rise to formation of eight-membered O4H4 rings (1) and polymeric chains (2). The 5-aza-2,8-dioxasilabicyclo[3.3.01.5]octanes show intramolecular N→Si interactions at distances of 2.961(2) (3) and 2.970(2) (4) Å, respectively. Also reported is the molecular structure of the hexachloridostannate salt [Ph(H)N(CH2CH2OH)2]2SnCl6 (6a) that was serendipitously obtained from the reaction of compound 3 with Ph3CSnCl5 under non-inert reaction conditions. Furthermore, DFT calculations on 3 and 4 as well as cyclovoltammetric studies were performed.

Progress toward the Total Synthesis of Gukulenin A: Photochemically Triggered Two-Carbon Ring Expansion Key to α-Tropolonic Ether Synthesis

The ex-chiral-pool synthesis of an advanced gukulenin A precursor from (-)-piperitone is revealed. Key C/C connecting maneuvers to the synthesis of a C2 dissymmetric bis(α-tropolonic) ether building block are a ring-contracting Meinwald rearrangement, a photochemically triggered two-carbon ring expansion, and a homodimerization by cross-metathesis.

Development of an Alkyne‐de Mayo Reaction for the Synthesis of Medium‐Sized Carbacycles and Cyclohepta[b]indoles

Embedded medium-sized carbacycles and cyclohepta[b]indoles occur frequently as scaffold elements in natural products and bioactive compounds. Described herein is a conceptionally novel photochemically triggered cascade process to these scaffolds. Key to the cascading ring-expansion process is an unprecedented intramolecular alkyne analogue of the de Mayo reaction.

Crystal structure of 4-(4-meth­oxy­phen­oxy)benzaldehyde

The title compound, C14H12O3, was synthesized via the nucleophilic addition of 4-methoxyphenol to 4-fluorobenzaldehyde. The dihedral angle between the least-squares planes of the benzene rings is 71.52 (3)° and the C—O—C angle at the central O atom is 118.82 (8)°. In the crystal, weak C—H⋯O hydrogen bonds link the molecules to generate supramolecular layers in the bc plane. The layers are linked by weak C—H⋯π interactions.

[4-(Di-tert-butyl-fluoro-silan-yl)phenyl]methanol.

The asymmetric unit of the title compound, C15H25FOSi, contains two independent molecules. Each of the Si atoms approximates the expected tetrahedral geometry with Si—F bond lengths of 1.6128 (11) and 1.6068 (11) Å in the two independent molecules. In the crystal, supramolecular chains along a are found mediated by O—H⋯O hydrogen bonds.