Quantitative structure-selectivity relationships. Comparison of the inhibition of Escherichia coli and bovine liver dihydrofolate reductase by 5-(substituted-benzyl)-2,4-diaminopyrimidines.

In our previous publication (Blaney, J. M.; Dietrich, S. W.; Reynolds, M. A.; Hansch, C. J. Med. Chem. 1979, 22, 614), correlation equations were presented for the inhibition of bovine liver and Escherichia coli dihydrofolate reductase (DHFR) by 5-(substituted benzyl)-2,4-diaminopyrimidines. These equations brought out differences in the way these two enzymes interact with substituents, which explain the high selectivity of drugs like trimethoprim. We have tested and further developed these equations in this report. It is of particular interest that our previously published correlation equation for E. coli DHFR accurately predicted the potency of a commercial competitor of trimethoprim (tetroxoprim) now in clinical use. We believe that new and effective competitors for trimethoprim can be designed by means of the two correlation equations.

Confidence interval estimators for parameters associated with quantitative structure-activity relationships.

Use of the "jackknife" as a statistical tool for construction of both point and confidence interval estimators for parameters which are functions of regression coefficients and/or iteratively estimated parameters is described. Examples are presented demonstrating its utility in constructing estimators for log P0 and pi 0 using the parabolic and bilinear quantitative structure-activity relationship (QSAR) models relating nonlinear dependence of activity on hydrophobicity and for log [1/Ki(app)] assuming competitive enzyme inhibition.

Quantitative structure-activity relationship of 5-(X-benzyl)-2,4-diaminopyrimidines inhibiting bovine liver dihydrofolate reductase.

The inhibitory effect for a set of 23 5-(X-benzyl)-2,4-diaminopyrimidines acting on bovine liver dihydrofolate reductase (DHFR) had led to the following quantitative structure-activity relationship (QSAR): log 1/C = 0.62pi3 + 0.33epsilon sigma + 4.99, where r = 0.931 and s = 0.146. C in this expression is the molar concentration of inhibitor producing 50% inhibition, pi3 is the hydrophobic parameter for substituents on the 3 position of the phenyl moiety, and epsilon sigma is the the sum of the Hammett sigma constants for the 3, 4, and 5 substituents of the phenyl ring.

Inhibition of dihydrofolate reductase. 3. 4.6-Diamino-1,2-dihydro-2,2-dimethyl-1-(2-substituted-phenyl)-s-triazine inhibition of bovine liver and mouse tumor enzymes.

Inhibition of dihydrofolate reductase from bovine liver and murine L5178YR-C3 tumor cells has been examined for a series of 4,6-diamino-1,2-dihydro-2,2-dimethyl-1-(2-X-phenyl)-s-triazines. For both enzymes all 2-X substituents cause a decrease in inhibitory activity relative to X = H, with the notable exception of X = SH which is 7.4-12 times as active as X = H. Although there is a high correlation between the activities of these compounds vs. these two enzymes, significant deviations from this correlation for three of the triazines (X = CF3, CH2CN, and Cl) suggest that (a) there may exist significant differences in the two enzymes and their interactions with these triazines and (b) exploitation of such differences might allow for the selective inhibition of enzyme from tumor cells.

Quantitative structure-selectivity relationships. Comparison of the inhibition of Escherichia coli and bovine liver dihydrofolate reductase by 5-(substituted-benzyl)-2,4-diaminopyrimidines.

A quantitative structure-activity relationship (QSAR) has been formulated for the inhibition of purified E. coli dihydrofolate reductase by 23 5-(substituted benzyl)-2,4-diaminopyrimidines: log 1/C = 1.14MR'3,4,5 + 5.73; r = 0.887; s = 0.285. In this expression, MR'3,4,5 refers to the sum of MR values for X in the 3, 4 and 5 positions of the phenyl moiety. MR' signifies that the effective value of MR is limited to 0.79. Comparison of the QSAR for E. coli enzyme inhibition with that previously obtained for bovine enzyme offers the first general explanation for the great selectivity of the important antibacterial agent trimethoprim. Such QSSR promise to be of value in devising more selective drugs.

Comparison of the inhibition of methotrexate-sensitive and -resistant Lactobacillus casei cell cultures with purified Lactobacillus casei dihydrofolate reductase by 4,6-diamino-1,2-dihydro-2,2-dimethyl-1-(3-substituted-phenyl)-s-triazines. Use of quantitative structure-activity relationships in making inferences about the mechanism of resistance and the structure of the enzyme is situ compared with the enzyme in vitro.

The inhibitory action of a set of 4,5-diamino-1,2-dihydro-2,2-dimethyl-1-(3-substituted-phenyl)-s-triazines on Lactobacillus casei dihydrofolate reductase is compared with their action on methotrexate-resistant and methotrexate-sensitive cell cultures by means of quantitative structure-selectivity analysis. The analysis uncovers major differences in the steric and hydrophobic interactions of the substituents X with the three different systems. Correlation analysis is used to define the hydrophobic binding site for 3-X in the isolated enzyme. This is shown to be similar to that of the sensitive cells but different from that in the resistant cells, which have a larger hydrophobic binding site. When X has the general structure 3-CH2ZC6H4-Y (Z = O or NH), it is shown that Y does not interact with the isolated enzyme, but in the living cells, Y interacts with a molecular barrier in a way that can be quantitatively related to the molar refractivity of X. The methotrexate-resistant cells are resistant to highly hydrophilic inhibitors such as methotrexate but are not able to resist hydrophobic inhibitors. The results with the inhibition of L. casei dihydrofolate reductase are compared with the inhibition of enzyme from bovine liver.

Thyroxine analogues. 23. Quantitative structure-activity correlation studies of in vivo and in vitro thyromimetic activities.

Quantitative structure-activity correlation studies of thyroid hormone analogues have been utilized to examine (1) in vivo rat antigoiter activities; (2) in vitro binding affinities to intact rat hepatic nuclei, solubilized rat hepatic nuclear protein receptors, and the plasma protein thyroxine binding globulin; and (3) correlations between in vivo antigoiter activities and in vitro binding to nuclear receptors. These studies provide a more precise elucidation of the relative importance of the physiochemical factors which influence thyromimetic activities. In particular, they (1) provide the first systematic QSAR examination of drug-receptor interactions and of the dependence of in vivo activity on such interactions; (2) demonstrate the importance of the interactive effects of the 3' and 5' substituents and of the 4'-OH with each other as well as with nuclear receptors in influencing binding affinity; (3) support the hypothesis that binding to nuclear receptors is the first step in initiating the events which lead to subsequent hormonal expression; (4) show that the free energy of binding to nuclear receptors can be factored into the contributing physicochemical properties of the substituents; and (5) suggest factors that need to be considered in designing new analogues.

A model for thyroid hormone--receptor interactions.

Theoretical electronic structure calculations on the thyroid hormones and analogues, as well as model hormone--receptor interactions, have been carried out. These studies (a) support the concept that the 4'-OH group is a H-bond donor to the in vivo nuclear receptor and suggest that at the receptor this OH group is trans to the 3' (distal) substituent; (b) indicate that there is an important intramolecular interaction between 3' and 4' substituents, and those 3' substituents that most favor both 4' OH orientation trans to the 3' group and a more acidic OH group substantially increase binding and biological activity; and (c) support the concept that there is a direct correlation between the conformational free energy of the aromatic rings and biological activity.

Crystallography, quantitative structure-activity relationships, and molecular graphics in a comparative analysis of the inhibition of dihydrofolate reductase from chicken liver and Lactobacillus casei by 4,6-diamino-1,2-dihydro-2,2-dimethyl-1-(substituted-phenyl)-s-triazine s.

The inhibition of dihydrofolate reductase from chicken liver and from Lactobacillus casei has been studied with 4,6-diamino-1,2-dihydro-2,2-dimethyl-1-(substituted-phenyl)-s-triazines. It was found that for the chicken enzyme, inhibitor potency for 101 triazines was correlated by the following equation: log 1/Kiapp = 0.85 sigma tau' - 1.04 log (beta X 10 sigma tau' + 1) + 0.57 sigma + 6.36. The parameter tau' indicates that for certain substituents, tau = 0. In the case of the L. casei DHFR results, meta and para derivatives could not be included in the same equation. For 38 meta-substituted compounds, it was found that log 1/Kiapp = 0.38 tau'3-0.91 log (beta X 10 tau'3 + 1) + 0.71I + 4.60 and for 32 para-substituted phenyltriazines log 1/Kiapp = 0.44 tau'4-0.65 log (beta tau'4 + 1') - 0.90 upsilon + 0.69I + 4.67. In the L. casei equation, I is an indicator variable for substituents of the type CH2ZC6H4-Y and ZCH2C6H4-Y, where Z = O, NH, S, or Se. The parameter upsilon is Charton's steric parameter, which is similar to Taft's Es. The mathematical models obtained from correlation analysis are compared with stereo color graphics models.

Synthesis of chiral and achiral pyranenamine derivatives. Potent agents with topical ocular antiallergic activity.

The SS, RR and meso stereoisomers of pyranenamine SK&F 84210 were synthesized stereospecifically starting from commercially available (R)-(-)- or (S)-(+)-2,2-dimethyl-1,3-dioxolane-4-methanol. In addition, two achiral pyranenamines 19 and 26 were also synthesized. When evaluated by intravenous and topical routes in the rat passive ocular anaphylaxis (POA) assay, (SS)- and meso-2 as well as achiral compounds 19 and 26 were found to be more potent antiallergic agents than (RR)-2.

Mean geometry of the thiopeptide unit and conformational features of dithiopeptides and polythiopeptides.

The mean geometry of the thiopeptide [Ca-N-C(=S)-Ca] unit has been derived from an analysis of X-ray crystal structure data, as well as MM2 and Gaussian 80/82 calculations. The conformational flexibilities of dithiopeptides with glycl- and alanyl-side chains have been investigated by molecular mechanics. Minimum energy conformations were examined using interactive computer graphics molecular modeling techniques. Alanyl-dithiopeptide substitution within an oligopeptide results in considerable restriction of conformational freedom whereas the effect is minimal for glycyl-dithiopeptide substitution. Polyglycyl-thiopeptide adopts a left-handed three or fourfold or right-handed threefold helical structure with favorable interchain C = S...H-N hydrogen bond interactions. A poly-L-alanyl-thiopeptide prefers a left-handed threefold poly-L-proline-like helical structure.

Geometry of proline and hydroxyproline I: An analysis of X-ray crystal structure data.

We have carried out an analysis of crystal structure data on prolyl and hydroxyprolyl moieties in small molecules. The flexibility of the pyrrolidine ring due to the pyramidal character of nitrogen has been defined in terms of two projection angles delta 1 and delta 2. The distribution of these parameters in the crystal structures is found to be consistent with results of the energy calculations carried out on prolyl moieties in our laboratory.