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S Wyrick

Publications and source records attributed to S Wyrick.

9 recordsLinked to original sources
PubMed1999

Quantitative structure-activity relationship modeling of dopamine D(1) antagonists using comparative molecular field analysis, genetic algorithms-partial least-squares, and K nearest neighbor methods.

Several quantitative structure-activity relationship (QSAR) methods were applied to 29 chemically diverse D(1) dopamine antagonists. In addition to conventional 3D comparative molecular field analysis (CoMFA), cross-validated R(2) guided region selection (q(2)-GRS) CoMFA (see ref 1) was employed, as were two novel variable selection QSAR methods recently developed in one of our laboratories. These latter methods included genetic algorithm-partial least squares (GA-PLS) and K nearest neighbor (KNN) procedures (see refs 2-4), which utilize 2D topological descriptors of chemical structures. Each QSAR approach resulted in a highly predictive model, with cross-validated R(2) (q(2)) values of 0.57 for CoMFA, 0.54 for q(2)-GRS, 0.73 for GA-PLS, and 0.79 for KNN. The success of all of the QSAR methods indicates the presence of an intrinsic structure-activity relationship in this group of compounds and affords more robust design and prediction of biological activities of novel D(1) ligands.

Algorithms↗
PubMed1990

In vitro biotransformations of tetrachloro(d,l-trans)-1,2-diaminocyclohexaneplatinum(IV) (tetraplatin) in rat plasma.

The in vitro biotransformation of tetrachloro(d,l-trans)-1,2,-diaminocyclohexaneplantinum(IV) (tetraplatin) in the plasma of Fischer 344 rats were studied by the two-column high-performance liquid chromatography technique described previously (Mauldin et al., Cancer Res., 48: 5136-5144, 1988). The reduction of tetraplatin to dichloro(d,l-trans)-1,2-diaminocyclohexaneplatinum(II) [PtCl2(dach)] was extremely rapid. From experiments with diluted plasma, it was possible to estimate a t1/2 for tetraplatin of approximately 3 s at 37 degrees C in undiluted plasma. By titrating with N-ethylmaleimide, it was possible to show that sulfhydryl groups were responsible for 70-80% of the total reducing potential of plasma. The rapid reduction of tetraplatin to PtCl2(dach) was followed by slower substitution reactions involving the chloro ligands of PtCl2(dach). The t1/2 for PtCl2(dach) in plasma at 37 degrees C was 1.5 h. The monoaquamonochloro complex was an important biotransformation product at early times, reaching 10 to 12% of the total platinum present from 15 min to 2 h, when it was gradually replaced with more stable biotransformation products. Three major stable biotransformation products accumulated in the plasma. One of these biotransformation products was identified as the Pt(methionine)(dach) complex. The other two were tentatively identified as the Pt(cysteine)(dach) or Pt(ornithine)(dach) complex and the Pt(urea)(dach) or Pt(citrato)(dach) complex on the basis of coelution in two different high-performance liquid chromatography separation systems. These biotransformation products could play a role in tetraplatin effectiveness and/or toxicity.

Amino Acids↗
PubMed1989

Rapid reduction of tetrachloro(D,L-trans)1,2-diaminocyclohexaneplatinum(IV) (tetraplatin) in RPMI 1640 tissue culture medium.

Tetrachloro(D,L-trans)1,2-diaminocyclohexaneplatinum(IV) (tetraplatin) is a new platinum analogue which is less nephrotoxic than cisplatin and is effective in some cell lines which have become resistant to cisplatin. Since platinum(IV) compounds are thought to require reduction to their platinum(II) analogues for activity, the biotransformations of tetraplatin and its platinum(II) analogue, dichloro(D,L-trans)1,2-diaminocyclohexaneplatinum(II) [PtCl2(trans-dach)], were studied. For L1210 cells cultured in RPMI 1640 medium, the time course for inhibition of DNA synthesis and cytotoxicity was virtually identical for both drugs. The time course for binding to fetal calf serum in the tissue culture medium was also the same for both drugs. In the complete tissue culture medium, tetraplatin was reduced to PtCl2(trans-dach) with a half-life of 5 to 15 min, depending on the level of protein sulfhydryl in the medium. The major reducing agent in the medium was the protein sulfhydryl, with glutathione and glucose making minor contributions. No other component of the medium reacted with tetraplatin. The rapid reduction of tetraplatin to PtCl2(trans-dach) was followed by much slower substitution reactions involving the chloro ligands of PtCl2(trans-dach). The major transformation products which accumulated in RPMI 1640 medium were identical for both drugs. These data suggest that tetraplatin should be considered a prodrug which is very rapidly converted to PtCl2(trans-dach) with subsequent biotransformations as expected for the platinum(II) analogue. These data also indicate that in tissue culture most of the tetraplatin is reduced extracellularly.

Antineoplastic Agents↗
PubMed1989

Structural requirements for activation of the glycine coagonist site of N-methyl-D-aspartate receptors expressed in Xenopus oocytes.

Five structural features important for activation of the glycine recognition site on N-methyl-D-aspartate (NMDA) receptors were identified by structure-activity studies of more than 60 glycine analogues in voltage-clamped Xenopus oocytes injected with rat brain mRNA. First, sterically unhindered and ionized carboxyl and amino termini were essential for action at this site. Second, an increase in the interterminal separation by greater than one carbon (e.g., beta-alanine) markedly attenuated activity at this site. Third, activity at the glycine site was stereoselective. The D-isomers of alanine and serine were approximately 20 and 30 times more potent than the L-isomers. Fourth, only small sterically unobtrusive substitutions at the alpha-carbon could be tolerated. alpha-Methyl (D-alanine) and alpha-cyclopropyl (1-amino-cyclopropane carboxylic acid) (ACC) substitutions were effective as agonists but most larger aliphatic and aromatic alpha-carbon substitutions were simply inactive. Glycine, D-alanine, and ACC probably have only a two-point attachment to the receptor. Finally the alpha-carbon substituent of D-serine is envisioned as binding to a third site on the receptor probably via hydrogen bonding of the omega-terminal hydroxyl group. Thus, serine, an hydroxymethyl substitution of glycine, permitted activation of NMDA receptor-mediated currents, whereas isosteric substitutions incapable of hydrogen bonding (e.g., 2-aminobutyric acid) were inactive. Additionally, the position and size of the hydroxyl-containing group is critical for agonist action; D-threonine, DL-homoserine, and hydroxyphenolic substitutions at the alpha-carbon were all inactive. Halogenated analogs of a size comparable to D-serine but capable only of proton acceptance at the omega-terminus (beta-fluoro-D-alanine and beta-chloro-D-alanine) possessed agonist action, whereas an analog capable of only proton donation (1,2-diaminopropionic acid) was inactive. Full concentration-response curves were constructed for those analogs displaying greater than 25% of the effect of glycine when tested at 3 microM. With the exception of (R)-(+)cycloserine and beta-fluoro-D-alanine, all compounds were nearly full agonists and had Hill coefficients not significantly different from unity. The order of relative potency of the active analogs was ACC greater than glycine greater than D-serine greater than D-alanine greater than beta-fluoro-D-alanine greater than (R)-(+)-cycloserine greater than L-serine greater than L-alanine. Molecular modelling of a series of active and inactive analogs with close structural relation to glycine was undertaken. These results were complementary to those data obtained from the electrophysiological investigation.(ABSTRACT TRUNCATED AT 400 WORDS)

Amino Acids↗
PubMed1986

Compounds that inhibit chymotrypsin and cell replication.

Several compounds have been tested for their ability to inhibit bovine pancreatic alpha-chymotrypsin (Ki) and their ability to inhibit cell replication (IC50). There is good agreement over three orders of magnitude between the Ki and the IC50 values of these compounds. The data support the hypothesis that a cellular, chymotrypsin-like activity is necessary for cell replication.

Animals↗
PubMed1979

Synthesis of active site-directed organometallic irreversible protease inhibitors.

p-Antimonybenzenesulfonyl fluoride and p-mercurybenzenesulfonyl fluoride irreversibly inhibit chymotrypsin (EC 3.4.21.1), trypsin (EC 3.4.21.4), and chromosomal protease, and these inhibitors appear to be as active as phenylmethanesulfonyl fluoride. The pretreatment of the proteases interferes with the phosphorylation of the active-site serine by diisopropylfluorophosphate suggesting that the organometallic inhibitors may also interact with the active site serine. The organometallic inhibitors may be used for localization of proteases in different parts of the cell by electron microscopy and p-mercurybenzenesulfonyl fluoride could also be used for isolation of proteases by sulfhydryl affinity chromatography.

Animals↗