Angiotensin-converting enzyme inhibitors. 2. Perhydroazepin-2-one derivatives

Enantioselective Nickel-Catalyzed Migratory Hydrocyanation of Nonconjugated Dienes

Metal-catalyzed chain-walking reactions have recently emerged as a powerful strategy to functionalize remote positions in organic molecules. However, a chain-walking protocol for nonconjugated dienes remains scarcely reported, and developments are currently ongoing. In this Communication, a nickel-catalyzed asymmetric hydrocyanation of nonconjugated dienes involving a chain-walking process is demonstrated. The reaction exhibits excellent regio- and chemoselectivity, and a wide range of substrates were tolerated, delivering the products in high yields and enantioselectivities. Deuterium-labeling experiments support the chain-walking process, which involves an iterative β-H elimination and reinsertion processes. Gram-scale synthesis, regioconvergent experiments, and downstream transformations gave further insights into the high potential of this transformation.

Palladium-Catalyzed Enantioselective Relay Heck Arylation of Enelactams: Accessing α,β-Unsaturated δ-Lactams

In this Communication, we describe the construction of chiral α,β-unsaturated δ-lactams, widely used as pharmacophores, in high yields and excellent enantioselectivities using an oxidative relay Heck arylation reaction. This strategy also allows facile access to 7-substituted α,β-unsaturated ε-lactam products and δ-lactams containing a tetrasubstituted nitrogen-bearing stereocenter.

Synthesis of γ-, δ-, and ε-lactams by asymmetric transfer hydrogenation of N-(tert-butylsulfinyl)iminoesters

Highly enantiomerically enriched γ- and δ-lactams have been prepared by a simple and very efficient procedure that involves the asymmetric transfer hydrogenation of N-(tert-butylsulfinyl)iminoesters followed by desulfinylation of the nitrogen atom and spontaneous cyclization to the desired lactams during the basic workup procedure. Five- and six-membered ring lactams bearing aromatic, heteroaromatic, and aliphatic substituents have been obtained in very high yields and ee's up to >99%. A slight modification of the procedure also allowed the preparation of ε-lactams in good yields and very high enantioselectivities. Both enantiomers of the final lactams could be prepared with equal efficiency by changing the absolute configuration of the sulfinyl chiral auxiliary.

Matrix metalloproteinase-2 inhibition by temocapril and its important role in peritoneal transport

1. Matrix metalloproteinase (MMP)-2 plays an important role in tissue remodelling during peritoneal injury caused by peritoneal dialysis (PD), but MMP-2 inhibitors have not yet been used clinically. Recently, it was reported that captopril, an angiotensin-converting enzyme inhibitor (ACEI), can inhibit MMP-2. 2. To investigate the potential usefulness of ACEI during PD, the molecular interaction between the MMP-2 active site and the active form of temocapril (temocaprilat) was investigated using molecular modelling. Furthermore, the effects of temocapril on MMP-2 activity in peritoneal effluents and the peritoneal solute transport rate of PD patients were determined. 3. Temocaprilat bound to the MMP-2 active centre and recognized two hydrophobic substrate-binding sites in the MMP-2 molecular model. Matrix metalloproteinase-2 activity in peritoneal effluents was directly inhibited by temocaprilat (IC(50) 0.47 μmol/L). In one patient given temocapril, the peritoneal solute transport rate decreased gradually during PD. 4. Temocapril may prove to be an important candidate for development as a novel therapeutic agent for MMP-2 inhibition to prevent peritoneal injury caused by PD.

Influence of ionization state on the activation of temocapril by hCES1: a molecular-dynamics study

Temocapril is a prodrug whose hydrolysis by carboxylesterase 1 (CES1) yields the active ACE inhibitor temocaprilat. This molecular-dynamics (MD) study uses a resolved structure of the human CES1 (hCES1) to investigate some mechanistic details of temocapril hydrolysis. The ionization constants of temocapril (pK1 and pK3) and temocaprilat (pK1, pK2, and pK3) were determined experimentally and computationally using commercial algorithms. The constants so obtained were in good agreement and revealed that temocapril exists mainly in three ionic forms (a cation, a zwitterion, and an anion), whereas temocaprilat exists in four major ionic forms (a cation, a zwitterion, an anion, and a dianion). All these ionic forms were used as ligands in 5-ns MS simulations. While the cationic and zwitterionic forms of temocapril were involved in an ion-pair bond with Glu255 suggestive of an inhibitor behavior, the anionic form remained in a productive interaction with the catalytic center. As for temocaprilat, its cation appeared trapped by Glu255, while its zwitterion and anion made a slow departure from the catalytic site and a partial egress from the protein. Only its dianion was effectively removed from the catalytic site and attracted to the protein surface by Lys residues. A detailed mechanism of product egress emerges from the simulations.

Potent, orally bioavailable calcitonin gene-related peptide receptor antagonists for the treatment of migraine: discovery of N-[(3R,6S)-6-(2,3-difluorophenyl)-2-oxo-1- (2,2,2-trifluoroethyl)azepan-3-yl]-4- (2-oxo-2,3-dihydro-1H-imidazo[4,5-b]pyridin- 1-yl)piperidine-1-carboxamide (MK-0974)

Calcitonin gene-related peptide (CGRP) has been implicated in the pathogenesis of migraine. Herein we describe optimization of CGRP receptor antagonists based on an earlier lead structure containing a (3R)-amino-(6S)-phenylcaprolactam core. Replacement of the phenylimidazolinone with an azabenzimidazolone gave stable derivatives with lowered serum shifts. Extensive SAR studies of the C-6 aryl moiety revealed the potency-enhancing effect of the 2,3-difluorophenyl group, and trifluoroethylation of the N-1 amide position resulted in improved oral bioavailabilities, ultimately leading to clinical candidate 38 (MK-0974).

Caprolactams as potent CGRP receptor antagonists for the treatment of migraine

Calcitonin gene-related peptide (CGRP) has been implicated in the pathogenesis of migraine. Replacements for the benzodiazepine core of an earlier lead structure 1 including 5-, 6-, and 7-membered lactams were explored. Within the 7-membered ring scaffold, phenyl substitution at various positions afforded the potent (3R)-amino-(6S)-phenyl caprolactam template. The phenylimidazolinone privileged structure gave additional potency enhancements, as 24 showed good potency in both CGRP binding (K(i)=2 nM) and cAMP (IC(50)=4 nM) assays and was orally bioavailable in rats (27%).

A novel route to synthesize Freidinger lactams by micowave irradiation*

The incorporation of a Freidinger-like lactam structure into the backbone of peptides has been proven to be an useful strategy in the design of a variety of conformationally restricted targets. Several different strategies have been developed toward Freidinger lactams but no one resulted to be completely facile. Here, we report an efficient strategy that involves the iodo-derivatives in side chain of an appropriate amino acid used as electrophilic agent, and the standard solid phase peptide synthesis assisted by microwave irradiation. The methodology developed could be useful to perform Freidinger-like lactams with defined stereochemistry for routine use in solid phase peptide chemistry.

Homologs of 1,2,5-hexahydro-3-one-1H-1,4-diazepine (DAP) as novel dipeptidomimetics and molecular scaffolds: efficient preparation of synthons

Structurally constraint dipeptidomimetics represent an important class of conformationally rigid dipeptide surrogates and molecular scaffolds, which are frequently employed in peptide-based structure-activity relationships (SAR) and construction of combinatorial libraries. We report on the design of an improved and general synthetic procedure to prepare synthons related to the trisubstituted 1,2,5-hexahydro-3-one-1H-1,4-diazepines [DAP(Xxx)(alpha7)] (DAP: 1,2,5-hexahydro-3-one-1H-1,4-diazepine; DAP(Xxx)(alpha7): the homologous series of DAP in which alpha refers to the location of the chiral carbon in the i(th) amino acid, Xxx represents the three letter notation for the i-1 amino acids, and 7 denotes the number of atoms in the ring) and their higher homologs [DAP(Xxx)(alphaN)] [Xxx = Phe, Asp(beta-OcHex) (cHex: cyclohexyl), and Arg(N(G)-Tos] (Tos: p-toluenesulfonyl); N = 8-10]. These dipetidomimetic structures are generated by reductive alkylation-mediated Calpha(i)-to-N(i-1) bridging between a Calpha (i)-(CH(2))(i-1)(n)-COSEt (n = 1-4) and H(2)N-C(i-1)HR-CO(2)Fm (Fm: 9-fluorenylmethyl) followed by H(2)N(i)-to-C(i-1)-CO(2)H lactam formation. We also describe the preparation of blocked N-Ac-[DAP(Phe)(alphaN)]-CONMe(2) (N = 8-10), which serve as model systems for detailed conformational analysis reported in the accompanying article.

Improved electron-conformational method of pharmacophore identification and bioactivity prediction. Application to angiotensin converting enzyme inhibitors

The electron-conformational (EC) method of pharmacophore (Pha) identification and bioactivity prediction, suggested earlier, is given here two major improvements. First, an atomic index of orbital and charge controlled interaction is introduced to better represent the ligand (substrate) in its interaction with the bioreceptor. Second, the multiconformational problem is considered in view of ligand-receptor binding states, resulting in essential simplification of the expression of bioactivity. The details of the improved EC method are demonstrated in application to the problem of angiotensin converting enzyme (ACE) inhibitors. The Pha of the latter is identified by separation of the heavily populated conformations of the chosen 51 compounds (the training set), calculation of the electronic structure, construction of their EC matrixes of congruity, and processing of the latter in comparison with the activities to reveal a common submatrix of all the active only compounds that describes the Pha. The latter contains three oxygen atoms plus a fourth atom X = S, N, O at certain interatomic distances and with restricted electronic parameters (within assumed tolerances), the position of the atom X being more changeable from one active compound to another. For quantitative prediction of the bioactivity, an expression is deduced which takes into account the duly parametrized influence of auxiliary groups (AG) which, being positioned outside the Pha, either diminish the activity (antipharmacophore shielding) or enhance it. It is shown that in case of many conformations of the same compound only one of them, that of the lowest energy which has the Pha, should be parametrized. The 15 parameters chosen to represent the AG in case of ACE inhibitors are weighted by variational (adjustable) coefficients which are determined from a regression treatment of the calculated versus known activities in the training set. Then the formulas with known coefficients are used to validate the method by calculating the bioactivity of other compounds not used in the training set. The prediction of the activity proved to be more than 90% (within experimental error and available compounds) qualitatively (yes, no) and about 60%-70% quantitatively.

Dual metalloprotease inhibitors. 6. Incorporation of bicyclic and substituted monocyclic azepinones as dipeptide surrogates in angiotensin-converting enzyme/neutral endopeptidase inhibitors

A series of substituted monocyclic and bicyclic azepinones were incorporated as dipeptide surrogates in mercaptoacetyl dipeptides with the desire to generate a single compound which would potently inhibit both angiotensin-converting enzyme (ACE) and neutral endopeptidase (NEP). Many of these compounds displayed excellent potency against both enzymes. Two of the most potent compounds, monocyclic azepinone 2n and bicyclic azepinone 3q, demonstrated a high level of activity versus ACE and NEP both in vitro and in vivo.

Conformationally restricted peptides through short-range cyclizations

The various types of conformationally restricted peptides obtained by short-range cyclizations, from residue i to residue i + 1, are presented. Relevant examples of N in equilibrium C alpha, C' in equilibrium C alpha, N in equilibrium C', C alpha in equilibrium C alpha, C' in equilibrium C', and N in equilibrium N cyclizations are reported and the pertinent literature listed. In the discussion emphasis is place on the conformational consequences for peptides from the incorporation of such ring structures.