Kevin R. Flower

The development and application of ruthenium catalysed oxidations of a hydroxamic acid and in situ Diels–Alder trapping of the acyl nitroso derivative

Ruthenium( II) complexes can be used to oxidise N-Boc-hydroxylamine in the presence of tert-butyl hydroperoxide (TBHP) to the corresponding nitroso dienophile, which is trapped by cyclohexa-1,3-diene as the hetero-Diels–Alder adduct. Direct evidence has been obtained for the intervention of a triphenylphosphine oxide-stabilised ruthenium( IV) oxo-complex as the catalytically active species. Use of a chiral bidentate bis-phosphine derived ruthenium ligand (BINAP or PROPHOS) results in very low asymmetric induction (8 and 11%). Ruthenium( II) salen complexes also catalyse the oxidation of N-Boc-hydroxylamine in the presence of TBHP, to give the N-Boc-nitroso compound which can be efficiently trapped with a range of dienes. However, use of an enantiopure ruthenium salen complex does not produce asymmetric induction via the trapping of the intermediate acyl nitroso dienophile with cyclohexadiene, which strongly suggests that the intermediate dissociates readily from the chiral ruthenium complex involved in the oxidation step prior to Diels–Alder cycloaddition.

Highlighting a need to distinguish cell cycle signatures from cellular responses to chemotherapeutics in SR-FTIR spectroscopy

Previous research has seen difficulties in establishing clear discrimination by principal component analysis (PCA) between drug-treated cells analysed by single point SR-FTIR spectroscopy, relative to multisampling cell monolayers by conventional FTIR. It is suggested that the issue arises due to signal mixing between cellular-response signatures and cell cycle phase contributions in individual cells. Consequently, chemometric distinction of cell spectra treated with multiple drugs is difficult even with supervised methods. In an effort to separate cell cycle chemistry from cellular response chemistry in the spectra, renal carcinoma cells were stained with propidium iodide and fluorescent-activated cell sorted (FACS) after exposure to a number of chemotherapeutic compounds; 5-fluorouracil (5FU) and a set of novel gold-based experimental compounds. The cell spectra were analysed separately by PCA in G(1), S or G(2)/M phase. The mode of action of established drug 5FU, known to disrupt S phase, was confirmed by FACS analysis. The chemical signature of 5FU-treated cells discriminated against both the control and gold-compound (KF0101)-treated cell spectra, suggesting a different mode of action due to a difference in cellular response.

The action of all-trans-retinoic acid (ATRA) and synthetic retinoid analogues (EC19 and EC23) on human pluripotent stem cells differentiation investigated using single cell infrared microspectroscopy

All trans-retinoic acid (ATRA) is widely used to direct the differentiation of cultured stem cells. When exposed to the pluripotent human embryonal carcinoma (EC) stem cell line, TERA2.cl.SP12, ATRA induces ectoderm differentiation and the formation of neuronal cell types. We have previously generated synthetic analogues of retinoic acid (EC23 and EC19) which also induce the differentiation of EC cells. Even though EC23 and EC19 have similar chemical structures, they have differing biochemical effects in terms of EC cell differentiation. EC23 induces neuronal differentiation in a manner similar to ATRA, whereas EC19 directs the cells to form epithelial-like derivatives. Previous MALDI-TOF MS analysis examined the response of TERA2.cl.SP12 cells after exposure to ATRA, EC23 and EC19 and further demonstrated the similarly in the effect of ATRA and EC23 activity whilst responses to EC19 were very different. In this study, we show that Fourier Transform Infrared Micro-Spectroscopy (FT-IRMS) coupled with appropriate scatter correction and multivariate analysis can be used as an effective tool to further investigate the differentiation of human pluripotent stem cells and monitor the alternative affects different retinoid compounds have on the induction of differentiation. FT-IRMS detected differences between cell populations as early as 3 days of compound treatment. Populations of cells treated with different retinoid compounds could easily be distinguished from one another during the early stages of cell differentiation. These data demonstrate that FT-IRMS technology can be used as a sensitive screening technique to monitor the status of the stem cell phenotype and progression of differentiation along alternative pathways in response to different compounds.

Investigating cellular responses to novel chemotherapeutics in renal cell carcinoma using SR-FTIR spectroscopy.

SR-FTIR spectroscopy was evaluated as a technique to discriminate spectral signals of cellular response at the single cell level, when cancer cells are exposed to chemotherapeutics. 5-Fluorouracil, an established drug of known mode of action, was tested against a renal carcinoma cell line (Caki-2), along with two experimental analogues of gold-based compounds. The use of unsupervised principal component analysis (PCA) failed to clearly define any distinction between control and drug treated cell spectra. Supervised principal component linear discriminant analysis (PC-LDA) did have some potential to reveal signatures of cell response and repair but again failed to distinctly discriminate groups of spectra with different drug treatments. Alternatively, clear PCA discrimination was observed in spectra from average cell populations via single point benchtop spectroscopy, probing several cells simultaneously with an increased aperture. The Caki-2 cell line initially appeared to be sensitive to the novel compounds, inducing a cellular response prior to subsequential cell recovery which was assessed by both PCA and cell viability assays.

A novel cis-push–pull effect in cycloruthenated azobenzene thiocarbonyl-containing complexes: crystal and molecular structures of [RuX(CS)(η2-C,N-C6H4NNPh)(PPh3)2](X=Cl, I)

Abstract Treatment of [RuHCl(CS)(PPh3)3] with Hg(o-C6H4NNC6H5)2 affords [RuCl(CS)(η2C,N-o-C6H4NNC6H5)(PPh3)2] (1) in good yield, where the cyclometallated azobenzene ligand coordinates through an ortho-C and one azo-N to give a five-membered chelate ring. Reaction of 1 with AgNO3 followed by NaBr or NaI affords the chloride-exchanged products [RuX(CO)(η2C,N-o-C6H4NNC6H5)(PPh3)2] (2, 3), whereas reaction of 1 with AgOC(O)Me or NaS2CNEt2·2H2O gives the halide mono-phosphine-substituted complexes [Ru(CS)(LL)(η2C,N-o-C6H4NNC6H5)(PPh3)] (4, 5). In the solid-state structures of 1 and 3 there are significant changes in the bond lengths for the cyclometallated azobenzene ligand are observed relative to free azobenzene. These are discussed, with the aid of spectroscopic and crystallographic data, in terms of a cis-push–pull effect.

Azo-containing phosphine complexes of palladium(II) and platinum(II) and their effectiveness in the Heck reaction: crystal and molecular structure of [PdCl2{PPh2{1-(4-MeC6H4N2)-2-OC(O)MeC10H5}]·2EtOH

Abstract Reaction of Na[MCl4] (M=Pd or Pd) with the azo-containing phosphines Ph2P{1-(4-RC6H4N2)-2-OR′-C10H5} {R=Me (I), NMe2 (II); R′=C(O)Me} affords the complexes [MCl2L2] (1–4) in good yield. Complexes 1–4 have all been fully characterised by elemental analysis, 1H-, 13C{1H}-, and 31P{1H}-NMR spectroscopy and UV–visible spectroscopy. The use of 1 in the Heck reaction has been investigated and shown to effect up to 1000 turnovers.

First synthesis and structural characterisation of a tertiary phosphine containing an azo linkage

Abstract Tertiary phosphines containing an azo linkage have been synthesised for the first time and one has been characterised by a single crystal X-ray diffraction study of its oxide.

Cationic but-2-yne complexes of tungsten(II). Preparation and spectral properties of [WI(CO)L(dppm)(η2-MeC2Me)][BF4] (L = neutral monodentate oxygen and sulphur donor ligands). Crystal structure of [WI(CO){SC(NH2)2}(dppm)-(η2-MeC2Me)][ClO4]

Abstract Equimolar quantities of the cationic mono-but-2-yne complex [WI(CO)(NCMe)-(dppm)(η 2 -MeC 2 Me)][BF 4 ] and L {L = SC(NH 2 ) 2 , SC(NMe 2 ) 2 , SC(NH 2 )(NHPh- o -Me), SC(NHPh) 2 , SC(NH 2 )Me, OC(NH 2 ) 2 and OC(NH 2 )Me} react in acetone at room temperature to give the new substituted compounds [WI(CO)L(dppm)(η 2 -MeC 2 Me)][BF 4 ] ( 1–7 ). An X-ray diffraction study of the thiourea complex [WI(CO){SC(NH 2 ) 2 }(dppm)(η 2 -MeC 2 Me)][ClO 4 ](1) showed the crystals to be monoclinic, space group Cc (No. 9), with a 19.203(7), b 11.468(5), c 18.559(3) A and β 91.52(2)°. The structure was refined to R and R w values of 0.039 and 0.044, respectively, for the 339 variables and 3267 data for which F o > 3σ( F o ). The geometry about the tungsten can be considered to be pseudo-octahedral, with the but-7-yne trans to the iodide ligand. 13 C NMR spectroscopy suggests that the but-2-yne ligand donates four electrons to the metal in compounds 1–7 .

Structural relationships between o-, m- and p-tolyl substituted R3EI2 (E = As, P) and [(R3E)AuX] (E = As, P; X = Cl, Br, I)

The compounds R3EI2 (R = o-tolyl, E = As, 1a; R = m-tolyl, E = P 1c; R = p-tolyl, E = As, 1d, P, 1e), which display the charge transfer spoke structure, and [(o-tolyl3As)AuCl] 2 have been synthesised and their solid state structures compared to the related complexes [(R3P)AuX] (R = o-tolyl, X = Cl, I, Ia; Br, II; I, III; R = m-tolyl, X = Cl, IV; R = p-tolyl, X = Cl, V, Va; Br, VI; I, VII) on the basis of a similarity of their molecular shape and volume. All of the new compounds 1a, 1c–1e and 2 have been fully spectroscopically characterised and by single crystal X-ray crystallography. The sterically demanding exo3o-tolyl ring conformation is observed for 1a, which is comparable to that reported for o-tolyl3PI21b, with a long As–I bond 2.7351(14) A and short I⋯I distance 2.9528(11) A. The exo3o-tolyl ring conformation is maintained on complexation to gold(I) in 2, but has no significant impact on the expected bond lengths, with As–Au 2.3443(15) A and Au–Cl 2.284(4) A. The exo3 conformation appears to be stabilised in both cases by the formation of a six-fold edge-to-face (EF)6 embrace. It is found that in some cases the structures of the dihalogen adducts and the gold(I) complexes are isomorphous indicating that ligand packing requirements are most significant i.e. for 1c and IV. Where the structures digress this is due either to the greater ability of the dihalogen adduct to engage in hydrogen bonding 1a, b and I–III; or subtle changes in the nature of the tolyl ring embraces 1d, e and V–VII. Subtle changes in the nature of the tolyl ring embraces also account for the different polymorphs I and Ia and V and Va. There is no credible evidence to suggest that the aurophilic contact, seen in only one polymorph Va, exerts any influence on the overall crystal packing. The structural comparisons presented here add further to the applicability of the recently recognised structural mimicking ability of the R3PX2 systems and [R3PAuX] complexes, and that the aurophilic contact is a poor supramolecular synthon.

Design and biological evaluation of synthetic retinoids: probing length vs. stability vs. activity

All trans-retinoic acid (ATRA) is widely used to direct the differentiation of cultured stem cells. When exposed to the pluripotent human embryonal carcinoma (EC) stem cell line, TERA2.cl.SP12, ATRA induces ectoderm differentiation and the formation of neuronal cell types. We report in this study that novel polyene chain length analogues of ATRA require a specific chain length to elicit a biological responses of the EC cells TERA2.cl.SP12, with synthetic retinoid AH61 being particularly active, and indeed more so than ATRA. The impacts of both the synthetic retinoid AH61 and natural ATRA on the TERA2.cl.SP12 cells were directly compared using both RT-PCR and Fourier Transform Infrared Micro-Spectroscopy (FT-IRMS) coupled with multivariate analysis. Analytical results produced from this study also confirmed that the synthetic retinoid AH61 had biological activity comparable or greater than that of ATRA. In addition to this, AH61 has the added advantage of greater compound stability than ATRA, therefore, avoiding issues of oxidation or decomposition during use with embryonic stem cells.