Synthesis and structural characterization of the mono- and diphosphine-containing diiron propanedithiolate complexes related to [FeFe]-hydrogenases. Biomimetic H2 evolution catalyzed by (mu-PDT)Fe2(CO)4[(Ph2P)2N(n-Pr)

As the new H-cluster models, six diiron propanedithiolate (PDT) complexes with mono- and diphosphine ligands have been prepared and structurally characterized. The monophosphine model complex (μ-PDT)Fe₂(CO)₅[Ph₂PNH(t-Bu)] (1) was prepared by reaction of parent complex (μ-PDT)Fe₂(CO)₆ (A) with 1 equiv of Ph₂PNH(t-Bu) in refluxing xylene, whereas A reacted with 1 equiv of Me₃NO · 2H₂O in MeCN at room temperature followed by 1 equiv of Ph₂PH to give the corresponding monophosphine model complex (μ-PDT)Fe₂(CO)₅(Ph₂PH) (2). Further treatment of 2 with 1 equiv of n-BuLi in THF at −78 °C followed by 1 equiv of CpFe(CO)₂I from −78 °C to room temperature afforded monophosphine model complex (μ-PDT)Fe₂(CO)₅[Ph₂PFe(CO)₂Cp] (3), whereas the diphosphine model complexes (μ-PDT)Fe₂(CO)₄(Ph₂PC₂H₄PPh₂) (4), (μ-PDT)Fe₂(CO)₄[(Ph₂P)₂N(n-Pr)] (5) and (μ-PDT)Fe₂(CO)₄[(Ph₂P)₂N(n-Bu)] (6) were obtained by reactions of A with ca.1 equiv of the corresponding diphosphines in refluxing xylene. All the new model complexes were characterized by elemental analysis, spectroscopy and particularly for 1 and 3-6 by X-ray crystallography. On the basis of electrochemical and spectroelectrochemical studies, model 5 was found to be a catalyst for HOAc proton reduction to H₂, and for this electrocatalytic reaction an ECCE mechanism was proposed.     

[Co{Ph2P(O)CH2P(O)Ph2}3][CoCl4] · 8CHCl3: Crystal structure and formation from [Co2(Ph2PCH2PPh2)(CO)6] in chloroform

When a solution of [Co₂(Ph₂PCH₂PPh₂)(CO)₆] in chloroform or deuterochloroform is allowed to stand in air at room temperature, it deposits dark green crystals of [Co{Ph₂P(O)CH₂P(O)Ph₂}₃][CoCl₄] · 8CHCl₃. The same product is formed more quickly and in much higher yield (80% based on Co) if the reaction is carried out in the presence of 2 equiv. of [Ph₂PCH₂PPh₂]; the Co^II appears to catalyse the air-oxidation of [Ph₂PCH₂PPh₂]. The salt was characterised by X-ray crystallography and shown to contain octahedral Co^II cations and Co^II tetrahedral anions having normal bond lengths and angles.     

Conformational preferences of modified nucleoside N(2)-methylguanosine (m(2)G) and its derivative N(2), N(2)-dimethylguanosine (m(2)(2)G) occur at 26th position (hinge region) in tRNA

Conformational preferences of the modified nucleosides N²-methylguanosine (m²G) and N², N²-dimethylguanosine (m₂²G) have been studied theoretically by using quantum chemical perturbative configuration interaction with localized orbitals (PCILO) method. Automated complete geometry optimization using semiempirical quantum chemical RM1, along with ab initio molecular orbital Hartree–Fock (HF-SCF), and density functional theory (DFT) calculations has also been made to compare the salient features. Single-point energy calculation studies have been made on various models of m²G26:C/A/U44 and m₂²G26:C/A/U44. The glycosyl torsion angle prefers “syn” (χ = 286°) conformation for m²G and m₂²G molecules. These conformations are stabilized by N(3)–HC2′ and N(3)–HC3′ by replacing weak interaction between O5′–HC(8). The N²-methyl substituent of (m²G26) prefers “proximal” or s-trans conformation. It may also prefer “distal” or s-cis conformation that allows base pairing with A/U44 instead of C at the hinge region. Thus, N²-methyl group of m²G may have energetically two stable s-trans m²G:C/A/U or s-cis m²G:A/U rotamers. This could be because of free rotations around C–N bond. Similarly, N², N²-dimethyl substituent of (m₂²G) prefers “distal” conformation that may allow base pairing with A/U instead of C at 44th position. Such orientations of m²G and m₂²G could play an important role in base-stacking interactions at the hinge region of tRNA during protein biosynthesis process.     

Synthesis and bioactivity of 5-(1-aryl-1H-tetrazol-5-ylsulfanylmethyl)-N-xylopyranosyl-1,3,4-oxa(thia)diazol-2-amines

A series of new N′-[N-(2,3,4-tri-O-acetyl-β-d-xylopyranosyl)thiocarbamoyl]-2-[(1-aryl-1H-tetrazol-5-yl)sulfanyl]acetohydrazides 5a–5e were synthesized rapidly in high yields from 2-(1-aryl-1H-tetrazol-5-ylsulfanyl)acetohydrazides 3a–3e and 2,3,4-tri-O-acetyl-β-d-xylopyranosyl isothiocyanate 4, then 5a–5e were converted to a series of new 5-(1-aryl-1H-tetrazol-5-ylsulfanylmethyl)-N-(2,3,4-tri-O-acetyl-β-d-xylopyranosyl)-1,3,4-oxadiazole-2-amines 6a–6e and 5-(1-aryl-1H-tetrazol-5-ylsulfanylmethyl)-N-(2,3,4-tri-O-acetyl-β-d-xylopyranosyl)-1,3,4-thiadiazole-2-amines 7a–7e, respectively under mercuric acetate/alcohol system or acetic anhydride/phosphoric acid system, then deacetylated in the solution of CH₃ONa/CH₃OH. All of the novel compounds were characterized by IR, ¹H NMR, ¹³C NMR, MS and elemental analysis. The structures of compounds 2e, 3e, 5a and 5c have been determined by X-ray diffraction analysis. Some of the synthesized compounds displayed PTP1B inhibition and microorganism inhibition.     

Synthesis, structure, and catalytic activity of chiral Cu(II) and Ag(I) complexes with (S,S)-1,2-diaminocyclohexane-based N4-donor ligands

Condensation of (S,S)-1,2-cyclohexanediamine with 2 equiv. of 2-pyridine carboxaldehyde in toluene in the presence of molecular sieves at 70 °C gives N,N′-bis(pyridin-2-ylmethylene)-(S,S)-1,2-cyclohexanediamine (S,S-1) in 95% yield. Reduction of 1 with an excess of NaBH₄ in MeOH at 50 °C gives N,N′-bis(pyridin-2-ylmethyl)-(S,S)-1,2-cyclohexanediamine (S,S-2) in 90% yield. Reaction of 1 or 2 with 1 equiv. of CuCl₂ · 2H₂O in methanol gives complexes [N-(pyridin-2-ylmethylene)-(S,S)-1,2-cyclohexanediamine]CuCl₂ (3) and [Cu(S,S-2)(H₂O)]Cl₂ · H₂O (4), respectively, in good yields. Complex 4 can further react with 1 equiv. of CuCl₂ · 2H₂O in methanol to give [Cu(S,S-2)][CuCl₄] (5) in 75% yield. The rigidity of the ligand coupled with the steric effect of the free anion plays an important role in the formation of the helicates. Treatment of ligand S,S-1 with AgNO₃ induces a polymer helicate {[Ag(S,S-1)][NO₃]}_n (6), while reaction of ligand 2 with AgPF₆ or AgNO₃ in methanol affords a mononuclear single helicate [Ag(S,S-2)][PF₆] (7) or a dinuclear double helicate [Ag₂(S,S-2)₂][NO₃]₂ · 2CH₃OH (8) in good yields, respectively. All compounds have been characterized by various spectroscopic data and elemental analyses. Compounds 1, 3-5, 7 and 8 have been further subjected to single-crystal X-ray diffraction analyses. The Cu(II) complexes do not show catalytic activity for allylation reaction, in contrast to Ag(I) complexes, but they do show catalytic activity for Henry reaction (nitroaldol reaction) that Ag(I) complexes do not.     

Synthesis and coordination of the bifunctionalized ylides Ph2P(CH2)n(Ph)2PCHCOOMe (n = 1, 2) and ketenylidene Ph2P(CH2)2(Ph)2PCCO to Pd and Pt complexes

In this paper it is reported the synthesis of the phosphonium salts [Ph₂P(CH₂)_n(Ph)₂PCH₂COOMe]Br (n = 1 (1), 2 (2)) and [Ph₂P(CH₂COOMe)(CH₂)_n(Ph)₂PCH₂COOMe]Br₂ (n = 3 (3)) derived from the reactions of the diphosphines dppm, dppe and dppp with methyl bromoacetate. By reaction of the monophosphonium salt of dppm and dppe with the strong base Na[N(SiMe₃)₂] the corresponding carbonyl stabilized ylides Ph₂P(CH₂)_n(Ph)₂PCHCOOMe (n = 1 (4), 2 (5)) were obtained. The Ph₂P(CH₂)₂(Ph)₂PCHCOOMe (5) ylide was reacted with Pd(II) and Pt(II) substrates. From these reactions were isolated exclusively complexes in which the ylide was chelated to the metal through the free phosphine group and the ylidic carbon atom. A further reaction of the Ph₂P(CH₂)₂(Ph)₂PCHCOOMe (5) ylide with 1.5 equiv. of Na[N(SiMe₃)₂] gives the bifunctionalized ketenylidene Ph₂P(CH₂)₂(Ph)₂PCCO (6) system. This cumulenic ylide reacts with Pt(II) complexes to form a chelated derivative in which IR and NMR spectra suggest the breaking of the CC bond of the -CCO group.     

Synthesis of (+)-(R)- and (−)-(S)-trans-8-hydroxy-2-[N-n-propyl-N-(3′-iodo-2′-propenyl)] aminotetralin: New 5-HT1A receptor ligands

(R,S)-trans-8-Hydroxy-2-[N-n-propyl-N-(3′-iodo-2′-propenyl)amino]tetralin 7 , a new radioiodinated ligand based on 8-OH-DPAT, was reported as a potential ligand for 5-HT_1A receptors. The optically active (+)-(R)- and (?)-(S)- 7 were prepared to investigate the stereoselectivity of (R,S)- 7 . Racemic intermediate 8-methoxy-2-N-n-propyltetralin was reacted with the acyl chloride of (?)-(R)-O-methylmandelic acid to form a mixture of (S,R)- and (R,R)-diastereoisomers, which were separated by flash column chromatography. After removing the N-acyl group from the diastereoisomers, the desired (+)-(R)-or (?)-(S)- 7 was obtained by adding an N-iodopropenyl group. In vitro homogenate binding studies showed the stereoselectivity of this new compound for 5-HT_1A receptors. (+)-(R)- 7 isomer displayed 100-fold higher affinity than the (?)-(S)- 7 isomer. Biochemical study indicated that (+)-(R)- 7 potently inhibited forskolin-stimulated adenylyl cyclase activity in hippocampal membranes (E_max and EC₅₀ were 24.5% and 5.4 nM, respectively), while (?)-(S)- 7 showed no effect at 1 μM. The radioiodinated (+)-(R)- and (?)-(S)-[¹²⁵I] 7 were confirmed by coelution with the resolved unlabeled compound on HPLC (reverse phase column PRP-1, acetonitrile/pH 7.0 buffer, 80/20). The active isomer, (+)-(R)-[¹²⁵I] 7 , displayed high binding affinity to 5-HT_1A receptors (K_d = 0.09 ± 0.02 nM). In contrast, the (?)-(S)- 7 isomer displayed a significantly lower affinity to the 5-HT_1A receptor (K_d > 10 nM). Thus, (+)-(R)-[¹²⁵I]trans-8-OH-PIPAT, (+)-(R)- 7 , an iodinated stereoselective 5-HT_1A receptor agonist, is potentially useful for study of in vivo and in vitro function and pharmacology of 5-HT_1A receptors in the central nervous system. © 1995 Wiley-Liss, Inc.     

The influence of substituents (R) at N atom of thiophene-2-carbaldehyde thiosemicarbazones {(C4H3S)HCN-N(H)-C(S)NHR} on bonding, nuclearity and H-bonded networks of copper(I) complexes

The nuclearity, bonding and H-bonded networks of copper(I) halide complexes with thiophene-2-carbaldehyde thiosemicarbazones {(C₄H₃S)HC²N³-N(H)-C¹(S)N¹HR} are influenced by R substituents at N¹ atom. Thiophene-2-carbaldehyde-N¹-methyl thiosemicarbazone (HttscMe) or thiophene-2-carbaldehyde-N¹-ethyl thiosemicarbazone (HttscEt) have yielded halogen-bridged dinuclear complexes, [Cu₂(μ-X)₂(η¹-S-Htsc)₂(Ph₃P)₂] (Htsc, X: HttscMe, I, 1; Br, 2; Cl, 3; HttscEt, I, 4; Br, 5; Cl, 6), while thiophene-2-carbaldehyde-N¹-phenyl thiosemicarbazone (HttscPh) has yielded mononuclear complexes, [CuX(η¹-S-HttscPh)₂] (X, I, 7a; Br 8; Cl, 9) and a sulfur bridged dinuclear complex, [Cu₂(μ-S-HttscPh)₂(η¹-S-HttscPh)₂I₂] 7b co-existing with 7a in the same unit cell. These results are in contrast to S-bridged dimers [Cu₂(μ-S-Httsc)₂(η¹-Br)₂(Ph₃P)₂] · 2H₂O and [Cu₂(μ-S-Httsc)₂(η¹-Cl)₂(Ph₃P)₂] · 2CH₃CN obtained for R = H and X = Cl, Br (Httsc = thiophene-2-carbaldehyde thiosemicarbazone) as reported earlier. The intermolecular CH_Ph?π interaction in 1-3 (2.797 Å, 1; 3.264 Å, 2; 3.257 Å, 3) have formed linear polymers, whereas the CH_Ph?X and N³?HCH interactions in 4-6 (2.791, 2.69 Å, 5; 2.776, 2.745 Å, 6, respectively) have led to the formation of H-bonded 2D polymer. The PhN¹H?π, interactions (2.547 Å, 8, 2.599 Å, 9) have formed H-bonded dimers only. The Cu?Cu separations are 3.221-3.404 Å (1-6).     

Synthesis and X-ray crystal structure of a polymeric copper(II) complex containing the novel ligand 4,4-(1,4-phenylene)bis[3-phenyl-5-(2-pyridyl)-4H-1,2,4-triazole]

The synthesis and X-ray crystal structure of the complex {[Cu^II(Ph₂PBPT)(bpy)](ClO₄)₂ · 2DMF}_∞ where Ph₂PBPT=4,4^′-(1,4-phenylene)bis[3-phenyl-5-(2-pyridyl)-4H-1,2,4-triazole], bpy=2,2^′-bipyridine and DMF=N,N-dimethylformamide are reported. In this one-dimensional coordination polymer the Cu²⁺ ions are in a distorted octahedral N₆ coordination environment made up of two Ph₂PBPT molecules, each chelating via one pyridine and one triazole nitrogen, and one bpy co-ligand. Within the zig-zag chain thus formed the shortest distance between two metal centres across the Ph₂PBPT ligand is 13.305(3) Å while it is 10.009(3) Å between two chains. This complex represents the first structurally characterised example of a coordination compound incorporating a chelating 4,4^′-bis(4H-1,2,4-triazole) as a ligand.     

The preparation and structural elucidation of uranium (VI) complexes and salts of the phosphorus ylides Ph3PCHCOPh, Ph3PC(COMe)(COPh) and Ph3PCHCOOCH2CH3

The reaction in methanol of the phosphorus ylides Ph₃PCHCOPh, benzoylmethylenetriphenylphosphorane (BPPY), and Ph₃PC(COMe)(COPh), α-acetyl-α-benzoylmethylenetriphenylphosphorane (ABPPY) with UO₂(NO₃)₂ · 6H₂O at 273 K leads to the formation of O-coordinated bis(ylide)-uranium (VI) complexes of the type [UO₂(ylide)₂(NO₃)₂], whereas the reaction of BPPY and UO₂(NO₃)₂ · 6H₂O under reflux in benzene yields the salt . The reaction of Ph₃PCHCOOCH₂CH₃, carbethoxymethylenetriphenylphosphorane (EPPY) with UO₂(CH₃COO)₂ · 2H₂O produces the salt [H-EPPY]⁺[UO₂(CH₃COO)₃]⁻. The structures of the free ylides ABPPY and EPPY are also discussed.     

Syntheses and structures of the heterometallic clusters [(Ph3PAu)3Re(CO)4], [(Ph3PAu)4Re(CO)4], [(Ph3PAu)6AuRe2(CO)8], and [(Ph3PAu)6Re(CO)3]

The reaction of [HRe₃(CO)₁₂]²⁻ with an excess of Ph₃PAuCl in CH₂Cl₂ yields [(Ph₃PAu)₄Re(CO)₄]⁺ as the main product, which crystallizes as [(Ph₃PAu)₄Re(CO)₄]PF₆ · CH₂Cl₂ (1 · CH₂Cl₂) after the addition of KPF₆.The crystal structure determination reveals a trigonal bipyramidal Au₄Re cluster with the Re atom in equatorial position.If [(Ph₃PAu)₄Re(CO)₄]⁺ is reacted with PPh₄Cl, a cation [Ph₃PAu]⁺ is eliminated as Ph₃PAuCl, and the neutral cluster [(Ph₃PAu)₃Re(CO)₄] (2) is formed.It combines with excess [(Ph₃PAu)₄Re(CO)₄]⁺ to afford the cluster cation, [(Ph₃PAu)₆AuRe₂(CO)₈]⁺. It crystallizes from CH₂Cl₂ as[(Ph₃PAu)₆AuRe₂(CO)₈]PF₆ · 4CH₂Cl₂ (3 · 4CH₂Cl₂). In [(Ph₃PAu)₃Re(CO)₄] the metal atoms are arranged in form of a lozenge while in [(Ph₃PAu)₆AuRe₂(CO)₈]⁺ two Au₄Re trigonal bipyramids are connected by a common axial Au atom.The treatment of [(Ph₃PAu)₄Re(CO)₄]⁺ with KOH and Ph₃PAuCl in methanol yields the cluster cation [(Ph₃PAu)₆Re(CO)₃]⁺, which crystallizes with from CH₂Cl₂ as [(Ph₃PAu)₆Re(CO)₃]PF₆ · CH₂Cl₂ (4 · CH₂Cl₂). The metal atoms in this cluster form a pentagonal bipyramid with the Re atom in the axial position.     

Kinetic studies on the reactions of HCl with trans-[MoL(CNPh)(Ph2PCH2CH2PPh2)2] (L=N2, H2 or CO)

The kinetics of the reactions between anhydrous HCl and trans-[MoL(CNPh)(Ph₂PCH₂CH₂PPh₂)₂] (L=CO, N₂ or H₂) have been studied in thf at 25.0 °C. When L=CO, the product is [MoH(CO)(CNPh)(Ph₂PCH₂CH₂PPh₂)₂]⁺, and when L=H₂ or N₂ the product is trans-[MoCl(CNHPh)(Ph₂PCH₂CH₂PPh₂)₂]. Using stopped-flow spectrophotometry reveals that the protonation chemistry of trans-[MoL(CNPh)(Ph₂PCH₂CH₂PPh₂)₂] is complicated. It is proposed that in all cases protonation occurs initially at the nitrogen atom of the isonitrile ligand to form trans-[MoL(CNHPh)(Ph₂PCH₂CH₂PPh₂)₂]⁺. Only when L=N₂ is this single protonation sufficient to labilise L to dissociation, and subsequent binding of Cl⁻ gives trans-[MoCl(CNHPh)(Ph₂PCH₂CH₂PPh₂)₂]. At high concentrations of HCl a second protonation occurs which inhibits the substitution. It is proposed that this second proton binds to the dinitrogen ligand. When L=CO or H₂, a second protonation is also observed but in these cases the second protonation is proposed to occur at the carbon atom of the aminocarbyne ligand, generating trans-[MoL(CHNHPh)(Ph₂PCH₂CH₂PPh₂)₂]²⁺. Addition of the second proton labilises the trans-H₂ to dissociation, and subsequent rapid binding of Cl⁻ and dissociation of a proton yields the product trans-[MoCl(CNHPh)(Ph₂PCH₂CH₂PPh₂)₂]. Dissociation of L=CO does not occur from trans-[Mo(CO)(CHNHPh)(Ph₂PCH₂CH₂PPh₂)₂]²⁺, but rather migration of the proton from carbon to molybdenum, and dissociation of the other proton produces [MoH(CO)(CNPh)(Ph₂PCH₂CH₂PPh₂)₂]⁺.     

Glycosylation reactions — present status future directions

A short review of the present status of glycosylation reactions is presented. The reactivity of both proven and newer glycosylation methods are briefly discussed. Emphasis is placed on the control of stereochemistry and regiochemistry. As well, the identification and avoidance of side reactions is covered. Polymer-supported synthesis of oligosaccharides is noted as a promising direction for eliminating some of the problems associated with purification. It is suggested that a better understanding of the mechanism of glycosylation reactions is necessary for future improvements to stereoselectivity and regioselectivity. A key advance would be methods for enhancing the reactivity of weakly nucleophilic hydroxyls.Abbreviations BF₃ OEt₂ boron trifluoride diethyl ether complex - TMSOTf trimethylsilyl trifluorometh-anesulfonate - NIS NBS N-iodosuccinimide andN-bromosuccinimide - TfOH trifluoromethanesulfonic acid or triflic acid - AgOTf CuOTf₂ silver triflate and copper(II)triflate - Tf₂O triflic anhydride - IDCP iodonium dicollidine perchlorate - TEP triethyl phosphite - HfCp₂Cl₂ hafnium dicyclopentadienyl dichloride - Ac acetyl - Bz benzoyl - Bn benzyl - Ph phenyl - Me methyl - Et ethyl - Bu₄NOTf tetrabutylammonium triflate - Ph₂IOTf diphenyliodinium triflate - PhSeNPhth N-(phenylseleno)phthalimide - Pent 4-pentenyl - TCI trichloroactemidyl - TBDPS t-butyl diphenylsilyl - DTBP 2,6-di-t-butylpyridine - Tr trityl or triphenylmethyl Dedicated to Professor J.J. Krepinsky on the occasion of his 60th birthday     

Synthesis of AZT analogues: 7-(3-azido-2hydroxypropyl)-, 7-(3-amino-2-hydroxypropyl)-, 7-(3-triazolyl-2-hydroxypropyl)theophyllines

Nucleophilic displacement of the tosyloxy group in 7-(2-hydroxy-3-p-toluenesulfonyloxypropyl)theophylline (1) with azide anion afforded 7-(3-azido-2-hydroxypropyl)theophylline (2). Reduction of the 3-azido group in 2 with Ph₃P/Py/NH₄OH afforded the 3-amino derivative 4, alternatively obtained by regioselective amination of 7-(2,3-epoxypropyl)theophylline (3). Selective acetylation of 4 gave the N-acetyl derivative 5. 1,3-Dipolar cycloaddition of the azide group in 2 with N¹-propargyl thymine (6) afforded the regioisomeric triazole 7.     

Synthesis, structure, and catalytic activity of chiral silver(I) and copper(II) complexes with biaryl-based nitrogen-containing ligands

A series of chiral Ag(I) and Cu(II) complexes have been prepared from the reaction between AgX (X = NO₃, PF₆, OTf) or CuX₂ (X = Cl, ClO₄) and chiral biaryl-based N-ligands. The rigidity of the ligand plays an important role in the Ag(I) complex formation. For example, treatment of chiral N₃-ligands 1-3 with half equiv of AgX (X = NO₃, PF₆, OTf) gives the chiral bis-ligated four-coordinated Ag(I) complexes, while ligand 4 affords the two-coordinated Ag(I) complexes. Reaction of AgX with 1 equiv of chiral N₄-ligands 5, 7, 8 and 10 gives the chiral, binuclear double helicate Ag(I) complexes, while chiral mono-nuclear single helicate Ag(I) complexes are obtained with N₄-ligands 6 and 9. Treatment of either N₃-ligand 1 or N₄-ligand 9 or 10 with 1 equiv of CuX₂ (X = Cl, ClO₄) gives the mono-ligated Cu(II) complexes. All the complexes have been characterized by various spectroscopic techniques, and elemental analyses. Seventeen of them have further been confirmed by X-ray diffraction analyses. The Cu(II) complexes do not show catalytic activity for allylation reaction, in contrast to Ag(I) complexes, but they do exhibit catalytic activity for Henry reaction (nitroaldol reaction) that Ag(I) complexes do not.     

The structural definition of adducts of stoichiometry MX:dpex (2:3)(∞), M = Cu, Ag, X = simple anion, dpex = Ph2E(CH2)xEPh2, E = P, As

Single crystal X-ray structural characterizations are recorded for a number of adducts of MX:dpex (2:3) stoichiometry (MX = simple univalent copper or silver salt; dpex = Ph₂E(CH₂)_xEPh₂ (E = P, As)). CuX:dppe (2:3) (X = Cl, Br, I, CN) are binuclear [(dppe-P,P′)CuX(P-dppe-P′)CuX(P,P′-dppe)], all centrosymmetric. AgX:dpex (2:3) (dpex = ‘dpae’ (Ph₂As(CH₂)₂AsPh₂), X = Br, F₃CCO₂ (= ‘tfa’), F₃CSO₃ (≡ ‘tfs’); dpex = ‘dpape’ (Ph₂As(CH₂)₂PPh₂), X = CN, SCN, OClO₃) are one-dimensional polymers ?-E′)₁AgX(E-dpex-E′)₂-AgX(E-dpex-E′)₁AgX?, P, As sites scrambled in the latter. AgNO₃:dpam (2:3) is also a one-dimensional polymer, ?AgO·NO·OAg(As-dpam-As)AgO·NO·OAg? (‘dpam’ ≡ Ph₂As(CH₂)₂AsPh₂). AgX:dpae (2:3) (X = I, CN, ClO₄, NO₃) and AgX:dpape (2:3) (X = Br, I, NO₃) are two-dimensional polymers with large 30-membered macrocyclic rings; similar webs are found for dppx ligands in AgOH:dppb (2:3) and AgNCO, Agtfa:dpph (2:3) with 42- and 54-membered rings. Complexes AgX:dpape (1:3) (X = Cl, Br) are defined as mono-nuclear [XAg(Ph₂P(CH₂)₂AsPh₂)₃] arrays, the unidentate ligands predominantly P-bound. Synthetic procedures for the adducts are reported, selected compounds being characterized both in solution (¹H, ³¹P NMR, ESI MS) and in the solid state (IR).     

Antisymbiosis. Preferential coordination of anionic oxygen versus neutral sulfur donor atoms of methylsulfanyl- or methylsulfinyl-acetato, 2-benzoato and 2-phenolato to the cis-Pt(PPh3)2 and Pt(dppe) residues

The interaction of an excess of the title ligands L⁻ with the cis-Pt(phos)₂ moieties gives compounds a-bcis-[Pt(L-O)₂(phos)₂] (a, phos = P(Ph)₃; b, phos = 1/2 dppe), in which O- is preferred to S-coordination. Such preference is confirmed by the fact that the same products are obtained by reaction of excess of L⁻ with the previously reported a-d complexes [Pt(L-O,S)(phos)₂]⁺, (c, phos = PPh₃, d, phos = 1/2 dppe), for which chelate ring opening occurs with rupture of Pt-S rather than Pt-O bonds. Compound a can be obtained also by oxidative addition of HL to [Pt(PPh₃)₃]. The Pt-O bonds in compounds a-d are stable towards substitution by Me₂SO, pyridine and tetramethylthiourea. Substitution of L’s occurs with N,N′-diethyldithiocarbamate, which forms a very stable chelate with Pt(II). Thiourea and N,N′-dimethylthiourea also react, because they give rise to cyclometallated products [Pt(phos)₂(NRC(S)NHR)]⁺ (R = H, CH₃), with one ionised thioamido group, as revealed by an X-ray investigation of [Pt(PPh₃)₂(NHC(S)NH₂)]⁺. The preference of O versus S coordination, as well as the stability of the Pt-O bonds, are discussed in terms of antisymbiosis.     

Enzymatic synthesis of N-acetylglucosaminobioses by reverse hydrolysis: characterisation and application of the library of fungal β-N-acetylhexosaminidases

The regioselectivity of 20 extracellular β-N-acetylhexosaminidases of fungal origin was screened in the reverse hydrolysis with 2-acetamido-2-deoxy- -glucopyranose. Most of the enzymes used yielded 2-acetamido-2-deoxy-β- -glucopyranosyl-(1→4)-2-acetamido-2-deoxy- -glucopyranose (3) and 2-acetamido-2-deoxy-β- -glucopyranosyl-(1→6)-2-acetamido-2-deoxy- -glucopyranose (4). So far unknown product of enzymatic condensation, 2-acetamido-2-deoxy-β- -glucopyranosyl-(1→3)-2-acetamido-2-deoxy- -glucopyranose (2) was synthesised using the β-N-acetylhexosaminidases from Penicillium funiculosum CCF 1994, P. funiculosum CCF 2325 and Aspergillus tamarii CCF 1665. Addition of salts ((NH₄)₂SO₄ or MgSO₄ (0.1–1.0 M)) to the reaction increased the yields and also enhanced the β-N-acetylhexosaminidase regioselectivity.     

Unusual ruthenium hydride complexes supported by the [N(2-PPh2-4-Me-C6H3)2] pincer ligand

Complexes of Ru(II) containing the pincer ligand [⁻N(2-PPh₂-4-Me-C₆H₃)₂] (PNP^Ph) were prepared. The complex (PNP^PhH)RuCl₂ (1) was treated with 2 equiv AgOTf to produce the triflate complex (PNP^PhH)Ru(OTf)₂ (2). Complex 1 was also treated with an excess of NaBH₄ to give a bimetallic complex [(PNP^Ph)RuH₃]₂ (3). A number of methods, including X-ray crystallography, NMR spectroscopy, and computational studies, were used to probe the structure of 3. Addition of Lewis bases to 3 resulted in octahedral complexes containing a hydride ligand trans to a dihydrogen ligand.     

A Fluorescence-Based Homogeneous Assay for Measuring Activity of UDP–3-O-(R-3-Hydroxymyristoyl)-N-acetylglucosamine Deacetylase

UDP–3-O-(R-3-hydroxymyristoyl)-N-acetylglucosamine deacetylase (LpxC) is one of the key enzymes of bacterial lipid A biosynthesis, catalyzing the removal of the N-acetyl group of UDP–3-O-(R-3-hydroxymyristoyl)-N-acetylglucosamine. The lpxC gene is essential in Gram-negative bacteria but absent from mammalian genomes, making it an attractive target for antibacterial drug discovery. Current assay methods for LpxC are not suitable for high throughput screening, since they require multiple product separation steps and the use of radioactively labeled material that is difficult to prepare. A homogenous fluorescence-based assay was developed that uses UDP–3-O-(N-hexyl-propionamide)-N-acetylglucosamine as a surrogate substrate. This surrogate can be prepared from commercially available UDP–GlcNAc by enzymatic conversion to UDP–MurNAc, which is then chemically coupled to n-hexylamine. Following the LpxC reaction, the free amine of the deacetylation product can be derivatized by fluorescamine, thus generating a fluorescent signal. This surrogate substrate has a K_m of 367 μM and k_cat of 0.36 s⁻¹, compared to 2 μM and 1.5 s⁻¹ for the natural substrate. Since no separation is needed, the assay is easily adaptable to high throughput screening. IC₅₀s of LpxC inhibitors determined using this assay method is similar to those measured by traditional method with the natural substrate.