Search results for "Squaric acid"

Synthesis crystal structure and magnetic properties of [Fe2(bpym)(C5O5)2(H2O)4]·2H2O and two polymorphs of [Fe2(bpym)(C4O4)2(H2O)6]·2H2O (bpym = 2,2′…

1998

Abstract Two dinuclear iron(II) complexes of formulae [Fe2(bpym)(C5O5)2(H2O)4]·2H2O (1) and [Fe2(bpym)(C4O4)2(H2O)6]·2H2O (2) (bpym = 2,2-bipyrimidine, C5O52 = dianion of croconic acid (4,5-dihydroxycylopent-4-ene-1,2,3-trione) and C4O42 = dianion of squaric acid (3,4-dihydroxycyclobut-3-ene-1,2-dione)) were prepared and their crystal structures (at 103 K) determined by X-ray diffraction methods. The structure of 1 consists of neutral centrosymmetric [Fe2(bpym)(C5O5)2(H2O)4] units and water molecules of crystallization which are linked by an extensive network of hydrogen bonds. The coordination geometry around each iron atom is that of a compressed octahedron with bpym nitrogen atoms and cr…

ChemInform Abstract: Selective “One-Pot” Synthesis of Functionalized Cyclopentenones.

2012

Reaction of squaric acid derivatives with vinyl magnesium bromide followed by treatment with trifluoroethanol allows a new and stereoselective access to functionalized cyclopentenones of type (III)/ (V).

Iron(III), chromium(III) and cobalt(II) complexes with squarate: Synthesis, crystal structure and magnetic properties

2011

The preparation and variable temperature-magnetic investigation of three squarate-containing complexes of formula [Fe 2 (OH) 2 (C 4 O 4 ) 2 (H 2 O) 4 ]·2H 2 O ( 1 ) [Cr 2 (OH) 2 (C 4 O 4 ) 2 (H 2 O) 4 ]·2H 2 O ( 2 ) and [Co(C 4 O 4 )(H 2 O) 4 ] n ( 3 ) [H 2 C 4 O 4  = 3.4-dihydroxycyclobutene-1,2-dione (squaric acid)] together with the crystal structures of 1 and 3 are reported. Complex 1 contains discrete centrosymmetric [Fe 2 (OH) 2 (C 4 O 4 ) 2 (H 2 O) 4 ] diiron(II) units where the iron pairs are joined by a di-μ-hydroxo bridge and two squarate ligands acting as bridging groups through adjacent oxygen atoms. Two coordinated water molecules in cis position complete the octahedral environ…

Squaric acid mediated chemoselective PEGylation of proteins: reactivity of single-step-activated α-amino poly(ethylene glycol)s.

2012

The covalent attachment of poly(ethylene glycol) (PEG) to therapeutically active proteins (PEGylation) has become an important method to deal with the pharmacological difficulties of these polypeptides, such as short body-residence times and immunogenicity. However, the derivatives of PEG used for PEGylation lack further functional groups that would allow the addition of targeting or labeling moieties. Squaric acid diethyl ester was used for the chemoselective single-step activation of poly(ethylene glycol)s into the respective ester amides. The resultant selective protein-reactive poly(ethylene glycol)s were investigated with respect to their selectivity towards amino acid residues in bovi…

ChemInform Abstract: A Simple and Efficient Route to 1,4-Diketones from Squaric Acid.

2010

Abstract Squaric acid derivatives react with organolithium compounds at room temperature to afford with excellent yields after hydrolysis, symmetrical and unsymmetrically substituted oxygenated 1,4 diketones bearing alkyl, aryl or heteroaryl groups at the carbonyl positions. In the case of aromatic or heteroaromatic ketones the enol tautomers are also obtained.

Erweiterte Konjugation in unsymmetrischen Stilbenylsquarainen

1998

Extended Conjugation in Stilbenylsquaraines Unsymmetrical 1-aryl-3-stilbenylsquaraines 2a–e and 1,3-bis(stilbenyl)squaraines 3a–c were prepared by CC coupling reactions of the corresponding substituted arenes with derivatives of squaric acid (Schemes 2 and 3). Dialkylamino and alkoxy groups enhance the solubility of these dyes and enlarge the intramolecular charge transfer of these donor–acceptor–donor systems. The extended conjugation of the stilbene units – in comparison with arene building blocks – leads to significant bathochromic shifts in the Vis/NIR absorption spectra.

Development of FAP-inhibitors based on squaric acid linked DOTA and DATA5m chelators

2020

Synthesis, Labeling and Preclinical Evaluation of a Squaric Acid Containing PSMA Inhibitor Labeled with 68 Ga: A Comparison with PSMA‐11 and PSMA‐617

2020

The L-lysine urea-L-glutamate (KuE) represents a key motif in recent diagnostic and therapeutic radiopharmaceuticals targeting the prostate specific membrane antigen (PSMA). Using a squaric acid moiety for coupling of KuE with a radioactive label, the squaric acid as a linker in the PSMA ligand seems to mimic the aromatic structure of the naphthylalanine unit on PSMA-617. In this work, we investigate the influence of squaric acid moiety on the biological activity of the compound carrying a KuE motif and three typical chelates. The derivatives TRAM.SA.KuE, DOTAGA.SA.KuE and NODAGA.SA.KuE were all synthesized in straightforward organic reactions and purified by HPLC afterward. Different amoun…

Squaric Acid-Based Radiopharmaceuticals for Tumor Imaging and Therapy.

2021

Targeting vectors bound to a chelator represent a significant fraction of radiopharmaceuticals used nowadays for diagnostic and therapeutic purposes in nuclear medicine. The use of squaramides as coupling units for chelator and targeting vector helps to circumvent the disadvantages of several common coupling methods. This review gives an overview of the use of squaric acid diesters (SADE) as linking agents. It focuses on the conjugation of cyclic chelators, e.g., DOTA (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid), as well as hybrid chelators like AAZTA5 (6-pentanoic acid-6-amino-1,4-diazepine tetracetic acid) or DATA5m (6-pentanoic acid-6-amino-1,4-diazapine-triacetate) to diff…

Crystal structures and magnetic properties of the squarate-O1,On-bridged dinuclear copper(II) complexes [Cu2(phen)4(C4O4)](CF3SO3)2 · 3H2O (n=2) and …

1999

Abstract Two dinuclear copper(II) complexes of the formula [Cu2(phen)4(C4O4)](CF3SO3)2 · 3H2O (1) and [Cu2(bipy)4(C4O4)](CF3SO3)2 · 6H2O (2) [phen=1,10-phenanthroline, bipy=2,2′-bipyridine and C4O4 2−=dianion of 3,4-dihydroxy-3-cyclobuten-1,2-dione (squaric acid)] have been synthesized and characterized by single-crystal X-ray diffraction. Their structures consist of [Cu2(phen)4(C4O4)]2+ (1) and [Cu2(bipy)4(C4O4)]2+ (2) dinuclear copper(II) cations, uncoordinated CF3SO3 − anions and crystallization water molecules. The copper is in a distorted square pyramidal environment: one squarate-oxygen atom and three phen- (1) or bipy- (2) nitrogen atoms of two phen (1) or bipy (2) terminal ligands f…