Synthesis and reactivity of 4'-deoxypentenosyl disaccharides.

4-Deoxypentenosides (4-DPs) are versatile synthons for rare or higher-order pyranosides, and they provide an entry for structural diversification at the C5 position. Previous studies have shown that 4-DPs undergo stereocontrolled DMDO oxidation; subsequent epoxide ring-openings with various nucleophiles can proceed with both anti or syn selectivity. Here, we report the synthesis of α- and ß-linked 4'-deoxypentenosyl (4'-DP) disaccharides, and we investigate their post-glycosylational C5' additions using the DMDO oxidation/ring-opening sequence. The α-linked 4'-DP disaccharides were synthesized by coupling thiophenyl 4-DP donors with glycosyl acceptors using BSP/Tf2O activation, whereas ß-linked 4'-DP disaccharides were generated by the decarboxylative elimination of glucuronyl disaccharides under microwave conditions. Both α- and ß-linked 4'-DP disaccharides could be epoxidized with high stereoselectivity using DMDO. In some cases, the α-epoxypentenosides could be successfully converted into terminal l-iduronic acids via the syn addition of 2-furylzinc bromide. These studies support a novel approach to oligosaccharide synthesis, in which the stereochemical configuration of the terminal 4'-DP unit is established at a post-glycosylative stage.

Late SV40 factor: a key mediator of Notch signaling in human hepatocarcinogenesis.

AIM: To investigate the relationship between late SV40 factor (LSF) and Notch signaling in the development and progress of hepatocellular carcinoma (HCC). METHODS: Liver cancer tissue specimens from 25 patients were analyzed for Notch-1 and LSF expression by immunohistochemistry. The correlation between expression and the biological effects of Notch-1 and LSF were analyzed using genetic and pharmacological strategies in HCC cell lines and human normal cell lines, including hepatic stellate cells (HSC) and human embryonic kidney epithelial cells (HEK). RESULTS: Immunohistochemistry showed that both Notch-1 and LSF were significantly upregulated in HCC samples (76%, 19/25, P < 0.0001 and 84%, 21/25, P < 0.0001, respectively) compared with non-cancer samples. Activation of Notch-1 by exogenous transfection of Notch1 intracellular domain increased LSF expression in HSC and HEK cells to levels similar to those seen in HepG2 cells. Furthermore, blocking Notch-1 activation with a γ-secretase inhibitor, DAPT, downregulated LSF expression in HepG2 cells. Additionally, a biological behavior assay showed that forced overexpression of LSF promoted HepG2 cell proliferation and invasion. CONCLUSION: LSF is a key mediator of the Notch signaling pathway, suggesting that it might be a novel therapeutic target for the treatment of HCC.

[Hypoxia induced by CoCl2 influencing the expression and the activity of matrix metalloproteinase-2 in rat hepatic stellate cells].

OBJECTIVE: To investigate the effects of hypoxia induced by cobalt chloride on the expression and the activity of matrix metalloproteinase-2 (MMP-2) in rat hepatic stellate cells (HSC-T6) and to clarify the possible mechanisms. METHODS: HSC-T6 cell line was grown in Dulbecco's modified Eagle medium with 10% fetal calf serum at 37 degrees C and 5% CO2. When reaching confluence, the cells were incubated with serum-free medium in the presence of cobalt chloride (0, 50, 100, 200 micromol/L) for six hours, and then the supernatant and the cells were harvested. The expression of the MMP-2 mRNA and HIF-1alpha protein in HSC-T6 cells was detected using RT-PCR and Western blot respectively. The activity of the MMP-2 in the supernatant was detected by zymography. The binding reaction between HIF-1a protein and MMP-2 gene sequence was investigated by electrophoresis mobility shift assay. RESULTS: When the concentration of CoCl2 increased from 0 micromol/L to 200 micromol/L, the expressions of MMP-2 mRNA (the rate of light density) were increased from 0.53+0.12 to 1.57+0.11 and the differences among these four groups were significant (F=34.21). The activity of MMP-2 (the value of light density*band area) decreased gradually from 84.49+5.38 to 53.70+3.42, and the differences among these four groups were also significant (F=29.54). The expressions of HIF-1a were increased gradually with the increase of the CoCl2 concentration. The shift band in the lane of the nuclear protein extraction and the MMP-2 probe containing hypoxia response element showed delays when compared with the lane of the sole probe, and the binding was partially abolished when competing sense oligonucleotides were used. CONCLUSIONS: Our results suggest that chemical hypoxia can up-regulate the expression of MMP-2 mRNA and decrease the activity of the enzyme. HIF-1alpha may play a part in the regulation of MMP-2 transcription under hypoxic conditions.

Orthogonal sulfation strategy for synthetic heparan sulfate ligands.

[reaction: see text] An orthogonal sulfation strategy involving six different protecting groups has been developed for generating sulfated carbohydrate libraries based on heparan. Chemoselective cleavage conditions (optimized for a heparan disaccharide) can be performed in the presence of sulfate esters as well as the remaining protecting groups.

Facile preparation of beta-fluoro amines by the reaction of aziridines with potassium fluoride dihydrate in the presence of Bu4NHSO4.

Potassium fluoride combined with tetrabutylammonium bisulfate is an efficient reagent to convert a variety of aziridines derived from cyclic and acyclic alkenes to beta-fluoro amine derivatives in high yield.

Formation of P-ylide under neutral and metal-free conditions: transformation of aziridines and epoxides to conjugated dienes in the presence of phosphine.

A general approach to formation of the P-ylide from the reaction of aziridines or epoxides with organophosphine under neutral and metal-free conditions is realized. Conjugated diene derivatives based on this kind of P-ylide were prepared in a facile and convenient way.

Tetrabutylammonium bisulfate: a new effective catalyst for the hydrolysis of aziridines or epoxides.

Bu4NHSO4 (TBAHS) is an effective catalyst for the hydrolysis of aziridines and epoxides under mild and non-metal conditions to give the corresponding beta-amino alcohols and 1,2-diols in high yields. The catalyst can be recycled.

Efficient ring-opening reaction of epoxides and aziridines promoted by tributylphosphine in water.

Tributylphosphine was found to be an effective promoting reagent for the ring-opening reaction of various epoxides and aziridines with nucleophile to produce corresponding anti-bifunctional products in moderate to excellent yields in water.

Tributylphosphine: a remarkable promoting reagent for the ring-opening reaction of aziridines.

Tributylphosphine was found to be an effective promoting reagent for ring opening of a variety of aziridines and nucleophiles to produce anti-bifunctional products in good to excellent yield. The study showed that the reaction is initiated through the attack of tributylphosphine as a nucleophile at the carbon atom of the aziridine ring.