Renin inhibitors. Dipeptide analogs of angiotensinogen utilizing a dihydroxyethylene transition-state mimic at the scissile bond to impart greater inhibitory potency

Abstract

The synthesis of diol-containing renin inhibitors has revealed that a simple vicinal diol functionality corresponding to the scissile Leu-Val bond in human angiotensinogen is capable of imparting inhibitory activity at a comparable or higher level than either the corresponding aldehyde or hydroxymethyl functionality (compare inhibitors 2a-c or 3a-c). This finding has led to the further optimization of a series of small transition-state analogue inhibitors by the inclusion of a second hydroxyl group in the Leu-Val surrogate to give compounds that inhibited human renin in the 200-700-pM range (e.g. 43, 45, 63, 66). The magnitude of effect of the second hydroxyl group on potency is not only dictated by the absolute stereochemistry of the diol but also by the side chain of the P1 residue. Molecular modeling of the diol-containing inhibitors suggests that one of the hydroxyl groups hydrogen bonds to Asp 32 and Asp 215, while the second hydrogen bonds to Asp 215. These diol inhibitors are extremely selective for human renin over the related enzymes cathepsin D, pepsin, and gastricsin. At high concentrations, compounds containing a leucine or phenylalanine rather than a histidine at the P2 position gave only minor amounts of inhibition of the other enzymes. Inhibitor 43 suppressed plasma renin activity completely and lowered mean blood pressure in monkeys after both intravenous and intraduodenal administration, but the blood pressure drop lasted less than 1 h. Monitoring the blood levels of 43 by enzyme inhibition assay after intraduodenal administration to monkeys or oral administration to rats revealed low absorption and rapid clearance. While intratracheal administration to dogs gave approximately 50% bioavailability, rapid clearance was still a problem. After examination of inhibitor 45 in a sensitive primate model in which monkeys were rendered both hypertensive and hyperreninemic, the effects on lowering systolic but not diastolic pressure were apparent even after 22 h postdosing. Details on the synthesis, in vitro structure-activity relationships, molecular modeling, in vivo activity, and metabolism of these inhibitors are described.

Pyrrolinone-Based Peptidomimetics.“Let the Enzyme or Receptor be the Judge”

“…Elements of several known renin inhibitors23 were employed in our initial design. Ultimately, monopyrrolinone 32 and bispyrrolinone 33 were selected based on modeling studies, and constructed via our first generation synthetic protocol (Figure 6).…”

Renin inhibitors

“…177 Oral administration of the highly insoluble diol inhibitor 12-19 (10 mg/kg in a banana) to renal hypertensive monkeys yielded a prolonged suppression of diastolic blood pressure (>22 h), although systolic pressure (and presumably plasma renin activity) returned to pretreatment levels. 160 Although comparisons of effects of renin inhibitors on PRA and BP after intravenous versus oral administration might suggest oral absorption in the 5-15% range for some, it is likely that without formulation, none is more than 5% absorbed.…”

Discovery of a well-absorbed, efficacious renin inhibitor, A-74273.

“…Several in vitro techniques for the determination of potency and specificity based on inhibition of activity have been described previously: purified human renal renin, pH 6.0, 13 human plasma renin, pH 7.4, 14 bovine cathepsin D, 13 porcine pepsin, 13 human gastricsin, 15 and human pepsin. 15 The IQo values for animal plasma renins determined at pH 7.4 were quantified by a modification of the human plasma assay in the presence of 3 mM ethylenediaminetetraacetic acid (EDTA), 1.4 mM phenylmethylsulfonyl fluoride (PMSF), and 1% dimethyl sulfoxide 14 ; the respective incubation times at 37°C and the fractions of incubate used for the radioimmunoassay of angiotensin I (Ang I) were 1 hour and 100% for the monkey, 1 hour and 50% for the ferret, 1 hour and 40% for the dog, and 1 hour and 100% for the rat. To avoid possible overestimation of activity, 8-hydroxyquinoline was omitted from the assay.…”