Biomedical subjects

A Gogoll

Publications and source records attributed to A Gogoll.

8 recordsLinked to original sources

PubMed2001

Rapid homogeneous-phase Sonogashira coupling reactions using controlled microwave heating.

A microwave-enhanced, rapid and efficient homogeneous-phase version of the Sonogashira reaction is presented. It has been applied to the coupling of aryl iodides, bromides, triflates, and aryl chloride, as well as pyridine and thiophene derivatives with trimethylsilylacetylene. Excellent yields (80-95%) for substrates containing a large variety of substituents in different positions are obtained in 5-25 min.

Journal Article↗

PubMed2001

Determination of absolute configuration of (pi-allyl) palladium complexes by NMR spectroscopy and stereoselective complexation.

The chiral chelating ligand N,N'-bis(phenylethyl)bispidine (1) forms a rigid cavity which accommodates (pi-allyl)palladium species with high selectivity. In the resulting complex, the absolute configuration of the pi-allyl ligand can be determined by the detection in NMR spectra of a few unambiguous interligand NOEs. Dynamic processes involving the pi-allyl ligand can be investigated. Depending on the analytical target, ligand (S,S)-1 or (R,R)-1 may be used.

Journal Article↗

PubMed2001

Synthesis, receptor binding affinities and conformational properties of cyclic methylenedithioether analogues of angiotensin II.

Cyclic 12-, 13- and 14-membered ring angiotensin II analogues related to disulfides but encompassing methylene-dithioether bridges have been prepared. The affinity data from these derivatives were compared to those from the disulfides. The methylenedithioether analogues displayed good binding affinities to rat liver AT1 receptors although in most cases somewhat lower than their disulfide counterparts. One of the methylenedithioethers with a 13-membered ring system demonstrated the highest binding affinity among the thioethers. Theoretical conformational analysis of model compounds of the two series were performed suggesting a similarity between the disulfide and the corresponding methylenedithioether analogues and also between the ring size homologues. This analysis also suggested that some of the model compounds were prone to adopt inverse gamma-turn conformations, which was further supported by use of NMR spectroscopy of the 12-membered ring analogue in the series. The easily executed methylenedithioether cyclization should constitute a valuable complement to the common disulfide methodology for fine-tuning and for probing the bioactive conformation of peptides.

Angiotensin II↗

PubMed1999

Angiotensin II analogues encompassing 5,9- and 5,10-fused thiazabicycloalkane tripeptide mimetics.

A simple experimental procedure on solid phase for the construction of new tripeptidic 5,9- and 5,10-fused thiazabicycloalkane scaffolds that adopt beta-turns has been developed. This N-terminal-directed bicyclization, relying on masked aldehyde precursors derived from glutamic acid as key building blocks, provides a complement to the related bicyclization previously reported, where an aspartic acid-derived precursor was employed to induce cyclization toward the C-terminal end of the peptide. Thus, the regioselectivity of the bicyclization can be altered simply by varying the chain length of the incorporated aldehyde precursor. Four analogues of the hypertensive octapeptide angiotensin II, comprising the new scaffolds in the 3-5- and 5-7-positions, were synthesized. One of these conformationally constrained angiotensin II analogues exhibited AT(1) receptor affinity (K(i) = 750 nM). Results from theoretical conformational analysis of model compounds of the bicyclic tripeptide mimetics are presented, and they demonstrate that subtle differences in geometry have a strong impact on the affinity to the AT(1) receptor.

Angiotensin II↗

PubMed1999

Bicyclic tripeptide mimetics with reverse turn inducing properties.

Analogues of the hypertensive octapeptide angiotensin II, comprising novel constrained 5,8-bicyclic and 5,9-bicyclic tripeptide units adopting nonclassical beta-turn geometries, as deduced from theoretical conformational analysis, have been synthesized. Spontanous bicyclization upon acid-catalyzed deprotection of a model peptide, encompassing a protected omega-formyl alpha-amino acid in position 5 and cysteine residues in positions 3 and 7, revealed a strong preference for bicyclization toward the C-terminus. The bicyclic thiazolidine related angiotensin II analogues synthesized exhibited no affinity for the angiotensin II AT1 receptor.

Angiotensin II↗

PubMed1997

Design, synthesis, and biological activities of four angiotensin II receptor ligands with gamma-turn mimetics replacing amino acid residues 3-5.

Disulfide cyclization is a powerful method for reducing the conformational space of a peptide. This in turn may enable the study of its bioactive conformation. Several analogues of angiotensin II (Ang II) containing a disulfide bridge between amino acids 3 and 5 have been reported. Among these the cyclic octapeptides c[Hcy3,5]-Ang II, c[Cys3,5]-Ang II, and c[Pen 3,5]-Ang II showed significant activity at Ang II receptors. We have performed conformational analysis studies using theoretical calculations and 1H-NMR spectroscopy on tripeptide model compounds of these cyclic octapeptides which show that the cyclic moieties of c[Cys3,5]-Ang II and c[Pen3,5]-Ang II preferentially assume an inverse gamma-turn conformation. On the basis of these results, we substituted amino acid residues 3-5 in Ang II with two different gamma-turn mimetics giving four diastereomeric Ang II analogues. Interestingly, two of these are equipotent to Ang II in binding to AT1 receptors. In the contractile test using rabbit aorta rings, one of the analogues is an agonist with full contractile activity approximately equipotent to c[Pen3,5]-Ang II but 300-fold less potent than Ang II. This low potency may suggest that Ang II does not adopt a gamma-turn in the 3-5 region when interacting with the receptor.

Angiotensin II↗

PubMed1992

Mechanisms for plasma-mediated activation of human blood cell aldehyde dehydrogenase.

Aldehyde dehydrogenase (ALDH; EC 1.2.1.3) activity assays were carried out on isolated human blood cells in phosphate-buffered saline (PBS) and in PBS mixed with human plasma. In assays with intact erythrocytes or sonicated leukocytes, the presence of 50% (v/v) or greater of plasma in the reaction mixtures produced a 2-fold increase in the rate of aldehyde oxidation. In corresponding assays with sonicated erythrocyte samples, the ALDH activity was enhanced on an average 1.5-fold, whereas a slight decrease was observed in assays with intact leukocytes. The ALDH inhibitor disulfiram almost completely abolished the enzyme activity both in the absence and presence of plasma. In assays with sonicated leukocytes, the activation effect could be antagonized by EDTA, indicating that it was caused largely by divalent cations. With sonicated erythrocytes, a significantly reduced ALDH activity was found only with the highest concentration of EDTA tested, and since a similar reduction was obtained also when plasma was omitted, the plasma-mediated activation of erythrocyte ALDH was suggested to be due to a different mechanism. After separation of plasma by gel filtration, an active fraction was identified by GC-MS and 1H-NMR to contain pyruvic acid, lactic acid and glucose. When tested at physiological plasma concentrations, pyruvic acid caused an increase in erythrocyte ALDH activity similar to that obtained with plasma, while lactic acid and glucose did not. Pyruvic acid did not activate the leukocyte ALDH. Based on these results, it is indicated that the plasma-mediated activation of erythrocyte ALDH is due to pyruvic acid, which reoxidizes NADH via lactate dehydrogenase (EC 1.1.1.27) and, thereby, increases the rate of dissociation of NADH from the terminal enzyme-NADH complex, the rate-limiting step in the ALDH pathway.

Aldehyde Dehydrogenase↗

PubMed1992

Analogues of the muscarinic agent 2'-methylspiro[1-azabicyclo[2.2.2]octane-3,4'-[1,3]dioxolane]: synthesis and pharmacology.

A number of tetrahydrofuran analogues of 2'-methylspiro[1-azabicyclo[2.2.2]octane-3,4'-[1,3]dioxolane] (1) have been prepared with the aim to obtain information about the relative importance of each of the oxygens in 1 for efficacy and for selectivity. In addition, the dimethyl and desmethyl analogues of 1 were prepared. The new compounds were compared to cis- and trans-1 with regard to their ability to displace (-)-[3H]-3-quinuclidinyl benzilate ((-)-[3H]QNB) from muscarinic receptors in cerebral cortex, heart, parotid gland, and urinary bladder from guinea pigs. Functional studies were made on isolated guinea pig bladder and ileum. The new compounds exhibited both lower affinity and efficacy than cis-1. A conformational study was performed, and the effects of steric and electronic factors on the biological activity of the compounds are discussed.

Animals↗