Wolf-Walther du Mont

Structure-activity correlation between natural glutathione peroxidase (GPx) and mimics: a biomimetic concept for the design and synthesis of more efficient GPx mimics.

Among the organoselenium compounds that mimic the action of the natural enzyme glutathione peroxidase (GPx), there are certain basic differences in the activity, substrate specificity and mechanism. These differences arise mainly from the nature of the substituents near the reaction center, and stability and reactivity of the intermediates. As an attempt to draw some general concepts for the development of new mimics, a structure–activity correlation between natural GPx and some existing mimics is described.

Reactions of Organoselenenyl Iodides with Thiouracil Drugs: An Enzyme Mimetic Study on the Inhibition of Iodothyronine Deiodinase

The proposed mechanism of iodothyronine deiodinase inhibition by the thiourea-derived drugs 6-n-propylthiouracil (PTU) and 6-methylthiouracil is supported by experimental evidence. Model reactions with sterically or coordinatively stabilized organoselenyl iodides as enzyme-mimetic substrates (E-SeI; see scheme) support the proposal that PTU reacts not with the enzyme but with the enzyme-SeI intermediate containing a covalent Se-I bond, and suggest that the Se-I bond is kinetically activated by basic amino acid groups such as histidine.

1,2‐Bis(3‐methyl‐imidazolin‐2‐ylium iodobromoselenanide)ethane: Oxidative Addition of IBr at the Se Atom of a >C=Se Group

Almost linear I-Se-Br groups with d(Se-Br)>d(Se-I) occur in 1⋅2u2009IBr, the first T-shaped Se adduct with IBr, which was synthesized by the oxidative addition of IBr to 1,2-bis(3-methylimidazoline-2-selonyl)ethane (1) in MeCN. Density functional theory calculations indicate the intramolecular Br⋅⋅⋅H interactions as being responsible for the peculiar structural features of the I-Se-Br groups.

Biomimetic Studies on Iodothyronine Deiodinase Intermediates: Modeling the Reduction of Selenenyl Iodide by Thiols

Enzyme mimetic studies on the crucial intermediate (E−SeI) of the iodothyronine deiodinase cycle have been carried out by using an areneselenenyl iodide stabilized by intramolecular Se⋅⋅⋅N interactions. Treatment of this compound with aromatic thiols and thiobenzoxazole in the presence of NEt3 affords areneselenenyl sulfides that are stable towards disproportionation reactions. The structures of three of the areneselenenyl sulfides were determined by X‐ray crystallography. In one case, in the absence of NEt3, a diselenide can be formed rather than the selenenyl sulfide. The areneselenenyl iodide also reacts with a related selenol to produce the corresponding diselenide, and this reaction is found to be much faster than that with thiols. The high reactivity of the selenenyl iodide with the selenol suggests that a reduced selenol group (R′−SeH) may react with the E−SeI intermediate to produce a diselenide (E−Se−Se−R′) without any thiol cosubstrate. The intermediacy of selenenyl sulfides during the reduction of selenenyl iodide by thiols and its possible relevance to the iodothyronine deiodinase catalytic cycle is also described.

Novel trichlorosilylation and trichlorogermylation of a P-chlorophosphaalkene leading to functionally substituted diphosphenes

The reactions of P-chlorobis(trimethylsilyl)methylenephosphane with hexachlorodisilane or with dichlorogermylene-dioxane afford the new Si-functionalised ditrisyldiphosphene derivative [(Me 3 Si) 2 (Cl 3 Si)CP] 2 and the related trichlorogermyl diphosphene [(Me 3 Si) 2 (Cl 3 Ge)CP] 2

Selenenyl iodide: a new substrate for mammalian thioredoxin reductase

Areneselenenyl iodide stabilised by internal chelation has been synthesized and evaluated as a substrate of thioredoxin reductase (TrxR). The reactivity of TrxR obtained from human placenta towards selenenyl iodide was found to be much higher than that of the E. coli enzyme, indicating the essential nature of a selenocysteine residue in the active site of the human enzyme. The addition of thioredoxin (Trx) significantly enhanced the TrxR-catalysed reduction of selenenyl iodide 1. These studies on the reduction of a selenenyl iodide by the thioredoxin system suggest that stable selenenyl iodides could be new substrates for human TrxR. The Trx system could act as a cofactor for iodothyronine deiodinase by reducing the selenenyl iodide intermediate in the second-half of the deiodinase catalytic cycle to regenerate the active site. The TrxR-catalysed reduction of 1 was not inhibited by the anti-thyroid drug, PTU, suggesting that the involvement of the Trx system in the deiodinase cycle may be responsible for the insensitivity of certain deiodinases towards clinically useful thiourea drugs.

Mesityl­selenenyl iodide

The title compound, C9H11ISe, displays the following dimensions involving selenium: Se—I 2.5360u2005(11)u2005A, Se—C1 1.923u2005(6)u2005A and C—Se—I 100.2u2005(2)°. Short Se⋯I and I⋯I contacts link the molxadecules into ribbons parallel to the b axis.

Nitrogen-bridged bidentate phosphaalkene ligands

Nitrogen-bridged bidentate phosphaalkenes reveal several exceptional properties as a new class of P=C-unsaturated diphosphinoamine (PNP) ligands: N–Si bond cleavage of the first N-silylimino-bridged bis-phosphaalkene (R2C=P)2NSiMe3 (R = iPrMe2Si) with chlorides of AgI, AuI, and RhI leads to complexes of the 5c-6π-heteropentadienide imidobisphosphaalkene anion; double Cl– transfer from PtCl2 and PdCl2 to coordinated phosphaalkene phosphorus atoms of P-diphenylphosphanylamino phosphaalkenes R2C=PN(R)PPh2 (R = Me3Si or iPrMe2Si; R = tBu, 1-Ada) furnishes unprecedented bis-chelate P-chloroylid complexes M[R2CP(Cl)N(R)PPh2]2 (M = Pd, Pt); CO- and RhI-induced coupling of two P-diphenylphosphanylamino phosphaalkenes under disilylketene elimination provides trigonal–bipyramidal RhIII complexes with novel tetradentate dianionic “PNP–C–PNP” ligands R2C[P(–)N(R)PPh2]2.

Do halogen and methyl substituents have electronic effects on the structures of simple disilanes? An experimental and theoretical study of the molecular structures of the series X3SiSiMe3 (X = H, F, Cl and Br)

The gas-phase molecular structures of a series of halogen-substituted disilanes [X3SiSiMe3 (Xxa0=xa0H, F, Cl and Br)], 1,1,1-trimethyldisilane (H3SiSiMe3), 1,1,1-trifluoro-2,2,2-trimethyldisilane (F3SiSiMe3), 1,1,1-trichloro-2,2,2-trimethyldisilane (Cl3SiSiMe3) and 1,1,1-tribromo-2,2,2-trimethyldisilane (Br3SiSiMe3), have been determined in the gas phase by electron diffraction. Ab initio calculations at the HF and MP2 level were used to support the experimental investigation using the SARACEN method. All of the investigated structures were determined to adopt a staggered structure with C3v symmetry. The effect of substitution on the Si–Si bond and the Si–Si–X bond angle was investigated and these results were compared to results obtained from a recent study of halogen-substituted disilanes [X3SiSiXMe2 (Xxa0=xa0F, Cl, Br and I)] to consider the effect of the methyl groups on the substituted disilanes.

mer-Bis[2-(6-fluoro-3-methyl­quinoxalin-2-yl-κN1)phen­yl][3-phenyl-5-(2-pyridyl-κN)-1,2,4-triazol-1-yl]iridium(III) dichloro­methane disolvate

The title compound, [Ir(C15H10FN2)2(C13H9N4)]·2CH2Cl2 or C43H29F2IrN8·2CH2Cl2, shows the appreciable trans influence of the C donors; the Ir—N bond lengths trans to C are 2.129u2005(2) and 2.210u2005(2)u2005A, cf. the Ir—N distances trans to N, of 2.055u2005(2) and 2.070u2005(2)u2005A. The three chelating ligands are approximately perpendicular to each other.