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Due to its function in the rate limiting initial step of the renin-angiotensin system, renin is a particularly promising target for drugs designed to control hypertension, a growing risk to health worldwide. Despite vast efforts over more than two decades, no orally efficacious renin inhibitor had reached the market. As a result of a structure-based topological design approach, we have identified a novel class of small-molecule inhibitors with good oral blood-pressure lowering effects in primates. Further lead optimization aimed for improvement of in vivo potency and duration of action, mainly by P2' modifications at the hydroxyethylene transition-state isostere. These efforts resulted in the discovery of aliskiren (46, CGP060536B, SPP100), a highly potent, selective inhibitor of renin, demonstrating excellent efficacy in sodium-depleted marmosets after oral administration, with sustained duration of action in reducing dose-dependently mean arterial blood pressure. Aliskiren has recently received regulatory approval by the U.S. Food and Drug Administration for the treatment of hypertension.

The action of renin is the rate-limiting step of the renin-angiotensin system (RAS), a key regulator of blood pressure. Effective renin inhibitors directly block the RAS entirely at source and, thus, may provide a vital weapon for hypertension therapy. Our efforts toward identifying novel small-molecule peptidomimetic renin inhibitors have resulted in the design of transition-state isosteres such as 1 bearing an all-carbon 8-phenyl-octanecarboxamide framework. Optimization of the extended P3 portion of 1 and extensive P2' modifications provided analogues with improved in vitro potencies in the presence of plasma. X-ray resolution of rh-renin/38a in the course of SAR work surprisingly unveiled the exploitation of a previously unexplored pocket (S3sp) important for strong binding affinities. Several inhibitors demonstrated oral efficacy in sodium-depleted marmosets. The most potent, 38a, induced dose-dependently a pronounced reduction in mean arterial blood pressure, paralleled by complete blockade of active plasma renin, up to 8 h post-dose. Oral bioavailability of 38a was 16% in marmosets.

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