Degradation of the gamma-Carboxyl-Containing Diarylpropane Lignin Model Compound 3-(4'-Ethoxy-3'-Methoxyphenyl)-2-(4'-Methoxyphenyl)Propionic Acid by the Basidiomycete Phanerochaete chrysosporium

The white-rot basidiomycete Phanerochaete chrysosporium metabolized 3-(4'-ethoxy-3'-methoxyphenyl)-2-(4'-methoxyphenyl)propionic acid (V) in low-nitrogen, stationary cultures, conditions under which ligninolytic activity is expressed. The ability of several fungal mutant strains to degrade V reflected their ability to degrade [C]lignin to CO(2). 1-(4'-Ethoxy-3'-methoxyphenyl)-2-(4'-methoxyphenyl)-2- hydroxyethane (VII), anisyl alcohol, and 4-ethoxy-3-methoxybenzyl alcohol were isolated as metabolic products, indicating an initial oxidative decarboxylation of V, followed by alpha, beta cleavage of the intermediate (VII). Exogenously added VII was rapidly converted to anisyl alcohol and 4-ethoxy-3-methoxybenzyl alcohol. When the degradation of V was carried out under O(2), O was incorporated into the beta position of the diarylethane product (VII), indicating that the reaction is oxygenative.     

Arylglycerol-γ-Formyl Ester as an Aromatic Ring Cleavage Product of Nonphenolic β-O-4 Lignin Substructure Model Compounds Degraded by Coriolus versicolor

4-Ethoxy-3-methoxyphenylglycerol-γ-formyl ester (compound IV) was identified as a degradation product of both 4-ethoxy-3-methoxyphenylglycerol-β-syringaldehyde ether (compound I) and 4-ethoxy-3-methoxyphenylglycerol-β-2,6-dimethoxyphenyl ether (compound II) by a ligninolytic culture of Coriolus versicolor. An isotopic experiment with a ¹³C-labeled compound (compound II′) indicated that the formyl group of compound IV was derived from the β-phenoxyl group of β-O-4 dimer as an aromatic ring cleavage fragment. However, compound IV was not formed from 4-ethoxy-3-methoxyphenylglycerol-β-guaiacyl ether (compound III). γ-Formyl arylglycerol (compound IV) could be a precursor of 4-ethoxy-3-methoxyphenylglycerol (compound VI), because 3-(4-ethoxy-3-methoxyphenyl)-1-formyloxy propane (compound VII) was cleaved to give 3-(4-ethoxy-3-methoxyphenyl)-1-propanol (compound VIII) by C. versicolor. 4-Ethoxy-3-methoxyphenylglycerol-β,γ-cyclic carbonate (compound V), previously found as a degradation product of compound III by Phanerochaete chrysosporium (T. Umezawa, and T. Higuchi, FEBS Lett., 25:123-126, 1985), was also identified from the cultures with compound I, II, and III and degraded to give the arylglycerol (compound VI). An isotopic experiment with ¹³C-labeled compounds II′ and III′ indicated that the carbonate carbon of compound V was derived from the β-phenoxyl groups of β-O-4 substructure.     

Microbial Reduction of 1,3-Dioxo-2-Methyl-2-(3′-Oxo-6′-Carbomethoxyhexyl)-Cyclopentane to Form 1β-Hydroxy-3-Oxo-2β-Methyl-2α-(3′-Oxo-6′-Carbomethoxy-hexyl)-Cyclopentane, an Intermediate for Steroid Total Synthesis

The rate and extent of stereoselective reduction of 1,3-dioxo-2-methyl-2-(3′-oxo-6′-carbomethoxyhexyl)-cyclopentane to form the 1β-hydroxy-2β-methyl isomer by cultures of Schizosaccharomyces pombe ATCC 2476 was dramatically increased by addition to the fermentation of certain α,β-unsaturated ketones and allyl alcohol.     

Metabolism of Radiolabeled β-Guaiacyl Ether-Linked Lignin Dimeric Compounds by Phanerochaete chrysosporium

Phanerochaete chrysosporium metabolized the radiolabeled lignin model compounds [γ-¹⁴C]guaiacylglycerol-β-guaiacyl ether and [4-methoxy-¹⁴C]veratrylglycerol-β-guaiacyl ether (VI) to ¹⁴CO₂ in stationary and in shaking cultures. ¹⁴CO₂ evolution was greater in stationary culture. ¹⁴CO₂ evolution from [γ-¹⁴C]guaiacyl-glycerol-β-guaiacyl ether and [4-methoxy-¹⁴C]veratrylglycerol-β-guaiacyl ether in stationary cultures was two- to threefold greater when 100% O₂ rather than air (21% O₂) was the gas phase above the cultures. ¹⁴CO₂ evolution from the metabolism of the substrates occurred only as the culture entered the stationary phase of growth. The presence of substrate levels of nitrogen in the medium suppressed ¹⁴CO₂ evolution from both substrates in stationary cultures. [¹⁴C]veratryl alcohol and 4-ethoxy-3-methoxybenzyl alcohol were formed as products of the metabolism of VI and 4-ethoxy-3-methoxyphenylglycerol-β-guaiacyl ether, respectively.     

7-Deaza-2′-deoxyadenosine and 3-deaza-2′-deoxyadenosine replacing dA within d(A6)-tracts: differential bending at 3′- and 5′-junctions of d(A6)·d(T6) and B-DNA

7-Deaza-2′-deoxyadenosine (1, c⁷A_d) and 3-deaza-2′-deoxyadenosine (2, c³A_d) have been incorporated into d(AAAAAA) tracts replacing dA at various positions within oligonucleotides. For this purpose suitably protected phosphonates have been prepared and oligonucleotides were synthsized on solid-phase. The oligomers were hybridized with their cognate strands. The duplexes were phosphorylated at OH-5′ by polynucleotide kinase and self-ligated to multimers employing T4 DNA ligase. Oligomerized DNA-fragments were analyzed by polyacrylamide gel electrophoresis and the bending was determined from anomalies of electrophoretic mobility. Replacement of dA by c³A_d decreased the bending more than replacement by c⁷A_d. Reduction of bending was much stronger when the modified nucleosides replaced one or several dA residues at the 3′-site of an d(AAAAAA)-tract whereas replacement at the 5′-site showed no significant influence [1, 2].     

NMR solution structures of Runella slithyformis RNA 2′-phosphotransferase Tpt1 provide insights into NAD+ binding and specificity

Tpt1, an essential component of the fungal and plant tRNA splicing machinery, catalyzes transfer of an internal RNA 2′-PO₄ to NAD⁺ yielding RNA 2′-OH and ADP-ribose-1′,2′-cyclic phosphate products. Here, we report NMR structures of the Tpt1 ortholog from the bacterium Runella slithyformis (RslTpt1), as apoenzyme and bound to NAD⁺. RslTpt1 consists of N- and C-terminal lobes with substantial inter-lobe dynamics in the free and NAD⁺-bound states. ITC measurements of RslTpt1 binding to NAD⁺ (K_D ∼31 μM), ADP-ribose (∼96 μM) and ADP (∼123 μM) indicate that substrate affinity is determined primarily by the ADP moiety; no binding of NMN or nicotinamide is observed by ITC. NAD⁺-induced chemical shift perturbations (CSPs) localize exclusively to the RslTpt1 C-lobe. NADP⁺, which contains an adenylate 2′-PO₄ (mimicking the substrate RNA 2′-PO₄), binds with lower affinity (K_D ∼1 mM) and elicits only N-lobe CSPs. The RslTpt1·NAD⁺ binary complex reveals C-lobe contacts to adenosine ribose hydroxyls (His99, Thr101), the adenine nucleobase (Asn105, Asp112, Gly113, Met117) and the nicotinamide riboside (Ser125, Gln126, Asn163, Val165), several of which are essential for RslTpt1 activity in vivo. Proximity of the NAD⁺ β-phosphate to ribose-C1″ suggests that it may stabilize an oxocarbenium transition-state during the first step of the Tpt1-catalyzed reaction.     

Isolation of 4′-Hydroxyechinenone from Micrococcus roseus

The carotenoid 4′-hydroxyechinenone (4′-hydroxy-β, β-carotene-4-one) was isolated from Micrococcus roseus. It is proposed as an intermediate between echinenone and canthaxanthin.     

Transformation of 2,2′-Bimorphine to the Novel Compounds 10-α-S-Monohydroxy-2,2′-Bimorphine and 10,10′-α,α′-S,S′-Dihydroxy-2,2′-Bimorphine by Cylindrocarpon didymum

Whole-cell suspensions of Cylindrocarpon didymum were observed to transform 2,2′-bimorphine to the compounds 10-α-S-monohydroxy-2,2′-bimorphine and 10,10′-α,α′-S,S′-dihydroxy-2,2′-bimorphine. Mass spectrometry and ¹H nuclear magnetic resonance spectroscopy confirmed the identities of these new morphine alkaloids.     

AarI, a restriction endonuclease from Arthrobacter aurescens SS2-322, which recognizes the novel non-palindromic sequence 5′-CACCTGC(N)4/8-3′

A new type II restriction endonuclease AarI has been isolated from Arthrobacter aurescens SS2-322. AarI recognizes the non-palindromic heptanucleotide sequence 5′-CACCTGC(N)_4/8-3′ and makes a staggered cut at the fourth and eighth bases downstream of the target duplex producing a four base 5′-protruding end. AarI activity is stimulated by oligodeoxyribonucleotide duplexes containing an enzyme-specific recognition sequence.     

The Cytoprotective Effects of E-α-(4-Methoxyphenyl)-2’,3,4,4'-Tetramethoxychalcone (E-α-p-OMe-C6H4-TMC)—A Novel and Non-Cytotoxic HO-1 Inducer

Cell protection against different noxious stimuli like oxidative stress or chemical toxins plays a central role in the treatment of many diseases. The inducible heme oxygenase isoform, heme oxygenase-1 (HO-1), is known to protect cells against a variety of harmful conditions including apoptosis. Because a number of medium strong electrophiles from a series of α-X-substituted 2’,3,4,4’-tetramethoxychalcones (α-X-TMCs, X = H, F, Cl, Br, I, CN, Me, p-NO₂-C₆H₄, Ph, p-OMe-C₆H₄, NO₂, CF₃, COOEt, COOH) had proven to activate Nrf2 resulting in HO-1 induction and inhibit NF-κB downstream target genes, their protective effect against staurosporine induced apoptosis and reactive oxygen species (ROS) production was investigated. RAW264.7 macrophages treated with 19 different chalcones (15 α-X-TMCs, chalcone, 2’-hydroxychalcone, calythropsin and 2’-hydroxy-3,4,4’-trimethoxychalcone) prior to staurosporine treatment were analyzed for apoptosis and ROS production, as well as HO-1 protein expression and enzyme activity. Additionally, Nrf2 and NF-κB activity was assessed. We found that amongst all tested chalcones only E-α-(4-methoxyphenyl)-2’,3,4,4''-tetramethoxychalcone (E-α-p-OMe-C₆H₄-TMC) demonstrated a distinct, statistically significant antiapoptotic effect in a dose dependent manner, showing no toxic effects, while its double bond isomer Z-α-p-OMe-C₆H₄-TMC displayed no significant activity. Also, E-α-p-OMe-C₆H₄-TMC induced HO-1 protein expression and increased HO-1 activity, whilst inhibition of HO-1 by SnPP-IX abolished its antiapoptotic effect. The only weakly electrophilic chalcone E-α-p-OMe-C₆H₄-TMC reduced the staurosporine triggered formation of ROS, while inducing the translocation of Nrf2 into the nucleus. Furthermore, staurosporine induced NF-κB activity was attenuated following E-α-p-OMe-C₆H₄-TMC treatment. Overall, E-α-p-OMe-C₆H₄-TMC demonstrated its effective cytoprotective potential via a non-toxic induction of HO-1 in RAW264.7 macrophages. The observed cytoprotective effect may partly be related to both, the activation of the Nrf2- and inhibition of the NF-κB pathway.     

Localization of an Amikacin 3′-Phosphotransferase in Escherichia coli

A plasmid-encoded enzyme reported by us to phosphorylate amikacin in a laboratory strain of Escherichia coli has been localized in the bacterial cell. More than 88% of this amikacin phosphotransferase (APH) activity was retained in spheroplasts formed by ethylenediaminetetraacetate-lysozyme treatment of an APH-containing E. coli transconguant known to form spheroplasts readily. By comparison, the spheroplasts retained 94% of deoxyribonucleic acid polymerase I and 98% of glutamyl-transfer ribonucleic acid synthetase, two internal markers, whereas less than 10% of the activity of a periplasmic marker, acid phosphatase, was present in spheroplasts. Treatment of whole cells of the transconjugant with chemical probes incapable of crossing the plasma membrane obliterated acid phosphatase activity, whereas the internal markers deoxyribonucleic acid polymerase I, glutamyl-transfer ribonucleic acid synthetase, and β-galactosidase were virtually unaffected after treatment for 5 min; more than 60% of the APH activity remained. As a control, similar chemical treatment of sonic extracts, in which enzymes were not protected by bacterial compartmentalization, produced more extensive reduction in the activities of all test enzymes, including APH. Spheroplasts preincubated with adenosine triphosphatase were shown by thin-layer chromatography to phosphorylate amikacin. Spheroplasts of cells grown in the presence of H₃³²PO₄ were shown to utilize internally generated adenosine 5′-triphosphate in the phosphorylation of amikacin. The absence of ³²P-phosphorylated amikacin after incubation of [γ-³²P]adenosine 5′-triphosphate with spheroplasts confirmed that exogenous adenosine 5′-triphosphate was not used in the reaction. These results suggest an internal location for APH. This conclusion has implications for the role of such enzymes in aminoglycoside resistance of gram-negative bacteria.     

Oligoribonuclease Is Encoded by a Highly Conserved Gene in the 3′-5′ Exonuclease Superfamily

Oligoribonuclease, a 3′-to-5′ exoribonuclease specific for small oligoribonucleotides, was purified to homogeneity from extracts of Escherichia coli. The purified protein is an α2 dimer of 40 kDa. NH₂-terminal sequence analysis of the protein identified the gene encoding oligoribonuclease as yjeR (o204a), a previously reported open reading frame located at 94 min on the E. coli chromosome. However, as a consequence of the sequence information, the translation start site of this open reading frame has been revised. Cloning of yjeR led to overexpression of oligoribonuclease activity, and interruption of the cloned gene with a kanamycin resistance cassette eliminated the overexpression. On the basis of these data, we propose that yjeR be renamed orn. Orthologs of oligoribonuclease are present in a wide range of organisms, extending up to humans.     

Preparation of selective and segmentally labeled single-stranded DNA for NMR by self-primed PCR and asymmetrical endonuclease double digestion

We demonstrate a new, efficient and easy-to-use method for enzymatic synthesis of (stereo-)specific and segmental ¹³C/¹⁵N/²H isotope-labeled single-stranded DNA in amounts sufficient for NMR, based on the highly efficient self-primed PCR. To achieve this, new approaches are introduced and combined. (i) Asymmetric endonuclease double digestion of tandem-repeated PCR product. (ii) T4 DNA ligase mediated ligation of two ssDNA segments. (iii) In vitro dNTP synthesis, consisting of in vitro rNTP synthesis followed by enzymatic stereo-selective reduction of the C2′ of the rNTP, and a one-pot add-up synthesis of dTTP from dUTP. The method is demonstrated on two ssDNAs: (i) a 36-nt three-way junction, selectively ¹³C₉/¹⁵N₃/²H_{(1′,2″,3′,4′,5′,5″)}-dC labeled and (ii) a 39-nt triple-repeat three-way junction, selectively ¹³C₉/¹⁵N₃/²H_{(1′,2″,3′,4′,5′,5″)}-dC and ¹³C₉/¹⁵N₂/²H_{(1′,2″,3′,4′,5′,5″)}-dT labeled in segment C20-C39. Their NMR spectra show the spectral simplification, while the stereo-selective ²H-labeling in the deoxyribose of the dC-residues, straightforwardly provided assignment of their C1′–H2′ and C2′–H2′ resonances. The labeling protocols can be extended to larger ssDNA molecules and to more than two segments.     

A Lithium-Sensitive and Sodium-Tolerant 3′-Phosphoadenosine-5′-Phosphatase Encoded by halA from the Cyanobacterium Arthrospira platensis Is Closely Related to Its Counterparts from Yeasts and Plants

3′-Phosphoadenosine-5′-phosphatase (PAPase) is required for the removal of toxic 3′-phosphoadenosine-5′-phosphate (PAP) produced during sulfur assimilation in various eukaryotic organisms. This enzyme is a well-known target of lithium and sodium toxicity and has been used for the production of salt-resistant transgenic plants. In addition, PAPase has also been proposed as a target in the treatment of manic-depressive patients. One gene, halA, which could encode a protein closely related to the PAPases of yeasts and plants, was identified from the cyanobacterium Arthrospira (Spirulina) platensis. Phylogenic analysis indicated that proteins related to PAPases from several cyanobacteria were found in different clades, suggesting multiple origins of PAPases in cyanobacteria. The HalA polypeptide from A. platensis was overproduced in Escherichia coli and used for the characterization of its biochemical properties. HalA was dependent on Mg²⁺ for its activity and could use PAP or 3′-phosphoadenosine-5′-phosphosulfate as a substrate. HalA is sensitive to Li⁺ (50% inhibitory concentration [IC₅₀] = 3.6 mM) but only slightly sensitive to Na⁺ (IC₅₀ = 600 mM). The salt sensitivity of HalA was thus different from that of most of its eukaryotic counterparts, which are much more sensitive to both Li⁺ and Na⁺, but was comparable to the PAPase AtAHL (Hal2p-like protein) from Arabidopsis thaliana. The properties of HalA could help us to understand the structure-function relationship underlying the salt sensitivity of PAPases. The expression of halA improved the Li⁺ tolerance of E. coli, suggesting that the sulfur-assimilating pathway is a likely target of salt toxicity in bacteria as well.     

Tuning of conformational preorganization in model 2',5'- and 3',5'-linked oligonucleotides by 3'- and 2'-O-methoxyethyl modification

Conformational properties of trimeric and tetrameric 2′,5′-linked oligonucleotides, 3′-MOE-A₃^2′,5′ (1) and 3′-MOE-A₄^2′,5′ (2), and their 3′,5′-linked analogs, 2′-MOE-A₃^3′,5′ (3) and 2′-MOE-A₄^3′,5′ (4), were examined with the use of heteronuclear NMR spectroscopy. The temperature-dependent ³J_HH, ³J_HP and ³J_CP coupling constants, acquired in the range of 273–343 K, gave insight into the conformation of sugar rings in terms of a two-state North ↔ South (N ↔ S) pseudorotational equilibrium and into the conformation of the sugar–phosphate backbone in the model antisense oligonucleotides 1–4. 2′,5′-linked oligomers 3′-MOE-A₃^2′,5′ (1) and 3′-MOE-A₄^2′,5′ (2) show preference for N-type conformers and indication of A-type conformational features, which is prerequisite for antisense hybridization. The drive of N ↔ S equilibrium in 1–4 has been rationalized with the competing gauche effects of 2′/3′-phosphodiester and 3′/2′-MOE groups, anomeric and steric effects. Furthermore, the pairwise comparisons of 3′-MOE with 3′-OH and 3′-deoxy 2′,5′-linked adenine trimers emphasized the fine tuning of N ↔ S equilibrium in 3′-MOE-A₃^2′,5′ (1) and 3′-MOE-A₄^2′,5′ (2) by the steric effects of 3′-MOE group and the possibility of water-mediated H-bonds with vicinal phosphodiester functionality. In full correspondence, the drive of N ↔ S equilibrium towards N by 2′-MOE in 3′,5′-linked analogs 2′-MOE-A₃^3′,5′ (3) and 2′-MOE-A₄^3′,5′ (4) is weaker in comparison with 3′-OH group in the corresponding ribo analogs. β^t, γ⁺ and ε^– rotamers are preferred in both 2′,5′- and in 3′,5′-linked oligonucleotides 1–4.     

Reduction of the 2,2′-Azinobis(3-Ethylbenzthiazoline-6-Sulfonate) Cation Radical by Physiological Organic Acids in the Absence and Presence of Manganese

Laccase is a copper-containing phenoloxidase, involved in lignin degradation by white rot fungi. The laccase substrate range can be extended to include nonphenolic lignin subunits in the presence of a noncatalytic cooxidant such as 2,2′-azinobis(3-ethylbenzthiazoline-6-sulfonate) (ABTS), with ABTS being oxidized to the stable cation radical, ABTS^·+, which accumulates. In this report, we demonstrate that the ABTS^·+ can be efficiently reduced back to ABTS by physiologically occurring organic acids such as oxalate, glyoxylate, and malonate. The reduction of the radical by oxalate results in the formation of H₂O₂, indicating the formation of O₂^·− as an intermediate. O₂^·− itself was shown to act as an ABTS^·+ reductant. ABTS^·+ reduction and H₂O₂ formation are strongly stimulated by the presence of Mn²⁺, with accumulation of Mn³⁺ being observed. Additionally, 4-methyl-O-isoeugenol, an unsaturated lignin monomer model, is capable of directly reducing ABTS^·+. These data suggest several mechanisms for the reduction of ABTS^·+ which would permit the effective use of ABTS as a laccase cooxidant at catalytic concentrations.     

Structural and Functional Insight into the Carbohydrate Receptor Binding of F4 Fimbriae-producing Enterotoxigenic Escherichia coli

Enterotoxigenic Escherichia coli (ETEC) strains are important causes of intestinal disease in humans and lead to severe production losses in animal farming. A range of fimbrial adhesins in ETEC strains determines host and tissue tropism. ETEC strains expressing F4 fimbriae are associated with neonatal and post-weaning diarrhea in piglets. Three naturally occurring variants of F4 fimbriae (F4_ab, F4_ac, and F4_ad) exist that differ in the primary sequence of their major adhesive subunit FaeG, and each features a related yet distinct receptor binding profile. Here the x-ray structure of FaeG_ad bound to lactose provides the first structural insight into the receptor specificity and mode of binding by the poly-adhesive F4 fimbriae. A small D′-D″-α1-α2 subdomain grafted on the immunoglobulin-like core of FaeG hosts the carbohydrate binding site. Two short amino acid stretches Phe¹⁵⁰–Glu¹⁵² and Val¹⁶⁶–Glu¹⁷⁰ of FaeG_ad bind the terminal galactose in the lactosyl unit and provide affinity and specificity to the interaction. A hemagglutination-based assay with E. coli expressing mutant F4_ad fimbriae confirmed the elucidated co-complex structure. Interestingly, the crucial D′-α1 loop that borders the FaeG_ad binding site adopts a different conformation in the two other FaeG variants and hints at a heterogeneous binding pocket among the FaeG serotypes.     

NADP(H) Phosphatase Activities of Archaeal Inositol Monophosphatase and Eubacterial 3′-Phosphoadenosine 5′-Phosphate Phosphatase

NADP(H) phosphatase has not been identified in eubacteria and eukaryotes. In archaea, MJ0917 of hyperthermophilic Methanococcus jannaschii is a fusion protein comprising NAD kinase and an inositol monophosphatase homologue that exhibits high NADP(H) phosphatase activity (S. Kawai, C. Fukuda, T. Mukai, and K. Murata, J. Biol. Chem. 280:39200-39207, 2005). In this study, we showed that the other archaeal inositol monophosphatases, MJ0109 of M. jannaschii and AF2372 of hyperthermophilic Archaeoglobus fulgidus, exhibit NADP(H) phosphatase activity in addition to the already-known inositol monophosphatase and fructose-1,6-bisphosphatase activities. Kinetic values for NADP⁺ and NADPH of MJ0109 and AF2372 were comparable to those for inositol monophosphate and fructose-1,6-bisphosphate. This implies that the physiological role of the two enzymes is that of an NADP(H) phosphatase. Further, the two enzymes showed inositol polyphosphate 1-phosphatase activity but not 3′-phosphoadenosine 5′-phosphate phosphatase activity. The inositol polyphosphate 1-phosphatase activity of archaeal inositol monophosphatase was considered to be compatible with the similar tertiary structures of inositol monophosphatase, fructose-1,6-bisphosphatase, inositol polyphosphate 1-phosphatase, and 3′-phosphoadenosine 5′-phosphate phosphatase. Based on this fact, we found that 3′-phosphoadenosine 5′-phosphate phosphatase (CysQ) of Escherichia coli exhibited NADP(H) phosphatase and fructose-1,6-bisphosphatase activities, although inositol monophosphatase (SuhB) and fructose-1,6-bisphosphatase (Fbp) of E. coli did not exhibit any NADP(H) phosphatase activity. However, the kinetic values of CysQ and the known phenotype of the cysQ mutant indicated that CysQ functions physiologically as 3′-phosphoadenosine 5′-phosphate phosphatase rather than as NADP(H) phosphatase.     

CO substitution and diphosphine ligand chelation in the reaction between 4,5-bis(diphenylphosphino)-4-cyclopenten-1,3-dione (bpcd) and Re(2(CO)8(μ-H)(μ-η,η-C CPh)

The reaction between the redox-active diphosphine ligand 4,5-bis(diphenylphosphino)-4-cyclopenten-1,3-dione (bpcd) and the dirhenium compound Re₂(CO)₈(μ-H)(μ-η¹,η²-C CPh) in CH₂Cl₂ at room temperature proceeds by CO loss to give the dirhenium complex Re₂(CO)₇(bpcd)(μ-H)(η¹-C CPh) (1). This new complex was characterized in solution by IR and NMR (¹H and ³¹P) spectroscopy and in the solid state by X-ray diffraction analysis. Re₂(CO)₇(bpcd)(μ-H)(η¹-C CPh) crystallizes in the triclinic space group

Full-size image

γ = 69.240(6)°, V = 2024.9(3) ų, Z = 2, d_calc = 1.862 g cm⁻³ R = 0.0221, R_w = 0.243 for 4066 observed reflections. The bpcd ligand in 1 adopts a chelating mode with a linear phenylacetylide ligand being located on the adjacent rhenium center cis to the bpcd ligand. This complex represents the first structurally characterized example of a hydrido-bridged dirhenium complex possessing both a linear acetylide ligand and a chelating diphosphine ligand.