Stereospecific inhibition of CETP by chiral N,N-disubstituted trifluoro-3-amino-2-propanols.

Chiral N,N-disubstituted trifluoro-3-amino-2-propanols represent a recently discovered class of compounds that inhibit the neutral lipid transfer activity of cholesteryl ester transfer protein (CETP). These compounds all contain a single chiral center that is essential for inhibitory activity. (R,S)SC-744, which is composed of a mixture of the two enantiomers, inhibits CETP-mediated transfer of [(3)H]cholesteryl ester ([(3)H]CE) from HDL donor particles to LDL acceptor particles with an IC(50) = 200 nM when assayed using a reconstituted system in buffer and with an IC(50) = 6 microM when assayed in plasma. Upon isolation of the enantiomers, it was found that the (R,+) enantiomer, SC-795, was about 10-fold more potent than the mixture, and that the (S,-) enantiomer, SC-794, did not have significant inhibitory activity (IC(50) > 0.8 microM). All of the activity of the (S,-)SC-794 enantiomer could be accounted for by contamination of this sample with a residual 2% of the highly potent (R,+) enantiomer, SC-795. The IC(50) of (R,+)SC-795, 20 nM, approached the concentration of CETP (8 nM) in the buffer assay. These chiral N,N-disubstituted trifluoro-3-amino-2-propanols were found to associate with both LDL and HDL, but did not disrupt overall lipoprotein structure. They did not affect the on or off rates of CETP binding to HDL disk particles. Inhibition was highly specific since the activities of phospholipid transfer protein and lecithin cholesterol acyl transferase were not affected. Competition experiments showed that the more potent enantiomer (R)SC-795 prevented cholesteryl ester binding to CETP, and direct binding experiments demonstrated that this inhibitor bound to CETP with high affinity and specificity. It is estimated, based on the relative concentrations of inhibitor and lipid in the transfer assay, that (R)SC-795 binds approximately 5000-fold more efficiently to CETP than the natural ligand, cholesteryl ester. We conclude that these chiral N,N-disubstituted trifluoro-3-amino-2-propanol compounds do not affect lipoprotein structure or CETP-lipoprotein recognition, but inhibit lipid transfer by binding to CETP reversibly and stereospecifically at a site that competes with neutral lipid binding.

Effects of SC-52458, an angiotensin AT1 receptor antagonist, in the dog.

We have previously reported on the basic pharmacologic properties of SC-52458 (5-[(3,5-dibutyl-1H-1,2,4-triazol-1-yl) methyl]-2-[2-(1H-tetrazol-5-ylphenyl)]pyridine), a novel angiotensin (AII) receptor antagonist that binds potently to AT1 receptors in rat adrenal cortex and blocks AII-mediated contraction in isolated rabbit aorta. In the present study, the ability of SC-52458 to block AII pressor responses in conscious dogs was measured. In addition, we determined whether SC-52458 lowered mean arterial pressure in dogs with 2 kidney/1 clip renal hypertension when given daily for 4 days. In conscious, normotensive dogs, SC-52458 at 30 mg/kg orally, blocked the pressor response to AII (50 ng/kg, intravenously) with maximal inhibition (91%) observed 2 h after dosing. Plasma concentrations of SC-52458 measured by HPLC also were highest at the 2-h time point. After 24 h, the AII pressor response remained inhibited (by 35%) and SC-52458 was still measurable in plasma from treated dogs. In dogs made hypertensive by constriction of the left renal artery, SC-52458 lowered mean arterial pressure compared to vehicle treatment although heart rate was not different in the two groups. The maximal blood pressure lowering achieved with SC-52458 was similar to the maximal effect observed with the angiotensin converting enzyme inhibitor lisinopril. We conclude that SC-52458 blocks AII mediated pressor responses in normotensive, conscious dogs and SC-52458 is an efficacious antihypertensive agent in dogs with 2 kidney/1 clip renal hypertension.

Effects of SC-56525, a potent, orally active renin inhibitor, in salt-depleted and renal hypertensive dogs.

SC-56525 is a nanomolar inhibitor of plasma renin activity in human, cynomolgus monkey, dog, guinea pig, Yucatan micropig, and rabbit but is less active in rat. The oral bioavailability of SC-56525 in conscious dogs at doses of 5 mg/kg IV and 30 mg/kg PO was 66.1 +/- 16.4%. Oral dosing with SC-56525 at 3, 10, and 30 mg/kg in salt-depleted dogs induced a dose-dependent reduction in mean arterial pressure and inhibition of plasma renin activity with no significant effect on heart rate. In two-kidney, one clip renal hypertensive dogs, SC-56525 given orally at 10, 30, and 60 mg/kg daily for 4 days lowered blood pressure significantly. In conscious dogs monitored in their home cages via radiotelemetry, no significant changes in heart rate occurred in response to large drops in blood pressure in both renal hypertensive and salt-depleted dogs with the renin inhibitor SC-56525. SC-56525 is a nanomolar, orally active inhibitor of renin and effectively lowers blood pressure in both salt-depleted and renal hypertensive dogs.

A new class of orally active glycol renin inhibitors containing phenyllactic acid at P3.

We prepared a new series of renin inhibitors based on dipeptide glycols, replacing the P4-P3 subsites with an O-(N-morpholinocarbonyl)-3-L-phenyllactic acid residue. This modification proved bioisosteric with Boc-L-phenylalanine, giving rise to highly potent human renin inhibitors (1-5 nM), e.g., SC-46944 (IC50 = 5 nM). Moreover, this change produced compounds that are orally efficacious in reducing plasma renin activity in salt-depleted marmosets.

Enhanced potency dipeptide glycol renin inhibitors: studies in vitro and in the conscious rhesus.

We prepared a series of novel dipeptide amides of the formula Boc-Phe-Leu-X, where X is a 3-amino-3-alkyl-1,2-propanediol with lower alkyl substitutions at C-1, in order to probe accessory binding sites in the enzyme renin. This approach was successful in generating potent inhibitors of human and hog renin in vitro. Moreover, these inhibitors were able to effect in vivo reduction of plasma renin activity (PRA) in the conscious salt-depleted rhesus monkey (i.v. route); this effect was related to the size of the C-1 alkyl group.

Dipeptide glycols: a new class of renin inhibitors.

The discovery of a new class of novel renin inhibitors consisting of protected dipeptide amides derived from aminoglycols (Formula I) prompted a study of structure-activity in vitro and efficacy in vivo. Thus, Boc-L-Phe-N-[(1S,2R)-1-benzyl-(2,3-dihydroxy)propyl]-L-leucinamide (1) and the corresponding histidinamide (2) inhibit human renin in vitro (IC50: 8.7 X 10-6 M and 2.6 X 10-6 M, respectively). Compound 1 has a slight inhibitory effect on pepsin and compound 2 does not inhibit pepsin at all (at 10-4M); these compounds are inactive against rat renin. Compound 1 is efficacious in lowering plasma renin activity in the Rhesus monkey (i.v.). Results indicate that this new class of low molecular weight inhibitors is specific for human renin and thus constitutes a new source of drug candidates.

New class of inhibitors specific for human renin.

Seven active tetrapeptide amides characterized by a C-terminal phenylalanyl aminoadamantane (PheNHAd) sequence, were identified by selective testing for human renin inhibitory activity among compounds with adjacent hydrophobic groups and molecular size equivalent to 3-5 amino acid residues. The new inhibitors were compared with known renin inhibitors (RIP, pepstatin, H-77) and opioid analgesic agents (Met-enkephalin, morphine), with the following results: The new inhibitors were active against human renin (IC50 approximately 10-5M), but inactive against rat renin and pepsin. Although active in opiate receptor binding studies (IC50 approximately 10(-7)M), they were, with few exceptions, inactive in the mouse writhing and hot plate tests for analgesia. SAR studies suggested a separation of the renin inhibitory from the analgesic activity of enkephalin analogs. Preliminary experiments with sodium-depleted rhesus monkeys indicated hypotensive activity for three of the new inhibitors at 3 mg/kg i.v., and RIP at 1 mg/kg. The recently reported clinical hypotensive properties of RIP (Zusman et al., Trans. Assoc. Am. Physicians 96:365, 1983) along with the present comparative studies suggest that the new inhibitors may lead to clinically useful agents.