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G A Hoyer

Publications and source records attributed to G A Hoyer.

At least 19 recordsLinked to original sources
PubMed1994

Rational design of hirulog-type inhibitors of thrombin.

The two crystal structures of thrombin complexed with its most potent natural inhibitor hirudin and with the active-site inhibitor D-Phe-Pro-Arg-CH2Cl [Rydel, T.J. et al., J. Mol. Biol., 221 (1991) 583; Bode, W. et al., EMBO J., 8 (1989) 3467] were used as a basis to design a new inhibitor, combining the high specificity of the polypeptide hirudin with the simpler chemistry of an organic compound. In the new inhibitor, the C-terminal amino acid residues 53-65 of hirudin are linked by a spacer peptide of four glycines to the active-site inhibitor NAPAP (N alpha-(2-naphthyl-sulfonyl-glycyl)-DL-p-amidinophenylalanyl-piperi dine). Energy minimization techniques served as a tool to determine the preferred configuration at the amidinophenylalanine and the modified piperidine moiety of the inhibitor. The predictions are supported by the interaction energies determined for D- and L-NAPAP in complex with thrombin, which are in good agreement with experimentally determined dissociation constants. The conformational flexibility of the linker peptide in the new inhibitors was investigated with molecular dynamics techniques. A correlation between the Pl' position and the interactions of the linker peptide with the protein is suggested. Modifications of the linker peptide are proposed based on the distribution of its main-chain torsion angles in order to enhance its binding to thrombin.

Amino Acid Sequence↗
PubMed1992

The binding of triazine herbicides to the photosynthetic reaction center of Rhodopseudomonas viridis. Energy minimization studies.

The binding of six herbicides of the triazine family to the photosynthetic reaction center of Rhodopseudomonas viridis was investigated with energy-minimization techniques, in order to correlate experimental with calculated data. The inhibitors were modeled in the active site according to the X-ray structure analysis of the complex formed between the triazine terbutryn (2-ethylamino-4-t-butylamino-6-methylthio-s-triazine) and the reaction center of R. viridis [Michel, H., Epp. O. & Deisenhofer, J. (1986) EMBO J. 5, 2445-2451]. 40 different energy minimizations were carried out with varying cutoff radii, partial charges on inhibitor atoms and dielectric constants, i.e. 10 different combinations of these were tested. The impact of these parameters on the calculated binding and interaction energy was either examined for all protein/triazine complexes or, in the case of the dielectric constant, a smaller sample was used. The calculated energies are dominated by van der Waals interactions, which change by up to 20% when extending the cutoff radius from 0.8 nm to 1.5 nm. The use of uniform or distance-dependent dielectric constant or partial charges on the inhibitor atoms does not severely influence the resulting structures, but shows a great impact on the calculated energies. In the two groups of triazines, each containing three inhibitors with methoxy or methylthio substituents, correlations of biological and calculated data were found quite often, but only once with all six triazines. The energy-minimized structures were compared and analysed. A third hydrogen bond, not seen in the X-ray analysis of the reaction center/tertubryn complex, was found between the t-butylamino moiety of terbutryn (and equivalent moieties in the other triazines) and the carbonyl oxygen of TyrL222.

Chemical Phenomena↗
PubMed1988

Aldosterone metabolism in rat renal tissue in vitro. Formation of lipid soluble metabolites.

In the present study the formation of lipid soluble metabolites from 3H-aldosterone was investigated in vitro in isolated kidneys and kidney and liver slices of Sprague Dawley rats. The steroids were separated by HPLC (forward and reversed phase systems) and detected on-line as UV- or 3H-chromatograms. Apart from an unenzymatically formed substance, isoaldosterone, three less polar metabolites were traced (A1, A2, A3). The structure of the quantitatively most important metabolite (A1), was identified as 5 alpha-dihydroaldosterone using a combination of techniques such as chromatographic comparison with reference steroids, antibody binding and mass spectrometry. Evidence for further conversion of DHaldo to 3 alpha, 5 alpha-tetrahydroaldosterone was obtained in chromatographic and antibody binding studies. The formation of metabolites was not dependent on glomerular filtration. Furthermore it displayed regional heterogeneity with highest activity in the outer medulla. Finally it was observed that the in vitro metabolism of aldosterone was not saturable over a range of initial aldo concentration of 10(-9) to 10(-5) M.

Aldosterone↗
PubMed1988

Identification of the main gestagen metabolite in marmoset (Callithrix jacchus) urine by NMR and MS spectroscopy.

Hydroxypregnanolone is the most abundant progesterone metabolite in the urine of marmoset monkeys (Callithrix jacchus). The substance is excreted as conjugate. The concentration of this steroid may be monitored by high performance, thin layer chromatography and postchromatographic derivatization. Hydroxypregnanolone was purified and subsequently identified by NMR spectroscopy and gas chromatography/mass spectroscopy. The exact chemical structure is 5 alpha-pregnane-3 alpha, 7 alpha-diol-20-one.

Animals↗
PubMed1987

Pharmacokinetics and metabolism of mespirenone, a new aldosterone antagonist, in rat and cynomolgus monkey.

The pharmacokinetics and metabolism of mespirenone were examined in rat and cynomolgus monkey using the tritiated drug. Following i.v. administration, mespirenone exhibited a short half-life and a high plasma clearance; after oral administration the unchanged compound was not detectable. Thus, mespirenone has to be considered a pro-drug. From rat urine three metabolites were isolated by h.p.l.c. and identified by mass spectra and 1H n.m.r., all having retained the 7 alpha-sulphur substituent as a thiomethyl or a sulphinylmethyl group. The 7 alpha-thiomethyl metabolite had a half-life of six hours in rat plasma and its AUC value was 35% of that for total 3H. As this metabolite has marked anti-aldosterone activity, it is an active metabolite that contributes to the pharmacological effect of mespirenone.

Administration, Oral↗
PubMed1986

HPLC isolation and GC-MS characterization of a compound strongly cross reacting with tetrahydroaldosterone antiserum.

Urines from patients with hypertension and elevated aldosterone levels, i.e. primary aldosteronism due to adrenal adenoma or hyperplasia or carcinoma were extracted, paper chromatographed and thereafter chromatographed repeatedly with normal phase and repeatedly with reversed phase HPLC systems in an attempt to find new metabolites of aldosterone. Specific 3 alpha-hydroxy-5 beta-tetrahydroaldosterone antiserum was used in a radioimmunoassay system to detect possible aldosterone metabolites in the HPLC fractions after each isolation step. The immunoactive HPLC fractions were derivatized and analysed by GC-MS. A relatively nonpolar compound, 11 beta:18(S),18:20 alpha-diepoxy-5 beta-pregnan-3 alpha-ol, was isolated and identified in this manner. This material was originally described by Kelly et al., in 1962 after loading human subjects with huge amounts (25-160 mg) of exogenous aldosterone. This material has not yet been described from endogenously produced aldosterone. Very small amounts, if any, were similarly isolated from the urine of a control subject. Therefore, this compound could prove to be a new marker for hypertension due to hyper-production of aldosterone.

Aldosterone↗
PubMed1986

[Structure elucidation of gestodene].

The structure of 17 alpha-ethinyl-17 beta-hydroxy-18-methyl-4,15-estradien-3-one (gestodene) was elucidated by the spectrometric methods UV, IR, NMR, MS.

Contraceptives, Oral↗
PubMed1984

Corticosteroid metabolism in isolated rat kidney in vitro. III. Structure analysis of lipid soluble metabolites of corticosterone.

We have previously demonstrated that isolated rat kidneys in vitro convert corticosterone (B). Four lipid soluble metabolites (met I, II, III and IV) have been identified which differ in polarity from the parent hormone [2, 5, 6, 11, 15, 16]. In the present experiments these metabolites have been extracted from perfusate after 4 h of recirculation through isolated kidneys of male and female rats. Subsequently they have been separated by HPLC using a polar stationary phase system and n-hexane and isopropanol as eluents. The chromatographic comparison of met II with authentic 20 alpha- and 20 beta-isomers documented that met II is identical with 20 beta-dihydro-B. Measurements of the mass spectra of the purified samples revealed the following structures: met I = 20 beta-dihydro-11-dehydro-B, met II = 20 beta-dihydro-B, met III = 5 alpha-H-4,5-dihydro-B and met IV = 11-dehydro-B.

Animals↗
PubMed1975

[On the role of pentachlorocyclohexene in the metabolism and action of hexachlorocyclohexane. I. Synthesis of beta-pentachlorocyclohexene and its identification as the monodehydrochlorination product of alpha-hexachlorocyclohexane (author's transl)].

It is the aim of a series of investigations to test whether or not beta-pentachloro-1-cyclohexene is an intermediate in the biodegradation of alpha-hexachlorocyclohexane. This paper describes attempts to synthesize this intermediate by chemical methods. 1) Pentachlorocyclohexene was synthesized by partial additive chlorination of chlorobenzene. Combined gas chromatography-mass spectrometry revealed that at least five different isomers of pentachlorocyclohexene had been formed. 2) Treatment of alpha-hexachlorocyclohexane with alkaline buffer (pH 8) produced trichlorobenzenes and, in small yield (4%), a pentachlorocyclohexene. This was isolated and identified as the beta-isomer by melting point (71.8 - 72.6 degrees C, uncorr.), IR- and mass spectrum. Dehydrochlorination of beta-pentachlorocyclohexene produced the trichlorobenzene isomers in a pattern which is characteristic of alpha-hexachlorocyclohexane. The position of the chlorine substituents in the beta-pentachlorocyclohexene molecule as judged from NMR studies is e-aeee. This confirms that it is the monodehydrochlorination product of alpha-hexachlorocyclohexane. The configurations of gamma- and delta-pentachlorocyclohexene, determined for comparison, are e-eeaa and e-eeee, respectively. The kinetics of dehydrochlorination of both alpha-hexachlorocyclohexane and beta-pentachlorocyclohexene in alkaline acetone/water (3 + 2) was studied by means of conductometry. Both reactions are of second order: kappa alpha-HCH 0.0495 [1 times mol- minus 1 times s- minus 1[; kappa beta-PCH 0.905 [1 times mol- minus 1 times s- minus 1] (3.6 degrees C). 3) Dehydrochlorination of alpha-hexachlorocyclohexane in pyridine/xylene (3 + 4) was also studied. An earlier report claiming that gamma-pentachlorocyclohexene (and not the beta isomer) is produced in this medium was confirmed, if the reaction was performed at high temperature (120 - 140 degrees C). Moreover, the ratio of trichlorobenzene isomers formed from alpha-hexachlorocyclohexane shifted to a pattern characteristic of the gamma (or gamma) isomer. However, at temperatures of 90 degrees C or less, beta-pentachlorocyclohexene was the main product. The results strongly suggest that in pyridine/xylene, the same isomer is primarily produced from alpha-hexachlorocyclohexane and is isomerized to the gamma, delta and at least two other isomers of pentachlorocyclohexene before further dehydrochlorination ensues. A simple method for the synthesis of beta-pentachlorocyclohexene is presented.

Biodegradation, Environmental↗
PubMedDate not supplied

Metabolism of the steroidal aromatase inhibitor atamestane in rats, cynomolgus monkeys and humans. Isolation and identification of the major metabolites.

The metabolism of the steroidal aromatase inhibitor atamestane was studied in the rat, the cynomolgus monkey and in the human. Metabolite patterns were recorded in plasma, urine and bile (rat only) before and after enzymatic cleavage of sulfate and glucuronide conjugates. Atamestane was rapidly and extensively metabolized by all three species. Major metabolites which were observed in the human, could be isolated from urine pools of treated monkeys by preparative high performance liquid chromatography and were identified by GC/MS and 1H-NMR analysis. The metabolite patterns observed in the animals and in the human were similar, although some species- and sex-related differences were observed. There seem to be two principal routes by which atamestane is metabolized: one route is characterized by the attack of 17 beta-hydroxysteroid dehydrogenase, the other route includes hydroxylation of the 1-methyl group with subsequent attack by 5 beta-reductase, followed by a hydroxylation at position C-6. Some of the metabolites which were identified still had some pharmacological activity, although less marked than the parent compound.

Administration, Oral↗