[Potassium channel openers. A new possible therapeutic principle in several diseases]

Potassium channels are ion channels in the cell membrane which are especially important for regulation of the membrane potential and the cell's excitability. Potassium channel openers are drugs that interfere with these channels, and several such substances have been developed. Existing substances show highest affinity to vascular smooth muscle. The clinical effect is relaxation of blood vessels resulting in lower blood pressure. However, current efforts are concentrated on finding substances which are selective for other cell types. Possible areas of application are treatment of hypertension, angina pectoris, arrhythmias, asthma and urinary bladder instability.

3-(Arylamino)-6,7-dihydro-6-methylpyrano[4,3-c]pyrazol-4(1H or 2H)-ones with antipyretic, analgesic, antiarrhythmic, hypotensive and other activities

The synthesis of 3-(arylamino)-6,7-dihydro-6-methylpyrano[4,3-c]pyrazol-4(1H or 2H)-ones by reaction of N-aryl-5,6-dihydro-4-hydroxy-6-methyl-2-oxo- 2H-pyrano-3-carbothioamides with hydrazine is described. Some compounds showed remarkable antipyretic, analgesic, antiarrhythmic and hypotensive activity in rats or mice, as well as weak antiinflammatory, local anesthetic and in vitro platelet antiaggregating activity.

Novel thieno[2,3-b]- and [3,4-b]pyrans as potassium channel openers. Thiophene systems--XVII

The syntheses and antihypertensive activity of the thieno[3,4-b]pyran and thieno[2,3-b]pyran isosteres of the potassium channel opener (PCO) RWJ 26629 (+/- 2a) are reported. While the unsubstituted thiophene derivatives were active at 20 mg/kg, introduction of a strong electron withdrawing group in the 2-position of the thieno[3,2-b] series increased potency. Similar substitution on the thieno[3,4-b] series significantly lowered potency. Compounds 26 and 30 are approximately 5-fold more potent than the prototypic PCO cromakalim (+/- 1).

Pharmacology of the dihydropyridine calcium antagonists: relationship between lipophilicity and pharmacodynamic responses

Importance of L-channels for calcium: Calcium L-channels, the specific target of calcium antagonists, appear to be the receptors for these therapeutic agents. Therefore, the accessibility of these channels/receptors to calcium antagonists is a major determinant of the response to these drugs in cardiovascular disorders, including essential hypertension. As with numerous other drugs, the concentration at the receptor level and its time-course largely determine not only the intensity but also the rate of onset and the duration of the drug's effect. Disadvantages of nifedipine: Within the series of dihydropyridine calcium antagonists, the first compound introduced was nifedipine, a relatively hydrophilic drug. Owing to its hydrophilic character the drug rapidly reaches the receptor, thus explaining the rapid onset of its vasodilator action. Accordingly, reflex tachycardia develops, which is not only triggered by the degree of vasodilation but also by the rapidity of its onset. In addition, nifedipine has a short duration of action, requiring the use of special galenic formulations to allow one dose a day. New dihydropyridine calcium antagonists: In view of the disadvantages of the hydrophilic calcium antagonists, attempts have been made to develop dihydropyridines with a slower onset and a longer duration of action. This may be achieved by drugs which are largely in the ionized state at a physiological pH (e.g. amlodipine) and therefore combine slowly with the receptor and bind firmly to various tissue compartments. Another logical approach is the use of highly lipophilic drugs such as lacidipine. Because of its physicochemical properties, the effect in equilibrium is reached very slowly, after up to 5 h in isolated tissues and after more than 2 h after intravenous administration. Lacidipine appears to slowly enter a lipid compartment surrounding the dihydropyridine binding site, which has to be saturated before an equilibrium effect is reached. In addition, the persistence of the drug in this lipid compartment contributes to its long-lasting vasodilator effect.

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.

2-(Alkylamino)nicotinic acid and analogs. Potent angiotensin II antagonists

A series of pyridines and other six-membered ring heterocycles connected to a biphenyltetrazole with a -CH2-NR'-link (1) were discovered to be potent angiotensin II antagonists. In the pyrimidine carboxylic acid series (W = CR, X = N, Y = CH, Z = COOH), compounds with an alkyl group (R') on the exocyclic nitrogen were much more potent than compounds with an alkyl group (R) on the heterocyclic ring. The corresponding pyridine, pyridazine, pyrazine, and 1,2,4-triazine carboxylic acids also showed potent in vitro angiotensin II antagonism. The pyridine (W, X, Y = CH, Z = COOH, R' = n-C3H7) demonstrated potent in vitro activity (pA2 = 10.10, rabbit aorta, and Ki = 0.61 nM, receptor binding in rat liver) as well as exceptional oral antihypertensive activity and bioavailability. Any nonacidic replacement for the carboxylic acid was detrimental for activity.

Quinoxaline N-oxide containing potent angiotensin II receptor antagonists: synthesis, biological properties, and structure-activity relationships

A series of novel quinoxaline heterocycle containing angiotensin II receptor antagonist analogs were prepared. This heterocycle was coupled to the biphenyl moiety via an oxygen atom linker instead of a carbon atom. Many of these analogs exhibit very potent activity and long duration of effect. Interestingly, the N-oxide quinoxaline analog was more potent than the nonoxidized quinoxaline as in the comparison of compounds 5 vs 30. In order to improve oral activity, the carboxylic acid function of these compounds was converted to the double ester. This change did result in an improvement in oral activity as represented by compound 44.

Metabolism of clentiazem in rats

Following oral dosing of [14C]clentiazem to rats the metabolites in urine and bile were separated and their chemical structures were investigated by HPLC and GC-MS analyses. Fifteen basic, 6 acidic, 2 neutral and 4 conjugated metabolites were found in urine and/or bile. Eight basic metabolites (MB1-8) were identified as the synthetic compounds; deacetyl clentiazem (MB1), N-monodemethyl clentiazem (MB2), deacetyl-N-monodemethyl clentiazem (MB3), deacetyl-O-demethyl clentiazem (MB4), N-monodemethyl-O-demethyl clentiazem (MB5), deacetyl-N-monodemethyl-O-demethyl clentiazem (MB6), O-demethyl clentiazem (MB7) and N-didemethyl clentiazem (MB8). The chemical structures of seven basic metabolites (MB9-15) were assigned as follows, deacetyl-N-didemethyl clentiazem (MB9), O-demethyl-N-didemethyl clentiazem (MB10), deacetyl-O-demethyl-N-didemethyl clentiazem (MB11), N-monodemethyl-2-hydroxy-methoxyphenyl clentiazem (MB12), deacetyl-2-hydroxy-methoxyphenyl clentiazem (MB13), deacetyl-N-monodemethyl-2-hydroxy-methoxyphenyl clentiazem (MB14) and deacetyl-N-didemethyl-2-hydroxy-methoxyphenyl clentiazem (MB15). Four acidic metabolites were identified as the synthetic compounds: (+)-(2S,3S)-3-(acetyloxy)-8-chloro-3,4-dihydro-2-(4-methoxyphenyl) -4-oxo-1, 5-benzothiazepin-5(2H)-acetic acid (MA1), deacetyl-MA1 (MA2), O-demethyl-MA1 (MA3) and deacetyl-O-demethyl-MA1 (MA4); and the two remaining acidic metabolites, MA5 and MA6, were presumed to be hydroxylated MA3 and MA4, respectively. Two neutral metabolites were identified as the synthetic compounds; (+)-(2S,3S)-3-(acetyloxy)-8-chloro-3,4-dihydro-2-(4-methoxyphenyl) -4-oxo-1, 5-benzothiazepin-5(2H)-acetonitrile (MN1) and deacetyl MN1 (MN2). Other two metabolites conjugated with glucuronic acid were found in bile and the structures were presumed to be 8-chloro-2,3-dihydro-3-hydroxy-5-(2-hydroxyethyl)-2-(4-hydroxyphenyl)-1, 5-benzothiazepin-4(5H)-one (MN3) and 2-methoxyphenyl MN3 (MN4). The glucuronide or sulfate of MA4 was also detected. These metabolites were formed by a number of pathways including deacetylation, deamination, N-demethylation, O-demethylation, aromatic hydroxylation and conjugation.

Structure-activity study of antihypertensive 1,4-dihydropyridine derivatives having nitrooxyalkyl moieties at the 3 and 5 positions

1,4-Dihydropyridine derivatives having two nitrooxyalkyl moieties as esters at the 3 and 5 positions possess antihypertensive activity. To understand how substituents affect the biological activity, the quantitative structure-activity relationship (QSAR) of 27 compounds was analyzed using the Fuzzy adaptive least-squares (FALS 91) method. The QSAR models suggested that the hydrophobicity and electronic effect at the 4 position of the 1,4-dihydropyridine along with the special structures of the nitrooxyalkylester components are important for antihypertensive activity.

A spectroscopic investigation of losartan polymorphs

Losartan, an antihypertensive agent in clinical development, was found to exist in two enantiotropic polymorphic forms, a low-temperature stable form (Form I) and a high-temperature stable form (Form II), the temperatures at which they are stable being related to the transition temperature. X-ray powder diffraction patterns indicated differences in the crystal packing of the two forms. The vibrational data from infrared and Raman spectroscopy suggested a subtle change in molecular conformation and crystal packing in the two forms. Solid-state 13C NMR data of the polymorphs concurred with the vibrational data and indicated that, while the observed line widths reflect no major changes in crystallinity, signal multiplicities and chemical shifts do reflect differences in molecular packing in the respective unit cells. Thus, in the absence of crystallographic data, useful structural information could be derived from spectroscopic results to identify each of the crystalline forms.

The liposome partitioning system for correlating biological activities of imidazolidine derivatives

The partitioning of 10 imidazolidines in various liposome/buffer systems (logK'm) has been determined and compared to partitioning in the n-octanol/buffer system (logP'). The logK'm, which was generally greater than the logP', increased or decreased upon the addition of dicetylphosphate (DCP) or stearylamine (STA), respectively, to dimyristoylphosphatidylcholine (DMPC) liposomes. Quantitative correlations of alpha 2-adrenergic potencies of imidazolidines have been made by regression analyses with logP', logK'm, binding affinity, and intrinsic activity. Both central and peripheral potencies correlated with logK'm but not with logP'. Multiple regressions yielded improved predictable quantification of these potencies. Thus, the liposomal membrane system shows certain advantages over the n-octanol/buffer system for the prediction of biological activities of the imidazolidines.

Synthesis and antihypertensive activities of new 1,4-dihydropyridine derivatives containing nitrooxyalkylester moieties at the 3- and 5-positions

We have synthesized new 1,4-dihydropyridine derivatives having nitrooxyalkylester moieties at the 3- and 5-positions in order to develop potent and long-lasting vasodilators. The antihypertensive activities of these compounds were compared with that of nifedipine. One of them, 2-nitrooxypropyl 3-nitrooxypropyl 2,6-dimethyl-4-(3-nitrophenyl)-1,4-dihydro-3,5- pyridinedicarboxylate (CD-349) was selected for further development. The structure-activity relationship is discussed.

Adrenomedullin: a novel hypotensive peptide isolated from human pheochromocytoma

A novel hypotensive peptide was discovered in human pheochromocytoma by monitoring the elevating activity of platelet cAMP. Since this peptide is abundant in normal adrenal medulla as well as in pheochromocytoma tissue arising from adrenal medulla, it was designated "adrenomedullin". The peptide, consisting of 52 amino acids, has one intramolecular disulfide bond and shows slight homology with calcitonin gene related peptide. It was found to elicit a potent and long lasting hypotensive effect. The peptide circulates in blood in a considerable concentration, but it was not found in brain. These data suggest that adrenomedullin is a new hormone participating in blood pressure control. Occurrence of adrenomedullin indicates the possible existence of a novel system for circulation control.

Discovery of losartan, the first specific non-peptide angiotensin II receptor antagonist

DISCOVERY OF LOSARTAN: Losartan (DuP 753, MK 954) is the first potent and selective non-peptide angiotensin II (Ang II) antagonist. The discovery of losartan followed an observation that several simple benzylimidazoles are weak Ang II antagonists. These compounds (e.g. S8307) lack potency but are orally active and selective for Ang II receptors (AT receptors). Losartan was synthesized using S8307 and other analogs of the benzylimidazoles as chemical leads.

ACTION OF LOSARTAN

Losartan selectively inhibits all Ang II responses that have been studied and lowers blood pressure in several animal models of renin-dependent hypertension. In animals, the antihypertensive efficacy of losartan is similar to that of angiotensin converting enzyme (ACE) inhibitors but, unlike ACE inhibitors, losartan is a more selective inhibitor of the renin-angiotensin system since it does not affect the metabolism of kinins. Compared with peptide Ang II antagonists (e.g. saralasin), losartan has significant advantages, including a long duration of action, effective oral absorption and no Ang II agonist activity.

CONCLUSIONS

The high selectivity and potency for AT receptors, the non-peptide structure and the oral activity of losartan represent a pharmacological breakthrough. This agent is now being used to elucidate the physiology of AT receptors and is likely to be useful in the therapeutic management of diseases in which the renin-angiotensin system is known to be involved.

Symphytoxide A, a triterpenoid saponin from the roots of Symphytum officinale

A new triterpenoidal saponin of hederagenin named symphytoxide A has been isolated from the ethanolic extract of the roots of Symphytum officinale and characterized on the basis of chemical investigations and spectroscopic studies as 3-O-[beta-D-glucopyranosyl-(1-->2)-beta-D-glucopyranosyl-(1-->4)- alpha-L-arabinopyranosyl] hederagenin. The structure of this new saponin was established on the basis of 1D and 2D NMR experiments including heteroCOSY, COSY-45 degrees as well as HMBC measurements and other spectroscopic techniques. The saponin exhibited hypotensive activity in anesthetized rats.

[Chemical studies of Strobilanthes cusia]

Seven compounds have been isolated from the whole plant of Strobilanthes cusia (Nees) O. Ktze. Three of them are triterpenes (I-III), two are indole alkaloids (IV, V), two are quinazolinone alkaloids (VI, VII). On the basis of spectral analysis and physicochemical properties, their structures were established as lupeol (I), betulin (II), lupenone (III), indigo (IV), indirubin (V), 4(3H)-quinazolinone (VI), 2,4(1H,3H)-quinazolinedione (VII). VI and VII were found from natural plant for the first time. The results of the pharmacological tests demonstrate that compound V has anticancer activity and compound VI has hypotensive action. Compound VII can be quantitatively determined by HPLC, which may serve as a quality control standard for materia medica and its preparations. Compounds VI and VII have been confirmed by means of synthesis.

Dihydropyrimidine angiotensin II receptor antagonists

The discovery of the nonpeptide angiotensin II (AII) receptor antagonist losartan, previously called DuP 753, has stimulated considerable interest in the synthesis of novel analogs of this compound. Our efforts in this area have resulted in the discovery of dihydropyrimidines as potent AII receptor antagonists. The chemistry leading to this novel class of AII antagonists and their biological properties are reported in this publication. Structure-activity studies showed that a variety of substituents are tolerated on the dihydropyrimidine ring, indicating that the AII receptor is permissive in accepting this region of the nonpeptide antagonists. As reported for imidazole-based AII antagonists, the tetrazolyl dihydropyrimidine analogs were found to be more potent than the corresponding carboxylic acids. Our studies show that dihydropyrimidine analogs 2-butyl-4-chloro-1,6-dihydro-6-methyl-1-[[2'-(1H-tetrazol-5-yl)[1, 1'-biphenyl]-4-yl]methyl]pyrimidine-5-carboxylic acid, ethyl ester (Ki = 8.3 nM), 2-butyl-4-chloro-1,6-dihydro-6-methyl-1- [[2'-(1H-tetrazol-5-yl)[1,1'-biphenyl]-4-yl]methyl]-5- pyrimidinecarboxylic acid (Ki = 1.0 nM), and 2-butyl-6-chloro-1,4-dihydro-4,4-dimethyl-1-[[2'-(1H-tetrazol-5-yl )[1,1'- biphenyl]-4-yl]methyl]-5-pyrimidinecarboxylic acid, ethyl ester (Ki = 1.1 nM), display affinities for the AII receptor which are comparable to or better than losartan (Ki = 9.0 nM). One of these derivatives, 2-butyl-4-chloro-1,6-dihydro-6-methyl-1-[[2'-(1H-tetrazol-5- yl)[1,1'-biphenyl]-4-yl]methyl]pyrimidine-5-carboxylic acid, ethyl ester, showed antihypertensive activity on oral administration to spontaneously hypertensive rats. These results demonstrate that the imidazole of losartan can be successfully replaced with a dihydropyrimidine ring.

Peptides as targets for antihypertensive drug development

AIM

To assess the potential for development of new classes of pharmacological drugs in the treatment of hypertension and cardiovascular disease.

BACKGROUND

Basis of pharmacological blood pressure reduction: Since the discovery of the renin-angiotensin system by Tigerstedt almost 100 years ago, a large number of vasoactive peptides have been discovered. By interaction with such peptides of endocrine, perivascular or endothelial origin, blood pressure may be modulated. BLOCKADE OF THE RENIN-ANGIOTENSIN SYSTEM: The success of the angiotensin converting enzyme (ACE) inhibitors in hypertension and congestive heart failure is generally attributed to reduced generation of angiotensin II. The recent development of specific and highly potent Ang II type 1 subtype receptor antagonists such as losartan (DuP753, MK954) have provided a new opportunity to inhibit the renin-angiotensin system, and this is currently being explored in hypertensive patients. In addition, blockade of the first and rate-limiting reaction of the renin-angiotensin system, inhibition of renin activity, is also a target for the development of antihypertensive drugs. However, this development is hampered at present by a compensatory increase in active renin that clinically offsets the antihypertensive action of renin inhibitors. PHARMACOLOGICALLY INDUCED INCREASE IN ATRIAL NATRIURETIC PEPTIDE (ANP): The availability of circulating or tissue ANP may be increased by inhibiting its metabolic clearance by NEP-24.11 inhibitor drugs. These agents induce a reduction in blood pressure and diuretic effects in animal models, and may become a new class of drugs for the clinical management of patients with hypertension and congestive heart failure. OTHER POTENTIAL PHARMACOLOGICAL TARGETS IN THE MANAGEMENT OF HYPERTENSION: There are several potential pharmacological targets that may lead to the development of novel antihypertensive agents in the future. These include the interaction or blockade of vasopressor peptides. Routes of development include neuropeptide Y1 receptor antagonists, which block the postjunctional vasopressor effect of neuropeptide Y, or endothelin antagonists, which block endothelin pressor actions at the endothelin A receptor site. The cardiovascular actions of the functional neuropeptide Y inhibitor alpha-trinositol (PP 56) provide a potential new mechanism for reducing blood pressure in hypertension. In addition, the recent discovery of small molecular agents with high potency and specificity for the endothelin A receptor subtype may also be of value in specific vascular disease states.

CONCLUSIONS

Future development is likely to provide us with novel drugs based on interactions with vasoactive peptides that may improve the management of specific cardiovascular disease states.

Thiophene systems. 14. Synthesis and antihypertensive activity of novel 7-(cyclic amido)-6-hydroxythieno[3,2-b]pyrans and related compounds as new potassium channel activators

The synthesis and antihypertensive activity of novel 7-(cyclic amido)-6-hydroxy-5,5-dimethylthieno[3,2-b]pyrans and related compounds are described. The compounds were tested for oral antihypertensive activity in spontaneously hypertensive rats (SHR) and selected compounds were evaluated in vitro for increases in 86Rb efflux in rabbit isolated mesenteric arteries. The effects on activity in SHR of lactam ring size, the presence of heteroatoms in the lactam ring, the relative stereochemistry at C-6 and C-7, and the substituents on the thiophene ring are examined. The best racemic compound in this series is 32, trans-5,6-dihydro-6-hydroxy-5,5-dimethyl-2-nitro-7-(2-oxopiperidin -1-yl)-5H- thieno[3,2-b]pyran, which is 10-fold more potent than cromakalim with an ED30 = 0.015 mg/kg in SHR. Compound 32 could be resolved and the antihypertensive activity determined to reside primarily in the (6S,7S)-(-)-enantiomer 41. Surprisingly, the elimination of water to give the enamides 50-52, thiophene isosteres of bimakalim, diminishes activity significantly.

New nonpeptide angiotensin II receptor antagonists. 2. Synthesis, biological properties, and structure-activity relationships of 2-alkyl-4-(biphenylylmethoxy)quinoline derivatives

A novel series of nonpeptidic angiotensin II (AII) receptor antagonists is reported, derived from linkage of the biphenylcarboxylic acid or biphenylyltetrazole moiety found in previously described antagonists via a methyleneoxy chain to the 4-position of a 2-alkyl quinoline. When evaluated in an in vitro binding assay using a guinea pig adrenal membrane preparation, compounds in this series generally gave IC50 values in the range 0.01-1 microM. Structure-activity studies showed the quinoline nitrogen atom and a short alkyl chain at the quinoline 2-position to be essential for receptor binding. On intravenous administration in a normotensive rat model, the more potent compounds inhibited the AII-induced pressor response with ED50 values in the range 0.1-2.0 mg/kg. One of the compounds, 2-ethyl-4-[[2'-(1H-tetrazol-5-yl)biphenyl-4-yl]methoxy]quinoline (5g), demonstrated good oral activity in two rat models. At doses in the range 1-10 mg/kg in AII-infused, normotensive rats, the compound exhibited a dose-related inhibition of the pressor response with a good duration of action at the higher doses. In a renal hypertensive rat model, compound 5g showed a rapid and sustained lowering of blood pressure at a dose of 5 mg/kg. On the basis of its profile, this compound, designated ICI D8731, has been selected for clinical evaluation.

Synthesis and biological activity of trans(+-)-N-methyl-2-(3-pyridyl)-2-tetrahydrothiopyrancarbothioamide 1-oxide (RP 49356) and analogues: a new class of potassium channel opener

The synthesis and biological activity of trans-(+-)-N-methyl-2-(3-pyridyl)-2-tetrahydrothiopyrancarbothioamid+ ++ e 1-oxide (8a, RP 49356) and analogues is reported. These compounds constitute a new structural class of K(+)-channel opener. The effects of changes in pyridyl group, thioamide, and thiane ring on in vitro K(+)-channel opening reactivity are discussed. A 3-pyridyl or 3-quinolyl group, a small N-alkyl thioamide function, and a thiane oxide ring, in which the sulfoxide is in a trans relationship to the thioamide, are preferred for activity. Selected compounds were tested intravenously in the normotensive anaesthetized rat for hypotensive effects, and the activities reflect their in vitro K(+)-channel opening activity. This led to further evaluation of compound 8a and the selection of the (-)-enantiomer 8b (RP 52891) for development as an antihypertensive and antianginal agent.

Flavones. 3. Synthesis, biological activities, and conformational analysis of isoflavone derivatives and related compounds

A series of 2-alkylisoflavone derivatives 1 was prepared with the intent to study the importance of the phenyl group (at the 3-position) of the isoflavone in imparting antihypertensive activity and the substitution effects at the 2-position of isoflavone. With the exception of the 2-isopropyl analog, the antihypertensive activity of these compounds appears to have a slow onset and long duration. None of the analogs appears better than the corresponding flavone (3) and 3-phenylflavone (2) analogs. An unsuccessful attempt to correlate the relationship between antihypertensive activity and the calculated torsional angle of C2-C3-C1'-C2' is discussed. Antiinflammatory activities of these compounds along with 7-(oxypropylamine)flavones were also evaluated and found to be not very potent. The antiinflammatory activity appears to be sensitive to steric effects of the alkyl group on the nitrogen and of substituents at the 2-position of the isoflavones, while the hydroxyl group of the propanolamine side chain is not essential.

Dihydropyrimidine calcium channel blockers. 4. Basic 3-substituted-4-aryl-1,4-dihydropyrimidine-5-carboxylic acid esters. Potent antihypertensive agents

We have examined a series of novel dihydropyrimidine calcium channel blockers that contain a basic group attached to either C5 or N3 of the heterocyclic ring. Structure-activity studies show that a 1-(phenylmethyl)-4-piperidinyl carbamate moiety at N3 and sulfur at C2 are optimal for vasorelaxant activity in vitro and impart potent and long-acting antihypertensive activity in vivo. One of these compounds (11) was identified as a lead, and the individual enantiomers 12a (R) and 12b (S) were synthesized. Two key steps of the synthesis were (1) the efficient separation of the diastereomeric ureido derivatives 29a/29b and (2) the high-yield transformation of 2-methoxy intermediates 30a/30b to the (p-methoxybenzyl)thio intermediates 31a/31b. Chirality was demonstrated to be a significant determinant of biological activity, with the dihydropyridine receptor recognizing the enamino ester moiety (12a) but not the carbamate moiety (12b). Dihydropyrimidine 12a is equipotent to nifedipine and amlodipine in vitro. In the spontaneously hypertensive rat, dihydropyrimidine 12a is both more potent and longer acting than nifedipine and compares most favorably with the long-acting dihydropyridine derivative amlodipine. Dihydropyrimidine 12a has the potential advantage of being a single enantiomer.

Novel indolodioxanes with antihypertensive effects: potent ligands for the 5-HT1A receptor

The synthesis and biological evaluation of a new family of tricyclic indolodioxanes is described. These compounds all contain the 2,3-dihydro-7H-1,4-dioxino[2,3-e]indole nucleus and bear substituents at the 2 and/or 8 positions. Thirteen members of this class were prepared and shown to be potent ligands for the 5-HT1A receptor, with several compounds displaying subnanomolar inhibition constants. These compounds also bind to the dopamine D-2 receptor, but generally with higher inhibition constants than those for 5-HT1A. Certain members of this novel structural class show in vivo activity in the mouse hypothermia assay. One of these compounds, U-86192A, has been shown to have antihypertensive effects in the cat, completely eliminating sympathetic nerve discharge at 1 mg/kg iv and lowering mean arterial pressure to 50% pretreatment levels. These effects can be reversed by the administration of spiperone, indicating that U-86192A is acting via a central serotonergic mechanism.