New renin inhibitors with pseudodipeptidic units in P(1)-P(1') and P(2')-P(3') positions

Non-Canonical Amino Acids in Analyses of Protease Structure and Function

All known organisms encode 20 canonical amino acids by base triplets in the genetic code. The cellular translational machinery produces proteins consisting mainly of these amino acids. Several hundred natural amino acids serve important functions in metabolism, as scaffold molecules, and in signal transduction. New side chains are generated mainly by post-translational modifications, while others have altered backbones, such as the β- or γ-amino acids, or they undergo stereochemical inversion, e.g., in the case of D-amino acids. In addition, the number of non-canonical amino acids has further increased by chemical syntheses. Since many of these non-canonical amino acids confer resistance to proteolytic degradation, they are potential protease inhibitors and tools for specificity profiling studies in substrate optimization and enzyme inhibition. Other applications include in vitro and in vivo studies of enzyme kinetics, molecular interactions and bioimaging, to name a few. Amino acids with bio-orthogonal labels are particularly attractive, enabling various cross-link and click reactions for structure-functional studies. Here, we cover the latest developments in protease research with non-canonical amino acids, which opens up a great potential, e.g., for novel prodrugs activated by proteases or for other pharmaceutical compounds, some of which have already reached the clinical trial stage.

Novel renin inhibitors containing derivatives of N-alkylleucyl-β-hydroxy-γ-amino acids

In search for new drugs lowering arterial blood pressure, which could be applied in anti-hypertensive therapy, research concerning agents blocking of renin-angiotensin-aldosteron system has been conducted. Despite many years of research conducted at many research centers around the world, aliskiren is the only one renin inhibitor, which is used up to now. Four novel potential renin inhibitors, having structure based on the peptide fragment 8-13 of human angiotensinogen, a natural substrate for renin, were designed and synthesized. All these inhibitors contain unnatural moieties that are derivatives of N-methylleucyl-β-hydroxy-γ-amino acids at the P2-P1' position: 4-[N-(N-methylleucyl)-amino]-3-hydroxy-7-(3-nitroguanidino)-heptanoic acid (AHGHA), 4-[N-(N-methylleucyl)-amino]-3-hydroxy-5-phenyl-pentanoic acid (AHPPA) or 4-[N-(N-methylleucyl)-amino]-8-benzyloxycarbonylamino-3-hydroxyoctanoic acid (AAHOA). The previously listed synthetic β-hydroxy-γ-amino acids constitute pseudodipeptidic units that correspond to the P1-P1' position of the inhibitor molecule. An unnatural amino acid, 4-methoxyphenylalanin (Phe(4-OMe)), was introduced at the P3 position of the obtained compounds. Three of these compounds contain isoamylamide of 6-aminohexanoic acid (ε-Ahx-Iaa) at the P2'-P3' position. The proposed modifications of the selected human angiotensinogen fragment are intended to increase bioactivity, bioavailability, and stability of the inhibitor molecule in body fluids and tissues. The inhibitor Boc-Phe(4-OMe)-MeLeu-AHGHA-OEt was obtained in the form of an ethyl ester. The hydrophobicity coefficient, expressed as log P varied between 3.95 and 8.17. In vitro renin inhibitory activity of all obtained compounds was contained within the range 10(-6)-10(-9) M. The compound Boc-Phe(4-OMe)-MeLeu-AHPPA-Ahx-Iaa proved to be the most active (IC50 = 1.05 × 10(-9) M). The compounds Boc-Phe(4-OMe)-MeLeu-AHGHA-Ahx-Iaa and Boc-Phe(4-OMe)-MeLeu-AHPPA-Ahx-Iaa are resistant to chymotrypsin.

Discovery of highly potent renin inhibitors potentially interacting with the S3' subsite of renin

To exploit the S3' subsite of renin active site for renin inhibitor design, 42 aliskiren derivatives with modified P2' portion were designed, synthesized and biologically evaluated. Some highly potent renin inhibitors (IC₅₀ < 3 nM) were identified, among which compounds 38 (IC₅₀ = 0.9 nM) and 39 (IC₅₀ = 0.7 nM) were over 2.5-fold more potent than aliskiren (IC₅₀ = 2.3 nM). SAR analysis indicated that incorporation of polar hydrophilic moieties into the P2' portion of renin inhibitors generally enhanced the potency. Consistently with this, molecular modeling study revealed that the triazole part of 39 could provide additional interactions to the S3' subsite of renin active site. Moreover, in vivo evaluation in the double transgenic mouse hypertension model demonstrated that 39 produced greater reduction of the mean arterial blood pressure than ariskiren at the doses of 17.0 and 34.0 μmol/kg, respectively. Taken together, the S3' subsite of renin active site merits further consideration for renin inhibitor design.

Direct Inhibition of Renin as a Cardiovascular Pharmacotherapy

The important role of renin-angiotensin-aldosterone system blockade in the treatment of systemic hypertension, heart failure, diabetic kidney disease, and atherogenesis has been clearly established. The theoretical therapeutic advantages for inhibiting the detrimental effects of the renin-angiotensin system at its most upstream point have served as the impetus for the development of renin inhibitors. The advent of aliskiren, the first in a novel class of orally active, nonpeptide, highly specific, human renin inhibitors, provides a new modality in the armamentarium of renin-angiotensin system antagonists. Studies in marmosets and rats demonstrated that aliskiren reduced blood pressure in a dose-dependent manner and is highly efficacious in blocking plasma renin activity with parallel reductions in the levels of the other downstream constituents of the renin-angiotensin system. Clinical trials in hypertensive patients have confirmed these benefits with aliskiren whose blood pressure-lowering efficacy is similar to or better than those of standard therapeutic doses of enalapril, losartan, irbesartan, and hydrochlorothiazide. Aliskiren is well tolerated, with few reported adverse effects even at the highest doses tested. Given the established beneficial effects of angiotensin-converting enzyme inhibitors and angiotensin receptor blockers in the treatment of cardiovascular and renovascular diseases, future studies may further elucidate a similar protective role for aliskiren both as a monotherapy and as part of a combination therapy.

New renin inhibitors containing pseudodipeptidic units in P3-P2 and P1-P1' positions

A series of four non-peptidic renin inhibitors have been designed and synthesized. All of them contain in their molecule (3S,4S)-4-amino-5-cyclohexyl-3-hydroxypentanoic acid (ACHPA), a hydrophobic portion at the C-terminus and a second dipeptide-like transition state analog or unnatural dipeptidic fragment at the N-terminus. Inhibitory activity of the compounds was measured in vitro by high performance liquid chromatography (HPLC). Their IC50 (M/l) values were: <10(-3) (12), 1.0 x 10(-6) (19), 4.0 x 10(-4) (23) and 1.0 x 10(-6) (29), respectively. All the compounds are stable against chymotrypsin.