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Simultaneous modeling of multiple end points in life-cycle toxicity tests.
Standard toxicity tests do not allow extrapolations to the population level, mainly because these tests apply a short, fixed exposure time and focus on a single end point only. These limitations can be overcome by (partial) life-cycle toxicity testing, although these test results are harder to analyze. DEBtox is an existing software tool for the process-based analysis of standardized bioassays, and this paper presents two extensions of this method, making it applicable to life-cycle tests: the simultaneous assessment of end points and the description of aging (senescence) of the animals. We demonstrate these adaptations by describing life-cycle tests with the springtail Folsomia candida, exposed to cadmium and triphenyltin in their food. The extended model is able to describe the data for all end points simultaneously overtime with few, physiologically relevant parameters. Furthermore, the analysis reveals these chemicals to have distinctly different modes of action: cadmium apparently decreases the assimilation of energy from the food whereas triphenyltin increases the maintenance costs. The model fit allows calculation of the intrinsic rate of population increase, integrating effects on survival and reproduction. As the analysis is process based, population responses under food limitation can be explored, which depends critically on the selected mode of action.
Trophic magnification of triphenyltin in a marine food web of Bohai Bay, North China: comparison to tributyltin.
Organotins, especially tributyltin (TBT) and triphenyltin (TPT), are of particular concern due to their ubiquity in the aquatic environment and theirtoxicityto aquatic organisms. This study reports field studies on trophic magnification factors (TMF) of TBT and TPT in a marine food web. TBT, TPT, and their metabolites in plankton, five benthic invertebrate species, and six fish species collected from Bohai Bay, North China were determined, and it was found that the concentrations of TPT in marine fish were unexpectedly higherthan those of TBT. A positive relationship was found between trophic levels and concentrations of TPT, indicating trophic magnification of TPT in this food web. The TMF of TPT was calculated to be 3.70. On the other hand, concentrations of TBT, dibutyltin (DBT) and monobutyltin (MBT) did not exhibit statistically significant trends with trophic levels, and the TMF of TBT was 0.59. Analysis of organotins in the water and surface sediment from Bohai Bay revealed low inputs of TPT to the environment, which indicated that the high concentrations of TPT found in fish from Bohai Bay were due to the food web magnification of TPT.
The reaction of dimethyltin(IV) dichloride with thiamine diphosphate (H2TDP): synthesis and structure of [SnMe2(HTDP)(H2O)]Cl.H2O, and possibility of a hitherto unsuspected role of the metal cofactor in the mechanism of vitamin-B1-dependent enzymes.
The complex [SnMe(2)(HTDP)(H(2)O)]Cl.H(2)O, synthesized by reaction between dimethyltin(IV) dichloride and thiamine diphosphate hydrochloride (H(3)TDPCl) in water, was characterized by X-ray diffractometry and IR and Raman spectroscopy in the solid state, and by electrospray mass spectrometry (ESMS) and NMR spectroscopy ((1)H, (13)C, (31)P, (119)Sn and inverse-detection (1)H,(15)N HMBC) in aqueous solution. In the solid state the HTDP(-) anion chelates the metal via one oxygen atom of each phosphate group [Sn-O = 2.062(3), 2.292(3) A], and another oxygen atom belonging to the terminal phosphate links the SnMe(2)(2+) cations into chains. The tin atom has distorted octahedral coordination involving the trans methyl groups, the above-mentioned diphosphate oxygen atoms, and the oxygen atom of the coordinated water molecule. The thiamine moiety has F conformation. NMR studies suggest that the interaction between the organometallic cation and the HTDP(-) ligand persists in D(2)O solution, which is in keeping with the ESMS spectrum showing a peak corresponding to [SnMe(2)(HTDP)]. Both in the solid state and in solution, the acidic HTDP(-) proton in the complex is located on the N(1') atom of the pyrimidine ring. The enzymatic behavior of native pyruvate decarboxylase (EC 4.1.1.1, PDC), obtained from baker's yeast, was compared in a coupled assay with that shown by the "SnMe(2)-holoenzyme" created by incubation of apoPDC with [SnMe(2)(HTDP)(H(2)O)]Cl.H(2)O. The SnMe(2)-holoenzyme exhibited about 34% of the activity of the native enzyme (with a Michaelis-Menten constant of 2.7 microM, as against 6.4 microM for native PDC), so confirming the very low specificity of PDC regarding the identity of its metal ion cofactor. In view of the observed protonation of N(1'), it is suggested that the role of divalent cations in the mechanism of thiamine-diphosphate-dependent enzymes may be not only to anchor the cofactor in its binding site but also to shift the acidic proton of HTDP(-) from the diphosphate group to N(1'); protonation of N(1') is widely believed to be important for enzyme function, but the origin of the proton has never been clarified.
Stille couplings catalytic in tin: the "Sn-O" approach.
A one-pot tandem Pd-catalyzed hydrostannylation/Stille coupling protocol for the stereoselective generation of vinyltins and their subsequent union, employing only catalytic amounts of tin, is described. By recycling the organotin halide Stille byproduct back to organotin hydride, a hydrostannylation/cross-coupling sequence can be carried out with catalytic amounts of tin. Such a process is most effective with Me(3)SnCl serving as the tin source. This protocol allows a 94% reduction of the tin requirement, while maintaining good yields (up to 90%) for a variety of Stille products. Furthermore, since one cycle requires the tin to undergo at least four transformations, each moiety of trialkyltin is experiencing a minimum of 60 reactions over the course of the hydrostannylation/Stille sequence.
Volatilization and photodecomposition of Plictran miticide.
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Synthesis and antiviral activity of 5-thien-2-yl-2'-deoxyuridine analogues.
A number of 5-heteroaromatic-substituted 2'-deoxyuridines were synthesized from 5-iodo-2'-deoxyuridine using tetraorganotin reagents and palladium complexes as catalyst. The palladium-catalyzed cross-coupling reaction between 5-iodo-2'-deoxyuridine and stannylated heteroaromatics was optimized for the synthesis of the 5-thien-3-yl-2'-deoxyuridine and 5-furan-3-yl-2'-deoxyuridine. 5-(5-Iodothien-2-yl)-2'-deoxyuridine was used as starting material for the synthesis of 5-(5-methylthien-2-yl)-2'-deoxyuridine, 5-(5-vinylthien-2-yl)-2'-deoxyuridine, and 5-(5-ethynylthien-2-yl)-2'- deoxyuridine. 5-(5-Nitrothien-2-yl)-2'-deoxyuridine was synthesized using ceric ammonium nitrate as reagent. 5-(Isoxazol-5-yl)-2'-deoxyuridine was synthesized from 5-(3-oxopropyn-1-yl)-2'-deoxyuridine. Finally, 5-(5-chlorothien-2-yl)-beta-D-arabinofuranosyluracil and 5-(5-bromothien-2-yl)-beta-D-arabinofuranosyluracil were obtained by halogenation of 5-thien-2-yl-beta-D-arabinofuranosyluracil. Introduction of an alkyl substituent in the 5-position of the thienyl group of 5-thien-2-yl-2'-deoxyuridine or substitution of the 2-deoxyribofuranose ring by an arabinofuranose moiety gave decreased activity against HSV-1 and VZV replication when compared with the 5"-halogenated-5-thien-2-yl-2'-deoxyuridines. 5-(5-Bromothien-2-yl)-2'-deoxyuridine caused prompt healing of HSV-1 keratitis when administered as eye drops (0.2%) to rabbits.
Antiviral activity of C-alkylated purine nucleosides obtained by cross-coupling with tetraalkyltin reagents.
2-, 6-, And 8-alkylated (methyl, ethyl, and vinyl) adenosine analogues were synthesized by a palladium-catalyzed cross-coupling of a tetraalkyltin with the halogenated purine nucleosides. The synthesis of the 8-substituted analogues was accomplished using a transient protection procedure. The 6-alkylated-9-beta-D-ribofuranosylpurines as well as 2-ethyladenosine were cytotoxic at relatively low concentrations (0.8-10 micrograms/mL). 8-Methyladenosine was a potent and selective inhibitor of vaccinia virus, whereas 8-ethyl- and 8-vinyladenosine were specifically inhibitory to respiratory syncytial virus. 8-Vinyladenosine displayed particular activity against herpes simplex virus (type 1).
Stille coupling reactions of 4-substituted-2,5-diphenyloxazoles.
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Chemistry of N-Boc-N-tert-butylthiomethyl-protected alpha-aminoorganostannanes: diastereoselective synthesis of primary beta-amino alcohols from alpha-aminoorganostannanes.
Reaction of N-Boc-N-tert-butylthiomethyl-protected alpha-aminoorganostannanes with n-BuLi generates the corresponding alpha-aminoorganolithiums. Reactions of these organolithiums with aromatic aldehydes provides N-protected beta-amino alcohols with diastereoselectivities up to >99:1 anti/syn; with aliphatic aldehydes, diastereoselectivities were typically 1:1. Diastereoselectivities varied depending on the amount of aldehyde used. The N-protected beta-amino alcohols could be deprotected to primary amines by treatment with NaH to generate oxazolidinones followed by basic hydrolysis. Alternatively, treatment of the protected amino alcohols with acid furnished cyclic acetals that could be deprotected to primary amines with BF(3).OEt(2) and HS(CH(2))(3)SH. Transmetalation of enantiomerically enriched organostannanes with n-BuLi at -95 degrees C provided organolithiums that, although less configurationally stable than N-Boc-N-methyl-protected alpha-aminoorganolithiums, could be trapped with aldehydes with near-complete retention of configuration.
Modeling and experiment reveal an unexpected stereoelectronic effect on conformation and scalar couplings of alpha-aminoorganostannanes, with possible relevance to the tin-lithium exchange reaction.
The solution conformation of N-methyl-2-(tributylstannyl)piperidines has been determined through the use of vicinal 119Sn-13C coupling constants, revealing a conformational distortion caused by an unexpected stereoelectronic effect in some cases. Specifically, the "equatorial" conformer is distorted into a half-chair, in which the nitrogen lone pair eclipses the C-Sn bond. This distortion, which "costs" approximately 1 kcal/mol, correlates with a conformational dependence of geminal 119Sn-15N couplings and a possible correlation with reactivity in the tin-lithium exchange reaction.
A tin-complexation strategy for use with diverse acylation methods in the preparation of 1,9-diacyldipyrromethanes.
The acylation of dipyrromethanes to form 1,9-diacyldipyrromethanes is an essential step in the rational synthesis of porphyrins. Although several methods for acylation are available, purification is difficult because 1,9-diacyldipyrromethanes typically streak extensively upon chromatography and give amorphous powders upon attempted crystallization. A solution to this problem has been achieved by reacting the 1,9-diacyldipyrromethane with Bu(2)SnCl(2) to give the corresponding dibutyl(5,10-dihydrodipyrrinato)tin(IV) complex. The reaction is selective for dipyrromethanes that bear acyl groups at both the 1- and 9-positions but otherwise is quite tolerant of diverse substituents. The diacyldipyrromethane-tin complexes are stable to air and water, are highly soluble in common organic solvents, crystallize readily, and chromatograph without streaking. Four methods (Friedel-Crafts, Grignard, Vilsmeier, benzoxathiolium salt) were examined for the direct 1,9-diacylation of a dipyrromethane or the 9-acylation of a 1-acyldipyrromethane. In each case, treatment of the crude reaction mixture with Bu(2)SnCl(2) and TEA at room temperature enabled facile isolation of multigram quantities of the 1,9-diacyldipyrromethane-tin complex. The diacyldipyrromethane-tin complexes could be decomplexed with TFA in nearly quantitative yield. Alternatively, use of a diacyldipyrromethane-tin complex in a porphyrin-forming reaction (reduction with NaBH(4), acid-catalyzed condensation with a dipyrromethane, DDQ oxidation) afforded the desired free base porphyrin in yield comparable to that obtained from the uncomplexed diacyldipyrromethane. The acylation/tin-complexation strategy has been applied to a bis(dipyrromethane) and a porphyrin-dipyrromethane. In summary, the tin-complexation strategy has broad scope, is compatible with diverse acylation methods, and greatly facilitates access to 1,9-diacyldipyrromethanes.
Stille cross-coupling of activated alkyltin reagents under "ligandless" conditions.
Monoalkyltins activated by a fluoride source are shown to be as reactive as their vinyl or aryl homologues in the Stille coupling reaction, thus providing an easy entry into the pallado-catalyzed formation of Csp3-Csp2 bonds. In addition to this uncommon reactivity, this methodology holds several advantages such as (i) a quantitative preparation of stable and easy to handle alkyltin reagents 2, (ii) a simplified coupling procedure without any phosphine added ligand under neutral conditions, and (iii) a facile purification step of the organic products from the inorganic nontoxic tin byproducts.
Asymmetric total syntheses of (-)-antofine and (-)-cryptopleurine using (R)-(E)-4-(tributylstannyl)but-3-en-2-ol.
The asymmetric total syntheses of the representative phenanthroindolizidine and phenanthroquinolizidine alkaloids, (-)-antofine and (-)-cryptopleurine, are described. An efficient synthetic pathway to the key intermediate 12, in enantiomerically pure form, was achieved by using a chiral building block (R)-9 and the Overman rearrangement with a total transfer of chirality. The problem of constructing the pyrrolidine and piperidine rings was successfully addressed, primarily by using a ring-closing metathesis reaction and a cross-metathesis reaction, respectively.
Copper-catalyzed cross-coupling of imines, acid chlorides, and organostannanes: a multicomponent synthesis of alpha-substituted amides.
A copper-catalyzed cross-coupling of organotin reagents with imines and acid chlorides is reported. The reaction proceeds efficiently with a range of vinyl-, alkyl-, aryl- and heteroaryl-substituted organostannanes as well as a diverse set of imines of non-enolizable aldehydes. Use of chloroformates also allows for the formation of N-protected alpha-substituted amines. This chemistry has been applied to the synthesis of isoquinoline alkaloid derivatives through the activation of cyclic imines.
Syntheses and synthetic applications of stannylated allylic alcohols.
Allenyl carbinols undergo regioselective hydrostannation in the presence of MoBl3, a catalyst originally developed for the hydrostannation of alkynes, giving rise to allyl stannanes. These allyl stannanes can easily be converted into useful synthetic building blocks such as allyl iodides or vinyl epoxides.
Reusable copper-catalyzed cross-coupling reactions of aryl halides with organotins in inexpensive ionic liquids.
A combination of Cu2O nanoparticles with P(o-tol)3 shows highly catalytic activity for the Stille cross-coupling reaction. A series of copper catalysts and ligands were evaluated, and Cu2O nanoparticles combined with P(o-tol)3 provided the best results. In the presence of Cu2O nanoparticles and P(o-tol)3, a variety of aryl halides including aryl chlorides underwent the Stille reaction with organotins smoothly in moderate to excellent yields using inexpensive TBAB (n-Bu4NBr) as the medium. It is noteworthy that the Cu2O/P(o-tol)3/TBAB system can be recovered and reused at least three times without any loss of catalytic activity among the reactions of aryl iodides and activated aryl bromides.
Microwave-assisted one-pot hydrostannylation/Stille couplings.
In a fraction of the time required by conventional methods, microwave-accelerated one-pot hydrostannylation/Stille coupling allows 1-alkynes to be efficiently transformed into 1,3-dienes or styrenes.