ABSTRACT
A general strategy for the preparation of the family of exo-[n.m.n.m]metacyclophanes (n,m > or = 3) in 6-steps (starting from 2-bromoanisole) that utilizes a [2 + 2] approach to furnish the exo-metacyclophane ring in good to moderate yield is described. The soluble copper catalyst [CuBr-LiSPh-LiBr-THF] is used to efficiently couple Grignard and alkyl or ether tosylate reagents in several of the synthetic steps, including the ring construction in the final step. The exo-[n.m.n.m]metacyclophane ring is conformationally mobile on the NMR time scale, and X-ray crystallography reveals that exo-[3.3.3.3]metacyclophane 2a assumes a cone conformation, and that exo-[6.6.6.6]metacyclophane 6a assumes a chair conformation. Molecular mechanics calculations show that both conformations for each exo-metacyclophane are very similar in energy. Regiocontrol over the alkylation and acylation of the phenolic oxygens of 2b is problematic, although the preparation of the tetraacetylated 18 and alkylation of 2b with CH2BrCl to furnish the methylene-linked mono- and bis-adducts 19 and 20 are straightforward.
ABSTRACT
Secondary insults such as hypotension and hypoxia with head injury are associated with increased mortality and morbidity in comparison with head injury alone. In the present study the changes of brain thromboxane A(2)(TXA(2)) and prostacyclin (PGI(2)) levels in a Marmarou's rodent model of diffuse brain injury with hypotension and hypoxia were observed and the effect of diaspirin cross linked haemoglobin solution (DCLHb) were also investigated. Thirty-two male Sprague-Dawley (SD) rats were randomized into four groups: sham; head injury alone; head injury with secondary insults; and injury with insults followed by DCLHb administration. The results showed that there were no changes in TXB(2)and 6-keto-PFG(1a)(metabolites of TXA(2)and PGI(2)) levels in the injury alone group, while TXB(2)levels in the secondary insults group were elevated significantly; both TXB(2)and 6-keto-PGF(1a)levels in the injury with insults followed by DCLHb administration group were augmented significantly in comparison with the corresponding value of sham at 4 postimpact. The only increase in TXA(2)levels in the secondary insults rats suggests that an imbalance in TXA(2)-PGI(2)production contributes to the traumatic secondary processes, which include ischaemia and oedema. It is hypothesized that DCLHb may exert its protective properties through increasing PGI(2)production in injured brain by improving blood supply to injured blood vessels. Copyright 1999 Harcourt Publishers Ltd.
ABSTRACT
A new fumonisin, iso-fumonisin B1 (iso-FB1, 1), has been isolated from liquid cultures of the fungus Fusarium moniliforme (Sheldon) NRRL 13616. On the basis of its spectroscopic data, its structure has been determined to differ from that of fumonisin B1 only in the presence of a hydroxyl function at C-4 instead of C-5.
ABSTRACT
Unlike the other silver halides, silver fluoride is positively charged in its saturated solution as determined by nonequilibrium electrophoresis measurements. In the absence of surface hydrolysis reactions, other fluoride salts (LiF, CaF2 , and MgF2 ) also are positively charged in their saturated solutions. Furthermore, the electrokinetic behavior of these fluoride salts is rather insensitive to the fluoride ion activity in neutral or acidic solutions, and reversal of the sign of the surface charge by fluoride addition is not possible. Based on FTIR transmission spectra to describe the water structure of ionic solutions, in situ FTIR/internal reflection spectroscopy (FTIR/IRS) has been used to spectroscopically characterize interfacial water at fluoride salt surfaces. The experimental spectra were examined by consideration of the O-H stretching region (3000-3800 cm-1 ) associated with the vibrational spectra of interfacial water. These results reveal a unique hydration state for fluorides and explain the anomalous electrokinetic behavior of fluoride salts such as LiF, CaF2 , and MgF2 , which show an unexpected insensitivity to the fluoride ion concentration in solution. It appears that this insensitivity is due to the formation of strong hydrogen bonding of the fluoride ions with water molecules. This hydration state prevents the accommodation of excess fluoride ions at surface lattice sites and accounts for the observed electrokinetic behavior.
ABSTRACT
Uterine leiomyomata and endometriosis are two common hormone-dependent pathologies effecting women of reproductive age. Prior to the introduction of gonadotropin releasing hormone agonists (GnRHa), there was no effective medical therapy for leiomyomata, and the most effective pharmaceutical intervention for endometriosis had unacceptable side effects. Early intranasal and non-depot formulations of GnRHa were effective treatments for these diseases but patient acceptance and compliance was poor. The introduction of depot microspheres of leuprorelin (leuprolide) acetate has provided efficacious and safe medical management of both endometriosis and uterine leiomyomata which is well tolerated by most patients.
ABSTRACT
Interaction forces between a silica sphere and an alpha-alumina substrate at various pH values were measured by atomic force microscopy (AFM). As expected, at pH values of 10.8 and 10.2 when the surfaces are similarly charged, a repulsive force was observed. On the other hand, at pH values of 5.5, 6.4, and 8.6 when the surfaces are oppositely charged, attractive forces were observed. Experimental force vs separation distance curves were found to be in good agreement with theoretical predictions based on electrostatic and van der Waals interactions. Interestingly, when the force/radius values at a particular separation distance were plotted against pH, the transition from an attractive to a repulsive force occurred at pH 9.3, which is very close to the point of zero charge (pzc) of alpha-alumina as determined from electrophoresis experiments. These results suggest that AFM force measurements can be used to estimate the pzc of materials. This method may be of particular significance for soluble salt minerals where conventional electrophoretic measurements are not possible at high ionic strengths. Finally, results from transmittance studies further confirmed the interaction between silica and alpha alumina particles in suspensions at various pH values as would be expected based on the results from atomic force microscopy measurements.
