Totalsynthese und absolute Konfiguration von natürlichem Multifloramin

The diphenol 1 was resolved into its antipodes and their absolute configuration was established. The levorotatory isomer R-(?)- 1 was oxidized to the dienone R-(?)- 6 , which was rearranged to afford natural (?)-multifloramine (R-(?)- 7 ), thus establishing that the latter has the R-configuration. By the same reaction sequences, the enantiomeric diphenol S-(+)- 1 was transformed to provide (+)-multifloramine (S-(+)- 7 ) of the S-configuration.     

Metal coordination polymers. II. Molecular weight studies of beryllium phosphinate polymers in toluene

The number-average molecular weights of beryllium 4-biphenyl(phenyl)phosphinate, di-n-pentylphosphinate, di-n-heptylphosphinate, and trifluoromethyl(phenyl)phosphinate are degraded by the presence of water in toluene. It is proposed that easily hydrolyzable P? O? P bonds contribute, in part, to the bonding of these polymers.     

A ferrocene based palladacyclic precatalyst for the Suzuki cross-coupling of aryl chlorides

Addition of palladium acetate to 2-(dicyclohexylphosphino)-phenylferrocene gave palladacycle 16 that is a very effective precatalyst for the Suzuki cross-coupling of aryl chlorides at room temperature (1 mol% 16) or 60 degrees C (> or = 0.01 mol% 16).     

New methodologies for the preparation of porphodimethenes and their conversion to trans-porphyrins with functionalized naphthyl spacers

The MacDonald [2 + 2]-type condensation of readily available 5-aryl-substituted dipyrromethanes with acenaphthenequinone leads to the trans-syn- and anti-porphodimethenes, which in turn can be converted to the alpha,alpha- and alpha,beta-porphyrin atropisomers, respectively. Treatment of the metalated or unmetalated porphodimethenes with KOH or NaOMe in THF followed by protonation with HCl results in a ring opening of the acenaphthenone and formation of the trans-8-carboxynaphthylporphyrins or their esters (NaOMe) after oxidation. Alternatively, the porphyrin formation can be accomplished by reaction of the porphodimethenes with acids in the presence of water or methanol. Reaction with NaBH(4) in a THF--methanol mixture yields the corresponding dialcohols in nearly quantitative yields. Sixteen different building blocks were prepared in order to evaluate the generality of this new synthetic approach, with Ar = 2,4,6-Me(3)C(6)H(2); 2,6-Cl(2)C(6)H(3); 2,6-F(2)C(6)H(3); 3,4-tBu(2)C(6)H(3); 3,4,5-(MeO)(3)C(6)H(2); 4-BrC(6)H(4); 4-MeC(6)H(4); and 4-MeOOCC(6)H(4) at the meso positions. The synthesized porphodimethenes and porphyrins have been fully characterized, and the X-ray structure analyses of three representative derivatives are presented.     

Syntheses of anomerically phosphodiester-linked oligomers of the repeating units of the Haemophilus influenzae types c and f capsular polysaccharides

Spacer-equipped dimers and trimers of the repeating units of the capsular polysaccharide of Haemophilus influenzae type c, -4)-3-O-Ac-beta-D-GlcpNAc-(1-->3)-alpha-D-Galp-(1-OPO(3-)-, and type f, -3)-beta-D-GalpNAc-(1-->4)-3-O-Ac-alpha-D-GalpNAc-(1-OPO(3-)-, have been synthesized for use in immunological studies. H-Phosphonate chemistry was used for the formation of the interglycosidic phosphate diester linkages. Two types of building blocks, a spacer glycoside disaccharide starting monomer (15 and 22) and an anomeric monoester alpha-H-phosphonate disaccharide elongating monomer (12 and 27), were built up for each serotype structure from properly protected monosaccharide precursors using mainly thioglycosides as glycosyl donors. Stereospecificity in the formation of the alpha-linked monoester H-phosphonate was possible in type c through crystallization of the pure alpha-anomer of the precursor hemiacetal from an alpha/beta-mixture, whereas in type f, the hemiacetal was isolated directly as exclusively the alpha-anomer. Subsequent phosphonylation using triimidazolylphosphine was performed without anomerization. Formation of the anomeric phosphate diester linkages was performed using pivaloyl chloride as coupling reagent followed by I(2)/H(2)O oxidation of the formed diester H-phosphonates. Original experiments afforded no diester product at all, but optimization of the oxidation conditions (lowering the temperature and dilution with pyridine prior to I(2) addition) gave the dimers in good yields (71% and 81%) and, subsequently, after removal of a temporary silyl protecting group in the dimers, the trimers in fair yields (36% and 37%), accompanied by hydrolysis of the dimer phosphate linkage. One-step deprotection through catalytic hydrogenolysis efficiently afforded the target dimer (30 and 36) and trimer structures (32 and 39). The synthetic scheme allows for further elongation to give higher oligomers.     

Dynamics of caged ions in glassy ionic conductors

At sufficiently high frequency and low temperature, the dielectric responses of glassy, crystalline, and molten ionic conductors all invariably exhibit nearly constant loss. This ubiquitous characteristic occurs in the short-time regime when the ions are still caged, indicating that it could be a determining factor of the mobility of the ions in conduction at longer times. An improved understanding of its origin should benefit the research of ion conducting materials for portable energy source as well as the resolution of the fundamental problem of the dynamics of ions. We perform molecular dynamics simulations of glassy lithium metasilicate (Li2SiO3) and find that the length scales of the caged Li+ ions motions are distributed according to a Levy distribution that has a long tail. These results suggest that the nearly constant loss originates from "dynamic anharmonicity" experienced by the moving but caged Li+ ions and provided by the surrounding matrix atoms executing correlated movements. The results pave the way for rigorous treatments of caged ion dynamics by nonlinear Hamiltonian dynamics.     

Studies on the determination of diacetyl guanfubase A concentration in rabbit plasma and pharmacokinetics

A gas chromatographic method for monitoring diacetyl guanfubase A in plasma is described. The procedure involved a single solvent extraction of drug from rabbit plasma into ethyl acetate with guanfubase A as an internal standard. The extract was analyzed subsequently on a gas chromatograph equipped with a hydrogen flame ionization detector. The recovery was 86.43% +/- 6.90% (+/- SD); the RSD of within-day and between-day was 2.81%-5.26% and 5.22%-8.24%, respectively; the regression line was linear over the concentration range of 25-200 micrograms/mL, the limit of detection was 10 micrograms/mL. No endogeneous interference was found in chromatograms of the biological samples. This method was applied to the pharmacokinetic study of diacetyl guanfubase A in rabbits.     

Synthesis and reactivity of dimeric Ar'TlTlAr' and trimeric (Ar"T1)3 (Ar', Ar" = bulky terphenyl group) thallium(I) derivatives: Tl(I)-Tl(I) bonding in species ligated by monodentate ligands

The synthesis and characterization of three new organothallium(I) compounds are reported. Reaction of (Ar'Li)(2) (Ar' = C(6)H(3)-2,6-(C(6)H(3)-2,6-Pr(i)(2))(2)) and Ar"Li (Ar" = C(6)H(3)-2,6-(C(6)H(3)-2,6-Me(2))(2)) with TlCl in Et(2)O afforded (Ar'Tl)(2) (1) and (Ar' 'Tl)(3) (2). The "dithallene" 1 is the heaviest group 13 dimetallene and features a planar, trans-bent structure with Ar'Tl-Tl = 119.74(14) degrees and Tl-Tl = 3.0936(8) A. Compound 2 is the first structurally characterized neutral, three-membered ring species of formula c-(MR)(3) (M = Al-Tl; R = organo group). The Tl(3) ring has Tl-Tl distances in the range ca. 3.21-3.37 A as well as pyramidal Tl geometries. The Tl-Tl bonds in 1 and 2 are outside the range (2.88-2.97 A) of Tl-Tl single bonds in R(2)TlTlR(2) compounds. The weak Tl-Tl bonding in 1 and 2 leads to their dissociation into Ar'Tl and Ar' 'Tl monomers in hexane. The Ar'Tl monomer behaves as a Lewis base and readily forms a 1:1 donor-acceptor complex with B(C(6)F(5))(3) to give Ar'TlB(C(6)F(5))(3), 3. Adduct 3 features an almost linear thallium C(ipso)-Tl-B angle of 174.358(7) degrees and a Tl-B distance of 2.311(2) A, which indicates strong association. Treatment of 1 with a variety of reagents resulted in no reactions. The lower reactivity of 1 is in accord with the reluctance of Tl(I) to undergo oxidation to Tl(III) due to the unreactive character of the 6s(2) electrons.