Positions of His-64 and a bound water in human carbonic anhydrase II upon binding three structurally related inhibitors.

The 3-dimensional structure of human carbonic anhydrase II (HCAII; EC 4.2.1.1) complexed with 3 structurally related inhibitors, 1a, 1b, and 1c, has been determined by X-ray crystallographic methods. The 3 inhibitors (1a = C8H12N2O4S3) vary only in the length of the substituent on the 4-amino group: 1a, proton; 1b, methyl; and 1c, ethyl. The binding constants (Ki's) for 1a, 1b, and 1c to HCAII are 1.52, 1.88, and 0.37 nM, respectively. These structures were solved to learn if any structural cause could be found for the difference in binding. In the complex with inhibitors 1a and 1b, electron density can be observed for His-64 and a bound water molecule in the native positions. When inhibitor 1c is bound, the side chain attached to the 4-amino group is positioned so that His-64 can only occupy the alternate position and the bound water is absent. While a variety of factors contribute to the observed binding constants, the major reason 1c binds tighter to HCAII than does 1a or 1b appears to be entropy: the increase in entropy when the bound water molecule is released contributes to the increase in binding and overcomes the small penalty for putting the His-64 side chain in a higher energy state.

Prediction of drug absorption using multivariate statistics.

Literature data on compounds both well- and poorly-absorbed in humans were used to build a statistical pattern recognition model of passive intestinal absorption. Robust outlier detection was utilized to analyze the well-absorbed compounds, some of which were intermingled with the poorly-absorbed compounds in the model space. Outliers were identified as being actively transported. The descriptors chosen for inclusion in the model were PSA and AlogP98, based on consideration of the physical processes involved in membrane permeability and the interrelationships and redundancies between available descriptors. These descriptors are quite straightforward for a medicinal chemist to interpret, enhancing the utility of the model. Molecular weight, while often used in passive absorption models, was shown to be superfluous, as it is already a component of both PSA and AlogP98. Extensive validation of the model on hundreds of known orally delivered drugs, "drug-like" molecules, and Pharmacopeia, Inc. compounds, which had been assayed for Caco-2 cell permeability, demonstrated a good rate of successful predictions (74-92%, depending on the dataset and exact criterion used).

Use of (S)-(trifloxymethyl)oxirane in the synthesis of a chiral beta-adrenoceptor antagonist, (R)- and (S)-9-[[3-(tert-butylamino)-2-hydroxypropyl]oximino]fluorene.

Two synthetic approaches were used to prepare, in chirally pure form, the beta-adrenoceptor antagonist 9-[[3-(tert-butylamino)-2-hydroxypropyl]oximino]fluorene (1a). One of these employed the oxazolidine (S)-6 generated from D-mannitol, while the other utilized (S)-[[(trifluoromethanesulfonyl)oxy]methyl]oxirane (4) as the chiral three-carbon fragment. This latter synthesis was designed to incorporate the amino function in the last step. In vitro, a beta 2 selectivity of only 2.2 was observed for 1a. The example, (S)-9-[[3-(tert-amylamino)-2-hydroxypropyl]oximino]fluorene (1b), was also prepared and found to be selective for the beta 1 receptor by a factor of 2.5. In contrast to other beta-adrenoceptor antagonists, the enantiomers of 1a exhibited no chiral preference; i.e., (S)-1a and (R)-1a possessed a similar order of beta-adrenoceptor antagonistic activity.

Application of the free energy perturbation method to human carbonic anhydrase II inhibitors.

An analysis of the free energy perturbation (FEP) method is presented that attempts to evaluate the efficacy of the FEP method in the drug discovery process. To accomplish this we have evaluated whether the FEP technique can accurately predict energetic and structural quantities relating to the inhibition of human carbonic anhydrase II (HCAII) by sulfonamides. Three well-characterized (both structurally and energetically) sulfonamide inhibitors of HCAII were examined in this study, 1a, 1b, and 1c. Results from FEP simulations on these compounds indicate that the FEP method can predict energetic trends reasonably well; however, the FEP method was less successful in reproducing detailed structural data. In particular, an expected movement of His-64 when inhibitor 1c was bound did not occur. We conclude that the FEP method can be used to determine relative free energies of binding but cannot be relied upon to reproduce subtle geometric changes.

Approaches to vasodilating/beta-adrenergic blocking agents: examples of the dihydrolutidine type.

The aminohydroxypropoxy moiety has been incorporated into the dihydrolutidine class of vasodilators. In the spontaneously hypertensive rat, one of these, (S)-4-[2-methyl-4-[3-(tert-butylamino)-2-hydroxypropoxy]phenyl]-3,5-dicarboethoxy-1,4-dihydrolutidine (4c), exhibited antihypertensive activity on the order of the standard 4-[2-(trifluoromethyl)phenyl]-3,5-dicarboethoxy-1,4-dihydrolutidine (2a). This antihypertensive activity could not be explained in terms of a vasodilating effect, as determined in the dog. In this latter model, 2a decreased both mean arterial and hindlimb perfusion pressures.

4-Trifluoromethylimidazoles and 5-(4-pyridyl)-1,2,4-triazoles, new classes of xanthine oxidase inhibitors.

The syntheses of a number of 2-substituted 4-trifluoromethylimidazoles and 3-substituted 5-(4-pyridyl)-1,2,4-triazoles are described. The trifluoromethylimidazoles were prepared from 3,3-dibromo-1,1,1-trifluoroacetone after hydrolysis with aqueous sodium acetate solution and condensation with an aldehyde in the presence of ammonia. Basic hydrolysis of the trifluoromethyl group was found to provide a facile method for the synthesis of imidazole-4-carboxylic acids. In the imidazole series a 2-aryl substituent and a free imino group were required for xanthine oxidase inhibitory activity. The triazoles were obtained through the reaction of an aroylhydrazine and an imino ether followed by thermal ring closure of the intermediate acylamidrazone. As in the imidazole series, a free imino group is an absolute requirement for in vitro activity. Additional structure-activity relationships of these compounds are presented.

3,5-disubstituted 1,2,3,4-triazoles, 1 new class of xanthine oxidase inhibitor.

3,5-Bis(4-pyridyl)-1,2,4-triazole (PPT), 3-(4-pyrimidinyl)-5-(4-pyridyl)-1,2,4-triazole (PMPT), and 3-(4-pyridazinyl)-5-(4-pyridyl)-1,2,4-triazole (PZPT) are among the most active competitive inhibitors of xanthine oxidase among a series of 3,5-disubstituted triazoles synthesized for this purpose, inhibition constants being less than 1 times 10(-7) M for each. ED50 values in squirrel monkeys derived from first-order rate constants for the first and rate-limiting step of the sequence, xanthine leads to uric acid leads to allantoin plus CO2, range from 0.04 to 0.08 mg kg-1 orally, with unusually long durations of action attributable to asymmetric distribution of inhibitor within liver and gut as a consequence of enterohepatic recirculation. Sensitivity of rats, dogs, and anthropoid species to these, as to other xanthine oxidase inhibitors, is markedly less than that of the squirrel monkey, but the triazoles are at least an order of magnitude more active than the representative purine analogs tested.

Heterocyclic analogues of the antihypertensive beta-adrenergic blocking agent (S)-2-[3-(ter-butylamino)-2-hydroxypropoxy]-3-cyanopyridine.

The synthesis of a series of isoelectronic analogues of (S)-2-[3-(tert-butylamino)-2-hydroxypropoxy]-3-cyanopyridine (1) are described; included in this group are examples of thiazole, isothiazole, thiadiazole, pyrazine, and the structurally related naphthyridines. All of the compounds are similar to 1 in that they contain a cyano group ortho to the aminohydroxypropoxy side chain and meta to the nitrogen heteroatom. In addition, several related examples, having additional nuclear substituents and/or groups other than CN in the position adjacent to the aminohydroxypropoxy group, were prepared, and beta-adrenoceptor antagonist activity and vasodilating potency were determined. Three compounds, thiazole 2 and isothiazoles 3 and 27, effectively lowered mean arterial pressure in the SH rat at 5 mg/kg. Compounds 2, 3, and 27 increased iliac blood flow and exhibited beta-adrenergic blocking properties in the dog.

Beta 1-selective adrenoceptor antagonists: examples of the 2-[4-[3-(substituted-amino)-2-hydroxypropoxy]phenyl]imidazole class.

A series of 2-[4-[3-(substituted-amino)-2-hydroxypropoxy]phenyl]imidazoles is described. The compounds were investigated in vitro for beta-adrenoceptor antagonism, and several examples were found to be selective for the beta 1-adrenoceptor. The structure--activity relationship exhibited by this series of compounds is discussed. (S)-2-[p-[3-[[2-(3,4-dimethoxyphenyl)ethyl]amino]-2-hydroxypropoxy]phenyl]-4-(2 -thienyl)imidazole [(S)-13] was over 100 times more selective than atenolol for the beta 1-adrenergic receptor and has been selected for in-depth studies.

An approach to peripheral vasodilator-beta-adrenergic blocking agents.

The syntheses of 2-phenyl- and 2-pyridyl-4-trifluoromethylimidazoles having a 3-tert-butylamino-2-hydroxypropoxy moiety attached to the aryl or heteroaryl substituent are described. Structure--activity relationships based on results from an evaluation of these compounds for antihypertensive, vasodilating, and beta-adrenergic blocking activities are discussed.

2-pyridylimidazoles as inhibitors of xanthine oxidase.

A series of 28 4-substituted and 4,5-disubstituted 2-pyridylimidazoles was synthesized and evaluated in vitro for inhibition of xanthine oxidase. Included within this group are examples of 2-pyridylimidazopyridines and halo-substituted 2-pyridylbenzimidazoles. Five compounds exhibited inhibitory activity in the same range as the standards, 4-hydroxypyrazolo[3,4-d]pyrimidine and 2-(4-pyridyl)-4-trifluoromethylimidazole (22). Two examples, 2-(4-pyridyl)-4,5-dicyanoimidazole (16) and 2-(4-pyridyl)-4-nitroimidazole (3), were at least an order of magnitude more active than the standards and therefore rank among the most potent known inhibitors of the enzyme.

Thienothiopyran-2-sulfonamides: a novel class of water-soluble carbonic anhydrase inhibitors.

An attempt to develop a water-soluble carbonic anhydrase inhibitor focused on exploring structure-activity relationships in the thienothiopyransulfonamide class. The strategy to influence water solubility while retaining carbonic anhydrase activity involved the introduction of a hydroxyl moiety and adjusting the oxidation state of the sulfur on the thiopyran portion of the molecule. Compounds 4 and 17 best fit the criteria of aqueous solubility and inhibitory potency vs. human carbonic anhydrase II and are candidates for evaluation as topically effective antiglaucoma agents.

Beta 1-selective adrenoceptor antagonists: examples of the 2-[4-[3-(substituted amino)-2-hydroxypropoxy]phenyl]imidazole class. 2.

An attempt to develop a highly cardioselective beta-adrenoceptor antagonist devoid of intrinsic sympathomimetic activity (ISA) focused on exploring structure-activity relationships around (S)-[p-[3-[[2-(3,4-dimethoxyphenyl)ethyl]amino]-2-hydroxypropoxy] phenyl]-4-(2-thienyl)imidazole. Strategies to reduce or eliminate ISA centered on structural changes that could influence activation of the receptor by the drug itself or by a metabolite. The approaches involved (a) eliminating the acidic imidazole N-H proton, (b) incorporating substituents ortho to the beta-adrenergic blocking side chain, (c) increasing steric bulk around the N-H moiety, (d) decreasing lipophilicity, (e) introducing intramolecular hydrogen bonding involving the imidazole N-H, and (f) displacing the imidazole ring from an activating position by the incorporation of a spacer element. The compounds were investigated in vitro for beta-adrenoceptor antagonism and in vivo for ISA. From these studies, the most successful variation involved the insertion of a spacer between the imidazole and aryl rings. (S)-4-Acetyl-2-[[4-[3-[[2-(3, 4-dimethoxyphenyl)ethyl]amino]-2-hydroxypropoxy]phenyl]methyl] imidazole (S-51) was demonstrated to be highly cardioselective (dose ratio beta 2/beta 1 greater than 9333) and devoid of ISA.

Structure-affinity relationships of arylquinolizines at alpha-adrenoceptors.

Hexahydroaryl[a]quinolizines comprise a prominent structural element in several alpha 2-adrenoceptor antagonists. Eight hexahydroheteroarylquinolizines were prepared as minimal ligands to investigate the relationship between the nature of the aromatic ring and affinity of these molecules for alpha-adrenoceptors. Affinity for alpha 1-and alpha 2-adrenoceptors was assessed by displacement of [3H]prasozin and [3H]clonidine, respectively. Lipophilicity of the aryl portion of the molecules, reflected by their partition coefficient between octanol and pH 7.4 buffer, correlated well with affinity at both receptor subtypes. Although some compounds showed nanomolar affinity for alpha-adrenoceptors, no subtype selectivity was observed. These results suggest that the aromatic ring enhances binding at both receptors chiefly through hydrophobic interactions and contributes little to subtype selectivity.

Diethyl 3,6-dihydro-2,4-dimethyl-2,6-methano-1,3-benzothiazocine-5,11- dicarboxylates as calcium entry antagonists: new conformationally restrained analogues of Hantzsch 1,4-dihydropyridines related to nitrendipine as probes for receptor-site conformation.

The pharmacological activity of rigid analogues of 1,4-dihydropyridine calcium entry antagonists 9-16 is demonstrated by dose-dependent inhibition of the calcium contraction in depolarized rat aortic strips and by a [3H]nitrendipine binding assay in using cardiac sarcolemmal membranes. From the results, a model is proposed as the receptor-bound conformation of the dihydropyridine calcium entry antagonists.

Topically active carbonic anhydrase inhibitors. 2. Benzo[b]thiophenesulfonamide derivatives with ocular hypotensive activity.

Derivatives of benzo[b]thiophene-2-sulfonamide were prepared to investigate their potential utility as topically active inhibitors of ocular carbonic anhydrase. Such an agent would be useful in the treatment of glaucoma. Among the compounds described are 6-hydroxybenzo[b]thiophene-2-sulfonamide (16) and its acetate ester (23), which are among the most potent ocular hypotensive agents in this class, as assessed in the alpha-chymotrypsinized rabbit. These compounds were selected for clinical evaluation.

Synthesis of 4-substituted 2H-naphth[1,2-b]-1,4-oxazines, a new class of dopamine agonists.

A series of tricyclic oxazines, namely, the 4-substituted 2H-naphth[1,2-b]-1,4-oxazines, have been synthesized and assayed for dopamine agonist activity. One of the members of this series, compound (+)VII-15, was found to be a remarkably potent agonist in vivo when tested in the standard 6-hydroxydopamine lesioned rat assay. The absolute configuration of the compound corresponds to that found in the active isomer of apomorphine. Its activity at the alpha 2 receptor (vs. [3H]clonidine) is relatively low. It also failed to stimulate the synthesis of cAMP in the carp retina assay, thus giving the compound a highly selective profile in favor of the D2 receptor.

Structure-activity, theoretical, and X-ray studies on the intramolecular interactions in a series of novel histamine H2 receptor antagonists.

The furan ring of the histamine H2 receptor antagonist 3-amino-4-[[2-[[[5-[(dimethylamino)methyl]-2-furanyl]-methyl] thio]ethyl]amino]-1,2,5-thiadiazole 1-oxide (1a) was replaced by thiophene, pyridine, benzene, and pyrrole. The relative receptor affinities of these analogues were estimated by in vitro and in vivo techniques. A theoretical model for the stacking interaction, observed by single crystal X-ray analysis of 1a, was developed, and the ability to enter into this type of interaction was estimated. The X-ray analysis of the pyridine analogue of 1a revealed no intramolecular stacking interaction. The theoretical studies were evaluated in light of the observed receptor affinities, and the relevance of the solid-state geometry of 1a to the receptor-bound geometry was assessed. It is suggested that the stacked geometry found in the X-ray structure of 1a does not represent a conformation that is relevant to that bound at the histamine H2 receptor.

beta-Adrenergic blocking agents with acute antihypertensive activity.

Modification of the pharmacological profile of the vasodilating/beta-adrenergic blocking agent 2-[4-[3-(tert-butylamino)-2-hydroxypropoxy]phenyl]-4-(trifluoromethyl)imidazole (1) has been investigated. Introduction of selected substitutents onto the imidazole ring, in place of the trifluoromethyl group, has yielded highly cardioselective beta-adrenergic blocking agents such as 7, 17, and 18. The placement of alkyl or chloro groups onto the aryl ring of 1, as illustrated by 33, has produced a class of compounds characterized as antihypertensive beta-adrenergic blocking agents. In these examples, the acute antihypertensive activity does not appear to be due to either vasodilating or beta 2-agonist properties.

Antihypertensive beta-adrenergic blocking agents: N-aralkyl analogues of 2-[3-(tert-butylamino)-2-hydroxypropoxy]-3-cyanopyridine.

An interest in dual-acting antihypertensive agents, specifically those related to (S)-2-[3-(tert-butylamino)-2-hydroxypropoxy]-3-cyanopyridine (1), led us to probe the contribution of the side-chain amino substituent in this series. The ability of 1 and its various analogues to displace radiolabeled alpha 1 (WB-4101 and prazosin) and beta (dihydroalprenolol) adrenergic receptor ligands was assessed by receptor-binding techniques. Most of the compounds exhibited high beta-adrenoceptor binding affinities, but only the N-aralkylamino-substituted compounds showed high alpha 1-adrenoceptor affinities. Therefore, the vasodilation shown by 1 was not due to an interaction with the alpha 1 adrenoceptor. The aralkylamino analogues of 1 in spontaneously hypertensive rats and anesthetized dogs exhibited antihypertensive activity and alpha 1-adrenoceptor blocking properties. Unlike the preference shown by beta-adrenoceptors for S enantiomers in this oxymethylene class of beta blockers, the chirality at the secondary hydroxy center made only a minor contribution to the affinity for the alpha 1-adrenoceptor and even less of a contribution to the observed antihypertensive effects. This lack of chiral influence at the hydroxy center confirmed what had been previously observed in more limited studies with the isomers of both labetalol and medroxalol.