René Frank

University of Leipzig, Leipzig, Saxony, Germany

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Publications (14)48.24 Total impact

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    ABSTRACT: Substitution of the dicarbaundecaborate anion nido-7,8-C2 B9 H12 (-) (1) by precise hydride abstraction followed by nucleophilic attack usually leads to symmetric products 10-R-nido-7,8-C2 B9 H11 . However, thioacetamide (MeC(S)NH2 ) as nucleophile and acetone/AlCl3 as hydride abstractor gave asymmetric 9-[MeC(NHiPr)S]-nido-7,8-C2 B9 H11 (2), whereas N,N-dimethylthioacetamide (MeC(S)NMe2 ) gave the expected symmetric 10-[MeC(NMe2 )S]-nido-7,8-C2 B9 H11 (4). For the formation of 2, acetone and thioacetamide are assumed to give the intermediate MeC(S)N(CMe2 ) (3), which then attacks 1 with formation of 2. Similarly, reaction of acetyliminium chloride [MeC(O)NH(CPh2 )]Cl (5) with 1 in THF gave a mixture of 9- and 10-substituted [MeC(NHCHPh2 )O]-nido-7,8-C2 B9 H11 (6 and 7, respectively). These reactions are the first examples in which compounds (here heterodienes) that unite the functionalities of both hydride acceptor and nucleophilic site react with 1 in a bimolecular fashion. Furthermore, the analogous reaction of 1 and 5 (in an equilibrium mixture with acetyl chloride and benzophenone imine) in MeCN afforded 10-[MeC(NCPh2 )NH]-nido-7,8-C2 B9 H11 (8) and MeC(O)NHCHPh2 (9).
    Chemistry 01/2014; 20(5):1440-6. · 5.93 Impact Factor
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    ABSTRACT: New phosphorus-containing, five-membered P,P,P and P,N,P heterocycles were synthesized and fully characterized. The P,P,P heterocycles, 1,2,3-triphospholanes, can be synthesized by two different facile pathways, whereas the P,N,P compound, a 1-aza-2,5-diphospholane, can only be obtained with silylamine.
    Chemistry 12/2013; · 5.93 Impact Factor
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    ABSTRACT: The first terminal organometallic alkylphosphanylidenetantalum(V) complexes [Cp*Ta{1,2-(NSiMe3)2C6H4}(PR)] were obtained with cyclohexyl (2) and isopropyl groups (3) at phosphorus, whereas adamantyl and tert-butyl substituents resulted in the formation of the paramagnetic tantalum(IV) complex [Cp*Ta{1,2-(NSiMe3)2C6H4}Cl] (4). DFT studies showed that the terminal cyclohexyl and isopropyl phosphanylidene complexes are stable towards dimerization and dissociation.
    Berichte der deutschen chemischen Gesellschaft 06/2013; 2013(18). · 2.94 Impact Factor
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    ABSTRACT: Short selective neuropeptide Y (NPY) analogs are highly attractive because of their facile synthesis. Based on the reduced-size NPY analog [Pro(30), Nle(31), Bpa(32), Leu(34)]NPY 28-36 position 32 was identified as a key position to alter the preferential activation pattern of the human neuropeptide Y receptors (hYRs). By replacing benzoylphenylalanine (Bpa) by a biphenylalanine (Bip) the photostability was first improved while the biological activity was maintained. SAR-studies showed that both aromatic rings have a high influence on the preferential hYR subtype activation. Interestingly, replacement of Bpa(32) by a strongly hydrophobic moiety changed the hYR subtype preference of the analog. Whereas the parent compound is able to activate the human neuropeptide Y(1) receptor (hY(1)R) subtype, the introduction of an N(ε)-ortho-carbaboranyl propionic acid modified lysine resulted in a loss of activity at the hY(1)R but in an increased activity at both the hY(2)R and the hY(4)R. However, subsequent receptor internalization studies with this novel analog revealed that receptor internalization can neither be triggered at the hY(2)R nor at the hY(4)R suggesting a biased ligand. Surprisingly, investigations by (1)H NMR spectroscopy revealed structural changes in the side chains of residues Pro(30) and Leu(34) which nicely correlates with the shift from hY(1)R/hY(4)R to hY(2)R/hY(4)R activation preference. Thus, position 32 has been identified to switch the bioactive conformation and subsequently influences receptor subtype activation behavior.
    Neuropeptides 01/2013; · 2.07 Impact Factor
  • Pure and Applied Chemistry 05/2012; 84(11):2289-2298. · 3.39 Impact Factor
  • ChemPlusChem 05/2012; 77(5).
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    ABSTRACT: Sulfenyl chlorides RSCl (R = p-C(6)H(4)OMe, Ph, p-C(6)H(4)NO(2), CN or 2-C(5)H(4)N) react with 7,8-nido-C(2)B(9)H(12)(-) with asymmetric substitution on the pentagonal C(2)B(3) face to give 9-RS-7,8-nido-C(2)B(9)H(11)(-) (R = p-C(6)H(4)OMe (3), Ph (4), p-C(6)H(4)NO(2) (5), CN (6)) and the zwitterion 9-(S-2-C(5)H(4)NH)-7,8-nido-C(2)B(9)H(11) (7), respectively, in high yield, while tBuSCl did not react and S(2)Cl(2) led to decomposition. Further reaction of 5-7 with iodine gave the corresponding iodo derivatives NMe(4) [9-I-11-RS-7,8-nido-C(2)B(9)H(10)] (R = p-C(6)H(4)NO(2) (8), CN (9)) and the zwitterion 9-I-11-(S-2-C(5)H(4)NH)-7,8-nido-C(2)B(9)H(11) (10), respectively. Compounds 3-10 were fully characterised by (1)H, (11)B, (11)B{(1)H}, (13)C{(1)H} spectroscopy, IR spectroscopy, mass spectrometry and elemental analysis, 3-7 also by (11)B-(11)B{(1)H} COSY NMR spectroscopy and 8-10 by X-ray structure determination.
    Dalton Transactions 04/2012; 41(20):6155-61. · 3.81 Impact Factor
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    Chemistry 05/2011; 17(22):6034-8. · 5.93 Impact Factor
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    ABSTRACT: Nontoxic ortho-carbaborane is one of the most promising structure for boron neutron capture therapy (BNCT). For directed uptake of ortho-carbaborane by tumor cells, receptor-subtype selective neuropeptide Y (NPY) and its derivatives were modified with ortho-carbaborane. The derivative [F(7), P(34)]-NPY has been shown to be a breast cancer selective ligand that binds to the Y(1)-receptor subtype, whereas [Ahx(5-24)]-NPY selectively addresses Y(2)-receptor subtypes that are found in neuroblastoma cells. ortho-Carbaboranyl propionic acid was synthesized and linked to the ε-amino group of N(α)-Fmoc protected L-lysine. The characterization of the compounds was performed by NMR, IR, and MS studies. The carbaborane-modified amino acid was incorporated into NPY, [F(7), P(34)]-NPY, and [Ahx(5-24)]-NPY by an optimized solid phase peptide synthesis using Fmoc protection. Binding studies and IP accumulation assays confirmed nanomolar affinity and activity of the modified analogues despite of the large carbaborane cluster. Internalization studies revealed excellent and receptor subtype specific uptake of the conjugates into respective cells.
    Journal of Medicinal Chemistry 03/2011; 54(7):2368-77. · 5.61 Impact Factor
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    ABSTRACT: The 1:1 or 1:2 stoichiometric reaction of [Na2(thf)4(P4Mes4)] (1; Mes = 2,4,6-Me3C6H2) with [{RhCl(cod)}2] (cod = 1,5-cyclooctadiene) gave a mixture of compounds of which [Na(thf)3][Rh(P3Mes3)(cod)] (2) with a trimesityltriphosphane-1,3-diide ligand was structurally characterized. Density functional calculations on 2 confirmed the structural parameters obtained by X-ray diffraction studies. Shared electron number and natural bond orbital analyses indicated only weak interactions between Na and P, which were found to be even weaker than the Na–Rh interactions with covalent contribution. When an excess of 1 was used (3:1 or 4:1), 2 was also obtained as the major product together with small amounts of the side-products cyclo-P6Mes6 (3) and [Na3(Et2O)(P4Mes4)(PHMes)]∞ (4). Compounds 3 and 4 were only characterized by single-crystal X-ray diffraction studies. Their formation indicates that the reaction includes the breaking and making of P–P bonds to give (P3Mes3)2–, PHMes–, and cyclo-P6Mes6, although the mechanism is unclear. Furthermore, the reaction of 1 with 2 equiv. of [AgCl(PPh3)2] gave the tetranuclear compound [Ag4(P6Mes6)2] (5) in which the novel (P6Mes6)2– ion also indicates degradation of the P4 chain followed by P–P bond formation.
    European Journal of Inorganic Chemistry 01/2011; 2011:739--747. · 3.12 Impact Factor
  • Eur. J. Inorg. Chem. 01/2011; 2011:739-747.
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    ABSTRACT: The synthesis of chiral ortho-carbaboranyl bis(aminohalophosphines) is presented, and spectroscopic and crystallographic data of these compounds are discussed. Furthermore, their reactivity toward alcoholysis was investigated. Quantum chemical calculations showed that the inhibition of methanolysis is of kinetic and not of thermodynamic origin. The disubstitution of the carbaboranes leads to P...P interactions as strong as a hydrogen bond that extremely lower the rate of the methanolysis.
    Inorganic Chemistry 07/2009; 48(13):6072-82. · 4.59 Impact Factor
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    ABSTRACT: Enantiomerically pure (RP,RP)- and (RP,SP)-1,2-bis[1-adamantyloxy-(–)-menthyloxyphosphanyl]-closo-dicarbaborane(12), 1,2-bis[bis(–)-menthyloxyphosphanyl]-closo-dicarbaborane(12)and 1,2-bis[bis(4-tert-butylphenyloxy)phosphanyl]-closo-dicarbaborane(12) were synthesised by the reaction of dilithiated 1,2-dicarba-closo-dodecaborane(12) with two equivalents of the corresponding chlorophosphite. The phosphonites are stable towards epimerisation, oxygen and water. P···P through-space coupling was observed, and the 3JPP coupling constants were determined by spectral simulation and DFT calculations. Late transition-metal complexes with molybdenum and rhodium were prepared to study the coordination properties of the bis(phosphanyl)carbaborane(12) compounds. Catalytic properties of various rhodium complexes were investigated in homogeneous catalytic hydroformylation reactions with various olefins. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)
    Berichte der deutschen chemischen Gesellschaft 05/2009; 2009(19):2776 - 2788. · 2.94 Impact Factor
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    ABSTRACT: Substitution at the dicarbaborate anion nido-7,8-C2B9H12− (1) with precise hydride abstraction leads to symmetric products 10-R-nido-7,8-C2B9H11, e.g., 10-[cyclo-(CH2)4O]-nido-7,8-C2B9H11 (2) and 10-[cyclo-(CH2)4S]-nido-7,8-C2B9H11 (3). However, this approach has been limited to acetaldehyde as hydride acceptor in an acidified, aqueous two-phase system. In expanding the concept of hydride abstraction, we have found that acetone, activated by AlCl3, is capable of accepting hydride with substitution of the symmetric B10 position in the presence of suitable donor molecules (Lewis bases). Thus, by employing a one-phase water-free system, 2 and 3 as well as moisture-sensitive 10-CH3CN-nido-7,8-C2B9H11 (4) were obtained in good to high yield. Reactions with 1 in neat acetone gave 10-HO-nido-7,8-C2B9H11− (7). An alternative reagent for hydride abstraction in 1 is tritylium tetrafluoroborate (Ph3CBF4), which gave 10-Ph2S-nido-7,8-C2B9H11 (11) in the presence of Ph2S. The Ph2S moiety in 11 could easily be replaced by pyridine and triethylamine, giving 10-C5H5N-nido-7,8-C2B9H11 (12) and 10-Et3N-nido-7,8-C2B9H11 (13). Additionally, reactions of 1 with CF3SO3H in the presence of CH3CN or CH3SCN gave 9-CH3C(NH2)-nido-7,8-C2B9H11 (5) and 9-CH3SC(NH2)-nido-7,8-C2B9H11 (6) by electrophilic substitution.
    Journal of Organometallic Chemistry · 2.00 Impact Factor