PubMed Health⌕ Search

Biomedical subjects

Weiping Su

Publications and source records attributed to Weiping Su.

14 recordsLinked to original sources
PubMed2006

Facile synthesis of monomeric alumatranes.

Alumatranes, tricyclic neutral molecules featuring a transannular N --> Al bond, can act as Lewis acids that activate substrates in the axial coordination site. Treatment of tris(2-hydroxy-3,5-dimethylbenzyl)amine with AlMe(3) afforded dimeric (AlL)(2) 1 [wherein L = tris(2-oxy-3,5-dimethylbenzyl)amine]. X-ray diffraction analysis revealed bridging between AlL monomers by two Al-O bonds. Reactions of 1 with substrates containing O or N donors generated the alumatranes THF-AlL 2, PhCHO-AlL 3, H(2)NCH(2)CH(2)NH(2)-AlL 4, and [PhO-AlL](-) 5, in which the apical added ligand on the five-coordinate aluminum center causes variation in the transannular bond distance. Water coordinates with 1 at -20 degrees C to form the alumatrane H(2)O-AlL 6 that undergoes partial hydrolysis at room temperature to produce 7, which X-ray crystallography showed to be composed of four AlL fragments linked by an (H(2)O)(2)(HO)(2)Al(OH)(2)Al(OH)(2)(H(2)O)(2) framework in which the O(4)AlO(2)AlO(4) moiety is of local D(2)(h)() symmetry. According to X-ray analysis, 7 can crystallize in at least two polymorphic modifications: triclinic 7a and monoclinic 7b. The reaction of 3 with water also generated 6 and 7, depending on the reaction temperature. Dimeric 1 was found to promote the reaction of benzaldehyde with trimethylsilyl cyanide at room temperature to provide 2-trimethylsilyoxyphenylacetonitrile in 95% yield.

Journal Article↗
PubMed2004

Highly active palladium catalysts supported by bulky proazaphosphatrane ligands for Stille cross-coupling: coupling of aryl and vinyl chlorides, room temperature coupling of aryl bromides, coupling of aryl triflates, and synthesis of sterically hindered biaryls.

A family of proazaphosphatrane ligands [P(RNCH2CH2)2N(R'NCH2CH2): R = R' = i-Bu, 1; R = Bz, R' = i-Bu, 3; R = R' = Bz, 4] for palladium-catalyzed Stille reactions of aryl chlorides is described. Catalysts derived from ligands 1 and 4 efficiently catalyze the coupling of electronically diverse aryl chlorides with an array of organotin reagents. The catalyst system based on the ligand 3 is active for the synthesis of sterically hindered biaryls (di-, tri-, and tetra-ortho substituted). The use of ligand 4 allows room-temperature coupling of aryl bromides and it also permits aryl triflates and vinyl chlorides to participate in Stille coupling.

Journal Article↗
PubMed2004

Pd2(dba)3/P(i-BuNCH2CH2)3N-catalyzed Stille cross-coupling of aryl chlorides.

[reaction: see text] The Pd(2)(dba)(3)/P(i-BuNCH(2)CH(2))(3)N (1d) catalyst system is highly effective for the Stille cross-coupling of aryl chlorides with organotin compounds. This method represents only the second general method for the coupling of aryl chlorides. Other proazaphosphatranes possessing benzyl substituents also generate very active catalysts for Stille reactions. Noteworthy features of the method are: (a) commercial availability of ligand 1d, (b) the wide array of aryl chlorides that can be coupled, and (c) applicability to aryl, vinyl, and allyl tin reagents.

Journal Article↗
PubMed2004

CD44-independent hepatocyte growth factor/c-Met autocrine loop promotes malignant peripheral nerve sheath tumor cell invasion in vitro.

Malignant peripheral nerve sheath tumors (MPNSTs) are invasive peripheral nerve neoplasms that express both the receptor tyrosine kinase c-Met and its ligand hepatocyte growth factor (HGF). The combined expression of these proteins has been implicated in tumor cell growth and metastasis. However, HGF/c-Met autocrine activity requires the presence of a serine protease, the HGF activator (HGFA), and, in some cells, the CD44 transmembrane glycoprotein. Here, we found that HGFA, HGF, c-Met, and CD44 are coexpressed in MPNSTs but their localization did not correlate with increased cell proliferation. The ST8814 MPNST cell line also expresses all of these proteins, can convert pro-HGF to active HGF, and exhibits constitutive c-Met phosphorylation. Blocking c-Met activity or expression inhibits the invasive behavior of these cells but not their proliferation. Interestingly, although a CD44 splice variant contributes to MPNST cell invasion and interacts with c-Met and HGF in ST8814 cells, it is not required for c-Met activation. These data indicate that an HGF/c-Met autocrine loop can promote MPNST invasion through a CD44-independent mechanism and suggest that c-Met, HGFA, and HGF are potential molecular targets to inhibit MPNST metastasis.

Autocrine Communication↗
PubMed2004

Experimental encephalomyocarditis virus infection in pregnant mice.

The present study was carried out to clarify the mode of encephalomyocarditis (EMC) virus infection in pregnant mice. Pregnant BALB/c mice were intraperitoneally inoculated with the D variant of EMC virus (EMC-D) (5 x 10(2) PFU/mouse) on 11 days of gestation and killed at 1, 3, and 5 days post-inoculation (DPI). The virus titer (dam's serum, placenta, and fetus), histopathology (fetus, placenta, and uterus), distribution of viral RNA (fetus, placenta and uterus), and ultrastructure (fetal heart and placenta) were examined. No deaths occurred to fetuses at 1 DPI but almost all fetuses died at 5 DPI. The virus titers of dam's serum and placenta were elevated at 1 DPI, peaked at 3 DPI, and the former was not detected at 5 DPI. The virus titer of fetus was first elevated at 3 DPI and the level was lower than those of others. Histopathological changes and signals of viral RNAs detected by in situ hybridization (ISH) were observed in the spongiotrophoblast layer of placenta and in the fetal myocardium and liver at 3 DPI. The uterus was free from lesions and signals of viral RNA. Ultrastructural changes developed in trophoblast cells and giant cells in the spongiotrophoblast layer at and after 1 DPI and in fetal myocardial cells at 3 DPI. In the cytoplasm of trophoblast cells and giant cells, aggregations of virus-like particles 20-30 nm in diameter were observed in crystalline array. These results suggest that trophoblast cells and giant cells in the spongiotrophoblast layer are the main target of EMC virus in the placenta and that placental damage as well as the direct effect of virus to fetuses may be a cause of fetal death.

Animals↗
PubMed2004

The susceptibility of pregnant mice to encephalomyocarditis (EMC) virus infection on different days of gestation.

Pregnant mice of the BALB/c CrSlc strain were experimentally infected with the D variant of encephalomyocarditis virus (EMC-D, 5 x 10(2) PFU/head) on three different gestational days (GD). Mice were intraperitoneally inoculated with EMC-D on 11, 13 and 15 GD and sacrificed 3 days post inoculation. There was no significant difference in the fetal mortality among all inoculation groups. Placenta showed higher virus titer than fetus and dam's serum in all inoculation groups, and the virus titer of the fetus was lowest in the 15GD group. Histopathological changes and signals of viral RNAs detected by in situ hybridization were observed almost restricted to the spongiotrophoblast layer of the placenta in all inoculation groups, and the signals were strongest in the 11GD group. In the fetus of the11GD group, signals of viral RNAs were also seen in myocardium and hepatocytes. Ultrastructurally, intracytoplasmic aggregations of virus-like particles in crystalline array were observed in trophoblast cells and giant cells in the spongiotrophoblast layer in all inoculation groups.

Animals↗
PubMed2003

P(RNCH2CH2)3N: catalysts for the head-to-tail dimerization of methyl acrylate.

The dimerization of methyl acrylate to the head-to-tail 2-methylene-pentanedioic acid dimethyl ester product was realized in 82 and 85% yield in only 4 h at room temperature in THF in the presence of catalytic amounts of P(RNCH2CH2)3N (R = i-Bu and Bn, respectively). These phosphines are to our knowledge the best nonmetallic catalysts so far reported for this reaction. In contrast, less sterically hindered P(MeNCH2CH2)3N failed to catalyze this dimerization, giving oligomer or polymer instead.

Journal Article↗
PubMed2003

Malignant peripheral nerve sheath tumor cell invasion is facilitated by Src and aberrant CD44 expression.

Malignant peripheral nerve sheath tumors (MPNSTs) are aggressive malignancies that arise within peripheral nerves. These tumors occur with increased incidence in patients with neurofibromatosis type 1 (NF1), exhibiting increased Ras activity due to loss of the NF1 gene product, neurofibromin, and abnormal expression of the epidermal growth factor receptor (EGFR). We previously found that MPNSTs express increased levels of the CD44 family of transmembrane glycoproteins that have been implicated in tumor cell invasion and metastasis. In two MPNST cell lines, we have found that elevated CD44 expression and cell invasion are dependent on Src kinase activity but are independent of mitogen-activated protein kinases (MAPK) kinase (MEK) activity. In contrast, inhibition of Src kinase activity has no influence on MPNST cell proliferation. Reduction of CD44 levels, using antisense oligonucleotides, results in reduced MPNST cell invasion in vitro, suggesting that Src contributes in part to MPNST cell invasion by increasing CD44 levels. At least some of this increased CD44 expression results from elevated EGFR levels through a Src-dependent mechanism, consistent with the notion that EGFR promotes constitutive Src activation in MPNSTs. These data indicate that Src and CD44 are putative targets for the treatment of MPNST invasion and metastasis.

Enzyme Inhibitors↗
PubMed2003

Susceptibility of primary culture neurons from rats of different ages to encephalomyocarditis (EMC) virus infection.

The changes in susceptibility of neurons to the D variant of EMC virus (EMC-D) (10(6) PFU/well) were investigated in developing hippocampal primary cultures from postnatal days of 1, 7, and 56 Fischer 344 rats (P1, P7, and P56) for up to 12 h after infection (12 HAI). The virus titer of primary culture neurons increased at 1 HAI, decreased at 2 HAI, increased at 3 HAI, peaked at 8 HAI, and decreased at 12 HAI in all age groups. The titers at 1 and 8 HAI were lowest in P56 cultures. The virus titer of neurons was always higher than that of culture media, especially at 1 HAI, in P1 cultures, whereas the former was lower than the latter from 2 to 3 HAI in P7 cultures and from 2 to 4 HAI in P56 cultures, respectively. Signals of viral RNA detected by in situ hybridization were first observed in the peripheral cytoplasm of neurons at 1 HAI in P1 and P7 cultures and at 4 HAI in P56 cultures, respectively. The signals spread to a large or whole area of cytoplasm and also to processes thereafter. The number of viral RNA-positive neurons and the amount of signals decreased with age. The present results indicated that the susceptibility of primary culture neurons to EMC-D decreased with age but viral replication still occurred in P56 cultures.

Aging↗
PubMed2002

Crystal of semiconducting quantum dots built on covalently bonded t5 [in(28)cd(6)s(54)](-12): the largest supertetrahedral cluster in solid state.

Periodic array of nanoparticles is essential for practical applications in optical devices. Periodic dot arrays often exhibit very interesting collective phenomenon. We report a periodic crystal of InCdS pseudo-T5 nanocluster, the largest supertetrahedral cluster found thus far in solid state. Each InCdS cluster behaves like a nanoparticle with the same size. Unlike the array of colloidal dots in which the dot-dot separation is large ( approximately 5 nm), the neighboring T5 clusters in [In28Cd6S54].[(CH3)4N]12[(HSCH2COOH)2]3.5 crystal form a natural point contact by sharing covalently bonded S atoms. Both experimental and theoretical studies show that this crystal is a semiconductor with a band gap of 3.0 eV.

Journal Article↗
PubMed2002

High-nuclearity sulfide-rich molybdenum[bond]iron[bond]sulfur clusters: reevaluation and extension.

High-nuclearity Mo[bond]Fe[bond]S clusters are of interest as potential synthetic precursors to the MoFe(7)S(9) cofactor cluster of nitrogenase. In this context, the synthesis and properties of previously reported but sparsely described trinuclear [(edt)(2)M(2)FeS(6)](3-) (M = Mo (2), W (3)) and hexanuclear [(edt)(2)Mo(2)Fe(4)S(9)](4-) (4, edt = ethane-1,2-dithiolate; Zhang, Z.; et al. Kexue Tongbao 1987, 32, 1405) have been reexamined and extended. More accurate structures of 2-4 that confirm earlier findings have been determined. Detailed preparations (not previously available) are given for 2 and 3, whose structures exhibit the C(2) arrangement [[(edt)M(S)(mu(2)-S)(2)](2)Fe(III)](3-) with square pyramidal Mo(V) and tetrahedral Fe(III). Oxidation states follow from (57)Fe Mössbauer parameters and an S = (3)/(2) ground state from the EPR spectrum. The assembly system 2/3FeCl(3)/3Li(2)S/nNaSEt in methanol/acetonitrile (n = 4) affords (R(4)N)(4)[4] (R = Et, Bu; 70-80%). The structure of 4 contains the [Mo(2)Fe(4)(mu(2)-S)(6)(mu(3)-S)(2)(mu(4)-S)](0) core, with the same bridging pattern as the [Fe(6)S(9)](2-) core of [Fe(6)S(9)(SR)(2)](4-) (1), in overall C(2v) symmetry. Cluster 4 supports a reversible three-member electron transfer series 4-/3-/2- with E(1/2) = -0.76 and -0.30 V in Me(2)SO. Oxidation of (Et(4)N)(4)[4] in DMF with 1 equiv of tropylium ion gives [(edt)(2)Mo(2)Fe(4)S(9)](3-) (5) isolated as (Et(4)N)(3)[5].2DMF (75%). Alternatively, the assembly system (n = 3) gives the oxidized cluster directly as (Bu(4)N)(3)[5] (53%). Treatment of 5 with 1 equiv of [Cp(2)Fe](1+) in DMF did not result in one-electron oxidation but instead produced heptanuclear [(edt)(2)Mo(2)Fe(5)S(11)](3-) (6), isolated as the Bu(4)N(+)salt (38%). Cluster 6 features the previously unknown core Mo(2)Fe(5)(mu(2)-S)(7)(mu(3)-S)(4) in molecular C(2) symmetry. In 4-6, the (edt)MoS(3) sites are distorted trigonal bipramidal and the FeS(4) sites are distorted tetrahedral with all sulfide ligands bridging. Mössbauer spectroscopic data for 2 and 4-6 are reported; (mean) iron oxidation states increase in the order 4 < 5 approximately 1 < 6 approximately 2. Redox and spectroscopic data attributed earlier to clusters 2 and 4 are largely in disagreement with those determined in this work. The only iron and molybdenum[bond]iron clusters with the same sulfide content as the iron[bond]molybdenum cofactor of nitrogenase are [Fe(6)S(9)(SR)(2)](4-) and [(edt)(2)Mo(2)Fe(4)S(9)](3-)(,4-).

Catalysis↗
PubMed2000

Bis[bis(N,N-diethyl-1,1-diselenocarbamato)copper(II)], [Cu(Se(2)CNEt(2))(2)](2).

The title centrosymmetric Cu(II) binuclear complex, bis(micro-N,N-diethyl-1,1-diselenocarbamato-Se,Se':Se)bis[(N,N-diethyl-1,1-diselenocarbamato-Se,Se')copper(II)], [Cu(Se(2)CNEt(2))(2)](2) or [Cu(2)(C(5)H(10)NSe(2))(4)], is built from two symmetry-related [Cu{Se(2)CN(Et)(2)}(2)] units by pairs of Cu-Se bonds. The coordination geometry at the unique Cu atom is distorted square pyramidal, with Cu-Se distances in the range 2.4091 (11)-2.9095 (10) A.

Journal Article↗