Human embryonic stem cells (hESCs) may provide a cell source for functional hepatocytes for clinical applications and drug development. Initially, the hESC population was enriched to be more than 85% definitive endoderm (DE) as assessed by the expression of CXCR4, SOX17, and FOXA2. We then successfully converted DE into hepatic progenitors with 93% of the cells being positive for a-feto protein within 9 days. The percentage of albumin positive cells gradually increased to 90% at days 20-22 after differentiation. Moreover, our hESC-derived hepatocytes (hEH) developed a complete biotransformation system including phase I and II metabolizing enyzmes and phase III transporters. Nuclear receptors, which are critical in regulating the expression of metabolizing enzymes, were also expressed by our hEH. Using ultraperformance liquid chromatography-tandem mass spectrometry technology, we identified seven metabolic pathways of the drug bufuralol including four newly-reported ones in our hEH, which are the same as those in freshly isolated human primary hepatocytes (hPH). In addition, the results of the metabolism of four drugs indicate that our hEH have the capacity to metabolize these drugs at levels that are comparable to hPH. In conclusion, we have generated a relatively homogenous population of hepatocytes from hESCs, which appear to have complete metabolic function that is comparable to primary liver cells. These results represent a significant step towards the efficient differentiation of mature hepatocytes for cell-based therapeutics as well as for pharmacology and toxicology studies. STEM CELLS 2010;28:674-686 Disclosure of potential conflicts of interest is found at the end of this article.
Switching the site-selectivity of C–H activation in aryl sulfonamides containing strongly coordinating N-heterocycles was achieved using a RhIII-catalyst.
The direct reactions of the large terphenyl thiols HSAr iPr4 (Ar iPr4 = −C 6 H 3 -2,6-(C 6 H 3 -2,6-iPr 2 ) 2 ) and HSAr iPr6 (Ar iPr6 = −C 6 H 3 -2,6-(C 6 H 2 -2,4,6-iPr 3 ) 2 ) with stoichiometric amounts of mesitylcopper(I) in THF at ca. 80 °C afforded the first well-characterized dimeric copper thiolato species {CuSAr iPr4 } 2 (1) and {CuSAr iPr6 } 2 (2) with elimination of mesitylene. The complexes 1 and 2 were characterized by NMR and electronic spectroscopy as well as by X-ray crystallography. They have dimeric Cu 2 S 2 core structures in which the two copper atoms are bridged by the sulfurs from the thiolato ligands and feature short Cu--Cu distances near 2.4 Å as well as a weak copper-flanking aryl ring interaction from a terphenyl substituent. The structures of the planar Cu 2 S 2 cores bear a resemblance to the Cu A site in nitrous oxide reductase in which two cysteines also bridge two copper atoms. The related dimeric Li 2 S 2 structural motif was also observed in the lithium congeners {LiSAr iPr4 } 2 (3) and {LiSAr iPr6 } 2 (4) which were synthesized directly from the thiols and n-BuLi in hexanes. However, despite the very similar effective ionic radii of the Li + (0.59 Å) and Cu + (0.60 Å) ions, the Li--Li structures display very much longer (by more than ca. 0.5 Å) separations than the corresponding Cu--Cu distances in 1 and 2, which may be due to weaker dispersion interactions.
Reaction of {LiC 6 H 2 À 2,4,6-Cyp 3 •Et 2 O} 2 (Cyp = cyclopentyl) (1) of the new dispersion energy donor (DED) ligand, 2,4,6-triscyclopentylphenyl with SnCl 2 afforded a mixture of the distannene {Sn(C 6 H 2 À 2,4,6-Cyp 3 ) 2 } 2 (2), and the cyclotristannane {Sn(C 6 H 2 À 2,4,6-Cyp 3 ) 2 } 3 (3). 2 is favored in solution at higher temperature (345 K or above) whereas 3 is preferred near 298 K. Van't Hoff analysis revealed the 3 to 2 conversion has a ΔH = 33.36 kcal mol À 1 and ΔS = 0.102 kcal mol À 1 K À 1 , which gives a ΔG 300 K = + 2.86 kcal mol À 1 , showing that the conversion of 3 to 2 is an endergonic process. Computational studies show that DED stabilization in 3 is À 28.5 kcal mol À 1 per {Sn-(C 6 H 2 À 2,4,6-Cyp 3 ) 2 unit, which exceeds the DED energy in 2 of À 16.3 kcal mol À 1 per unit. The data clearly show that dispersion interactions are the main arbiter of the 3 to 2 equilibrium. Both 2 and 3 possess large dispersion stabilization energies which suppress monomer dissociation (supported by EDA results).
Coupling reaction between aryl iodides and aliphatic diols was realized with a ligand-free copper catalyst under mild conditions. This method was successfully applied in the process of scale-up synthesis of medicinal candidate product EMB-3. Fig. 1 Representative ligands for the Ullmann reaction.Scheme 1 Ligand-free Cu-catalyzed O-arylation of aliphatic alcohols.
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