Inhibition of thermolysin and neutral endopeptidase 24.11 by a novel glutaramide derivative: X-ray structure determination of the thermolysin-inhibitor complex.

Determination of the X-ray structure of thermolysin-inhibitor complexes has proven useful in aiding our understanding of the mode of binding of inhibitors of related, physiologically important, mammalian zinc peptidases including neutral endopeptidase EC 3.4.24.11 and angiotensin-converting enzyme. Here we describe the mode of binding to crystalline thermolysin of N-[1-(2(R,S)-carboxy-4-phenylbutyl)-cyclopentylcarbonyl]-(S) -tryptophan (CCT). CCT is an analogue of both candoxatrilat, a potent inhibitor of neutral endopeptidase 24.11, and of the 5-indanyl ester prodrug candoxatril, which is under clinical evaluation as a potential therapy for congestive heart failure. CCT differs from the previously studied N-carboxyalkyl dipeptide CLT [N-(S)-(1-carboxy-3-phenylpropyl)-(S)-leucyl-(S)-tryptophan] in several important respects. It has a highly constrained gem-cyclopentyl P1' substituent and lacks the characteristic imino nitrogen substituent of CLT. The structure determination shows that, notwithstanding the conformational influence of the gem-cyclopentyl substituent, CCT binds within the active site of thermolysin in a similar manner to CLT. Although the characteristic hydrogen bond between the imino nitrogen of CLT and thermolysin is absent in CCT, the affinities of the two inhibitors for the enzyme are virtually identical. These results illustrate the importance of considering not only those hydrogen bonds that are formed in an enzyme-ligand complex but also the other hydrogen bonds that may be lost due to desolvation of the enzyme and ligand on formation of the complex. In addition, the overall conformational demands placed upon a ligand in order to achieve receptor interaction may be critically important.

UK-69,578, a novel inhibitor of EC 3.4.24.11 which increases endogenous ANF levels and is natriuretic and diuretic.

A search for potent inhibitors of EC 3.4.24.11, an enzyme which is found most abundantly in the kidney and which degrades atrial natriuretic factor, has led to the identification of UK-69,578. Structure-activity studies starting from substituted N-carboxymethyl dipeptide inhibitors resulted in the introduction of a cyclo-alkane P1' residue and in the replacement of the aza-link between P1 and P1' residues by a methylene group, with a net ten-fold potency gain. UK-69,578 increases endogenous ANF levels and produces natriuretic and diuretic responses intravenously in mice.

2,4-Diamino-6,7-dimethoxyquinazolines. 4. 2-[4-(substituted oxyethoxy) piperidino] derivatives as alpha 1-adrenoceptor antagonists and antihypertensive agents.

A series of 4-amino-6,7-dimethoxy-2-[4-(substituted oxyethoxy)piperidino] quinazoline derivatives (2) was synthesized and evaluated for alpha-adrenoceptor affinity and antihypertensive activity. Most compounds showed binding affinities within the nanomolar range for alpha 1-receptors, although 25 and 26 showed enhanced potency (Ki, ca. 1.5 X 10(-10) M), equivalent to that of prazosin. Series 2 also displaced [3H]clonidine from alpha 2-adrenoceptors, but at relatively high doses of 10(-6) M, and selectivity for alpha 1 sites still predominated. In a rabbit pulmonary artery preparation, 12, 16, and 25 were potent antagonists of the alpha 1-mediated, postjunctional vasoconstrictor activity of norepinephrine with no effect at the prejunctional alpha 2 sites which modulate transmitter release. Physicochemical measurements gave a pKa of 7.63 +/- 0.10 for 12, and N-1 protonation will be favored (60%) at physiological pH to provide the alpha 1-adrenoceptor pharmacophore, 28. Antihypertensive activity of series 2 was evaluated following oral administration to spontaneously hypertensive rats, and blood pressure was measured after 1 and 6 h. Compounds 12, 13, 16, 23, and 37 displayed moderate efficacy and duration of action in lowering blood pressure, but the plasma half-life (ca. 2 h) of 16 in dogs was not compatible with potential once-daily administration in humans.

2,4-Diamino-6,7-dimethoxyquinazolines. 2. 2-(4-Carbamoylpiperidino) derivatives as alpha 1-adrenoceptor antagonists and antihypertensive agents.

A series of 4-amino-2-(4-carbamoylpiperidino)-6,7-dimethoxyquinazolines (2) were synthesized and evaluated for alpha-adrenoceptor affinity and antihypertensive activity. These compounds displayed high binding affinity (Ki, 10(-9)-10(-10) M) and selectivity for alpha 1-adrenoceptors in vitro, and 12, 14, 21-26, and 29 showed similar potency to prazosin. Compounds 26 and 28 were also shown to be competitive antagonists of the postjunctional, vasoconstrictor action of norepinephrine with no significant activity at prejunctional alpha 2-sites. The high binding affinity for series 2 is rationalized in terms of enhanced basicity of the quinazoline nucleus (pKa's: 12, 7.38; 26, 7.53; prazosin, 6.8) and hydrophobic interactions of the carbamoyl substituents. Molecular mechanics calculations and computer-assisted superimposition suggest that the quinazoline 2-substituents in prazosin and 2 occupy the alpha 1-adrenoceptor site in different manners. Antihypertensive activity was evaluated after oral administration (5 mg/kg) to spontaneously hypertensive rats, and 11, 15, 21, 22, and 26 displayed sustained prazosin-like efficacy at the 6-h time point. The high alpha 1-adrenoceptor affinity demonstrated by series 2 in vitro suggests that these marked, and prolonged, falls in blood pressure result from selective blockade of the alpha 1-mediated vasoconstrictor effects of norepinephrine.

Promotion of carbohydrate oxidation in the heart by some phenylglyoxylic acids.

A series of phenylglyoxylic acids is described, many of which are able to promote carbohydrate oxidation in muscle tissue, thereby favorably altering the carbohydrate/fatty acid balance in situations where fatty acid utilization is elevated. Such situations are reported to occur in ischemic heart disease, particularly following myocardial infection. In an attempt to effectively deliver the phenylglyoxylic acids to the site of action within the cell, the L-(+)-phenylglycines were employed as prodrugs. These are known to be transaminated to phenylglyoxylic acids. L-(+)-2-(4-Hydroxyphenyl)glycine (25, oxfenicine) has been selected for clinical evaluation.