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.     

Nitrogen- and oxygen-bridged bidentate phosphaalkene ligands

An overview is given on synthesis and structures of new bidentate phosphaalkene ligands [(RMe₂Si)₂CP]₂E (E = O, NR, N^?) and (RMe₂Si)₂CPN(R′)PR′′₂. Exceptional properties of these ligands, extending beyond predictable properties of phosphaalkenes are: (i) the NSi bond cleavage of [(iPrMe₂Si)₂CP]₂NSiMe₃ with Au^I and Rh^I chloro complexes under mild conditions leading to binuclear complexes of the 6π-delocalised imidobisphosphaalkene anion [(iPrMe₂Si)₂CP]₂N^?, and (ii) the chlorotropic formation of molecular 1:2 Pd^II and Pt^II metallochloroylid complexes with novel ylid-type ligands [(RMe₂Si)₂CP(Cl)N(R)PR₂]^?, and the transformation of a P-platina-P-chloroylid complex into a C-platina phosphaalkene by intramolecular chlorosilane elimination. Properties of the heavier congeners [(RMe₂Si)₂CP]₂E (E = S, Se, Te, PR, P^?, As^?) and (RMe₂Si)₂CPEPR′′₂ (E = S, Se, Te) are also described.     

The Suprising Variety of Products from Reactions of P-P Bonds with Dichlorogermylene

Abstract

Insertion of dichlorogermylene (from GcCl₂-dioxane) into the P-P bonds of tetraalkyldiphosphanes ((PRR)₂ (2a: R, R ? i-Pr; 2b: R? t-Bu, R?i-Pr; 2C; R, R, ?t-Bu) leads 10 dichlorobis(dialkylphosphanyl)germanes 3a-c. With 2a. the insertion remains incomplete: 38 exists in an equilibrium with an adduct of diphosphane 2a with GeCI₂, Subsequently 3b and 3c undergo a-climinarions to dialkylchlorophosphanes Sb and Sc and the dimeric phosphanylgermylenes (RR PGeGl)² 4b and 4c [1]. Similar to the above (but in absence of dioxane), reacting the richlorogcrmylphosphane i-Pr(t-Bu)PGeCL₃, 7c [2] with the related trichlorosilylphosphanc i-Pr(t-Bu)PSiCl₃ provided a mixture of SiCl₄, 1c, 3c, 5c and 7c, 3a and 3c have been trapped as inert molybdenum complexes (CO)₄ MO(μ-PRR)₂ GeGl₂ 6a and 6c from cquilibrilia conraining la/ 2a/ 3a and 3c/ 4c / 5c / 7c respectively.     

P‐Aminophosphaalkenes with C‐Isopropyldimethylsilyl Groups

Amination of the C‐isopropyldimethylsilyl P‐chlorophosphaalkene (iPrMe₂Si)₂C=PCl ( 1 ) leads to the P‐aminophosphaalkenes (iPrMe₂Si)₂C=PN(R)R′ (R, R′ = Me ( 2 ), R = H, R′ = nPr ( 3 ), R = H, R′ = iPr ( 4 ), R = H, R′ = tBu ( 5 ), R = H, R′ = 1‐Ada ( 6 ), R = H, R′ = CPh₃ ( 7 ), R = H, R′ = Ph ( 8 ), R = H, RR′ = 2,6‐iPr₂Ph (= DIP) ( 10 ), R = H, R′ = 2,4,6‐Me₃Ph (= Mes) ( 11 ), R = H, R′ = 2,4,6‐tBu₃Ph (= Mes*)] ( 12 ), R = H, R′ = SiMe₃ ( 13 ), and R, R′ = SiMe₂Ph (1 4 ). ³¹P‐NMR spectra confirm that phosphaalkenes 2 – 7 and 10 – 14 are monomeric in solution; the structures of 7 , 10 , and 12 were determined by X‐ray crystallography. Freshly prepared (iPrMe₂Si)₂C=PN(H)Ph ( 8 ) is a monomer that dimerizes with (N→C) proton migration within several hours to the stable diazadiphosphetidine [(iPrMe₂Si)₂CHPNPh]₂ ( 9 ). NMR‐scale reactions of deprotonated 5 and 13 with tBuiPrPCl provide by P–P bond formation the P‐phosphanyl iminophosphoranes [(iPrMe₂Si)₂C=](RN=)PPtBu(iPr) [R = tBu ( 15 ), R = Me₃Si ( 17 )]. Deprotonated 5 and Me₃GeCl deliver by N–Ge bond formation the aminophosphaalkene (iPrMe₂Si)₂C=PN(tBu)GeMe₃ ( 20 ), which with elemental selenium 5 undergoes (N→C) proton migration to form the alkyl(imino)(seleno)phosphorane [(iPrMe₂Si)₂CH](tBuN=)P=Se ( 21 ), which is a selenium‐bridged cyclic dimer in the solid state.