Solid-phase synthesis of fullerene-peptides

The solid-phase synthesis of peptides (SPPS) containing [60]fullerene-functionalized amino acids is reported. A new amino acid, fulleropyrrolidino-glutamic acid (Fgu), is used for the SPPS of a series of analogues of different length based on the natural Leu(5)-Enkephalin and on cationic antimicrobial peptides. These fullero-peptides were prepared on different solid supports to analyze the influence of the resin on the synthesis. Optimized protocols for the coupling and deprotection procedures were determined allowing the synthesis of highly pure peptides in sufficient quantities for evaluation of biological activities. In particular, to avoid side reactions of the fullerene moiety with bases and nucleophiles, the removal of the protecting groups was performed under inert conditions (nitrogen or argon in the dark). We have encountered serious problems with the recovery of the crude compounds, especially when Fgu was inserted in the proximity of the resin core as fullero-peptides tend to remain embedded inside the resin. Eventually, all of the fullero-peptides were easily purified, and the cationic peptides were tested for their antimicrobial activities. They displayed a specific activity against the Gram-positive bacterium S. aureus and also lysed erythrocytes. The availability of a fullero-amino acid easily useable in the SPPS of fullero-peptides may thus open the way to the synthesis of new types of biologically active oligomers.     

Diastereoselective hydroxylation of 6-substituted piperidin-2-ones. An efficient synthesis of (2S,5R)-5-hydroxylysine and related alpha-amino acids

The synthesis of (2S,5R)-5-hydroxy-6-oxo-1,2-piperidinedicarboxylates (5) and related (3S,6R)-3-hydroxy-6-alkyl-2-oxo-1-piperidinecarboxylates has been developed. The approach is based on the asymmetric hydroxylation of enolates generated from the corresponding N-protected-6-substituted piperidin-2-ones. The utility of 5a as a precursor in the synthesis of (2S,5R)-5-hydroxylysine (1), an amino acid unique to collagen and collagen-like proteins, has also been demonstrated. (2S)-6-oxo-1,2-piperidinedicarboxylates (6) required for hydroxylation studies were prepared in 38-74% yield, starting from conveniently protected aspartic acid as inexpensive chiral adduct. Hydroxylation of 6 to 5 proceeds in high yield and excellent diastereoselectivity by treatment of their Li-enolate with (+)-camphorsulfonyloxaziridine at -78 degrees C. Ring opening of di-tert-butyl (2S,5R)-6-oxo-1,2-piperidinedicarboxylate ((5R)-5a) under reductive conditions afforded the corresponding 1,2-diol (17) in 91%, which was further transformed to (2S,5R)-5-hydroxylysine in four steps (84%). 17 is also a versatile intermediate in the preparation of tert-butyl (2S,5R)-2-[(tert-butoxycarbonyl)amino]-5-hydroxy-6-iodohexanoate (3) and tert-butyl (2S)-2-[(tert-butoxycarbonyl)amino]-4-[(2R)-oxiranyl]butanoate (4), two amino acid derivatives used in the total synthesis of the bone collagen cross-link (+)-pyridinoline (2a).     

Thermal photoionization in resonance ionization spectroscopy

In Resonance Ionization Spectroscopy, neutral atoms are usually produced by thermal effects, using an oven or a hot surface at high temperature. The radiation from these thermal sources is intense enough to effectively contribute to the photoionization of atoms excited by laser pumping. We show that, for the most common experimental conditions, the ratio of thermal to laser photoionization can be higher than one for excited levels which lie as far as a few thousand cm^–1 below the ionization threshold. This result is obtained with the use of the analytic expression for the photoionization cross-section of a hydrogen-like atom. We suggest two applications of this thermal photoionization. Namely, the study of highly excited states and Quasi Resonance Ionization Spectrometry, using only one laser of low radiance.Commissariat à l'Energie Atomique, Centre d'Etudes Nucléaires de Fontenay-aux-Roses DERDCA/DCAEA/SEA, BP no 6, F-92265 Fontenay-aux-Roses Cedex, France (Visiting scientist at Ecole Polytechnique from Commissariat à l'Energie Atomique)Commissariat à l'Energie Atomique, Centre d'Etudes Nucléaires de Saclay, IRF/DPHG/PAS. Bât 462, F-91191 Gif-sur-Yvette Cedex, France     

Monomeric, one- and two-dimensional networks incorporating (2,6-Me2C6H3S)2Pb building blocks

The amine coordination of lead(II) has been examined through the preparation and structural analysis of Lewis base adducts of bis(thiolato)lead(II) complexes. Reaction of Pb(OAc)(2) with 2,6-dimethylbenzenethiol affords (2,6-Me(2)C(6)H(3)S)(2)Pb (6) in high yield. The solubility of 6 in organic solvents allows for the preparation of the 1:2 Lewis acid-base adduct [(2,6-Me(2)C(6)H(3)S)(2)Pb(py)(2)](7), and 1:1 adducts [(2,6-Me(2)C(6)H(3)S)(2)Pb(micro(2)-bipy)](infinity](8) and [(2,6-Me(2)C(6)H(3)S)(2)Pb(micro(2)-pyr)](infinity)(9)(where py = pyridine, bipy = 4,4'-bipyridyl and pyr = pyrazine) from reaction with an excess of the appropriate amine. In contrast to 7, reaction of (C(6)H(5)S)(2)Pb (1) with pyridine afforded the 2:1 adduct [(C(6)H(5)S)(4)Pb(2)(py)](infinity)(10). Compounds were characterized via elemental analysis, FT-IR, solution (1)H and (13)C[(1)H](6) NMR spectroscopy, and X-ray crystallography (7-10). The structures of 7-9 show the thiolate groups occupying two equatorial positions and two amine nitrogen atoms occupying axial coordination sites, yielding distorted see-saw coordination geometries, or distorted trigonal bipyramids if an equatorial lone pair on lead is considered. The absence of intermolecular contacts in 7 and 8 result in monomeric and one-dimensional polymeric structures, respectively. Weak Pb...S intermolecular contacts in 9 result in the formation of a two-dimensional macrostructure. In contrast, the structure of , shows extensive intermolecular Pb...S interactions, resulting in five- and six-coordinate bonding environments for lead(II), and a complex polymeric structure in the solid state. This demonstrates the ability of the 2,6-dimethylphenylthiolate ligand to limit intermolecular lead-sulfur interactions, while allowing the axial coordination of amine Lewis base ligands.     

Synthesis,Structure and Reactivity of Organoindium 1,2-Benzenedithiolates and 2-Amidobenzenethiolates

Organoindium compounds of redox active 1,2-benzenedithiolate and 2-amidobenzenethiolate ligands were synthesized and tested for reactivity against mild oxidants. The reaction of Me₃In and (NCN)InMe₂ [NCN=2,6-bis(dimethylaminomethy)phenyl] with 3,4-toluenedithiol (H₂tdt) at room temperature afforded [MeIn(tdt)(py)]₂ ( 1 ) and (NCN)In(tdt) ( 2 ), respectively. A similar reaction of Me₃In with 2-aminobenzenethiol (H₂abt) in toluene under reflux afforded [MeIn(abt)(py)]₂ ( 3 ). The reaction of (NCN)InCl₂ with one equivalent of Li₂(abt) or two equivalents of Li(Habt) afforded the compounds [(NCN)In(abt)]⋅LiCl(thf)₂ ( 4 ⋅LiCl(thf)₂) and (NCN)In(Habt)₂ ( 5 ), respectively. The X-ray crystal structures of 1 and 3 are similar and show dimeric structures via μ-S-(tdt) and μ-N-(abt) ligands, respectively. Compounds 2 and 4 possess similar monomeric structures and tridentate NCN pincer ligands. DFT computational studies have been used to rationalize the observed solid-state structures and discern the potential reactivity of compounds 1 – 4 against oxidants. The reaction of 1 and 2 with excess iodine resulted in loss of the 3,4-toluenedithiolate ligand and the formation of the oligomeric disulfide [tdt]_n, while 3 and 4 showed no reactivity under similar conditions. This contrasts the reactivity of previously reported organoindium o-amidophenolate complexes which undergo oxidative addition of iodine to afford ligand-centered radical species.     

In-depth investigation of protein adsorption on gold surfaces: correlating the structure and density to the efficiency of the sensing layer

Protein A (PrA), mouse monoclonal anti-IgG antibody (SAb) and deglycosylated avidin (NAV) were adsorbed on gold surfaces to capture the model rabbit IgG and build three immunosensing platforms. The assembling of immunosensors, their specificity, and the receptor accessibility were monitored by polarization modulation reflection-absorption infrared spectroscopy (PM-RAIRS) and quartz crystal microbalance with dissipation measurement (QCM-D) at each step. Combining these two techniques allows us to compare both chemical and structural properties of the sensing layers with the former bringing chemical and semiquantitative information on the grafted protein layers, whereas the latter, in addition to the mass uptake, enables us to take the layer rigidity into account. Grafting of the three capture proteins to the transducer surfaces, covered with appropriate self-assembled monolayers, yielded protein layers with variable properties. NAV formed a dense and rigid molecular layer, likely containing protein aggregates, whereas the amount of PrA was below one monolayer resulting in a flexible layer. The amount of immobilized rabbit IgG was different for the three systems with the densest capture protein layer exhibiting the lowest binding capacity. The accessibility of antibodies on the resulting immunosensors measured by interaction with a secondary antirabbit IgG antibody was found to be closely dependent on their coverage as well as on the rigidity of the protein layer. The overall study provides in-depth information on three of the most common immunosensor recognition interfaces and demonstrates the crucial influence of both structure and density of the protein layer on the efficiency of the molecular recognition phenomena.     

Cationic carbon nanotubes bind to CpG oligodeoxynucleotides and enhance their immunostimulatory properties

Functionalized cationic carbon nanotubes are able to form a stable complex with CpG ODN based on charge interaction and to increase the immunostimulatory activity of CpG motifs.     

Substituent effects on indium-phosphorus bonding in (4-RC6H4S)3In.PR'3 adducts (R = H, Me, F; R' = Et, Cy, Ph): a spectroscopic, structural, and thermal decomposition study

The tris(arylthiolate)indium(III) complexes (4-RC(6)H(4)S)(3)In [R = H (5), Me (6), F (7)] were prepared from the 2:3 reaction of elemental indium and the corresponding aryl disulfide in methanol. Reaction of 5-7 with 2 equiv of the appropriate triorganylphosphine in benzene or toluene resulted in isolation of the indium-phosphine adduct series (4-RC(6)H(4)S)(3)In.PR'(3) [R = H, R' = Et (5a), Cy (5b), Ph (5c); R = Me, R' = Et (6a), Cy (6b), Ph (6c); R = F, R' = Et (7a), Cy (7b), Ph (7c)]. These compounds were characterized via elemental analysis, FT-IR, FT-Raman, solution (1)H, (13)C{(1)H}, (31)P{(1)H}, and (19)F (7a-c) NMR spectroscopy, and X-ray crystallography (5c, 6a, 6c, and 7a). NMR spectra show retention of the In-P bond in benzene-d(6) solution, with phosphine (31)P{(1)H} signals shifted downfield compared to the uncoordinated ligand. The X-ray structures show monomeric 1:1 adduct complexes in all cases. The In-P bond distance [2.5863(5)-2.6493(12) A] is influenced significantly by the phosphine substituents but is unaffected by the substituted phenylthiolate ligand. Relatively low melting points (88-130 degrees C) are observed for all adducts, while high-temperature thermal decomposition is observed for the indium thiolate reactants 5-7. DSC/TGA and EI-MS data show a two-step thermal decomposition process, involving an initial loss of the phosphine moiety followed by loss of thiolate ligand.     

Synthesis and structures of the first bismuth-ester complexes using heterobifunctional thiolate anchored ligands and mass spectrometric identification of ligand-bridged derivatives

The first systematic series of bismuth complexes involving ester donors, Bi(SCH(2)C(O)OCH(2)CH(3))Cl(2), Bi(SCH(2)C(O)OCH(3))(2)Cl, and Bi(SCH(2)COOCH(3))(3), has been isolated and characterized by spectroscopic (IR, Raman) and X-ray crystallographic data. In addition, these and other species have been identified by electron-impact, electrospray, and atmospheric pressure chemical ionization mass spectometry. The generally applicable synthetic methodology involves the use of heterobifunctional ligands containing a thiolate moiety as an anchor to facilitate coordinate interactions between weak donors (carbonyls) and weak acids (bismuth). The bifunctional nature of the ligands is manifested in both chelating and bridging roles. Important comparisons can be made with the pharmaceutical agent "colloidal bismuth subcitrate" (CBS). The observations allow for a new appreciation of bioactive bismuth compounds, by providing an approach to study the interaction of biorelevant functional groups with bismuth.