Traceless linkers--only disappearing links in solid-phase organic synthesis?

Traceless linkers, which enable the attachment of arenes and alkanes to a polymeric support, have received increased attention in recent years. These anchoring groups allow chemical transformations on the polymer-bound molecules, which can be cleaved from the resin leaving no residual functionality to bias the library. Various approaches based on different Group 14 to Group 16 heteroatoms have been developed in the past and used in new syntheses of diverse compound libraries.

A novel solid-phase synthesis of highly diverse guanidines: reactions of primary amines attached to the T2 linker.

The reaction of primary amines with the T2 diazonium resin generates polymer-bound triazenes, which can in turn be acylated by the addition of isothiocyanate. The formed thioureas are readily transformed into the corresponding guanidines by the reaction with amines in the presence of mercury(II) oxide, tosyl chloride, or silver nitrate. This reaction sequence furnishes trisubstituted guanidines that are potentially useful pharmacophores.

[2,2]paracyclophane-based N,O-ligands in alkenylzinc additions to aldehydes.

[reaction: see text] The application of planar and central chiral [2,2]paracyclophane-based N,O-ligands in asymmetric alkenylzinc additions to various aldehydes is described, which gives rise to very high ee's especially for difficult substrates. A fine-tuning of the alkenylzinc species by employing different transmetalation reagents is reported, allowing control of the steric bulk of the alkenylzinc species and thus the selectivity of the catalysis.

First detection of TEM-116 extended-spectrum ß-lactamase in a Providencia stuartii isolate from a Tunisian hospital.

PURPOSE: To study the resistance to third-generation cephalosporins in Providencia stuartii strain isolated from hospitalized patient in Tunisia and to identify the responsible genes MATERIALS AND METHODS: This strain was analysed by PCR and sequencing to identify the genes responsible for the ß-lactamase resistance phenotypes. The transferability of the phenotypes was tested by conjugation to Escherichia coli J53. The isoelectric point was determinate by isoelectrofocalisation. RESULTS: This resistance was carried by a 60 kb plasmid that encoded a ß-lactamase with a pI of 5.4. This ß-lactamase revealed identity with the blaTEM-1 gene encoding the TEM-1 ß-lactamase, except for a replacement of the Val residue at position 84 by Ile, and the Ala residue at position 184 by Val. These two mutations were encountered in TEM-116 ß-lactamase. CONCLUSION: This study demonstrates the first description of TEM-116 in the P. stuartii species in the world and the first one in a Tunisian hospital.

Prevalence of plasmid-mediated quinolone resistance determinants in Enterobacteriaceae from Tunisia.

The spread of plasmid-mediated quinolone resistance determinants (qnr-like determinants, aac(6')-Ib-cr and qepA genes) was evaluated in a collection of 281 nalidixic acid-resistant enterobacterial isolates recovered between September 2005 and December 2007 at the Sahloul Hospital, Sousse, Tunisia. Sixteen percent of those isolates carried qnr genes encoding the QnrB1, QnrB2, QnrA6 or QnrS1 determinants. Most qnr-positive isolates were extended-spectrum ß-lactamase (ESBL) producers, being predominantly of the CTX-M-15 type, but also of the SHV-28 and SHV-12 types. The qnr genes were located on plasmids with a size in the range 55-150 kb. The qnrB2 gene was associated with sul1-type integron structures and the qnrB1 gene was associated with orf1005, whereas the genetic environment of qnrA6 was unknown. In two isolates, the qnrS1 gene was located downstream of an ISEcl2 element on plasmids that often carried the narrow-spectrum ß-lactamase gene bla(LAP-2); qepA and aac(6')-Ib-cr were not detected. The present study highlights the wide spread of Qnr-like determinants in Tunisia, with an association with the ESBL CTX-M-15 in human clinical isolates.

[Characterization of the resistance mechanism to beta-lactams in Acinetobacter baumannii strains isolated in the university hospital Sahloul in Tunisia (2005)]. / Caractérisation des mécanismes enzymatiques de résistance aux beta-lactamines chez des souches de Acinetobacter baumannii isolées à l'hôpital universitaire Sahloul, Sousse en Tunisie (2005).

OBJECTIVE: The bacterial multiresistance to beta-lactams and imipenem is an emergent feature in the university hospital Sahloul in Tunisia. This study was conducted to elucidate natural and acquired mechanism of resistance to beta-lactams in strains of Acinetobacter baumannii isolated in different wards of the hospital. MATERIALS AND METHODS: A specimen of 26 clinical strains of Acinetobacter baumannii was studied. beta-lactamases characterization was done by isoelectric focusing on gel of crude enzymatic extract, phenotypic tests for detection of extended spectrum beta-lactamases (ESBL) and metallo-beta-lactamases (MBL) and finally by amplification (PCR) and sequencing of genes encoding naturally occurring AmpC, the insertion sequence ISAbaI and oxacillinase with carbapenemase activity. Study of clonality of strains was performed by analysis of genomic DNA digested by the restriction enzyme ApaI and separated by pulsed field gel electrophoresis (PFGE). RESULTS: The isoelectric focusing on gel revealed two bands of beta-lactamase activity with a pI upper than 8. None ESBL or MBL was detected. PCR for AmpC, ISAbaI and OXA-69 were positive for all studied strains. The sequencing of PCR products show high identity (99-100%) with genes described previously. PFGE analysis has demonstrated clonality of studied strains. CONCLUSION: Resistance to beta-lactams including imipenem is associated to the hyper production of the AmpC enzyme and expression of OXA-69. Those enzymatic mechanisms are associated with the natural low permeability to beta-lactams which characterize Acinetobacter baumannii strains. High clonal relationship of studied strains proved by PFGE analysis has shown the necessity of implementation of strict hygienic rules and rational antibiotic usage.

Solid-phase synthesis of urea and amide libraries using the T2 triazene linker.

Starting from Merrifield resin, primary amines were immobilized in two steps by triazene linkage (T2-linker). While reaction with isocyanates gave rise to resin-bound urea derivatives, acylation by acid chlorides or anhydrides furnished amides bound to solid support via the nitrogen atom, therefore representing a novel backbone amide linker. Cleavage from the resin was conducted using dilute trimethylsilyl chloride or trifluoroacetic acid, respectively, to yield ureas and amines/amides in a library format (altogether 60 examples; manual synthesis: 17 ureas, 6 mono-alkylated ureas [including dihydroxylation and ozonolysis/Wittig reaction]; automated synthesis: 15 ureas, 15 amides) in high purities and good overall yields. The synthesis of a small library (4 x 4 member) was successfully conducted on a Bohdan Neptune synthesizer.

LIM-domain protein cysteine- and glycine-rich protein 2 (CRP2) is a novel marker of hepatic stellate cells and binding partner of the protein inhibitor of activated STAT1.

Activation of hepatic stellate cells is considered to be the main step in the development of liver fibrosis, which is characterized by the transition of quiescent vitamin-A-rich cells to proliferative, fibrogenic and contractile myofibroblasts. The identification of regulatory genes during early cell activation and transdifferentiation is essential to extend our knowledge of hepatic fibrogenesis. In liver, the gene CSRP2 is exclusively expressed by stellate cells, whereas no transcripts are detectable in hepatocytes, sinusoidal endothelial cells or Kupffer cells. The early activation of stellate cells induced by platelet-derived growth factor is accompanied by an enhanced expression of CSRP2. During later stages of transdifferentiation, the expression of CSRP2 in these cells is suppressed in vitro and in vivo. The CSRP2-encoded cysteine- and glycine-rich double-LIM-domain protein (CRP)2 is proposed to function as a molecular adapter, arranging two or more as yet unidentified protein constituents into a macromolecular complex. To identify these proteins and assign a cellular function to CRP2, a human cDNA library was screened with full-length CRP2 as bait in a yeast two-hybrid screen. The protein inhibitor of activated STAT1 ('PIAS1') was shown to associate selectively with the C-terminal LIM domain of CRP2. Physical interaction of both proteins in the cellular environment was confirmed by co-localization experiments with confocal laser scanning microscopy and co-immunoprecipitation analysis. These results establish CRP2 as a potential new factor in the JAK/STAT-signalling pathway and suggest that the suppression of CSRP2 might be a prerequisite for the myofibroblastic transition of hepatic stellate cells.