132491-88-4Relevant articles and documents
Dendrimers with inherently axially chiral units
Lellek, Vit,Stibor, Ivan
, p. 1061 - 1073 (2000)
We have designed and successfully synthesised dendrimers with axially chiral units in the interior structure. Starting from chiral 2,2'-dimethoxy- 1,1'-binaphthalene building blocks 2 and 4 and from the four-directional initiator cores 7 and 8 the dendritic homochiral and heterochiral oligomers 9-16 were prepared. Using the [φ](D) and Δε values of monomers 2 and 4, we calculated [φ](D) and Δε values for dendrons 11, 13, and dendrimers 9, 10, 15 and 16. Although the observed molar optical rotation [φ](D) of the dendrimers agrees relatively well with the calculated values, the CD measurements of all the dendrimers in THF and CH2Cl2, except that of heterochiral dendrimer 16 in THF, were significantly different from the calculated values. The intensive hypochromism of the dendrimers (between 37- 59% in THF) and the agreement between the calculated and observed Δε values of the dendrons (between 14 and 6% in THF) led to the assumption that the hypochromic effect is caused by intramolecular interactions. From the NMR measurements it was proved that in the homochiral dendrimer 15, the N-H groups of the amides can form intramolecular hydrogen bonds that in CHCl3, with the help of the axially chiral moieties, cause a different conformation of the molecule than in the diastereomeric dendrimer 16.
Self-assembling, cystine-derived, fused nanotubes based on spirane architecture: Design, synthesis, and crystal structure of cystinospiranes
Ranganathan,Samant,Karle
, p. 5619 - 5624 (2001)
A novel family of cystine-based spirobicyclic peptides (cystinospiranes) has been synthesized by a single-step procedure involving condensation of pentaerythritol-derived tetrachloride with either the simple L-cystine dimethyl ester or its C,C′-extended bispeptides leading to a variety of 19-membered spirobicyclic peptides or its N,N′-extended bispeptides affording the ring-expanded 25-membered cystinospiranes. The design is flexible with respect to the ring size that can be adjusted depending upon the length of the N,N′-extended cystine bispeptide, and the choice of an amino acid, as illustrated here with the preparation of a large number of cystinospiranes containing a wide variety of amino acids. X-ray crystal structure of the parent spirane (5a) revealed nanotube formation by vertical stacking of relatively flat spirobicyclic molecules through contiguous NH- - -O=C hydrogen bonding. The fused pair of parallel nanotubes is open-ended, hollow, and extends to infinity. Crystallographic parameters are the following: C33H52N4O16S4, space group C2, a = 42.181(3) A, b = 5.1165(7) A, c = 11.8687(9) A, β = 106.23(1)°.
Fluorescently-labeled ferrichrome analogs as probes for receptor-mediated, microbial iron uptake
Weizman, Haim,Ardon, Orly,Mester, Brenda,Libman, Jacqueline,Dwir, Oren,Hadar, Yitzhak,Chen, Yona,Shanzer, Abraham
, p. 12368 - 12375 (2007/10/03)
Biomimetic analogs 1 of the microbial siderophore (iron carrier) ferrichrome were labeled with a fluorescent marker at a site which does not interfere with iron binding or receptor recognition to provide iron(III) carriers 5 and 10. These carriers were built from a tetrahedral carbon as an anchor which was symmetrically extended by three converging iron-binding chains and a single, exogenous anthracenyl residue. Carriers 5 varied in the nature of the amino acids (G = glycyl, A = alanyl and L = leucyl) linking the anchor with the iron-binding hydroxamate groups, while the alanyl derivative 10A differed from 5A in the spacer between the anthracenyl label and the anchor. Examination of these binders by 1H NMR confirmed that their conformations were analogous to those of the nonlabeled parent compounds. Titration experiments using UV/vis and fluorescence spectroscopy demonstrated the quenching of these compounds' fluorescence upon iron(III) loading and its recovery upon iron(III)'s release to a competing chelator. The quenching process fits the Perrin model for static quenching and was more efficient in derivatives 5, where the label could approach the iron-binding domain, than in derivative 10A, where the label's approach was prohibited. These data are in compliance with an intramolecular quenching process. In vivo examination of the labeled derivatives 5 with Pseudomonas putida as the indicator organism established that their behavior parallels that of the nonlabeled analogs 1, with the added benefit of signaling microbial activity by fluorescence emission. Thus incubation of P. putida with iron(III)-loaded (and therefore nonfluorescent) 5G caused buildup of the label's fluorescence in the culture medium. These observations provide direct evidence for a shuttle-mechanism of iron delivery where the fluorescent, iron-unloaded carrier is released to the medium. Inhibition of both phenomena by natural ferrichrome or NaN3 demonstrates the involvement of the microbial ferrichrome receptor and transport systems, respectively. On the other hand, 5A induced only modest iron(III) uptake by P. putida and failed to generate fluorescence in the culture medium, concurring with its action as an inhibitor. The fact that two strains of different Pseudomonas species did not respond to the ferrichrome analog 5G illustrates the specificity of these compounds. The performance of these carriers as structural and functional probes, paired with their high species specificity, encourage their consideration as diagnostic tools for the detection and identification of pathogenic bacteria and fungi.
