β -Cyclodextrin-Mediated Regioselective Hydrolysis of 5,10,15,20-tetrakis[2,4-bis(pivaloyloxy)phenyl]-21H,23H -porphine

The four peripheral ester moieties of the title compound 5 are regioselectively hydrolyzed under mild conditions in the presence of β -cyclodextrin ( 10 ), providing a new entry to tetraphenylporphyrin derivatives with differently substituted Ph groups in the meso-positions. UV, ¹H-NMR and mass spectroscopy of the inclusion complex 9 of 2,6-O-dimethyl-β-cyclodextrin ( 12 ) and 5 indicate a stoichiometry of 2:1 for 10/5 . Moreover, calculations confirm NOE experiments consistent with the fact that the cyclodextrins 10 and 12 approach the Ph groups of the porphyrin with the small opening of the cavity (primary face).     

Capillary electrophoresis coupled to mass spectrometer for automated and robust polypeptide determination in body fluids for clinical use

We describe the application of capillary electrophoresis (CE) coupled on-line to an electrospray ionization-time of flight-mass spectrometer (ESI-TOF-MS) to the analysis of human urine and serum for the identification of biomarkers for clinical diagnostics. CE-MS led to display > 1000 polypeptides present in complex biological samples within 45-60 min in a single analysis run. To extract the information of the CE-MS spectra in a timely fashion, a software was designed to automatically deconvolute and normalize the spectra. Both urine and serum contain several hundred polypeptides in samples from healthy individuals. Hence, it is possible to establish typical "normal urine" or "normal serum" polypeptide patterns. Samples from patients with different diseases display polypeptide patterns that differ significantly from those obtained from healthy individuals. Examining series of patients with the same disease allowed the establishment of polypeptide patterns typical for specific diseases. This permits the search for marker peptides specific for diseases. The data indicate that a single polypeptide present in all patients with the same disease, but absent in all healthy control individuals does not exist. The combination of several polypeptides found in either urine or serum or both are forming a specific pattern, which is indicative not only for the particular disease, but also for the stage of disease. CE-MS detects many polypeptides in single samples and the application of the software to the search of identical polypeptides excreted in urine allows the unbiased diagnosis based on a pattern and does not rely on single disease markers.     

Reactions of 4-(dimethylamino)pyridinium activated pentachloropyridine with nitrogen nucleophiles and hydride

Substitution reactions on 2′,3′,5′,6′-tetrachloro-4-dimethylamino-[1,4]bipyridinyl-1-ylium chloride with nitrogen nucleophiles such as n-propylamine, isopropylamine, glycine, morpholine, and piperidine were examined. Highly functionalized Cl²,Cl³,N⁴,Cl⁵,Cl⁶- and N²,Cl³,N⁴,Cl⁵,Cl⁶-substituted pyridines were obtained, in part possessing unsubstituted 4-amino groups due to dealkylation. Detailed NMR studies were performed in order to elucidate the regiochemistry of these dealkylations.     

Unified route to the palmarumycin and preussomerin natural products. Enantioselective synthesis of (-)-preussomerin G

The total syntheses of eight members of the palmarumycin family have been achieved, with identification of the absolute stereochemistry for three of these natural products. In addition, the ras-farnesyl transferase inhibitor (-)-preussomerin G has been synthesized, achieving the first enantioselective route for accessing this family of natural products. Highlights of the synthetic work include an asymmetric epoxidation of a cyclic enone in excellent yield and enantiomeric excess and a potentially biomimetic oxidative spirocyclization for the introduction of the bis-spiroketal array unique to the preussomerin natural products.     

Synthesen und Strukturen der Titan(III)‐siloxane [Ti(OSiPh3)3(thf)2] und [Ti(OSiPh3)3(py)2]

Syntheses and Structures of the Titanium(III) Siloxanes [Ti(OSiPh₃)₃(thf)₂] and [Ti(OSiPh₃)₃(py)₂] The new titaniumtrioxysilanes [Ti(OSiPh₃)₃(thf)₂] ( 1 ) and [Ti(OSiPh₃)₃(py)₂] ( 2 ) have been obtained from the reaction of titaniumtrichloride with LiOSiPh₃ in the presence of the corresponding bases tetrahydrofurane (thf) and pyridine (py). From the crystal structures of both compounds it is evident that the titanium atoms are in the centres of trigonal‐bipyramidal coordination figures, with the donor atoms in axial positions. The compounds 1 and 2 have slightly different structures (mean values: 1 : Ti‐O(Si) 1.897(9), Ti‐O(C) 2.136(8) Å; 2 : Ti‐O 1.902(9), Ti‐N2.252(8) Å) and have a single absorption band in the visible region of the UV‐spectrum. The exchange of the thf‐ligands in 1 by pyridine (in high molar excess) seems to be hindered as deduced from UV‐spectroscopy.     

The Crystal Structures of Zr3Al3C5, ScAl3C3, and UAl3C3and Their Relation to the Structures of U2Al3C4and Al4C3

Single crystals of Zr₃Al₃C₅—a carbide previously reported with the formula ZrAlC_2−x—were isolated from a sample prepared by reaction of ZrC with an excess of aluminum. The carbides ScAl₃C₃and UAl₃C₃were synthesized from the elemental components by arc-melting. The crystal structures of these three compounds were redetermined from four-circle X-ray diffractomter data. In the original structure determination of ZrAlC_2−x, the metal positions were found to form close-packed layers in the space groupP6₃/mmc, while the carbon atoms were assumed to occupy 5/6 of the octahedral voids at random. The present structure determination in the space groupP6₃/mc(R=0.024 for 519 structure factors and 23 variable parameters) shows that all carbon positions are fully occupied and one has a trigonal bipyramidal aluminum coordination. The structures of ScAl₃C₃and UAl₃C₃also have originally been determined in the space groupP6₃/mmc. The present structure refinements in the space groupP6₃mc(ScAl₃C₃:R=0.031 for 282Fvalues and 16 variables; UAl₃C₃:R=0.029 for 217Fvalues and 16 variables) essentially confirms the structures with the exception of one aluminum site. In all of these structures the metal atoms are arranged in close-packed layers and together with the previously reported structure of U₂Al₃C₄they form a homologous series with the general formulaT_1+nAl₃C_3+n, wheren=0, 1, 2 for ScAl₃C₃, U₂Al₃C₄, and Zr₃Al₃C₅, respectively. The packing of the metal atoms is represented by the Zhdanov symbols (4)₂, (5)₂, and (6)₂. The arrangement of the aluminum atoms is very similar to that of the binary carbide Al₄C₃, while the other metal atoms form a cubic stacking sequence, as it is found in the binary carbidesTC with NaCl type structure.     

Ternäre Chloride mit trigonal-bipyramidalen Clustern: [M5(C2)]Cl9 (M = La?Pr)

Ternary Chlorides with Trigonal-Bipyramidal Clusters: [M₅(C₂)]Cl₉ (M = La? Pr) The chlorides [M₅(C₂)]Cl₉ (M = La? Pr) are obtained by metallothermic reduction of the respective trichlorides MCl₃ with caesium in the presence of the lanthanide metal and carbon in sealed niobium ampoules at 800°C. They contain trigonal-bipyramidal clusters [M₅(C₂)] crystallizing with the triclinic crystal system. Only seven of the nine edges of the trigonal bipyramids are brigded by chloride (Clⁱ). Each cluster is surrounded by twelve terminal ligands (Cl^a) so that units of the composition [M₅(C₂)Cl₇ⁱ]Cl₁₂^a have to be considered. These are connected not only via Cl^i–a and Cl^a–a–a bridges. Rather, Cl^a–a (one linear and one bent) and Cl^i–i bridges are also observed.     

Strained heterocycles in radical chemistry

Over the last few decades the use of radicals in synthesis has witnessed an explosive growth through introduction of efficient chain and electron-transfer reactions. Strained heterocycles, in particular, have emerged as a highly versatile and readily available class of radical precursors. The generation of carbinyl radicals of heterocycles has resulted in many elegant applications of heteroatom-centered radicals, such as beta fragmentations, cyclizations, and intramolecular hydrogen atom abstractions. Direct electron transfer to strained heterocycles has been realized through the use of arene radical anions. The method combines the virtues of radical and organometallic chemistry to yield useful functionalized organolithium compounds. Epoxides have been opened with high regioselectivity by titanocene(III) reagents in either stoichiometric or catalytic quantities to yield beta-titanoxy radicals. This development has resulted in many new applications in natural product synthesis.