Species-differences in the in vitro biotransformation of trifluoroethene (HFO-1123).

1,1,2-Trifluoroethene (HFO-1123) is anticipated for use as a refrigerant with low global warming potential. Inhalation studies on HFO-1123 in rats indicated a low potential for toxicity (NOAELs ≥ 20,000 ppm). In contrast, single inhalation exposure of Goettingen® minipigs (≥ 500 ppm) and New Zealand white rabbits (≥ 1250 ppm) resulted in severe toxicity. It has been suggested that these pronounced species-differences in toxicity may be attributable to species-differences in biotransformation of HFO-1123 via the mercapturic acid pathway. Therefore, the overall objective of this study was to evaluate species-differences in glutathione (GSH) dependent in vitro metabolism of HFO-1123 in susceptible versus less susceptible species and humans as a basis for human risk assessment. Biotransformation of HFO-1123 to S-(1,1,2-trifluoroethyl)-L-glutathione (1123-GSH) and subsequent cysteine S-conjugate ß-lyase-mediated cleavage of the corresponding cysteine conjugate (1123-CYS) was monitored in hepatic and renal subcellular fractions of mice, rats, minipigs, rabbits, and humans. While 1123-GSH formation occurred at higher rates in rat and rabbit liver S9 compared to minipig and human S9, increased ß-lyase cleavage of 1123-CYS was observed in minipig kidney cytosol as compared to cytosolic fractions of other species. Increased ß-lyase activity in minipig cytosol was accompanied by time-dependent formation of monofluoroacetic acid (MFA), a highly toxic compound that interferes with cellular energy production via inhibition of aconitase. Consistent with the significantly lower ß-lyase activity in human cytosols, the intensity of the MFA signal in human cytosols was only a fraction of the signal obtained in minipig subcellular fractions. Even though the inconsistencies between GSH and ß-lyase-dependent metabolism do not allow to draw a firm conclusion on the overall contribution of the mercapturic acid pathway to HFO-1123 biotransformation and toxicity in vivo, the ß-lyase data suggest that humans may be less susceptible to HFO-1123 toxicity compared to minipigs.

Solid-state 29Si MAS NMR studies of diatoms: structural characterization of biosilica deposits.

Four different diatom species (Chaetoceros debilis, Chaetoceros didymum, Cylindrotheca fusiformis, Nitzschia angularis) were studied by solid-state (29)Si MAS NMR spectroscopy. To determine the Q(2):Q(3):Q(4) ratios in the biosilica deposits of the diatoms, quantitative (29)Si MAS NMR experiments were performed. This analysis did not reveal any differences regarding the molecular architecture of the silica (i.e. the degree of condensation of the SiOH units (2 identical with SiOH --> identical with Si-O-Si identical with + H(2)O)) from the different diatom species. However, complete cells showed significantly smaller Q(4):Q(3) ratios (1.8-1.9) than extracted cell walls (2.5-2.8), indicating the existence of intracellular pools of less condensed silica.

(MeLi)4(dem)1.5]infinity] and [(thf)3Li3M3[(NtBu)3S--how to reduce aggregation of parent methyllithium.

Organolithium compounds play the leading role among the organometallic reagents in synthesis and in industrial processes. Up to date industrial application of methyllithium is limited because it is only soluble in diethyl ether, which amplifies various hazards in large-scale processes. However, most reactions require polar solvents like diethyl ether or THF to disassemble parent organolithium oligomers. If classical bidentate donor solvents like TMEDA (TMEDA= N,N,N',N'tetramethyl-1,2-ethanediamine) or DME (DME=1,2-dimethoxyethane) are added to methyllithium, tetrameric units are linked to form polymeric arrays that suffer from reduced reactivity and/or solubility. In this paper we present two different approaches to tune methyllithium aggregation. In [[(MeLi)4(dem)1,5)infinity] (1; DEM = EtOCH2OEt, diethoxymethane) a polymeric architecture is maintained that forms microporous soluble aggregates as a result of the rigid bite of the methylene-bridged bidentate donor base DEM. Wide channels of 720 pm in diameter in the structure maintain full solubility as they are coated with lipophilic ethyl groups and filled with solvent. In compound 1 the long-range Li3CH3...Li interactions found in solid [[(MeLi)4]infinity] are maintained. A different approach was successful in the disassembly of the tetrameric architecture of [((MeLi)4]infinity]. In the reaction of dilithium triazasulfite both the parent [(MeLi)4] tetramer and the [[Li2[(NtBu)3S]]2] dimer disintegrate and recombine to give an MeLi monomer stabilized in the adduct complex [(thf)3Li3Me-[(NtBu)3S]] (2). One side of the Li3 triangle, often found in organolithium chemistry, is shielded by the tripodal triazasulfite, while the other face is mu3-capped by the methanide anion. This Li3 structural motif is also present in organolithium tetramers and hexamers. All single-crystal structures have been confirmed through solid-state NMR experiments to be the same as in the bulk powder material.

A new class of dianionic sulfur-ylides: alkylenediazasulfites.

The compounds [[(thf)Li2-[H2CS(NtBu)2]]2] (1) and [((thf)Li2[(Et)-(Me)CS(NtBu)2])2] (2) can be synthesized in a two-step reaction. Firstly addition of an alkyllithium to sulfur diimide gives the diazaalkylsulfinate [RS(NtBu)2] (R =Me, sBu). In a second step the alpha-carbon atom in R is metalated with one equivalent of methyllithium to give the S-ylides. This new class of compounds can be rationalized as sulfite analogues, in which two oxygen atoms are each isoelectronically replaced by a NtBu group and the remaining oxygen atom is replaced by a CR2 group. Similar to Corey's S-ylides (R2(O)S+-CR2) and Wittig's phosphonium ylides (R3P+ - -CR2), these molecules contain a positively charged sulfur atom next to a carbanionic center. Therefore nucleophilic addition reactions of the carbon atom are feasible. The reaction of a sulfur diimide with the anionic carbon center in [H2CS-(NtBu)2]2- gives the intermediate alkylbis(diazasulfinate) [(tBuN)2SCH2S(NtBu)2]2-. The acidity of the hydrogen atoms at the bridging CH2 group is high enough to give, upon deprotonation, the [(tBuN)2SCHS(NtBu)2]3- trianion in [[(thf)Li3[(tBuN)2SCHS(NtBu)2]]2] (3). In [(Et)(Me)CS(NtBu)2]2 the nucleophilic carbon atom is sterically hindered and transimidation instead of deprotonation is observed. In a complex redox process [(thf)6Li6S((NtBu)3S]2] is recovered. The two new classes of compounds broaden the rich coordination chemistry of the triazasulfites by the introduction of a hard carbon center.

Monocyclic zwitterionic lambda(5)Si-silicates with an SiO(2)FC(2) framework: syntheses and structural characterization in the solid state and in solution.

Treatment of the acyclic zwitterionic pentacoordinate silicate F(3)MeSiCH(2)NMe(2)H with 1 molar equiv of Me(3)SiOC(6)H(4)OSiMe(3), Me(3)SiOCH(2)C(O)OSiMe(3), Me(3)SiOC(Ph)=NOSiMe(3), or Me(3)SiOC(O)C(O)OSiMe(3) (solvent CH(3)CN, room temperature) yielded the respective monocyclic zwitterionic pentacoordinate silicates (11a), (12a), (13a), and (14a), along with 2 molar equiv of Me(3)SiF. The derivatives 11b-14b with a 2,2,6,6-tetramethylpiperidinio substituent instead of the dimethylammonio group were prepared analogously, starting from F(3)MeSiCH(2)NR(2)H (NR(2)H = 2,2,6,6-tetramethylpiperidinio). Single-crystal X-ray diffraction studies showed that the Si-coordination polyhedra of 11a.1.5CH(3)CN, 12a-14a, and 11b-14b are distorted trigonal bipyramids, the axial positions being occupied by the fluorine atom and one of the two oxygen atoms (12a/12b, carboxylate oxygen atom; 13a/13b, carbon-linked oxygen atom). These results are in agreement with the NMR data ((1)H, (13)C, (19)F, (29)Si) obtained for these compounds in solution. The chiral (C(1) symmetry) zwitterions 11a-14a and 11b-14b exist as pairs of (A)- and (C)-enantiomers in solution. VT (1)H NMR studies with 11b-14b in CH(3)CN in the temperature range 25-85 degrees C gave no indications for an enantiomerization process [(A)/(C)-enantiomerization] at the silicon atom.

Instrumentation of a tablet breaking-strength tester.

The instrumentation of a tablet breaking-strength tester, for the automatic recording of hardness values, is described. A comparison is made between a computerized hardness tester and another identical model hardness tester from the same manufacturer ("standard"). Three lots of placebo tablets at different hardness values were compared. No significant difference was observed between the computerized unit compared with the "standard" unit.

Naloxone reversal of drug-induced diarrhea in mice.

The potential role of endogenous opiates in the mediation of the diarrheal actions of prostaglandin-F2 alpha (PGF2 alpha), 5-hydroxytryptophan (5-HTP) and methacholine was investigated. The interaction of the antidiarrheal agents morphine, propantheline bromide and cyproheptadine on the course of PGF2 alpha-induced diarrhea in mice was studied, as were the effects of naloxone on PGF2 alpha-, methacholine-, and 5-hydroxytryptophan-induced diarrhea. The three diarrheal agents, administered intraperitoneally, showed dose-dependent and parallel dose-response curves with the following order of decreasing potency: PGF2 alpha, methacholine and 5-HTP. Naloxone significantly inhibited the diarrhea induced by these agents. The diarrheal action of PGF2 alpha was also significantly attenuated with morphine, propantheline and cyproheptadine. These results suggest that PGF2 alpha, methacholine and 5-HTP induce diarrhea via a common pharmacological mechanism(s) which may involve an interaction with endogenous opiate receptors. However, the antagonism of diarrhea with agents having diverse pharmacological actions would suggest that factors unrelated to an interaction with endogenous opiates may also be involved in the production of diarrhea by the diarrheagenic agents studied.

Canine gastrointestinal motility effects of prostaglandin F2 alpha in vivo.

Prostaglandin F2 alpha (PGF2 alpha) has recently been implicated in the pathogenesis of some diarrhea in man. PGF2 alpha has been shown to increase the smooth muscle contractile motility of some gastrointestinal muscles in vitro. The in vivo effects of PGF2 alpha on bowel smooth muscles are not clearly delineated. The aim of this study was to investigate the effect of PGF2 alpha on motility of the small and large intestine in the anesthetized dog. Six contractile force transducers were implanted to record contractions from both the circular and longitudinal muscles of the duodenum, ileum and colon. Blood pressure was monitored from the femoral artery and drug injections were made in the femoral vein. The i.v. administration of PGF2 alpha (1 microgram/kg/min) significantly stimulated duodenal circular muscle contractile frequency while depressing the longitudinal muscle contractile tone. In the ileum, PGF2 alpha markedly stimulated circular and longitudinal muscle contractions. In the circular ileum, tone was significantly increased while in the longitudinal ileum it was significantly decreased. In the colon PGF2 alpha did not significantly affect intestinal motility. These results suggest that the diarrheal effects of PGF2 alpha may be related to an effect on small bowel rather than on large bowel motility in the dog.

Effects of E prostaglandins on canine gastric potential difference.

Measurement of the gastric transmucosal potential difference (PD) was used to study the effect of gastric antisecretory prostaglandins on the integrity of the gastric mucosa of the Heidenhain pouch dog. Intragastric administration of SC-29333 [(+/-)-15-deoxy-16-alpha,beta-hydroxy-16-methyl PGE1 methyl ester] slightly but significantly increased the transmucosal PD when compared to vehicle control. In addition, SC-29333 administered either intravenously or intragastrically, significantly inhibited the PD fall induced by aspirin, a well-established barrier breaker. In contrast, the intragastric administration of 16,16-dimethyl PGE2 methyl ester (Me-PGE2) significantly lowered the transmucosal PD and failed to modify the actions of aspirin on the integrity of the gastric mucosa. However, the intravenous administration of either prostaglandin did not affect the basal transmucosal PD values. These studies suggest that SC-29333 may strengthen the integrity of the gastric mucosal barrier against aspirin, and this could have important therapeutic potential.

Effects of E prostaglandins, diphenoxylate and morphine on intestinal motility in vivo.

The mechanism of the gastrointestinal motility effects of diphenoxylate and morphine in preventing E prostaglandin (PG) diarrhea was investigated. Duodenal motility studies were conducted in the anesthetized dog. Two contractile force transducers were oriented to record contractions from both the circular and longitudinal muscles. In some experiments the basic electrical rhythm (BER) was also recorded. Blood pressure was monitored from the femoral artery and drug injections were made in the femoral vein. Diphenoxylate shared with morphine the capacity to stimulate circular muscle contractions which correlated with the appearance of spike potentials on the BER. Prostaglandin E1 methyl ester (PGE1ME) showed marked relaxation of the circular muscle and abolishment of spike potentials. PGE1ME also blocked the stimulatory effects of diphenoxylate and morphine on the circular muscle. PGE1ME and PGE2 were found to be equally potent in producing diarrhea in mice. Diphenoxylate and morphine were found to be equally potent in inhibiting PG's diarrhea. These studies suggest that the constipating actions of diphenoxylate and morphine are a consequence of the increased circular muscle activity of the intestine.