Identification of Inhibitors for Mycobacterial Protein Tyrosine Phosphatase B (MptpB) by Biology‐Oriented Synthesis (BIOS)

Protein phosphatases have recently emerged as important targets for research in chemical biology and medicinal chemistry, and new classes of phosphatase inhibitors are in high demand. BIOS (biology‐oriented synthesis) employs the criteria of relevance to nature and biological prevalidation for the design and synthesis of compound collections. In an application of the BIOS principle, an efficient solid‐phase synthesis of highly substituted indolo[2,3‐a]quinolizidines by using a vinylogous Mannich–Michael reaction in combination with phosgene‐ or acid‐mediated ring closure was developed. Screening of this library for phosphatase inhibitors yielded a new inhibitor class for the Mycobacterium tuberculosis phosphatase MptpB.     

Solvate‐Induced Semiconductor to Metal Transition: Flat [Bi1−] Zigzag Chains in Metallic KBi⋅NH3 versus [Bi1−] Helices in Semiconducting KBi

Polymeric [Bi]^? in KBi?NH₃ has planar zigzag chains with two‐connected Bi atoms and metallic properties, whereas KBi, which has helical chains of Bi atoms, is semiconducting. The isomerization of the Bi chain is induced by solvate molecules. In the novel layered solvate structure uncharged [KBi] layers are separated by intercalated NH₃ molecules. These layers are a structural excerpt of the iso(valence)electronic CaSi, whose metallic properties arise from the planarity of the zigzag chain of Si atoms. Computational studies support this view, they show an anisotropic metallic behavior along the Bi chain. Electron delocalization is also found in the new cyclic anion [Bi₆]^4? isolated in K₂[K(18‐crown‐6)]₂[Bi₆]?9 NH₃. Although [Bi₆]^4? should exhibit one localized double bond, electron delocalization is observed in analogy to the lighter homologues [P₆]^4? and [As₆]^4?. Both compounds were characterized by single‐crystal X‐ray structure determination.     

Cation–π Interactions Contribute to Substrate Recognition in γ‐Butyrobetaine Hydroxylase Catalysis

γ‐Butyrobetaine hydroxylase (BBOX) is a non‐heme Fe^II‐ and 2‐oxoglutarate‐dependent oxygenase that catalyzes the stereoselective hydroxylation of an unactivated C?H bond of γ‐butyrobetaine (γBB) in the final step of carnitine biosynthesis. BBOX contains an aromatic cage for the recognition of the positively charged trimethylammonium group of the γBB substrate. Enzyme binding and kinetic analyses on substrate analogues with P and As substituting for N in the trimethylammonium group show that the analogues are good BBOX substrates, which follow the efficiency trend N⁺>P⁺>As⁺. The results reveal that an uncharged carbon analogue of γBB is not a BBOX substrate, thus highlighting the importance of the energetically favorable cation–π interactions in productive substrate recognition.     

Platination of full length tRNA(Ala) and truncated versions of the acceptor stem and anticodon loop

Nuclear DNA is a well characterized target for many low molecular metal-based drugs, with cisplatin and related antineoplastic compounds as typical examples. Much less is known concerning to what extent targeting of RNA may influence the activity spectrum of these types of drugs. In a preliminary communication by us (Papsai et al., Dalton Trans., 2006, 3515) we were able to show that the folded, three-dimensionally well defined structure of tRNA(Ala) readily interacts with cisplatin. In the present study we have further analyzed the binding preferences within the preferentially targeted stem region (sMh(Ala)) by modulation of the sequence around the G-U wobble base-pair and the net charge of the 3' and 5' ends. Our data show that the adduct profile is strongly influenced by the presence of the 5' end phosphate group. Further, the adduct formation reaction can be prevented by replacement of the G-U wobble base-pair with the fully complementary G-C pair. To further investigate the influence from local sequence on the platination process, a model of the anticodon region (acMh(Ala)) was also investigated. In the absence of consecutive guanine-residues in the stem- and anticodon regions, preferential platination was found to take place at the terminal AG-site in the stem region. However, after introduction of a GG-pair in the anticodon loop, platination was observed also here. At 37 degrees C, pH 6.3 and C(Pt) = 0.10 mM the rate of platination was determined to be ca. 1 x 10(-4) s(-1), with the most rapid reaction observed for interaction with the anticodon model carrying two adjacent guanines in the single-stranded loop. Together, these data show that platination of RNA is highly sequence- and structure-dependent.     

Do Sulfonamides Interact with Aromatic Rings?

Aromatic rings form energetically favorable interactions with many polar groups in chemical and biological systems. Recent molecular studies have shown that sulfonamides can chelate metal ions and form hydrogen bonds, however, it is presently not established whether the polar sulfonamide functionality also interacts with aromatic rings. Here, synthetic, spectroscopic, structural, and quantum chemical analyses on 2,6-diarylbenzenesulfonamides are reported, in which two flanking aromatic rings are positioned close to the central sulfonamide moiety. Fine-tuning the aromatic character by substituents on the flanking rings leads to linear trends in acidity and proton affinity of sulfonamides. This physical-organic chemistry study demonstrates that aromatic rings have a capacity to stabilize sulfonamides via through-space NH–π interactions. These results have implications in rational drug design targeting electron-rich aromatic rings in proteins.     

A comparison of nano‐electrospray gas‐phase electrophoretic mobility macromolecular analysis and matrix‐assisted laser desorption/ionization linear time‐of‐flight mass spectrometry for the characterization of the recombinant coagulation glycoprotein von Willebrand factor

Von Willebrand factor (VWF), an adhesive glycoprotein with an approximate molecular weight (MW) of the monomer of 260 kDa, circulates in human blood plasma as a series of multimers ranging in size up to 20.000 kDa; thus the determination of the accurate MW of the monomer is of great importance and due to its high MW quite challenging. In this study accurate MW determination of intact recombinant VWF monomer (rVWF) was performed with GEMMA (gas‐phase electrophoretic mobility macromolecular analysis) and MALDI TOF MS (matrix‐assisted laser desorption/ionization linear time‐of‐flight mass spectrometry). Three rVWF preparations with differing buffer systems and glycoprotein concentrations were analyzed. First investigations directed towards heterogeneity determination by means of capillary gel electrophoresis (CGE)‐on‐the‐chip with a laser‐induced fluorescence detector revealed two compounds (MW of 277 kDa (migration time 44.3 s) and 341 kDa (migration time 49.5 s)) present in each sample to varying extents, namely mature and pro‐rVWF. MALDI MS analysis in the linear positive ion mode allowed the detection of mature rVWF with an exact MW of 256.1 kDa (±0.8%) and pro‐rVWF with a MW of 349.8 kDa (±0.8%). Two samples containing pro‐rVWF in very minor concentration resulted in GEMMA detection of the mature rVWF with a MW of 227.4 kDa (±2.5%), derived from the measured globular size of 10.9 nm. For one sample containing both rVWF species in almost equal concentrations no differentiation of the two species was possible with GEMMA. Due to its lower resolution only a peak representing a mixture of both species at 11.8 nm could be observed, yielding a MW of 298.8 kDa (±1.6%). Copyright © 2010 John Wiley & Sons, Ltd.