Search

Aromatische OligohydrazidMakrocyclen, deren Rückgrat durch DreizentrenWasserstoffbrücken in eine planare Anordnung gezwungen wird, entstehen in hohen Ausbeuten aus monomeren Disäurechloriden und Dihydraziden. Für Makrocyclen mit insgesamt sechs metaverknüpften Pyridin und Benzolringen beträgt der Innendurchmesser ca. 10Å. In größeren Spezies mit alternierend meta und paraverknüpften Benzolringen ragen einige Substituenten ins Ringinnere siehe Bild.

The shape of things to come: Aromatic oligohydrazide macrocycles with planar backbones enforced by threecenter hydrogen bonds are formed in high yield from monomeric diacid chlorides and dihydrazides. Macrocycles consisting of six metalinked pyridine and benzene residues have an internal cavity of about 10Å diameter, while those with alternating meta and paralinked benzene residues are larger and contain multiple convergent sites see picture.

The hydrogen bond rigidified backbones of aromatic oligoamides are temporarily interrupted by replacing the amide hydrogens with the acid-labile 2,4-dimethoxybenzyl (DMB) group, which allows the efficient preparation of long folding oligomers that, upon removal of the DMB groups, fold into multiturn helices.

Aromatic oligoureas are forced into well-defined conformation by incorporated intramolecular hydrogen bonds. Shape-persistent tetraureas macrocycles were obtained in a one-step [2 + 2] reaction in good yields.

No Abstract

No Abstract

Three N,N'-ethylenebis(l-amino acid) ligands have been obtained simultaneously with three a,a'-(1,4-piperazinediyl)bis[(S)-alkanoic acid] and four N,N'-ethylenedipeptide products, by reacting a mixture of l-histidine methyl ester and l-aspartic acid dimethyl ester with glyoxal in the presence of sodium cyanotrihydroborate in methanol. Europium(III) complexes with N,N'-ethylenebis(l-amino acid) ligands were useful as chiral NMR shift reagents for some unprotected natural a-amino acids as substrates in neutral aqueous solution, as characterized by large enantiomeric shift differences and unbroadened signal shapes on high-resolution NMR spectroscopy. In addition, the acid-dissociation constants of six bis(amino acid) ligands and the stability constant of the europium(III) complex with N,N'-ethylenedi(l-histidine) were obtained by potentiometric titration.

Structurally constrained ethyl (2S)-3-(4-hydroxyphenyl)-2-{[(3S)-3-(imidazole-4-yl)-methyl]-2-oxo-piperazine-1-yl}propionate (N,N′-ethylene-bridged-(S)-histidyl-(S)-tyrosine ethyl ester, eHY-OEt) was obtained by a one-pot reaction from (S)-histidine methyl ester and (S)-tyrosine ethyl ester with glyoxal. Four ligands, (Boc-Gly-eHY-OEt (HL1), Boc-Gly-eHY-NH2(HL2), Ac-eHY-OEt (HL3), and Ac-eHY-NH2(HL4), where Boc-Gly is t-butyloxycarbonyl-glycyl and Ac is acetyl) were derived from eHY-OEt. Also, corresponding copper(II) complexes, in which only amino acid side chains coordinate to the copper(II) ion, [Cu(L1-)2(H2O)] 1, [Cu(L2-)2(H2O)] 2, [Cu(L3-)2(H2O)] 3, and [Cu(L4-)2(H2O)] 4, were prepared and characterized by elemental analyses and the FAB-MS spectra. The conformational behaviors were confirmed by the 1H NMR spectra. UV-visible-NIR, CD and ESR spectra showed that copper(II) complexes are mononuclear square-pyramidal structures in both the solid and solution states. Cyclic voltammetry of HL1 and 1showed irreversible ligand oxidation. The acid-dissociation constants of HL4 were obtained as 6.38 (pKa1) and 9.67 (pKa2) by potentiometric titration, and the complex formation constants of 4were obtained as 7.16 (log K1) and 3.71 (log K2). Furthermore, thermogravimetric analyses (TGA) and differential thermal analyses (DTA) of 1and 2were measured.

A class of six-residue, shape-persistent aromatic oligoamide macrocycles bind the guanidinium ion with very high selectivity.

Aromatic tetrasulfonamide macrocycles carrying alkoxy side chains adopt a stable cone conformation in both the solid state and solution.

A novel dinuclear Mn(II) complex, [Mn(L)(H2O)]2(ClO4)2(1) where L is N,N-bis(2-pyridylmethyl)-(S)-histidinate, was synthesized. X-ray structure analysis of 1revealed that each Mn(II) ion is a doubly carboxylate-bridged sevencoordinate structure. Cyclic voltammmetry indicated that electrode reaction of 1was dependent on pH. The reactivity toward superoxide was evaluated by in vitroxanthine-xanthine oxidase-cytochrome cassay. The IC50value of 1is equal to 0.29 μM (1 M = 1 mol dm−3), which is one of the highest values in Mn(II) SOD mimetic complexes.

A novel chelating reagent, N,N'-ethylene-bridged (S)-histidyl-(S)-histidine methyl ester, has been synthesized by a one-step reaction of a Schiff-base of (S)-histidine methyl ester with aqueous glyoxal and sodium cyanoborohydride. Cu(II) complexes of its derivatives also have been synthesized and characterized.

[VO(pmH)(ClO4)], [VO(HeY)], and [VO((pm)2H)](ClO4) were prepared by reactions of VOSO4and pmH (N-2-pyridylmethyl-(S)-histidine), HeY (N,N′-ethylene-(S)-histidine-(S)-tyrosine), and (pm)2H (N,N-bis(2-pyridylmethyl)-(S)-histidine), respectively, and followed with Ba(ClO4)2. X-ray structure analysis of [VO(HeY)] showed that a pentadentate ligand and an oxoanion were coordinated with a vanadium(IV) ion, thereby forming a distorted octahedral geometry. In in vitro evaluation using isolated rat adipocytes, a tetradentate complex [VO(pmH)(ClO4)](IC50= 0.762 mM) was found to be more active at lower concentration than VOSO4(IC50= 3.56 mM) in term of IC50value, a 50% inhibition concentration of FFA release from the adipocytes. On the other hand, two VO complexes of pentadentate (HeY and (pm)2H) ligands were found to be inactive for insulin-like activities.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

No Abstract

No Abstract

For Abstract see ChemInform Abstract in Full Text.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.