Enhanced charge density wave with mobile superconducting vortices in La1.885Sr0.115CuO4.

Superconductivity in the cuprates is found to be intertwined with charge and spin density waves. Determining the interactions between the different types of order is crucial for understanding these important materials. Here, we elucidate the role of the charge density wave (CDW) in the prototypical cuprate La1.885Sr0.115CuO4, by studying the effects of large magnetic fields (H) up to 24 Tesla. At low temperatures (T), the observed CDW peaks reveal two distinct regions in the material: a majority phase with short-range CDW coexisting with superconductivity, and a minority phase with longer-range CDW coexisting with static spin density wave (SDW). With increasing magnetic field, the CDW first grows smoothly in a manner similar to the SDW. However, at high fields we discover a sudden increase in the CDW amplitude upon entering the vortex-liquid state. Our results signify strong coupling of the CDW to mobile superconducting vortices and link enhanced CDW amplitude with local superconducting pairing across the H - T phase diagram.

Regulatory mechanism of mesalazine on TLR4/MyD88-dependent pathway in mouse ulcerative colitis model.

OBJECTIVE: The aim of this study was to investigate the regulatory mechanism of mesalazine (MSLZ) on microRNA-21, microRNA-31 and Toll-like receptor 4/myeloid differentiation primary response 88 (TLR4/MyD88)-dependent pathway in 2,4,6-trinitrobenzene sulfonic acid (TNBS)/ethanol-induced ulcerative colitis (UC) model in mice. MATERIALS AND METHODS: The UC model was constructed by coloclysis of TNBS/ethanol in mice. 60 male mice were randomly assigned into control group, model group, MSLZ group and Azathioprine (AZA) group, with 15 mice in each. Corresponding drug or saline was i.g. injected in mice for consecutive 14 days. Pathological lesions in colon tissues were observed by hematoxylin and eosin (HE) staining under the microscope. The expression levels of microRNA-21 and microRNA-31 in mouse colon tissues were determined by quantitative Real Time-Polymerase Chain Reaction (qRT-PCR). The mRNA and protein levels of relative genes in TLR4/MyD88-dependent pathway in mouse colon tissues were detected by qRT-PCR and Western blot, respectively. RESULTS: A mouse UC model was successfully constructed based on scores of DAI, colonic damage and pathological lesions under the microscope. MSLZ markedly improved clinical symptoms and mucosal healing. Meanwhile, the protective effect of MSLZ was similar or even stronger than that of AZA. The expression levels of microRNA-21 and microRNA-31 in mouse colon tissues in the model group were significantly higher than those of the control group (p<0.01). Compared with the model group, both MSLZ and AZA treatment could remarkably inhibit the expressions of microRNA-21 and microRNA-31 (p<0.01). The mRNA and protein levels of relative genes in TLR4/MyD88-dependent pathway in mouse colon tissues were markedly upregulated in the model group when compared with those of the control group. The inhibitory effect of MSLZ on the expressions of upstream factors in TLR4/MyD88-dependent pathway (including TLR4, MyD88, TRAF-6 and NF-κB) was slightly stronger than AZA, which was weaker in inhibiting downstream factors (including TNF-α and IL-1ß). However, no significant difference in the inhibition of TLR4/MyD88-dependent pathway was found between MSLZ and AZA (p>0.05). CONCLUSIONS: In the TNBS/ethanol-induced UC mouse model, MSLZ could inhibit the expressions of microRNA-21 and microRNA-31 in colon tissues. Furthermore, MSLZ also inhibited the release of inflammatory factors by inhibiting the TLR4/MyD88-dependent pathway in UC mice.

Role of Hsa-miR-122-3p in steroid-induced necrosis of femoral head.

OBJECTIVE: To explore the clinical correlation between the hsa-miR-122-3p expression in bone marrow mesenchymal stem cells (BMSCs) and steroid-induced necrosis of femoral head (SONFH). PATIENTS AND METHODS: A total of 62 SONFH patients were selected as the experimental group, while another 72 patients with femoral neck fracture (FNF) were selected as the control group. The bone marrow was obtained from patients during operation and used to culture the BMSCs. The expression of hsa-miR-122-3p in BMSCs was detected via real-time quantitative polymerase chain reaction (qPCR) in both groups. The patients in experimental group were further divided into Ficat stage III group and stage IV group according to the Ficat stage, and the expression of hsa-miR-122-3p in BMSCs was also detected via qPCR in the two groups. RESULTS: The expression level of hsa-miR-122-3p in SONFH group was significantly lower than that in FNF group, and the difference was statistically significant (p<0.05). The expression level of hsa-miR-122-3p in Ficat stage IV group was significantly lower than that in stage III group (p<0.05). CONCLUSIONS: We demonstrated that the expression of hsa-miR-122-3p in BMSCs declined in SONFH group, indicating that hsa-miR-122-3p may be involved in the regulation of the pathological process of SONFH, and the expression level of hsa-miR-122-3p in BMSCs may be correlated with the progression of SONFH.

Observation of two types of charge-density-wave orders in superconducting La2-xSrxCuO4.

The discovery of charge- and spin-density-wave (CDW/SDW) orders in superconducting cuprates has altered our perspective on the nature of high-temperature superconductivity (SC). However, it has proven difficult to fully elucidate the relationship between the density wave orders and SC. Here, using resonant soft X-ray scattering, we study the archetypal cuprate La2-xSrxCuO4 (LSCO) over a broad doping range. We reveal the existence of two types of CDW orders in LSCO, namely CDW stripe order and CDW short-range order (SRO). While the CDW-SRO is suppressed by SC, it is partially transformed into the CDW stripe order with developing SDW stripe order near the superconducting Tc. These findings indicate that the stripe orders and SC are inhomogeneously distributed in the superconducting CuO2 planes of LSCO. This further suggests a new perspective on the putative pair-density-wave order that coexists with SC, SDW, and CDW orders.

Magnetic Excitations of the Classical Spin Liquid MgCr_{2}O_{4}.

We report a comprehensive inelastic neutron-scattering study of the frustrated pyrochlore antiferromagnet MgCr_{2}O_{4} in its cooperative paramagnetic regime. Theoretical modeling yields a microscopic Heisenberg model with exchange interactions up to third-nearest neighbors, which quantitatively explains all of the details of the dynamic magnetic response. Our work demonstrates that the magnetic excitations in paramagnetic MgCr_{2}O_{4} are faithfully represented in the entire Brillouin zone by a theory of magnons propagating in a highly correlated paramagnetic background. Our results also suggest that MgCr_{2}O_{4} is proximate to a spiral spin-liquid phase distinct from the Coulomb phase, which has implications for the magnetostructural phase transition in MgCr_{2}O_{4}.

Metformin relieves acute respiratory distress syndrome by reducing miR-138 expression.

OBJECTIVE: To investigate whether metformin can relieve acute respiratory distress syndrome (ARDS). Its potential mechanism was also explored. MATERIALS AND METHODS: The ARDS model was established by injecting LPS into mice that received metformin in advance and the mice in the control group. Pulmonary edema was detected by W/D ratios (wet-to-dry weight ratios), and the vascular exudation was reflected by the protein content and cell number of alveolar lavage fluid. Meanwhile, MPO (myeloperoxidase) activity assay was performed to analyze the neutrophil aggregation. The expression of inflammatory cytokines, including TNF-α, IL-1ß, IL-6, and IL-17, were detected by enzyme-linked immunosorbent assay (ELISA). This series of experiments reflected the alleviation effect of metformin on ARDS. To further study the mechanism, we cultured alveolar macrophages (NR8383) in vitro and treated them with LPS and metformin. Western blot was used to detect the phosphorylation levels of p38, ERK, NF-kB, and SIRT1 expression level. Bioinformatics method was then used to predict the binding of miR-138 to SIRT1. The mRNA and protein expression of SIRT1 was detected in NR8383 cells transfected with miR-138 inhibitor. The dual luciferase gene reporter assay was used to detect the relative luciferase activities of miR-138 and SIRT1. RESULTS: Pulmonary edema, vascular exudation, and neutrophil accumulation were observed in the ARDS model mice, and the levels of inflammatory cytokines including TNF-α, IL-1b, IL-6, and IL-17 were significantly increased. After metformin treatment, these pulmonic damage indicators were found to be partially reversed. At the same time, metformin could significantly reduce LPS-induced death. After NR8383 was treated with metformin and LPS, the expression of SIRT1 was higher than that of LPS treatment alone, but the expression of p-p38, p-ERK, and p-NF-κB was significantly decreased. After the addition of metformin in NR8383 after LPS treatment, the expression level of miR-138-5p was significantly decreased, and miR-138-5p was confirmed to target SIRT1 and regulate its expression. CONCLUSIONS: Metformin could reduce LPS-induced pulmonic injury and increase expression of inflammatory factors. A possible mechanism might be that metformin-induced low expression of mir-138-5p could target SIRT1 to increase its expression and suppress the MAPK pathway, thus alleviating ARDS.

Universal geometric frustration in pyrochlores.

Materials with the pyrochlore/fluorite structure have diverse technological applications, from magnetism to nuclear waste disposal. Here we report the observation of structural instability present in the pyrochlores A2Zr2O6O' (A = Pr, La) and Yb2Ti2O6O', that exists despite ideal stoichiometry, ideal cation-ordering, the absence of lone pair effects, and a lack of magnetic order. Though these materials appear to have good long-range order, local structure probes find displacements, of the order of 0.01 nm, within the pyrochlore framework. The pattern of displacements of the A2O' sublattice mimics the entropically-driven fluxional motions characteristic of and well-known in the silica mineral ß-cristobalite. The universality of such displacements within the pyrochlore structure adds to the known structural diversity and explains the extreme sensitivity to composition found in quantum spin ices and the lack of ferroelectric behavior in pyrochlores.

Analysis of risk factors and prevention strategies of post-ERCP pancreatitis.

OBJECTIVE: To analyze the relevant risk factors and preventive measures for post-endoscopic retrograde cholangiopancreatography (post-ERCP) pancreatitis (PEP) so as to improve the diagnosis and treatment levels of ERCP, thus reducing the prevalence rate of PEP. PATIENTS AND METHODS: The clinical data of 278 patients receiving ERCP from January 2014 to December 2016 were retrospectively analyzed. First, the univariate analysis was conducted for the factors such as gender, age, diameter of common bile duct, whether development occurred in the pancreatic duct and other factors. Then, the multivariate logistic regression analysis was performed for factors showing statistical significance in the univariate analysis so as to analyze the independent risk factors for PEP. RESULTS: The success rate of ERCP included in the study was 97.12%. The prevalence rate of PEP was 8.27%. Univariate analysis results showed that the prevalence rate of PEP in the group of patients younger than 60 years old was higher than that in the group of patients older than 60 years old (14.14% vs. 5.03%, p = 0.016); the prevalence rate of PEP in the group of patients with intubation difficulty was higher than that in the group of patients without intubation difficulty (19.61% vs. 5.73%, p = 0.004); the prevalence rate of PEP in the group of patients with operation time more than 60 min was higher than that in the group of patients with operation time less than 60 min (18.60% vs. 6.38%, p = 0.034); the prevalence rate of PEP in the group of patients with the pancreatic duct development was higher than that in the group of patients without the pancreatic duct development (50% vs. 6.72%, p < 0.001); the prevalence rate of PEP in the group of patients placed with nasobiliary drainage catheters was not higher than that in the group of patients not placed with nasobiliary drainage catheters (18.00% vs. 2.81%, p < 0.001). The above five relevant factors were included in the logistic regression equation for the multivariate analysis, which showed that the age less than 60 years old (p = 0.002) and the pancreatic duct development (p = 0.004) were independent risk factors for PEP, and nasobiliary drainage (p = 0.003) was a protective factor for PEP. CONCLUSIONS: The occurrence of PEP is associated with the age less than 60 years old, the pancreatic duct development, intubation difficulty and overlong operation time. Among them, the pancreatic duct development and the age less than 60 years old are independent risk factors for PEP. Placing nasobiliary drainage catheters after operation, avoiding the pancreatic duct development, improving the success rate of intubation, reducing ERCP operation time and other methods, can effectively reduce the occurrence of PEP.

Disordered Route to the Coulomb Quantum Spin Liquid: Random Transverse Fields on Spin Ice in Pr_{2}Zr_{2}O_{7}.

Inelastic neutron scattering reveals a broad continuum of excitations in Pr_{2}Zr_{2}O_{7}, the temperature and magnetic field dependence of which indicate a continuous distribution of quenched transverse fields (Δ) acting on the non-Kramers Pr^{3+} crystal field ground state doublets. Spin-ice correlations are apparent within 0.2 meV of the Zeeman energy. A random phase approximation provides an excellent account of the data with a transverse field distribution ρ(Δ)∝(Δ^{2}+Γ^{2})^{-1}, where Γ=0.27(1) meV. Established during high temperature synthesis due to an underlying structural instability, it appears disorder in Pr_{2}Zr_{2}O_{7} actually induces a quantum spin liquid.

[Effects of 13-cis-retinoic acid combined with interferon-α2b in mantle cell lymphoma cell lines (Jeko-1) in vitro].

Objectives: To explore the effects of 13-cis-retinoic acid (13cRA) alone or combined with interferonα-2b (IFNα-2b) for the inhibition of cell growth and apoptosis induction of mantle cell lymphoma cell lines Jeko-1 cells. Methods: Jeko-1 cells were treated by different concentrations of 13cRA alone or combined with IFN-α2b. CCK-8 was used to measure the inhibition effects by different treatments. Cell cycles were analyzed by flow cytometry. Effects on apoptosis were assessed by staining of Annexin Ⅴ/PI. And the levels of Cyclin D1, caspase-9 and Rb proteins were measured by Western blot method. Results: 13cRA alone at different doses and its combination with IFNα-2b inhibited Jeko-1 cells growth and induced apoptosis, but the combination had higher inhibition potential and significant apoptosis rate (P<0.05) . The growth inhibition and apoptosis induction in Jeko-1 cells increased significantly with the elevation of drugs concentration and treating duration (P<0.05) . As well as the percentage of Jeko-1 cells at G(1)/G(2) phases increased (P<0.05) and cells at S phase decreased (P<0.05) , the levels of Cyclin D1 and Rb decreased with elimination caspase-9. Conclusion: 13cRA, IFN-α2b and their combined administration inhibited cells growth and induced apoptosis, decreased the cell populations at S phase and blocked the cells at G(1)/G(2) phase. Combination of the drugs may have a cooperated action. The therapeutic synergistic effects of 13cRA and IFN-α2b were assumed to lower the expression of Cyclin D1 and Rb proteins, and induce apoptosis by activating caspase-9 pathway.

Analysis of circulating long non-coding RNA UCA1 as potential biomarkers for diagnosis and prognosis of osteosarcoma.

OBJECTIVE: The aim of this investigation was to examine the potential usefulness of long non-coding RNA UCA1 (UCA1) as a biomarker for diagnosis and prognosis in osteosarcoma. PATIENTS AND METHODS: The expression level of UCA1 was determined using TaqMan real-time PCR in human osteosarcoma tissues and patients' sera. Next, we investigated to clarify the relationship of UCA1 with clinicopathological features. The receiver operating characteristic (ROC) curve was performed to estimate the diagnostic value of UCA1. Finally, the prognosis of patients with osteosarcoma was assessed by Kaplan-Meier method and Cox proportional hazards model. RESULTS: We observed that UCA1 was significantly increased in osteosarcoma tissue compared with normal bone tissue (p<0.001) and the serum expression of UCA1 was significantly higher in patients with osteosarcoma than that in healthy controls (p<0.01). Up-regulation of UCA1 was correlated with clinical stage (p=0.001) and metastasis (p=0.007). Furthermore, serum UCA1 levels were observed to be robust in differentiating osteosarcoma patients from control subjects [area under the curve (AUC) = 0.831; 95% confidence interval (CI)= 0.746 to 0.916]. Kaplan-Meier analysis showed that that high UCA1 expression level was associated with poorer overall survival (p<0.001) and disease-free survival (p<0.001). Finally, Cox regression analyses showed that UCA1 expression might be an independent prognostic parameter to predict poor prognosis. CONCLUSIONS: Our study firstly showed that UCA1 could be a specific and noninvasive candidate biomarker for the diagnosis and prognosis of UCA1.

[Anti-tumor effects of 13-cis-retinoic acid combined with interferon α-2b in animal model of mantle cell lymphoma].

Objective: To determine the anti-tumor effects of 13-cis-retinoic acid (13cRA) combined with interferonα-2b (IFNα-2b) in mantle cell lymphoma (MCL) animal model. Methods: The animal model of MCL was established by introducing Jeko-1 cell line into severe combined immunodeficiency disease mice. The successfully tumor-developed mice were assigned to different groups treated with negative control group (solvents), 13cRA (high dose: 200mg/kg; middle dose: 100mg/kg; low dose: 50 mg/kg) alone, IFNα-2b alone or combination of different dose of 13cRA with IFNα-2b, and positive control group (bortezomib, rituximab, cyclophosphamide), respectively. Variations of tumor volume were observed regularly. The relative tumor proliferation rate and tumor inhibition rate were calculated. Immunohistochemistry stain was used to detect the Ki-67 expression and TUNEL was applied to measure the apoptosis of tumor cells. Furthermore, the levels of Cyclin D1, caspase 9 and Rb protein were measured by Western-blot method. Results: ① The relative tumor proliferation rates (T/C%)were 30%, 37%, 32% and 33% in middle dose, high dose groups of 13cRA as well as their combination with IFN α-2b, respectively. ② Comparing with the negative control, both 13cRA at different doses and its combination with IFNα-2b remarkably inhibited the tumor growth (P<0.05), while no statistic significance existed in different dose group of 13cRA. IFN-α 2b alone didn't demonstrate the tumor-inhibition effects (P>0.05). Middle dose of 13cRA and its combination with IFN-α-2b demonstrated relatively high tumor-inhibition effects (59.2% and 62.6% respectively), which were similar to the effects in positive control (69.4%). ③ There was no statistic difference of Ki-67 in each experimental group. ④ Comparing with negative control group, all doses of 13cRA and their combinations with IFNα-2b remarkably increased the apoptosis (P<0.05), similar to the positive control group (P>0.05). However, IFNα-2b alone didn' t promote the apoptosis of tumor tissue (P=0.098). ⑤ Comparing with negative control group, IFNα-2b combined with each dose of 13cRA significantly decreased the levels of cycling D1 and procaspase-9, while increased the level of cleaved caspase-9 (P<0.05), which were similar to the positive control group (P>0.05). Nevertheless, 13cRA alone didn't demonstrate such effects. Conclusion: In the MCL animal model, IFNα-2b alone showed no effects, but combined with IFNα-2b, 13cRA displayed anti-tumor effects at different doses. The anti-tumor mechanism of 13cRA combined with IFNα-2b was probably down-regulation of the cyclin D1 expression, inhibition of cell proliferation and induction of apoptosis by activating caspase-9.

Evidence for topologically protected surface states and a superconducting phase in [Tl4](Tl(1-x)Sn(x))Te3 using photoemission, specific heat, and magnetization measurements, and density functional theory.

We report the discovery of surface states in the perovskite superconductor [Tl4]TlTe3 (Tl5Te3) and its nonsuperconducting tin-doped derivative [Tl4](Tl0.4Sn0.6)Te3 as observed by angle-resolved photoemission spectroscopy. Density functional theory calculations predict that the surface states are protected by a Z2 topology of the bulk band structure. Specific heat and magnetization measurements show that Tl5Te3 has a superconducting volume fraction in excess of 95%. Thus Tl5Te3 is an ideal material in which to study the interplay of bulk band topology and superconductivity.

Quantum fluctuations in spin-ice-like Pr2Zr2O7.

Spin ice is a magnetic analog of H2O ice that harbors dense static disorder. Dipolar interactions between classical spins yield a frozen frustrated state with residual configurational Pauling entropy and emergent magnetic monopolar quasiparticles. Introducing quantum fluctuations is of great interest as this could melt spin ice and allow coherent propagation of monopoles. Here, we report experimental evidence for quantum dynamics of magnetic monopolar quasiparticles in a new class of spin ice based on exchange interactions, Pr2Zr2O7. Narrow pinch point features in otherwise diffuse elastic neutron scattering reflects adherence to a divergence-free constraint for disordered spins on long time scales. Magnetic susceptibility and specific heat data correspondingly show exponentially activated behaviors. In sharp contrast to conventional ice, however, >90% of the neutron scattering is inelastic and devoid of pinch points furnishing evidence for magnetic monopolar quantum fluctuations.

Quantum spin liquid in frustrated one-dimensional LiCuSbO4.

A quantum magnet, LiCuSbO4, with chains of edge-sharing spin-1/2 CuO6 octahedra is reported. While short-range order is observed for T<10 K, no zero-field phase transition or spin freezing occurs down to 100 mK. Specific heat indicates a distinct high-field phase near the 12 T saturation field. Neutron scattering shows incommensurate spin correlations with q=(0.47±0.01)π/a and places an upper limit of 70 µeV on any spin gap. Exact diagonalization of 16-spin easy-plane spin-1/2 chains with competing ferro- and antiferromagnetic interactions (J1=-75 K, J2=34 K) accounts for the T>2 K data.

Differential gene expression in fully-grown oocytes between gynogenetic and gonochoristic crucian carps.

Silver crucian carp (Carassius auratus gibelio) is a unique triploid bisexual species that can reproduce by gynogenesis. As all other gynogenetic animals, it keeps its chromosome integrity by inhibiting the first meiosis division (no extrusion of the first pole body). To understand the molecular events governing this reproduction mode, suppression subtractive hybridization was used to identify the genes differentially expressed in fully-grown oocytes of the gynogenetic and gonochoristic crucian carp (gyno-carp and gono-carp). From two specific subtractive cDNA libraries, the clones screened out by dot blots and virtual Northern blots were chosen to clone full-length cDNA by RACE. Four differentially expressed genes were obtained. Two are novel genes and are expressed specifically in the oocytes. The gyno-carp stores much more mRNA of cyclin A2, a new member of the fish A-type cyclin gene, in its fully-grown oocyte than in the gono-carp. The last gene is histone H2A. The histone H2As of these two closely related crucian carps are quite different in the C-terminus. Preliminary characterization of the four genes has been analyzed by nucleotide and deduced amino acid sequence and Northern analysis.

The anti-angiogenic agent fumagillin covalently binds and inhibits the methionine aminopeptidase, MetAP-2.

The inhibition of new blood vessel formation (angiogenesis) is an effective means of limiting both the size and metastasis of solid tumors. The leading anti-angiogenic compound, TNP-470, has proven to be effective in in vitro and in animal model studies, and is currently being tested in phase III antitumor clinical trials. Despite many detailed pharmacological studies, little is known of the molecular mode of action of TNP-470. Using a derivative of the TNP-470 parent compound, the fungal metabolite, fumagillin, we have purified a mammalian protein that is selectively and covalently bound by this natural product. This fumagillin binding protein was found to be a metalloprotease, methionine aminopeptidase (MetAP-2), that is highly conserved between human and Saccharomyces cerevisiae. In the absence of MetAP-1, a distantly related methionine aminopeptidase, MetAP-2 function is essential for vegetative growth in yeast. We demonstrate that fumagillin selectively inhibits the S. cerevisiae MetAP-2 protein in vivo. The binding is highly specific as judged by the failure of fumagillin to inhibit MetAP-1 in vivo. Hence, these results identify MetAP-2 as an important target of study in the analysis of the potent biological activities of fumagillin.

A systematic approach to the solid-phase synthesis of linear and cyclic pseudopeptide libraries containing psi[CH2NH] amide bond surrogates.

A systematic approach has been adopted for the synthesis and characterization of a series of linear and cyclic pseudopeptide mixtures containing the psi[CH2NH] amide replacement. The parent structures were based on biologically relevant compounds including an enkephalin analog, H-Tyr-D-Ala-Gly-Phe-Leu-OH, and an Arg-Gly-Asp peptide sequence. The linear mixtures containing 4 and 64 pseudopeptide components with 1, 2 or 3 amide bond surrogates were synthesized using Boc-SPPS. The amount of desired linear pseudopeptides in the mixtures ranged from 67 to 90% as determined by integration of HPLC peak areas. Comparative studies indicated: (i) racemization is not a problem in the synthesis of pseudopeptide mixtures containing the psi[CH2NH] surrogate; and (ii) protection of the psi[CH2NH] surrogate with a benzyloxycarbonyl group during the synthesis is beneficial. Cyclic mixtures containing 4 and 256 cyclic pseudopeptide components with a single amide bond surrogate were synthesized using a resin-bound cyclization approach featuring side-chain attachment of Boc-Asp-OFm to the solid support. Cyclization kinetic studies revealed that the newly developed HATU coupling reagent provided a fast cyclization rate for a pseudopeptide mixture and that the position of the reduced peptide bond within a peptide mixture had only a small effect on the cyclization rates of the mixture. Pseudopeptide libraries permit the more efficient bioassay of complex structures and can also be used to reveal more rapidly trends in physicochemical variables. For example, we observed that the expected increase in hydrophilicity with psi[CH2NH] substitutions during RP-HPLC analysis did not continue with several such replacements.

Synthesis and characterization of cyclic pseudopeptide libraries containing thiomethylene and thiomethylene-sulfoxide amide bond surrogates.

We describe the first examples of a series of cyclic pseudopeptide libraries that have been prepared in a systematic approach in order to facilitate both synthesis and subsequent deconvolution attempts. Our synthetic strategy involved the attachment of a trifunctional amino acid (Asp, Asn or Glu) to a polystyrene resin via its side chain, and stepwise chain elongation using either protected amino acids or a pseudodipeptide building block. Head to tail cyclic peptides were formed by removal of the temporary N- and C-terminal protecting groups followed by ring closure by amide formation. Cyclization of the hexa, hepta, and octapseudopeptides on the resin avoided dimer formation, as monitored by mass spectrometry. We utilized a 'psi-scan' approach in which a second fixed position was serially addressed by stepping a dipeptide surrogate, Pro psi [CH2S]Gly around the rings to generate a group of cyclic pseudopeptide sub-libraries. Oxidation of psi [CH2S] to psi [CH2SO] helped validate the synthesis and also provides a strategy for forming a new set of pseudopeptide libraries (previously described as 'libraries from libraries'). Our results suggest that libraries of cyclic pseudopeptides are an efficient method of preparing and assaying these synthetically more challenging entities as potential drug leads.