Discovery and structure-activity relationships of sulfonamide ETA-selective antagonists.

Random screening of compounds in an ETA receptor binding assay led to the discovery of a class of benzenesulfonamide ligands. Optimization led to the development of 5-amino-N-(3,4-dimethyl-5-isoxazolyl)-1-naphthalenesulfonamides which were functional antagonists. Structural features which were important to activity included a 1,5-substitution pattern on the naphthalene ring; a sulfonamide NH with a pK value < 7; an amine, preferably with alkyl substituents, at the 5-position; and methyl groups on both the 3- and 4-positions of the isoxazole.

A rapid and versatile method for screening endothelin converting enzyme activity.

A flexible two-step protocol has been developed for high-throughput assays of endothelin converting enzyme (ECE) activity. The method is illustrated using endothelial cell monolayers and crude cell extracts as enzyme sources for conversion of exogenous substrates (big endothelin isopeptides) to their respective vasoactive products (endothelin isopeptides). Cleavage conditions have been optimized to minimize substrate utilization (reducing cost) while maintaining sensitivity and selectivity for mature endothelin detection in receptor- and antibody-based assays. Endothelins are quantified in a separate step and comparable estimates of mature endothelin formation are obtained using both EIA and radioreceptor assays in 96-well formats. Human umbilical vein (HUVEC) and human aorta (HAEC) endothelial cells characterized by this method are found to preferentially convert the big endothelin-1 (big ET-1) isopeptide through a membrane-bound, thiorphan-insensitive, and phosphoramidon-sensitive zinc metalloendopeptidase. Both intact cells and membrane preparations used as the enzyme source predict similar IC50 values for phosphoramidon inhibition of ECE (ca 1 microM). The procedure described is simple, rapid, and suitable for high-volume screening.

1-Benzazepin-2-one calcium channel blockers--VI. Receptor-binding model and possible relationship to desmethoxyverapamil.

We have prepared a series of potent antihypertensive 1-benzazepin-2-one calcium channel blockers (CCBs) 1 that are structurally related to diltiazem 2. Structural studies and the preparation of conformationally constrained analogs of 1-benzazepin-2-ones have led us to postulate a receptor-bound conformation for both 1 and 2. We believe that these compounds bind to the calcium channel protein in an MI ("inboard") binding conformation in which the amine of the side chain is placed over the heptagonal benzazepione ring and in close proximity to the phenyl methyl ether pharmacophore. This receptor-bound conformation places the side chain amine and methyl ether pharmacophores in the same spatial relationship as 3-methoxyphenylethalamine. Combined with our SAR, this binding model rationalizes literature findings that desmethoxyverapamil can demonstrate pharmacology typical of both phenylalkylamine (PA) and benzothiazepinone (DTZ) calcium channel blockers. Simple experiments are proposed to test the hypothesis that desmethoxyverapamil can bind at the benzothiazepinone site on the calcium channel.

Structure-activity studies of endothelin leading to novel peptide ETA antagonists.

With the goal of producing receptor antagonists, numerous monocyclic and bicyclic endothelin analogs were prepared and tested for vasoconstrictor activity, receptor affinity and functional antagonist activity. Bis-penicillamine endothelin analogs containing Ala or Asn at position 18 were functional antagonists, with Ki values of 20-40 nM but KB values of about 1 microM (e.g., [Pen1,11, Nle7, Ala18]-endothelin-1, Ki = 42 nM, KB = 1.2 microM). While these peptides are antagonists at the ETA receptor, they appear to be at least partial agonists at another receptor subtype.

Site-specific biotinylation. A novel approach and its application to endothelin-1 analogs and PTH-analog.

We have developed an expeditious method for the incorporation of the biotinylaminocaproyl moiety on the epsilon-amino group of a lysine residue within a peptide chain in a site-specific manner. Using t-Boc chemistry for the solid phase synthesis approach and a base labile, acid stable protecting group (Fmoc-) for the epsilon-amino group of the target lysine, we prepared fully protected resin bound peptides which are site-specifically biotinylated. Following HF cleavage, the uniquely biotinylated peptides were obtained in a high degree of purity. Using this approach, a number of biotinylaminocaproyllysyl derivatives of a monocyclic Endothelin-1 analog were prepared. Synthesis of selected bicyclic analogs of high affinity monocycles led to the preparation of the bicyclic [Nle7]ET-1 analog containing epsilon-biotinylaminocaproyllysine at position-9. This peptide, with Kd = 0.08 nM, has 1000-fold higher affinity for the ETA receptor than the commercially available N alpha-biotinylated Endothelin-1. The general utility of this biotinylation methodology was demonstrated by the synthesis of a site-specifically biotinylated PTH analog which contained several side chain functionalized amino acid residues in its sequence. The synthetic method reported here is convergent in that it allows the facile variation of the length of the spacer and also offers the potential to introduce in a site specific manner other groups such as affinity labels and fluorescent tags.

Benzazepinone calcium channel blockers. 5. Effects on antihypertensive activity associated with N1 and aromatic substituents.

We have shown that the pyrrolidinylmethyl substituent on the lactam nitrogen (N1) of benzazepinone and benzothiazepinone calcium channel blocking agents is resistant to metabolic deamination and generally increases the duration and potency of antihypertensive activity in spontaneously hypertensive rats (SHR) relative to (N,N-dimethylamino)ethyl analogs. Additionally, compounds possessing a substituent on the fused aromatic ring are more resistant to metabolic deacylation of the C3 hydroxy function, which may explain why aromatic substituents also frequently increase the potency and/or duration of antihypertensive activity. Our data also indicate the increased antihypertensive activity associated with these structural modifications is independent of any effects of potency in vitro. Overall, we interpret these results to indicate that these structural modifications improve antihypertensive activity as a result of increased metabolic stability and, consequently, oral bioavailability.

Pharmacological characterization of potent, long-acting thromboxane receptor antagonists, SQ 33,261 and SQ 33,552.

SQ 33,261 ([1S-[1 alpha,2 alpha(Z),3 alpha,4 alpha]]-6-[3-[[2- [(phenylamino)carbonyl]hydrazono]methyl]-7-oxabicyclo[2.2.1]hept-2 - yl]-4-hexenoic acid) and SQ 33,552 ([1S-[1 alpha,2 alpha(Z),3 alpha,4 alpha]]-6-[3-[[[[(4- chlorophenyl)amino]carbonyl]hydrazono]methyl]-7- oxabicyclo[2.2.1]hept-2-yl]-4-hexenoic acid) are potent thromboxane (Tx) A2 receptor antagonists. They inhibited platelet aggregation in platelet-rich plasma induced by the TxA2 mimetic, U-46,619 (10 microM), with IC50 values of 200 and 70 nM, respectively. Neither compound inhibited ADP (20 microM)-induced platelet aggregation (IC50 greater than 1000 microM). SQ 33,261 and SQ 33,552 competitively antagonized U-46,619-induced contraction of rat aortic strips with respective pA2 values of 9.0 and 10.1 and KB values of 1.2 and 0.1 nM. They also competitively antagonized U-46,619-induced contraction of guinea pig tracheal strips with pA2 values of 8.9 and 9.9 and KB values of 1.9 and 0.4 nM, respectively. SQ 33,261 and SQ 33,552 (p.o.) were potent inhibitors of U-46,619 (2 mg/kg i.v.)-induced death in mice with ID50 values of 8 and 1 micrograms/kg, respectively. SQ 33,261 and SQ 33,552 (0.2 mg/kg p.o.), also had long duration of action in this assay with 50% survival times of 7 and 15 hr, respectively. SQ 33,261 at 0.01 and 1.0 mg/kg i.v., inhibited arachidonic acid-induced bronchoconstriction and reversed arachidonic acid-induced hypertension to a hypotensive response. SQ 33,552 inhibited TxA2 synthase at high concentrations (IC50 = 307 microM), whereas SQ 33,261 was inactive. Neither compound inhibited cyclooxygenase or caused an elevation of platelet cyclic AMP levels.(ABSTRACT TRUNCATED AT 250 WORDS)

Benzazepinone calcium channel blockers. 2. Structure-activity and drug metabolism studies leading to potent antihypertensive agents. Comparison with benzothiazepinones.

As part of a program to discover potent antihypertensive analogues of diltiazem (3a), we prepared 1-benzazepin-2-ones (4). Benzazepinones competitively displace radiolabeled diltiazem, and show the same absolute stereochemical preferences at the calcium channel receptor protein. Derivatives of 4 containing a trifluoromethyl substituent in the fused aromatic ring show potent and long-acting antihypertensive activity. Studies of the metabolism of 4 lead to the metabolically stable antihypertensive calcium channel blockers 5a and 5c. Benzazepinone 5a is a longer acting and more potent antihypertensive agent than the second generation diltiazem analogue TA-3090 (3e).

Benzazepinone calcium channel blockers. 3. Synthesis and structure-activity studies of 3-alkylbenzazepinones.

As part of a program aimed at identifying novel analogues of diltiazem, we developed several synthetic routes for 3-alkylbenzazepinones, both in racemic and nonracemic form. Structure-activity relationship studies in this series have led to identification of several analogues as potent calcium channel blocking agents, both in vitro and in vivo. Analogues containing a 6-trifluoromethyl substituent (17a and 17b) are the most potent vasorelaxants in vitro. The oral antihypertensive activity of these compounds is comparable to its 3-acetoxy derivative 1 (X = 6-CF3) and 8-chlorodiltiazem (2b). The 3-allyl analogue 17c is a more potent antihypertensive agent than 17a, 17b, or 8-chlorodiltiazem (2b), and has a longer duration of action in vivo.

Benzazepinone calcium channel blockers. 4. Structure-activity overview and intracellular binding site.

We have synthesized a series of benzazepinones (2) in order to determine the structure-activity relationships (SAR) for calcium channel blockers related to diltiazem. A prerequisite for calcium channel blocking activity in vitro and in vivo is the presence of two pharmacophores: a 4'-aryl methyl ether and a basic substituent appended to N1 with a pKa in the physiological range. When these constraints are satisfied, a wide variety of substitution is tolerated at C6, C7, and C3. The presence of an electron-withdrawing group at C6 appears to enhance potency in vitro and in vivo. For such benzazepinones, activity is primarily dependent upon lipophilicity, as measured by log P. We believe these compounds must partition into the cell membrane in order to access their receptor. The quaternary methiodide 15k was used to demonstrate that the binding site for benzazepinones is on the intracellular face of the membrane. This work represents the first comprehensive SAR of diltiazem-like calcium channel blockers.

Dihydropyrimidine calcium channel blockers. 3. 3-Carbamoyl-4-aryl-1,2,3,4-tetrahydro-6-methyl-5-pyrimidinecarboxylic acid esters as orally effective antihypertensive agents.

In order to explain the potent antihypertensive activity of the modestly active (IC50 = 3.2 microM) dihydropyrimidine calcium channel blocker 5, we carried out drug metabolism studies in the rat and found 5 is metabolized to compounds 6-10. Two of the metabolites, 6 (IC50 = 16 nM) and 7 (IC50 = 12 nM), were found to be responsible for the antihypertensive activity of compound 5. Potential metabolism of 6 into 7 in vivo precluded our interest in pursuing compounds related to 6. Structure-activity studies aimed at identifying additional aryl-substituted analogues of 7 led to 17g,j,p with comparable potential in vivo, though these compounds were less potent than 7 in vitro. To investigate the effects of absolute stereochemistry on potency, we resolved 7 via diastereomeric ureas 19a,b, prepared from 18 by treatment with (R)-alpha-methylbenzylamine. Our results demonstrate that the active R-(-)-enantiomer 20a of 7 is both more potent and longer acting than nifedipine (1) as an antihypertensive agent in the SHR. The in vivo potency and duration of 20a is comparable to the long-acting dihydropyridine amlodipine. The superior oral antihypertensive activity of 20a compared to that of previously described carbamates 2 (R2 = COOEt) could be explained by its improved oral bioavailability, possibly resulting from increased stability of the urea functionality.

Dihydropyrimidine calcium channel blockers. 2. 3-substituted-4-aryl-1,4-dihydro-6-methyl-5-pyrimidinecarboxylic acid esters as potent mimics of dihydropyridines.

To enhance the intrinsic potency of dihydropyrimidine calcium channel blockers, we have modified the structure of previously described 2-heteroalkyl-1,4-dihydropyrimidines 2 to 3-substituted 1,4-dihydropyrimidines 3. Structure-activity studies using potassium-depolarized rabbit aorta show that ortho, meta-disubstituted aryl derivatives are more potent than either ortho- or meta-monosubstituted compounds. While vasorelaxant activity was critically dependent on the size of the C5 ester group, isopropyl ester being the best, a variety of substituents (carbamate, acyl, sulfonyl, alkyl) were tolerated at N3. Our results show dihydropyrimidines 3 are significantly more potent than corresponding 2-heteroalkyl-1,4-dihydropyrimidines 2 and only slightly less potent than similarly substituted 2-heteroalkyl-1,4-dihydropyridines 4 and 5. Whereas dihydropyridine enantiomers usually show 10-15-fold difference in activity, the enantiomers of dihydropyrimidine 3j show more than a 1000-fold difference in activity. These results strengthen the requirement of an enamino ester for binding to the dihydropyridine receptor and indicate a nonspecific role for the N3-substituent.

Dihydropyrimidine calcium channel blockers: 2-heterosubstituted 4-aryl-1,4-dihydro-6-methyl-5-pyrimidinecarboxylic acid esters as potent mimics of dihydropyridines.

2-Heterosubstituted-4-aryl-1,4-dihydro-6-methyl-5-pyrimidinecar box ylic acid esters 8, which lack the potential CS symmetry of dihydropyridine calcium channel blockers, were prepared and evaluated for biological activity. Biological assays using potassium-depolarized rabbit aorta and radioligand binding techniques showed that some of these compounds are potent mimics of dihydropyridine calcium channel blockers. The combination of a branched ester (e.g. isopropyl, sec-butyl) and an alkylthio group (e.g. SMe) was found to be optimal for biological activity. When compared directly with similarly substituted 2-heteroalkyldihydropyridines 9, dihydropyrimidines 8 were found to be 30-fold less active. The solid-state structure of dihydropyrimidine analogue 8g shows that these compounds can adopt a molecular conformation which is similar to the reported conformation of dihydropyridine calcium channel blockers.

Minimum requirements for inhibition of smooth-muscle myosin light-chain kinase by synthetic peptides.

Although the amino acid residues that are important for peptide substrates of myosin light-chain kinase have been reported, those that are important for peptide inhibitors of this enzyme have not previously been investigated. Synthetic peptides based on the sequence Lys11-Lys12-Arg13-Ala-Ala-Arg16-Ala-Thr-Ser19 -Asn-Val21-Phe22-Ala of the chicken gizzard myosin light chain were tested as inhibitors of pig carotid-artery myosin light-chain kinase. The basic amino acid residues of the known myosin light-chain kinase inhibitor Lys-Lys-Arg-Ala-Ala-Arg-Ala-Thr-Ser-NH2 (IC50 = 14 microM) [Pearson, Misconi & Kemp (1986) J. Biol. Chem. 261, 25-27] were shown to be the important residues that contribute to inhibitor potency, as evidence by the finding that the hexapeptide Lys-Lys-Arg-Ala-Ala-Arg-NH2 had an IC50 value of 22 microM. This indicates that binding of the phosphorylatable serine residue to myosin light-chain kinase, which is of obvious importance for a substrate, does not enhance the potency of an inhibitor. With the aim of preparing more potent inhibitors, peptides Lys-Lys-Arg-Ala-Ala-Arg-Ala-Ala-Xaa-NH2 were prepared with a variety of amino acids substituted for the phosphorylatable serine residue. None of these peptides was a more potent inhibitor than the serine peptide.

Hydroxyamino acid specificity of smooth muscle myosin light chain kinase.

Synthetic peptides corresponding to the phosphorylation site in the myosin regulatory light chain from smooth muscle, Lys-Lys-Arg-Ala-Arg-Ala-Thr-Ser-Asn-Val-Phe-Ala ([Ala14,15]MLC(11-23] and containing a variety of hydroxyamino acid analogs at position 19, were tested as substrates for the smooth muscle myosin light chain kinase. Peptide analogs containing either D-serine or cis-hydroxyproline were not phosphorylated. The corresponding trans-hydroxyproline containing peptide was poorly phosphorylated with a Km of 2.3 microM and a Vmax of 3 X 10(-3) mumol.min-1.mg-1 compared to a Km of 12.5 microM and a Vmax of 1.43 mumol.min-1.mg-1 for the parent peptide. All three hydroxyamino acid analog peptides acted as relatively potent inhibitors of myosin light chain phosphorylation with Ki values in the range 7.5-10 microM, comparable to 7 microM for the parent peptide. Thus the failure of the hydroxyamino acid analog peptides to act as effective substrates was not the result of poor binding to the enzyme. In contrast, the same substitutions made in the peptide substrate for the cAMP-dependent protein kinase resulted in poor inhibitors. It is likely that the hydroxyl group of the substituting amino acids in the myosin light chain peptide analogs is not presented in the correct orientation in the active site for transfer of the phosphate group.

The preparation of leukocyte-poor red cells from AS-1 red cells by the spin-cool-filter method.

Ninety-eight units of AS-1 red cells (RBC) were studied to determine the optimal unit age for the preparation of leukocyte-poor red cells by the spin-cool-filter method. After 1 week of storage, the residual leukocyte counts of AS-1 units prepared by this method averaged 0.5 x 10(9) or fewer white cells, which indicated removal of more than 79 percent of the total white cells. The spin-cool-filter method, in conjunction with the rapid degeneration of the white cells in the AS-1 RBC, yielded leukocyte-poor units comparable to those prepared from citrate-phosphate-dextrose-adenine (CPDA-1) RBC.

SQ 27,786 and SQ 28,853: two angiotensin converting enzyme inhibitors with potent diuretic activity.

SQ 27,786 and SQ 28,853 were designed to possess both angiotensin converting enzyme (ACE) inhibitory and diuretic properties. Both compounds were given to conscious male Sprague-Dawley rats and mongrel female dogs to determine ACE inhibitory and diuretic activities. All animals had previously been equipped with indwelling arterial and venous catheters. Both compounds resulted in dose-related inhibition of an angiotensin I pressor response in rats after i.v. administration. The maximum response and duration of effect of both compounds were similar to that seen with equimolar doses of captopril. Oral doses of SQ 28,853 (50.0 mumol/kg) and SQ 27,786 (15.0 mumol/kg) resulted in 15 and 64% inhibition of ACE, respectively. In conscious normotensive dogs, both compounds (2.0 mg/kg, i.v.) resulted in complete inhibition of ACE. Urine volume was increased by 153 and 667% after SQ 27,786 and SQ 28,853, respectively. Similarly, sodium excretion was increased by 336% after SQ 27,786 and by 650% after SQ 28,853. SQ 27,786 and SQ 28,853 increased potassium excretion by 54 and 115%, respectively. No significant changes in blood pressure were observed with either compound in either species. These results demonstrate that both SQ 27,786 and SQ 28,853 are potent ACE inhibitors and diuretic agents in vivo.

Quantitation of ABO mixed-cell populations by a peroxidase-anti-peroxidase immunoenzyme method.

The peroxidase-anti-peroxidase immunoenzyme method was applied to red blood cell ghosts for the detection of ABO mixed-red blood cell populations. Red blood cell ghosts produced by acid-glycine lysis eliminated previous problems due to distorted red blood cell and hemoglobin-associated peroxidase activity. Anti-A,B was used to discriminate between various mixtures of test cells in group O cells. The positive-stained minor population of test cells stained dark brown following application of the peroxidase-anti-peroxidase method and the nonreactive group O cells were counterstained light blue with Coomassie brilliant blue which facilitated quantitation. The expected and observed numbers of positive-stained cells per 1000 cells were not significantly different as computed by X2. As low as a 0.5 percent minor population in an ABO red blood cell mixture could be accurately quantitated by this method.