Two Unusual Trimers of Diketene

Formation of two unknown, tricyclic trimers of diketene, 3 and 4 , was observed in diketene solutions containing (CH₃)₃SiCl/NaI or TsOH.     

Synthesis and Structure of a Macrocyclic Europium Complex and its possible role as a catalyst for phosphodiester transesterification

The synthesis and X-ray crystal structure of a europium macrocyctic complex 1 , an important catalyst used for the sequence-specific cleavage of RNA, is reported. The role of this metal complex in facilitating phosphate transesterification is discussed.     

Nucleation and crystal growth of copper(II) 8-hydroxyquinolinate precipitated from mixed solvents

The precipitation kinetics of copper(II) 8-hydroxyquinolinate, formed in water-acetone mixtures, have been studied in a stop-flow apparatus by spectrophotometric techniques. Three factors are found to be important in improving the physical characteristics of crystals precipitated from mixed solvents. Supersaturation and growth rate can be controlled uniformly by slow rate of change in solvent composition; the presence of acetone significantly reduces the number of effective nuclei; thirdly, large amounts of organic solvent cause a change in the crystal form and its growth mechanism. At room temperature, copper(II) 8-hydroxyquinolinate is precipitated as a dihydrate from water-acetone mixtures containing 0-60% acetone, and the crystal growth is limited by a diffusion-controlled process. Anhydrous copper(II) 8-hydroxyquinolinate is formed in 70% acetone solutions by a surface-controlled reaction.     

Synthese Eines Optisch Aktiven Penem-Zwischenprodukts Mittels Asymmetrischer Amidoalkylierung

Synthesis of an Optically Active Penem Intermediate by Asymmetric Amidoalkylation The amidoalkylation of an optically active, cationic glycine derivative with methyl acetoacetate furnishes an intermediate 10a (Scheme 2) that is transformed in six steps to the optically active, silyl-protected 4-acetoxy-3-(1-hydroxyenthyl)-2-azetidinon 18a , a well known intermediate in penem synthesis.     

Metallkomplexe von N-substituierten 3-Imino-isoindolinonen

Metal Complexes of N-substituted 3-Imino-isoindolinones The condensation of 3-imino-isoindolinone 4 and benzimidazoles or benzthiazoles containing activated methyl-, methylen- or aminogroups ( 5 resp. 6 ), yields the iso-indolinone-ligands 1 and 2. Metal ions such as Co²⁺, Ni²⁺, Cu²⁺ and Zn²⁺ form (1:2)-complexes with these ligands of very high chemical and photochemical stabilities. The magnetic properties of these complexes indicate that the geometry around the central atoms is distorted tetrahedral. A X-ray diffraction study of one of the Co(II)-complexes confirms these findings.     

Röntgenstrukturanalyse eines neuartigen spirocyclischen Diglycosides,eines Abbauproduktes der Antibiotika Papulacandin A,B and C

X-Ray Analysis of a Novel Spirocyclic Diglycoside, a Degradation Product of the Antibiotics Papulacandin A, B and C Structure 4 has been established for a novel spirocyclic diglycoside which is a degradation product of the antibiotics papulacandin A, B and C. By X-ray analysis the diglycoside was shown to consist of a galactose moiety connected by a β-1, 4-linkage to a glucose. This diglycoside is further connected by a spiro union to a oxaindan-diol moiety.     

The Total Synthesis and Biological Assessment of trans‐Epothilone A

The total synthesis of (12S,13S)‐trans‐epothilone A ( 1a ) was achieved based on two different convergent strategies. In a first‐generation approach, construction of the C(11) C(12) bond by Pd⁰‐catalyzed Negishi‐type coupling between the C(12)‐to‐C(15) trans‐vinyl iodide 5 and the C(7)‐to‐C(11) alkyl iodide 4 preceded the (nonselective) formation of the C(6) C(7) bond by aldol reaction between the C(7)‐to‐C(15) aldehyde 25 and the dianion derived from the C(1)‐to‐C(6) acid 3 . The lack of selectivity in the aldol step was addressed in a second‐generation approach, which involved construction of the C(6) C(7) bond in a highly diastereoselective fashion through reaction between the acetonide‐protected C(1)‐to‐C(6) diol 31 (‘Schinzer's ketone') and the C(7)‐to‐C(11) aldehyde 30 . As part of this strategy, the C(11) C(12) bond was established subsequent to the critical aldol step and was based on B‐alkyl Suzuki coupling between the C(1)‐to‐C(11) fragment 40 and C(12)‐to‐C(15) trans‐vinyl iodide 5 . Both approaches converged at the stage of the 3‐O, 7‐O‐bis‐TBS‐protected seco acid 27 , which was converted to trans‐deoxyepothilone A ( 2 ) via Yamaguchi macrolactonization and subsequent deprotection. Stereoselective epoxidation of the trans C(12) C(13) bond could be achieved by epoxidation with Oxone ^® in the presence of the catalyst 1,2 : 4,5‐di‐O‐isopropylidene‐L ‐erythro‐2,3‐hexodiuro‐2,6‐pyranose ( 42a ), which provided a 8 : 1 mixture of 1a and its (12R,13R)‐epoxide isomer 1b in 27% yield (54% based on recovered starting material). The absolute configuration of 1a was established by X‐ray crystallography. Compound 1a is at least equipotent with natural epothilone A in its ability to induce tubulin polymerization and to inhibit the growth of human cancer cell lines in vitro. In contrast, the biological activity of 1b is at least two orders of magnitude lower than that of epothilone A or 1a .