Synthesis of novel N-phosphonoalkyl dipeptide inhibitors of human collagenase

An Overview of Stereoselective Synthesis of α-Aminophosphonic Acids and Derivatives

An overview of all methodologies published during the last few years focused to the stereoselective (diastereoselective or enantioselective) synthesis of α-aminophosphonic acids and derivatives is reported. The procedures have been classified according a retrosynthetic strategy and taking into account the formation of each one of the bonds connected to the chiral centre.

C-bis-pivot lariat ethers: synthesis and spectral investigations on new 15- and 17-membered coronands containing dimethoxyphosphoryl groups

The reactions of dibenzo-diaza crown ethers (coronands) (1 and 2) with dimethylphosphite led to the formation of the mixture of meso and racemic C-bis-pivot lariat ethers (3 and 4) containing dimethoxyphosphoryl groups. We have failed to make the resolution of the mixture, nevertheless, the detailed characterization and spectral investigations of compounds 3 and 4 have been made by elemental analyses, FTIR, (1)H NMR, (13)C NMR, (31)P NMR, COSY, DEPT, HETCOR and HMBC spectral data. The salient features of the spectral data of these compounds have been presented.

Peptidomimetics: Fmoc solid-phase pseudopeptide synthesis

Peptidomimetic modifications or cyclization of linear peptides are frequently used as attractive methods to provide more conformationally constrained and thus more stable and bioactive peptides. Among numerous peptidomimetic approaches described recently in the literature, particularly attractive are pseudopeptides or peptide bond surrogates in which peptide bonds have been replaced with other chemical groups. In these peptidomimetics the amide bond surrogates possess three-dimensional structures similar to those of natural peptides, yet with significant differences in polarity, hydrogen bonding capability, and acid-base character. The introduction of such modifications to the peptide sequence is expected to completely prevent protease cleavage of amide bond and significantly improve peptides' metabolic stability. In this chapter we consider Fmoc solid-phase synthesis of peptide analogs containing the amide surrogate that tend to be isosteric with the natural amide. This includes synthesis of peptidosulfonamides, phosphonopeptides, oligoureas, depsides, depsipeptides, and peptoids.

Direct Access to Enantiomerically Enriched α-Amino Phosphonic Acid Derivatives by Organocatalytic Asymmetric Hydrophosphonylation of Imines

A simple and efficient organocatalytic enantioselective hydrophosphonylation of imines to enantiomerically enriched alpha-amino phosphonates is reported. By using 10 mol % of quinine as the catalyst in the enantioselective addition of diethyl phosphite to N-Boc protected imines, alpha-amino phosphonates are obtained in moderate to good yields and with up to 94% ee.

Asymmetric synthesis of cyclic alpha-amino phosphonates using masked oxo sulfinimines (N-sulfinyl imines)

Five-, six-, and seven-membered cyclic alpha-amino phosphonates, amino acid surrogates, are prepared in enantiomerically pure form via the highly diastereomeric addition of metal phosphonates to masked oxo sulfinimines. Hydrolysis of the resulting masked oxo alpha-amino phosphonates followed by reduction of the intermediate cyclic imino phosphonates affords the title compounds in good yield.

A thiazole-containing tripodal ligand: synthesis, characterization, and interactions with metal ions and matrix metalloproteinases

A new tripodal ligand, tris[2-(((2-thiazolyl)methylidene)amino)ethyl]amine (Tatren), has been synthesized and characterized by NMR, IR, and UV-visible absorbance spectroscopy and elemental analysis. Tatren forms stable complexes with transition metal ions (Zn(2+), 1; Mn(2+), 2; Co(2+), 3) and the alkaline earth metal ions (Ca(2+), 4; Mg(2+), 5). Single-crystal X-ray structures of 1, 2, and 5 revealed six-coordinate chelate complexes with formula [M(Tatren)](ClO(4))(2) in which the metal centers are coordinated by three thiazolyl N atoms and three acyclic imine N atoms. Crystals of 1, 2, and 5 are monoclinic, P2(1)/c space group. Crystals of 4 are triclinic, P space group. The Ca(2+) complex is eight-coordinate with all N atoms of Tatren and one water molecule coordinated to the metal ion. Spectrophotometric titrations show that formation constants for the chelates of metal ions are >>1 in methanol. Free Tatren inhibits the catalytic domain of matrix metalloproteinase-13 (MMP-13, collagenase-3) with K(i) = 3.5 +/- 0.6 microM. Molecular mechanics-based docking calculations suggest that one leg of Tatren coordinates to the catalytic Zn(2+) in MMPs-2, -9, and -13 with significant hydrogen bonding to backbone amide groups. High-level DFT calculations suggest that, in the absence of nonbonded interactions between Tatren and the enzyme, the most stable first coordination sphere of the catalytic Zn(2+) is achieved with three imidazolyl groups from His residues and two imine N atoms from one leg of Tatren. While complexes (1-3) do not inhibit MMP-13 to a significant extent, 4 does (K(i) = 30 +/- 10 microM). Hence, this study shows that tripodal chelating ligands of this class and their Ca(2+) complexes have potential as active-site inhibitors for MMPs.

Structural and spectroscopic studies of tripodal [MgL]2+ chelates containing only nitrogen donor atoms: alkaline earth metal complexes as potential drug delivery agents

Several tripodal diimine ligands, tris(2-(2-thiazolyl)methyliminoethyl)amine, 2-Tatren, tris(2-(4-(5-methyl)imidazolyl)methyliminoethyl)amine, 5-Me-4-Imtren, tris(2-(4-imidazolyl)methyliminoethyl)amine, 4-Imtren, tris(2-(2-imidazolyl)methyliminoethyl)amine, 2-Imtren, and their Mg(2+) complexes were prepared and characterized. X-ray diffraction studies show that the Mg(2+) ions are six-coordinate, with three acyclic imine N atoms and three imidazolyl or thiazolyl N atoms coordinated with the general formula [Mg(L)](ClO(4))(2) (L=4-Imtren (1), 2-Imtren (2), 2-Tatren (3), and 5-Me-4-Imtren (4)). These complexes are chiral with both Delta and Lambda isomers present in the unit cell. (1)H NMR titrations reveal that complexes also form in solution and that the chirality is maintained. Variable temperature (1)H NMR reveals that the Delta and Lambda isomers interconvert in the intermediate to slow time scale. The interconversion rate slows with increasing pK(a) of the ligand heterocycle, suggesting that interconversion proceeds through a partially dissociated state. These complexes undergo trans-metallation by Zn(2+), indicating that their ligands can be released in a kinetically facile manner to form more stable metal ion complexes.

Asymmetric hydrogenation of alpha,beta-unsaturated phosphonates with Rh-BisP* and Rh-MiniPHOS catalysts: scope and mechanism of the reaction

Optically active 1,2-bis(alkylmethylphosphino)ethanes and bis(alkylmethylphosphino)methanes are unique diphosphine ligands combining the simple molecular structure and P-stereogenic asymmetric environment. This work shows that these ligands exhibit excellent enantioselectivity in rhodium-catalyzed asymmetric hydrogenation of alpha,beta-unsaturated phosphonic acid derivatives. The enantioselective hydrogenation mechanism elucidated by NMR study is also described.

Conformationally constrained alpha-boc-aminophosphonates via transition metal-catalyzed/curtius rearrangement strategies

A transition metal-catalyzed/Curtius rearrangement sequence toward the development of conformationally constrained alpha-Boc-aminophosphonates 2-6 is described. An approach using the versatile tert-butylphosphonoacetate moieties 1a and 1b to derive an array of mono- and bicyclic alpha-Boc-aminophosphonate systems is presented. Conformational constraint is incorporated using either the ring-closing metathesis reaction catalyzed by the first generation Grubbs catalyst or intramolecular cyclopropanation mediated by Rh2(OAc)4. Using the tert-butyl ester functionality in 1a or 1b as a potential amino group, the Curtius rearrangement provides an efficient route toward the target alpha-Boc-aminophosphonates.

Asymmetric synthesis of quaternary alpha-amino phosphonates using sulfinimines

The addition of lithium diethylphosphonate to enantiopure ketosulfinimines is highly diastereoselective (>95%), affording the first examples of quaternary alpha-alkyl alpha-amino (arylmethyl)phosphonates.

Chemical conversion of cyclic alpha-amino acids to cyclic alpha-aminophosphonic acids

The oxidative decarboxylation of cyclic alpha-amino acids having urethane-type N-protecting groups with lead tetraacetate [Pb(OAc)4] gave 2-hydroxy derivatives, which were transformed into the corresponding alpha-aminophosphonic acid esters by treatment of trialkyl phosphites in the presence of Lewis acids. Deprotection and ester cleavage of the products in the usual manner afforded cyclic alpha-aminophosphonic acids. The convenient chemical conversion of five- and six-membered cyclic alpha-amino acids to the corresponding cyclic alpha-aminophosphonic acids has been accomplished.

Concept of improved rigidity: how to make enantioselective hydrophosphonylation of cyclic imines catalyzed by chiral heterobimetallic lanthanoid complexes almost perfect

The catalytic and enantioselective hydrophosphonylation of cyclic imines using cyclic phosphites is described for the first time. In contrast to the application of acyclic phosphites, significant improvements are presented arising from the concept of improved rigidity by utilization of cyclic phosphites in the lanthanoid BINOL complex catalyzed hydrophosphonylation of 3-thiazolines. Cyclic phosphites are shown to provide certain improvements within the catalytic cycle. Influence of parameters such as concentration of the catalyst and the phosphite on the catalysis is examined as well as the effects of the substituents on the starting material. The pharmacologically interesting thiazolidinyl phosphonates are synthesized in excellent optical purities of up to 99% ee and high chemical yields of up to 99%. The required amount of catalyst is reduced to 2.5 mol %. The highest efficiency of the reaction involving cyclic phosphites is achieved using the catalytic system "2.5 mol % (S)-YbPB/2.5 equiv phosphite/50 degrees C/48 h/THF-toluene (1:7)". On the basis of the results a refinement of the proposed catalytic cycle has been provided. For comparison cyclic phosphites were used in hydrophosphonylation with a chiral titanium catalyst.

Potent and selective non-peptidic inhibitors of endothelin-converting enzyme-1 with sustained duration of action

Potent and selective non-peptidic inhibitors of human endothelin-converting enzyme-1 (ECE-1) have been designed as potential modulators of endothelin (ET-1) production in vivo. Because of its unique structural characteristics and long duration of action in vivo, the dual ECE-1 and neutral endopeptidase 24.11 (NEP) inhibitor, CGS 26303, was selected as an attractive lead for further optimization of potency and selectivity. Replacement of the P(1)' biphenyl substituent of CGS 26303 by a conformationally restricted 3-dibenzofuranyl group led to more potent and more selective ECE-1 inhibitors, such as the tetrazole 27. The remarkable effect of this P(1)' modification allowed for the first time phosphonomethylcarboxylic acids, such as 29, to display both potent (IC(50) = 22 nM) and selective (104-fold vs NEP) ECE-1 inhibition. Chemoenzymatic syntheses of the new alpha-amino acid (S)-3-dibenzofuran-3-ylalanine intermediate were developed, and improved procedures to generate substituted alpha-aminoalkylphosphonic acids were devised to support the production of various analogues. Although additional gains in intrinsic ECE-1 inhibitory potency could occasionally be achieved by addition of a P(1) side chain, these compounds (e.g. 43a) showed poor functional activity in vivo in the big ET-1 pressor test. Phosphonoalkyl dipeptides featuring 3-dibenzofuranyl groups in both the P(1)' and P(2)' positions were also very potent ECE-1 inhibitors, albeit lacking the desired selectivity against NEP. Functionally, 27and 29 were the two most efficacious compounds from this study, producing sustained inhibition of ECE-1 activity in rats, as measured by their ability to block the hypertensive effects induced by big ET-1. This profile was similar to that of a potent ET(A)/ET(B) dual receptor antagonist, SB 209670. Due to their favorable in vitro and in vivo profiles, 27 (CGS 34043) and 29 (CGS 35066) constitute new pharmacological tools useful in assessing the role of ECE-1 in pathological conditions.

Asymmetric synthesis of alpha-methylphosphophenylalanine derivatives using sulfinimine-derived enantiopure aziridine-2-phosphonates

[formula: see text] 2-Methylaziridine-2-phosphonates were prepared from enantiopure sulfinimines and were demonstrated to be versatile synthetic intermediates for the synthesis of novel alpha-disubstituted and alpha,beta-trisubstituted alpha-aminophosphonate derivatives. The first asymmetric synthesis of both enantiomers of alpha-methylphosphophenylalanine is described.

Inhibition of adamalysin II and MMPs by phosphonate analogues of snake venom peptides

Phosphonate analogues of the peptidomimetic N-(Furan-2-yl)carbonyl-Leu-Trp-OH were prepared with the goal of evaluating the effect of phosphonate for carboxylate replacement on binding with snake venom metalloproteinases and MMPs. N-(Furan-2-yl)carbonyl-Leu-L-Trp(P)-(OH)2 showed a 75-fold increase of the inhibiting activity against adamalysin II, a snake venom metalloproteinase structurally related to MMPs and TACE. Both the phosphonate and carboxylate peptidomimetics fit into the active site adopting a retrobinding mode and provide the structural base for a new class of metalloproteinases inhibitors.

The asymmetric synthesis and in vitro characterization of succinyl mercaptoalcohol and mercaptoketone inhibitors of matrix metalloproteinases

A series of succinyl based mercaptoketones and diastereomeric mercaptoalcohols were prepared and evaluated in vitro as inhibitors of the matrix metalloproteinases collagenase-1 (MMP-1), stromelysin (MMP-3), and gelatinase-B (MMP-9).

Design, synthesis, and biochemical evaluation of phosphonate and phosphonamidate analogs of glutathionylspermidine as inhibitors of glutathionylspermidine synthetase/amidase from Escherichia coli

Three phosphapeptides designed to mimic two distinct tetrahedral intermediates formed during either the synthesis or hydrolysis of glutathionylspermidine (Gsp) were synthesized and evaluated as inhibitors of the bifunctional enzyme Gsp synthetase/amidase. While the polyamine-containing phosphapeptides were determined to be potent and selective inhibitors, they selectively inhibit the synthetase activity over the amidase domain. A phosphonate-containing tetrahedral mimic is a reversible mixed-type inhibitor of Gsp synthetase with an inhibition constant of 6 microM for the inhibitor binding to the free enzyme (Ki) and 14 microM for the inhibitor binding to the enzyme-substrate complex (Ki'). The corresponding phosphonamidate is a slow-binding inhibitor with a Ki of 24 microM and a Ki* (isomerization inhibition constant) of 0.88 microM. A non-polyamine-containing phosphonamidate exhibits no significant inhibition of the synthetase or amidase activity.

Angiotensin-converting enzyme secretase is inhibited by zinc metalloprotease inhibitors and requires its substrate to be inserted in a lipid bilayer

Mammalian angiotensin-converting enzyme (ACE; EC 3.4.15.1) is one of several proteins that exist in both membrane-bound and soluble forms as a result of a post-translational proteolytic processing event. For ACE we have previously identified a metalloprotease (secretase) responsible for this proteolytic cleavage. The effect of a range of structurally related zinc metalloprotease inhibitors on the activity of the secretase has been examined. Batimastat (BB94) was the most potent inhibitor of the secretase in pig kidney microvillar membranes, displaying an IC50 of 0.47 microM, whereas TAPI-2 was slightly less potent (IC50 18 microM). Removal of the thienothiomethyl substituent adjacent to the hydroxamic acid moiety or the substitution of the P2' substituent decreased the inhibitory potency of batimastat towards the secretase. Several other non-hydroxamate-based collagenase inhibitors were without inhibitory effect on the secretase, indicating that ACE secretase is a novel zinc metalloprotease that is realted to, but distinct from, the matrix metalloproteases. The full-length amphipathic form of ACE was labelled selectively with 3-trifluoromethyl-3-(m-[125I]iodophenyl)diazirine in the membrane-spanning hydrophobic region. Although trypsin was able to cleave the hydrophobic anchoring domain from the bulk of the protein, there was no cleavage of full-length ACE by a Triton X-100-solubilized pig kidney secretase preparation when the substrate was in detergent solution. In contrast, the Triton X-100-solubilized secretase preparation released ACE from pig intestinal microvillar membranes, which lack endogenous secretase activity, and cleaved the purified amphipathic form of ACE when it was incorporated into artificial lipid vesicles. Thus the secretase has an absolute requirement for its substrate to be inserted in a lipid bilayer, a factor that might have implications for the development of cell-free assays for other membrane protein secretases. ACE secretase could be solubilized from the membrane with Triton-X-100 and CHAPS, but not with n-octyl beta-D-glucopyranoside. Furthermore trypsin could release the secretase from the membrane, implying that like its substrate, ACE, it too is a stalked integral membrane protein.