Stereochemie von Metallocenen, 8. Mitt.: Die Absolute Konfiguration von Optisch Aktiven Benzol-chromtricarbonyl-derivaten; Asymmetrische Synthese und Kinetische Racematspaltung von Chiralen Metallocenen

Zusammenfassung Es wird über die Synthese und Racematspaltung von drei Benzol-chromtricarbonyl-derivaten sowie der -Methyl-ferrocen-carbonsäure berichtet. Die Absolutkonfiguration von (+)-(1-Tetralon)-Cr(CO)₃ konnte als (1S) ermittelt werden. Bei den beiden isomeren Säuren (+)- bzw. (–)-(o- bzw. m-Tolylsäure)-Cr(CO)₃ gelang erstmalig die konfigurative Korrelation eines -mit einem -disubstituierten Metallocen. Die Absolutkonfiguration des auch durch asymmetrische Synthese zugänglichen (+)-(o-Tolylsäure)-Cr(CO)₃ ließ sich auf Grund der Ergebnisse der kinetischen Racematspaltung der Anhydride der beiden racem. -Methyl-metallocen-carbonsäuren mit (–)-Menthol und (–)--Phenäthylamin als (1 S) bestimmen, da die Konfiguration der Methyl-ferrocencarbonsäure (nach chemischer Korrelation) bekannt war.

---

The synthesis and optical resolution of three benzene chromium tricarbonyl derivatives and of -methyl ferrocene carboxylic acid are reported. The absolute configuration of (+)-1-tetralone)-Cr(CO)₃ was established as (1S). In the case of the isomeric acids (+)-(o-toluic acid)- and (–)-(m-toluic acid)-Cr(CO)₃ resp. a configurational correlation of - and -disubstituted metallocenes was possible for the first time. The absolute configuration of (+)-(o-toluic acid)-Cr(CO)₃ (which is also accessible by asymmetric synthesis) could be established as (1S) by kinetic resolutions of the anhydrides of the two racemic -methyl metallocene carboxylic acids with (–)-menthol and (–)--phenethylamine, since (after chemical correlation) the configuration of methyl ferrocene carboxylic acid was known.

---

---

Mit 1 Abbildung

---

7. Mitt.:H. Falk undK. Schlögl, Tetrahedron [London], im Druck.     

The importance of ground-state vibronic mixing in molecular Raman scattering

We consider Albrecht's theory for Raman scattering of fundamentals in the far and pre-resonance regions. Destructive interferences inherent to the A and B terms augment the conventionally suppressed C term dramatically. Raman excitation profiles for the ν₁(a_1g) and ν₆(e_2g fundamentals in benzene can be well fitted with theoretical C-term profiles involving the ¹E_1u(π-π^*) state at 1800 A.     

Beiträge zur Chemie der Pyrrolpigmente, 38. Mitt.: Zur Assoziation von Gallenpigmenten

The long standing problem of solvent dependent absorption spectra of certain bile pigments such as bilirubindimethylester has been solved by measurement of molecular masses by means of vapour pressure osmometry. Using this method and the investigation of the concentration and temperature dependence of the absorption spectra on several model compounds an association equilibrium for pigments of the rubinoid structural type could be confirmed. Moreover the optical properties of the coexisting species and the corresponding equilibrium constants could be deduced by spectroscopic techniques. Verdinoid pigments lacking free carboxylic functions on the other hand tend to be monomeric in solution. A heteroassociated species involving equimolar amounts of a verdinoid and a rubinoid pigment could be verified existing on adsorbents like silicagel.

37. Mitt.:Falk, H., Thirring, K., Tetrahedron, im Druck.     

Chemistry of polyfunctional molecules-123. Reactions of BiBr3, SbI3 and AsI3 with LiN(PPh2)2; X-ray structure of a cyclophosphazene salt containing arsenic(I)

BiBr₃ or SbI₃ react at 20°C with LiN(PPh₂)₂ (1) to give elementary Bi or Sb and the P---P coupled phosphazene ligand Ph₂P---N=PPh₂---PPh₂=N---PPh₂ (2). The reaction of AsI₃ with 1 at room temperature formed yellow needles of the eight-membered heterocycle (3), whereas AsI₃ interacted at 80°C with 1 in the molar ratio of 1:3 to give elementary arsenic and 2. Treatment of AsI₃ and 1 at 20°C in a 1:2 stoichiometry yielded the seven-membered, cyclic arsenium(I) salt

Full-size image

I·4THF (5·4THF), which was characterized by elemental analysis, conductivity, mass, IR and NMR spectroscopy and single-crystal X-ray structural analysis.     

Structural basis for recognition of bacterial cell wall teichoic acid by pseudo-symmetric SH3b-like repeats of a viral peptidoglycan hydrolase

Endolysins are bacteriophage-encoded peptidoglycan hydrolases targeting the cell wall of host bacteria via their cell wall-binding domains (CBDs). The molecular basis for selective recognition of surface carbohydrate ligands by CBDs remains elusive. Here, we describe, in atomic detail, the interaction between the Listeria phage endolysin domain CBD500 and its cell wall teichoic acid (WTA) ligands. We show that 3′O-acetylated GlcNAc residues integrated into the WTA polymer chain are the key epitope recognized by a CBD binding cavity located at the interface of tandem copies of beta-barrel, pseudo-symmetric SH3b-like repeats. This cavity consists of multiple aromatic residues making extensive interactions with two GlcNAc acetyl groups via hydrogen bonds and van der Waals contacts, while permitting the docking of the diastereomorphic ligands. Our multidisciplinary approach tackled an extremely challenging protein–glycopolymer complex and delineated a previously unknown recognition mechanism by which a phage endolysin specifically recognizes and targets WTA, suggesting an adaptable model for regulation of endolysin specificity.

Combining genetic, biochemical and computational approaches, we elucidated the molecular mechanisms underlying the recognition of Listeria wall teichoic acid by bacteriophage-encoded SH3b repeats.     

Rapid synthesis of pomalidomide-conjugates for the development of protein degrader libraries

Current methods for the preparation of heterobifunctional pomalidomide-conjugates rely on methods that are often low yielding and produce intractable byproducts. Herein we describe our strategy for the reliable and succinct preparation of pomalidomide-linkers which is essential to the formation of these conjugates. We present the preparation of 18 pomalidomide-linkers in high yield compared to current literature methods. Our findings show that secondary amines consistently afford greater yields than their primary counterparts, a trend that we were able to exploit in the synthesis of several new pomalidomide homo-dimers in enhanced yields compared to similar literature syntheses. This trend was further utilised to develop the first one-pot synthesis of JQ1-pomalidomide conjugates in yields up to 62%, providing a method that is suited to rapid preparation of conjugate libraries as is frequently required for the development of new protein degraders.

Current methods for the preparation of heterobifunctional pomalidomide-conjugates rely on methods that are often low yielding and produce intractable byproducts. Herein we describe our strategy for the succinct preparation of pomalidomide-linkers.     

ZIF-8 degrades in cell media,serum, and some—but not all—common laboratory buffers

ABSTRACT

Drug delivery using metal-organic frameworks (MOF) has elicited interest in their biocompatibility; however, few studies have been conducted on their stability in common buffers, cell media, and blood proteins. In particular, the use of ZIF-8, a MOF interconnected by Zn and methylimidazole, has been frequently employed. In this study, we tested single crystals of ZIF-8 with common laboratory buffers, cell media, and serum, and noted several issues. Buffers containing phosphate and bicarbonate alter the appearance and composition of ZIF-8; however, these buffers do not appear to cause cargo to leak out even when the ZIF-8 itself is displaced by phosphates. On the other hand, serum dissolves ZIF-8, causing premature cargo release. Our results show that ZIF-8 undergoes surface chemistry changes that may affect the interpretation of cellular uptake and cargo release data. On the other hand, it provides a rational explanation as to how ZIF-8 neatly dissolves in vivo.     

Appointment-driven queueing systems with non-punctual customers

Queueing Systems - We consider a single-server queueing system where a finite number of customers arrive over time to receive service. Arrivals are driven by appointments, with a scheduled...     

q-polymatroids and their relation to rank-metric codes

Journal of Algebraic Combinatorics - It is well known that linear rank-metric codes give rise to q-polymatroids. Analogously to matroid theory, one may ask whether a given q-polymatroid is...