Potent Macrocyclic Inhibitors of Insulin-Regulated Aminopeptidase (IRAP) by Olefin Ring-Closing Metathesis

Department of Medicinal Chemistry, Uppsala University, Uppsala, Sweden.
Journal of Medicinal Chemistry (Impact Factor: 5.45). 06/2011; 54(11):3779-92. DOI: 10.1021/jm200036n
Source: PubMed

ABSTRACT Macrocyclic analogues of angiotensin IV (Ang IV, Val(1)-Tyr(2)-Ile(3)-His(4)-Pro(5)-Phe(6)) targeting the insulin-regulated aminopeptidase (IRAP) have been designed, synthesized, and evaluated biologically. Replacement of His(4)-Pro(5)-Phe(6) by a 2-(aminomethyl)phenylacetic acid (AMPAA) moiety and of Val(1) and Ile(3) by amino acids bearing olefinic side chains followed by macrocyclization provided potent IRAP inhibitors. The impact of the ring size and the type (saturated versus unsaturated), configuration, and position of the carbon-carbon bridge was assessed. The ring size generally affects the potency more than the carbon-carbon bond characteristics. Replacing Tyr(2) by β(3)hTyr or Phe is accepted, while N-methylation of Tyr(2) is deleterious for activity. Removal of the carboxyl group in the C-terminal slightly reduced the potency. Inhibitors 7 (K(i) = 4.1 nM) and 19 (K(i) = 1.8 nM), both encompassing 14-membered ring systems connected to AMPAA, are 10-fold more potent than Ang IV and are also more selective over aminopeptidase N (AP-N). Both compounds displayed high stability against proteolysis by metallopeptidases.

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    • "), with the D-Nva analog (IVDE78) being somewhat less potent. The compound IVDE77 displayed an almost 40 times higher affinity (pK i 8.77) compared to Ang IV, thus being the Ang IV-analogue with the highest affinity for IRAP known at present (Albiston et al., 2011; Andersson et al., 2011). "
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    ABSTRACT: The hexapeptide angiotensin IV (Ang IV) induces diverse biological effects such as memory enhancement and protection against ischemic stroke. Studies on the mechanism of Ang IV however are hampered by its instability and its lack of selectivity. The high-affinity binding site for Ang IV is the insulin-regulated aminopeptidase (IRAP, EC, but Ang IV also acts as a weak agonist for the Ang II-receptor (AT(1)), implying the need for stable and highly selective Ang IV-analogues. Here we present the screening of novel Ang IV-analogues, selected on basis of high affinity for IRAP, high selectivity (compared to aminopeptidase N and the AT(1) receptor) and resistance against proteases. The selected compound IVDE77 possesses a number of advantages compared to Ang IV: (i) it has a 40 times higher affinity for IRAP (K(i) 1.71nM), (ii) it does not activate the AT(1) receptor, (iii) it is easily radiolabeled with tritium and (iv) it is resistant to proteolysis, even in human plasma. In addition, pre-treatment of intact CHO-K1 cells with IVDE77 led to a virtually complete inhibition of subsequent intracellular accumulation of [(3)H]IVDE77-IRAP complexes. IVDE77 thus represents the first Ang IV-analogue able to abolish IRAP-availability completely at the cell surface in vitro. In summary, IVDE77 is a useful tool for the detection of IRAP under physiological conditions, and may contribute to elucidating the mechanism of Ang IV to ascertain which functions are IRAP-dependent.
    European journal of pharmacology 01/2013; 702(1-3). DOI:10.1016/j.ejphar.2013.01.026 · 2.53 Impact Factor
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    • "In the absence of chelators, the binding affinity of the 14-membered macrocyclic compounds to IRAP is 10 times higher than that of Ang IV. N-Methylation of the peptide bond between residues one and two reduces the activity, suggesting that the amide nitrogen and the N-terminal primary amine nitrogen are coordinated to the zinc atom in the active site of the protease [179]. Incorporation of a methylene group adjacent to the N-terminal amino group, as in AL-11 and AL-40 (Figure 9), and replacement of the C-terminal carboxyl group with bioisosteres seem to be the obvious next steps in efforts to improve the inhibitors. "
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    ABSTRACT: The hexapeptide angiotensin IV (Ang IV) is a metabolite of angiotensin II (Ang II) and plays a central role in the brain. It was reported more than two decades ago that intracerebroventricular injection of Ang IV improved memory and learning in the rat. Several hypotheses have been put forward to explain the positive effects of Ang IV and related analogues on cognition. It has been proposed that the insulin-regulated aminopeptidase (IRAP) is the main target of Ang IV. This paper discusses progress in the discovery of inhibitors of IRAP as potential enhancers of cognitive functions. Very potent inhibitors of the protease have been synthesised, but pharmacokinetic issues (including problems associated with crossing the blood-brain barrier) remain to be solved. The paper also briefly presents an overview of the status in the discovery of inhibitors of ACE and renin, and of AT1R antagonists and AT2R agonists, in order to enable other discovery processes within the RAS system to be compared. The paper focuses on the relationship between binding affinities/inhibition capacity and the structures of the ligands that interact with the target proteins.
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