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Biomedical subjects

T Theophanides

Publications and source records attributed to T Theophanides.

25 records · Page 2Linked to original sources
PubMed1976

Structural features and protective activity of dexamethasone and pregnenolone-16 alpha-carbonitrile.

Pretreatment with dexamethasone acetate or pregnenolone-16 alpha-carbonitrile markedly diminished the pharmacological effect of zoxazolamine in rats. This prophylactic action was associated with significantly decreased plasma drug levels, which, in turn, were correlated with enhanced hepatic drug biotransformation, induced by the steroids. Dexamethasone proved to be more active than pregnenolone-16 alpha-carbonitrile in this respect. The A-ring conformation as well as the distances of O-3-O-11, O-11-O-17, and the O-3-mean plane C-5-C-17 may be key factors in glucocorticoid activity, and the longer the distances, the greater the potency. These characteristics have no bearing on catatoxic activity for which the 16 alpha-substituent appears to be a structural prerequisite.

Animals↗
PubMed1975

X-ray photoelectron spectroscopy of DNA-Pt complexes. Evidence of O6 (Gua)-N7 (Gua) chelation of DNA with cis- dichlorodiamine platinum(II).

The binding energies of nitrogen, oxygen, phosphorus, chlorine and Pt in several DNA - Pt (II) complexes are reported and discussed. The nitrogen band of DNA is slightly shifted upon complexation with Pt. Oxygen binding energies in the complexes studied clearly show that cis-Pt(NH3)2Cl2 forms a specific chelate N7(Gua) - O6 (Gua) with DNA as opposed to trans-Pt(NH3)2Cl2 and the other Pt compounds which react only with the N7(Gua) site of DNA.

Binding Sites↗
PubMed1975

Platinum complexes of nucleotides.

The reaction of [Pt(dien)Cl1Cl (dien = NH2CH2CH2NHCH2CH2NH2) with nucleotides has been studied by nuclear magnetic resonance. It has been found that the CMP (cytidine 5'-monophosp-ate) and GMP (guanosine 5'-monophosphate/coordinate to the platinum atom through N3 and N7, respectively. The reaction of the platinum salt with the nucleotide is complete when one to one ratio of platinum to nucleotide is used and no evidence of phosphate group binding to platinum has been found. No additional binding sites have been detected except the N7 site on the guanylic group of GMP even in the presence of a large excess of [Pt(dien) Cl1Cl. The AMP (adenosine 5'monophosphate] coordinates to the platinum at the N1 and/or N7 sites. The reaction of AMP and platinum is complete is complete at a ratio of four platinum to one AMP.

Adenosine Monophosphate↗
PubMed1975

DNA-platinum interactions in vitro with trans- and cis-Pt(NH3)2Cl2.

In the present study the nature and the hydrolysis of DNA-Pt complexes with the platinum compounds, [Pt(dien)Cl]Cl, trans- and cis-Pt(NH3)2Cl2, using potentiometric chloride determinations, have been investigated. The trans-Pt(NH3)2Cl2 and the [Pt(dien)Cl]Cl react with the GC planes at the N7(G) sites, while the cis-Pt(NH3)2Cl2 compound reacts with the GC planes and forms a chelate by using the N7(G) and O6(G) sites. The complex is a specific 1:1 Pt:DNA adduct. The platinum atom in cis-Pt(NH3)2Cl2 liberates both chlorine atoms on chelation. A mechanism for the in vivo antitumor activity of the cis-Pt(NH3)2Cl2 is proposed and the structure activity relationship is discussed.

Binding Sites↗
PubMedDate not supplied

Radiolysis of 4-benzylideneamino-2,2,6,6-tetramethylpiperidine-1-oxyl (BAPO) in aqueous didodecyldimethyl-ammonium bromide (DDAB) membrane mimetic systems.

The influence of solubilisation upon the reactivity of the nitroxyl BAPO with the free radicals produced in irradiated vesicle systems was investigated. The decomposition yield G(-BAPO) determined in didodecyldimethyl-ammonium bromide (DDAB) vesicle systems was found to be only 0.04, while in homogeneous aqueous solutions a value of 1.50 was observed. These results, as well as the EPR spectra of irradiated and nonirradiated samples, lead to the conclusion that BAPO is localized in the interior of the bilayer. This behavior is consistent with the hydrophobic character of the nitroxyl molecule due to its benzylidene group.

Cyclic N-Oxides↗
PubMedDate not supplied

Radiolysis of 4-benzylideneamino-2,2,6,6-tetramethylpiperidine-1-oxyl (BAPO) and 3-carboxamido-2,2,5,5-tetramethyl-pyrrolidine-1-oxyl (CATPO) in aqueous solutions.

The mechanism of the gamma-radiolysis of the free nitroxyl radicals BAPO and CATPO in neutral deaerated as well as in N2O-saturated aqueous solutions was investigated. The decomposition of BAPO and CATPO was followed spectrophotometrically by measuring the absorbance at 249 and 233 nm, respectively. The yields G(-BAPO) and G(-CATPO) observed under several conditions are reported and discussed in relation to the yield of OH radicals, H atoms and e-aq, produced in irradiated aqueous solutions. It was found, on the analogy of other nitroxyls, that the corresponding hydroxylamines were formed when BAPO and CATPO react with H atoms, e-aq and hydroxyalkyl radicals. The H atoms and e-aq also react partly with BAPO and CATPO by addition to the aromatic nucleus and by elimination of NH3, respectively. The OH radicals react with BAPO by addition to the aromatic nucleus and by abstraction of H atoms from the 3 or 5 positions or from the methyl groups of the 2 or 6 positions. The reaction of OH radicals with CATPO consists in the abstraction of H atoms from the 3 or 4 positions or from the methyl groups of the 2 or 5 positions. The EPR spectra suggest that in both nitroxyls the final radiolysis products are stable biradicals and other paramagnetic compounds.

Cyclic N-Oxides↗