Cytotoxic alkaloids and a flavan from the bulbs of Crinum asiaticum var. japonicum

A new pyrrolophenanthridone alkaloid, criasiaticidine A (1), was isolated from the bulbs of Crinum asiaticum var. japonicum, together with pratorimine (2), lycorine (3) and 4'-hydroxy-7-methoxyflavan (4). The structure of the new alkaloid was determined to be 4,5-etheno-9,10-dihydroxy-6-phenanthridone by spectroscopic means. The cytotoxicity of the isolated compounds 1-4 was evaluated in vitro against Meth-A (mouse sarcoma) and Lewis lung carcinoma (mouse lung carcinoma) tumor cell lines. Furthermore, 3 was examined for in vivo antitumor activity with LLC tumor cells.     

阴离子型聚氨酯水分散液与明胶相互作用的研究

将明胶作为皮蛋白的模型化合物与阴离子型聚氨酯水分散液（ＡＰＵ）反应，来探讨聚合物型助剂与皮革在分子水平上的相互作用机理．该文采用紫外 可见光谱、红外光谱研究了混合体系对ｐＨ值的依赖性，明胶／ＡＰＵ配比、极性化合物对体系相互作用的影响．     

Association of DNA-dependent protein kinase with hypoxia inducible factor-1 and its implication in resistance to anticancer drugs in hypoxic tumor cells

Tumor hypoxia contributes to the progression of a malignant phenotype and resistance to ionizing radiation and anticancer drug therapy. Many of these effects in hypoxic tumor cells are mediated by expression of specific set of genes whose relation to therapy resistance is poorly understood. In this study, we revealed that DNA-dependent protein kinase (DNA-PK), which plays a crucial role in DNA double strand break repair, would be involved in regulation of hypoxia inducible factor-1 (HIF-1). HIF-1beta-deficient cells showed constitutively reduced expression and DNA-binding activity of Ku, the regulatory subunit of DNA-PK. Under hypoxic condition, the expression and activity of DNA- PK were markedly induced with a concurrent increase in HIF-1alpha expression. Our result also demonstrated that DNA-PK could directly interact with HIF-1, and especially DNA-PKcs, the catalytic subunit of DNA-PK, could be involved in phosphorylation of HIF-1alpha, suggesting the possibility that the enhanced expression of DNA- PK under hypoxic condition might attribute to modulate HIF-1alpha stabilization. Thus, the correlated regulation of DNA-PK with HIF-1 could contribute to therapy resistance in hypoxic tumor cells, and it provides new evidence for developing therapeutic strategies enhancing the efficacy of cancer therapy in hypoxic tumor cells.     

Donor atom dependent geometric isomers in mononuclear oxo-molybdenum(V) complexes: implications for coordinated endogenous ligation in molybdoenzymes

We have previously demonstrated that the complex [(L1O)MoOCl(2)], where L1OH = (2-hydroxy-3-tert-butyl-5-methylphenyl)bis(3,5-dimethylpyrazolyl)methane, exists as both cis and trans isomers (Kail, B.; Nemykin, V. N.; Davie, S. R.; Carrano, C. J.; Hammes, B. S.; Basu, P. Inorg. Chem. 2002, 41, 1281-1291). Here, the cis isomer is defined as the geometry with the heteroatom in the equatorial position, and the trans isomer is designated as the geometry with the heteroatom positioned trans to the terminal oxo group. The trans isomer represents the thermodynamically more stable geometry as indicated by its spontaneous formation from the cis isomer. In this report, we show that for complexes of [(LO)MoOCl(2)], where LOH is the sterically less restrictive (2-hydroxyphenyl)bis(3,5-dimethylpyrazolyl)methane, only the trans isomer could be isolated, while in the corresponding thiolate containing ligand (2-dimethylethanethiol)bis(3,5-dimethylpyrazolyl)methane (L3SH) only the cis isomer could be observed. In addition, we have isolated and structurally characterized the complex [(L1O)MoO(OPh)(Cl)], a rare example of a species possessing both cis and trans phenolates. Using DFT calculations, we have investigated the origins of the differences in stability between the cis and trans isomers in these complexes and suggest that they are related to the trans influence of the oxo-group. Crystal data for [(LO)MoOCl(2)] (1) include that it crystallizes in the triclinic space group P(-)1 with cell dimensions a = 8.9607 (12) A, b = 10.596 (4) A, c = 13.2998 (13) A, alpha = 98.03 (2) degrees, beta = 103.21 (2) degrees, gamma = 110.05(2) degrees, and Z = 2. [(L1O)MoO(OPh)Cl].2CH(2)Cl(2) (2.2CH(2)Cl(2)) crystallizes in the triclinic space group P(-)1 with cell dimensions a = 12.2740 (5) A, b = 13.0403 (5) A, c = 13.6141 (6) A, alpha = 65.799 (2) degrees, beta = 64.487 (2) degrees, gamma = 65.750 (2) degrees, and Z = 2. [(L3S)Mo(O)Cl(2)] (3) crystallizes in the orthorhombic space group Pna2(1), with cell dimensions a = 13.2213 (13) A, b = 8.817 (2) A, c = 15.649 (4) A, and Z = 4. The implications of these results on the function of mononuclear molybdoenzymes such as sulfite oxidase, and the DMSO reductase, are discussed.     

Radester, a novel inhibitor of the Hsp90 protein folding machinery

[reaction: see text]. The antitumor antibiotics radicicol and geldanamycin are potent inhibitors of the Hsp90 protein folding machinery. Radester is a hybrid composed of radicicol's resorcinol ring and geldanamycin's quinone through an isopropyl ester. Radester was prepared, and the cytotoxicity of it and the corresponding hydroquinone were determined in MCF-7 breast cancer cells to be 13.9 and 7.1 microM, respectively. Protein degradation assays were performed on Hsp90-dependent client proteins, Her-2 and Raf, to correlate Hsp90 inhibition to cytotoxicity.     

Recombinant squalene synthase. A mechanism for the rearrangement of presqualene diphosphate to squalene

Squalene synthase (SQase) catalyzes the condensation of two molecules of farnesyl diphosphate (FPP) to form presqualene diphosphate (PSPP) and the subsequent rearrangement and NADPH-dependent reduction of PSPP to squalene (SQ). These reactions are the first committed steps in cholesterol biosynthesis. When recombinant SQase was incubated with FPP in the presence of dihydroNADPH (NADPH3, an unreactive analogue lacking the 5,6-double bond in the nicotinamide ring), three products were formed: dehydrosqualene (DSQ), a C30 analogue of phytoene; 10(S)-hydroxysqualene (HSQ), a hydroxy analogue of squalene; and rillingol (ROH), a cyclopropylcarbinyl alcohol formed by addition of water to the tertiary cyclopropylcarbinyl cation previously proposed as an intermediate in the rearrangement of PSPP to SQ (Poulter, C. D. Acc. Chem. Res. 1990, 23, 70-77). The structure and absolute stereochemistry of the tertiary cyclopropylcarbinyl alcohol were established by synthesis using two independent routes. Isolation of ROH from the enzyme-catalyzed reaction provides strong evidence for a cyclopropylcarbinyl-cyclopropylcarbinyl rearrangement in the biosynthesis of squalene. By comparing the SQase-catalyzed solvolysis of PSPP in the absence of NADPH3 to the reaction in the presence of NADPH3, it is apparent that the binding of the cofactor analogue substantially enhances the ability of SQase to control the regio- and stereochemistry of the rearrangements of PSPP.     

Infrared matrix isolation study of the 1:1 molecular complex of OVCl3 with (CH3)2O

The 1:1 complex of OVCl(3) with (CH(3))(2)O has been isolated in argon matrices at 14 K, and characterized by infrared spectroscopy. The complex is relatively strongly bound, with significant shifts to vibrational modes of both the acid and base subunits in the complex. For example, the OC(2) symmetric stretch of (CH(3))(2)O shifted from 925 to 891 cm(-1) upon complex formation, while the VCl(3) antisymmetric stretching mode shifted from 505 to 474 cm(-1). Product identification and band assignments were confirmed by isotopic labeling. Attempts to convert the initial 1:1 complex into secondary intermediates by either thermal or photochemical processes were unsuccessful, suggesting that an active hydrogen atom is a key element in determining the pathway for reactions of OVCl(3).     

Total synthesis of thiostrepton. Retrosynthetic analysis and construction of key building blocks

The first phase of the total synthesis of thiostrepton (1), a highly complex thiopeptide antibiotic, is described. After a brief introduction to the target molecule and its structural motifs, it is shown that retrosynthetic analysis of thiostrepton reveals compounds 23, 24, 26, 28, and 29 as potential key building blocks for the projected total synthesis. Concise and stereoselective constructions of all these intermediates are then described. The synthesis of the dehydropiperidine core 28 was based on a biosynthetically inspired aza-Diels-Alder dimerization of an appropriate azadiene system, an approach that was initially plagued with several problems which were, however, resolved satisfactorily by systematic investigations. The quinaldic acid fragment 24 and the thiazoline-thiazole segment 26 were synthesized by a series of reactions that included asymmetric and other stereoselective processes. The dehydroalanine tail precursor 23 and the alanine equivalent 29 were also prepared from the appropriate amino acids. Finally, a method was developed for the direct coupling of the labile dehydropiperidine key building block 28 to the more advanced and stable peptide intermediate 27 through capture with the highly reactive alanine equivalent 67 under conditions that avoided the initially encountered destructive ring contraction process.     

Acid beverage floc: protein-saponin interactions and an unstable emulsion model

The occurrence of acid beverage floc (ABF) in acidified carbonated beverages has long been attributed to the presence of saponins. We have examined this assertion and have found evidence to suggest that traces of protein may also be a key factor, along with lipid material present in the floc. Turbidity levels of beet sugar protein (0.001 wt.%) and saponin (0.001 wt.%) solutions were examined over time using spectrophotometry. At neutral pH, no change in turbidity was observed in any combination (individually or mixed). Furthermore, acidified (pH 2) saponin and protein solutions, considered separately, also exhibited no change. However, a mixture of equal concentrations at pH 2 showed an initial increase in turbidity up to 2 h after mixing, followed by a decrease over the ensuing 12 h. Interfacial tension measurements also indicated interactions between the protein and saponin at pH 2. Photon correlation spectroscopy (PCS-Malvern Zetasizer 4) was used to quantitatively examine the particle size distributions and aggregation of a model, highly dilute dispersion, of bromohexadecane in 20 wt.% sucrose solution, prepared with a jet homogenisor. Beet sugar saponin (0.001 wt.%) and protein (0.001 wt.%) were added to the dispersion, and their emulsion-stabilising effects examined via oil droplet size measurement over time. At neutral pH, the size of oil droplets in the dispersion was unaffected by the addition of saponin or protein. At pH 2, the presence of saponin again caused no effect on droplet size. However, in acid conditions, protein appeared to destabilise the dispersion. The results indicate that the key to controlling the ABF problem may be the ratio of saponin to protein in the product, which may or may not stabilise dispersed lipid, depending on their interactions.     

Visualization of bed compression in an axial compression liquid chromatography column

The consolidation of a packed bed undergoing axial compression was studied in glass columns using an on-column visualization process. In this visualization process the refractive indices of the mobile phase (carbon tetrachloride) and the stationary phase (YMC C18 silica) matched perfectly, hence the otherwise opaque stationary phase became transparent to the eye. Alumina layers, which have a different refractive index, were placed at regular intervals along the column bed. These layers were therefore visible and their movement could be tracked during the axial compression of the bed. Consequently, the Young's modulus could be measured at three radial locations and at four bed depths below the head fitting. Theresults showed that the bed was heterogeneous in packing density, both radially (with the bed density increasing from the column center toward the wall) and axially (with the density increasing from the column top toward its center). Furhermore, the bed was shown to be non-symmetrical about the column axis. This was thought to be due to the column inlet head fitting making contact with the packing material on one side of the column first, rather than making contact with the entire cross section of the packing simultaneously.