Dipeptide proline diphenyl phosphonates are potent, irreversible inhibitors of seprase (FAPα)

Dipeptidyl peptidase IV (DPP-IV) and seprase belong to a small group of membrane-bound, proline-specific serine proteases, the serine integral membrane proteases (SIMPs). Whilst DPP-IV is the most exhaustively studied peptidase in this class, relatively less is known about the inhibitor/substrate specificity of its close homolog seprase. Additionally, whereas, DPP-IV expression is largely ubiquitous, seprase expression is restricted to tumour and tissue remodelling sites in vivo. Consequently, the highly restricted expression and distribution of seprase potentially make it an excellent therapeutic target for the modulation of neoplastic invasion and metastasis. Against this background, we now wish to report on the design, synthesis, and kinetic testing of a series of dipeptide proline diphenyl phosphonates, against DPP-IV and seprase. The most potent inhibitor of DPP-IV and seprase was found to be Gly-ProP(OPh)2, which exhibited overall second-order rate constants of inactivation of 5.24 x 105 M-1 min-1 and 1.06 x 104 M-1 min-1 against DPP-IV and seprase, respectively. Both proteases displayed differing profiles of susceptibility towards the other members of the series of inhibitors synthesised. In addition, Gly-ProP(OPh)2 and Tyr-ProP(OPh)2 were found to exert a considerable, dose-dependent anti-invasive effect on the LOX melanoma cell line, in vitro.

Fluorination-Free Synthesis of a 4,4-Difluoro-3,3-Dimethylproline Derivative

A Claisen rearrangement/iodolactamization sequence starting from commercially available trifluoroacetaldehyde methyl hemiacetal, followed by a classical chemical resolution, provided enantiomerically pure 4,4-difluoro-3,3-dimethylproline (S)-1. No hazardous fluorination reagents were used, and the overall yield over 12 steps was greater than 28%.

Stereoselective synthesis of alpha,alpha'-biprolines

A means to induce dehydrodimerization of Seebach's oxazolidinone (5), the stereochemical outcome of which is entirely temperature dependent, is described. The resultant dimers 3 and 4 are precursors to (R,R)-alpha,alpha'-biproline (1) and meso-alpha,alpha'-biproline (2), respectively. An organohypobromite and an iminium halide are proposed to serve as electrophiles in the reaction with the enolate of 5 to give 3 and 4, respectively.

Synthesis and Characterization of Oligoproline-Based Molecular Assemblies for Light Harvesting

Helical oligoproline arrays provide a structurally well-defined environment for building photochemical energy conversion assemblies. The use of solid-phase peptide synthesis (SPPS) to prepare four such arrays, consisting of 16, 17, 18, and 19 amino acid residues, is described here. Each array contains the chromophore [Rub'(2)m](PF(6))(2) (b' = 4,4'-diethylamidocarbonyl-2,2'-bipyridine; m = 4-methyl-2,2'-dipyridine-4'-carboxylic acid) and the electron transfer donor PTZ (phenothiazine). The arrays differ systematically in the distance between the redox-active metal complex and PTZ sites. They have been used in photophysical studies to provide insight into the distance dependence of electron transfer. (J. Am. Chem. Soc. 2004, 126, 14506-14514). This work describes the synthesis, purification, and characterization of the oligoproline arrays, including a general procedure for the synthesis of related arrays.

Stereoselective Synthesis of (Z)-Alkene-Containing Proline Dipeptide Mimetics

In peptides and proteins, the peptide bond between an amino acid and proline exists as an equilibrium mixture of the cis-imide and trans-imide due to the low energy barrier in their interconversion. This feature greatly influences the structure and function of the proline-containing peptides and proteins. Therefore, restricting the amide bond with an (E)- or (Z)-alkene should provide a promising method for elucidating the structure-activity relationships of the peptide and the proteins. In this report, the regio- and stereoselective synthesis of cis-alanylproline (Ala-Pro) type (Z)-alkene dipeptide mimetic is described. The key steps of this synthesis are to introduce a C3 unit onto a gamma-phosphoryloxy-alpha,beta-unsaturated-delta-lactam with an organocopper-mediated anti-S(N)2' reaction and subsequently construct a five-membered proline-like cyclic structure with an intramolecular Suzuki coupling reaction. Hydrolysis of the amide bond in the resulting bicyclic lactam yields the desired cis-Ala-Pro type (Z)-alkene dipeptide isostere. The presented synthetic methodology should be applicable to the general syntheses of other cis-aminoacylproline type (Z)-alkene dipeptide mimetics.

Identification of a novel spiropiperidine opioid receptor-like 1 antagonist class by a focused library approach featuring 3D-pharmacophore similarity

A focused library approach identifying novel leads to develop a potent ORL1 antagonist is described. Beginning from a compound identified by random screening, an exploratory library that exhibited a diverse display of pharmacophores was designed. After evaluating ORL1 antagonistic activity, a highly focused library was designed based on 3D-pharmacophore similarity to known actives. A novel D-proline amide class was identified in this library and was found to possess potent ORL1 antagonistic activity.

Novel potent hepatitis C virus NS3 serine protease inhibitors derived from proline-based macrocycles

The hepatitis C virus (HCV) NS3 protease is essential for viral replication. It has been a target of choice for intensive drug discovery research. On the basis of an active pentapeptide inhibitor, 1, we envisioned that macrocyclization from the P2 proline to P3 capping could enhance binding to the backbone Ala156 residue and the S4 pocket. Thus, a number of P2 proline-based macrocyclic alpha-ketoamide inhibitors were prepared and investigated in an HCV NS3 serine protease continuous assay (K(i*)). The biological activity varied substantially depending on factors such as the ring size, number of amino acid residues, number of methyl substituents, type of heteroatom in the linker, P3 residue, and configuration at the proline C-4 center. The pentapeptide inhibitors were very potent, with the C-terminal acids and amides being the most active ones (24, K(i*) = 8 nM). The tetrapeptides and tripeptides were less potent. Sixteen- and seventeen-membered macrocyclic compounds were equally potent, while fifteen-membered analogues were slightly less active. gem-Dimethyl substituents at the linker improved the potency of all inhibitors (the best compound was 45, K(i*) = 6 nM). The combination of tert-leucine at P3 and dimethyl substituents at the linker in compound 47 realized a selectivity of 307 against human neutrophil elastase. Compound 45 had an IC(50) of 130 nM in a cellular replicon assay, while IC(50) for 24 was 400 nM. Several compounds had excellent subcutaneous AUC and bioavailability in rats. Although tripeptide compound 40 was 97% orally bioavailable, larger pentapeptides generally had low oral bioavailability. The X-ray crystal structure of compounds 24 and 45 bound to the protease demonstrated the close interaction of the macrocycle with the Ala156 methyl group and S4 pocket. The strategy of macrocyclization has been proved to be successful in improving potency (>20-fold greater than that of 1) and in structural depeptization.

Two separate and distinct syntheses of stereospecifically deuteriated samples of (2S)-proline

Two distinct syntheses of samples of the amino acid L-proline which are stereospecifically deuteriated on the beta-carbon atom are reported. In the first of these, the labelled diazoketones 6, prepared by a chemico-enzymatic synthesis, have been photolysed in alkaline conditions to give the corresponding labelled methyl pyroglutamates 10 via hydrolysis and intramolecular trapping of the resultant ketene intermediates 9. These were then converted into (2S,3S)-[3-(2)H1]- and (2S,3R)-[2,3-(2)H2]-proline, 1a and 1b respectively. The second synthesis provides (2S)-[3,3-(2)H2]-, (2S,3S)- and (2S,3R)-[3-(2)H1]-proline, 1d, 1a and 1c respectively, and has as its key step the highly stereoselective hydrolysis of the silylenol ethers 14 and 14a respectively in which deuteriation or protonation occurs from the re-face of the enol ether.

Synthesis and pharmacochemical study of novel polyfunctional molecules combining anti-inflammatory, antioxidant, and hypocholesterolemic properties

We have designed and synthesized a series of novel molecules having a residue of a classical NSAID and an antioxidant moiety, both attached through amide bonds to a known nootropic structure, an L-proline, trans-4-hydroxy-L-proline or DL-pipecolinic acid residue. The compounds were found to retain anti-inflammatory and antioxidant activities, to acquire hypocholesterolemic action, and to possess a greatly reduced gastrointestinal toxicity. The novel molecules could find useful applications, among others, in slowing the progression or delaying the onset of neurodegenerative diseases.

New synthesis ofcis 5-tert-butyl-L-proline via cuprate. Evaluation as acis proline mimetic in a biological active octapeptide

cis 5-tert-butyl-L-proline (Cbp) was prepared rapidly and efficiently by the addition of low-valent tert-butyl cuprate to an aminal derived from proline. [Cbp(2), D-Leu(5)]-OP was then synthesized, showing a predominant cis peptide bond conformation, as confirmed by NMR.

Synthesis, biological evaluation, and pharmacokinetic study of prolyl-1-piperazinylacetic acid and prolyl-4-piperidinylacetic acid derivatives as VLA-4 antagonists

A series of prolyl-1-piperazinylacetic acid and prolyl-4-piperidinylacetic acid derivatives were synthesized and evaluated for their activity as VLA-4 antagonists. Of 22 compounds synthesized, 19 compounds showed potent activity with low nanomolar IC50 values. In addition, the representative compounds 11o and 11p with a hydroxy group in the pyrrolidine ring showed moderate plasma clearance in rats (11o, 30 ml/min/kg and 11p, 21 ml/min/kg) and in dogs (11o, 12 ml/min/kg and 11p, 9 ml/min/kg).

An Access to 3,4-(Aminomethano)proline in Racemic and Enantiomerically Pure Form

Protected racemic and enantiomerically pure 3,4-(aminomethano)prolines rac-9 and (2S,2'R,3R,4R)-9 have been prepared applying a titanium-mediated reductive cyclopropanation as a key step. Thus, cyclopropanations of N,N-dibenzylformamide with titanacyclopropanes generated in situ from racemic or enantiomerically pure tert-butyl N-Boc-3,4-dehydroprolinates rac-8 or (S)-8 proceed diastereoselectively, and furnish the protected racemic and enantiomerically pure diamino acid 9. The latter was incorporated into three tripeptides containing glycyl, alanyl and phenylalanyl moieties.

Locked conformations for proline pyrrolidine ring: synthesis and conformational analysis of cis- and trans-4-tert-butylprolines

The motional restrictions of the proline pyrrolidine ring allow this secondary amine amino acid to act as a turn inducer in many peptides and proteins. The pyrrolidine ring is known to exhibit two predominant pucker modes (i.e., C-4 (Cgamma) exo and endo envelope conformers whose ratio can be controlled by proper substituents in the ring). In nature, the exo puckered 4(R)-hydroxy-l-proline plays a crucial role as a building block in collagen and collagen-like structures. It has been previously concluded that the electronegativity of the 4-cis-substituent increases the endo puckering while the electronegativity of the 4-trans-substituent favors the exo puckering. Here, we have introduced a sterically demanding tert-butyl group at C-4 in trans- and cis-configurations. In the case of trans-substitution, the induced puckering effect on the pyrrolidine ring was studied with X-ray crystallography and 1H NMR spectral simulations. Both cis- and trans-4-tert-butyl groups strongly favor pseudoequatorial orientation, thereby causing opposite puckering effects for the pyrrolidine ring, cis-exo and trans-endo for l-prolines, in contrast to the effects observed in the case of electronegative C-4 substituents. The syntheses and structural analysis are presented for the conformationally constrained 4-tert-butylprolines. The prolines were synthesized from 4-hydroxy-l-proline, substitution with t-BuCuSPhLi being the key transformation. This reaction gave N-Boc-trans-4-tert-butyl-l-proline tert-butyl ester in 94% ee and 57% de. Enantioselectivity was increased to 99.2% ee by crystallization of N-Boc-trans-4-tert-butyl-l-proline in the final step of the synthesis.

Asymmetric Halo-Mannich-Type Reaction Provides Access to Pyrrolidines and β-Proline Derivatives

[reaction: see text] A new halo-Mannich-type reaction is reported using cyclopropyl carbonyl-derived enolates and sulfonyl-protected imines. Chiral oxazolidinones auxiliaries were found to be effective for completely controlling the stereochemistry of the products. Variations in the oxazolidinone, protecting group, and imine components show this to be a quite general reaction. The initial iodo-Mannich products were found to be readily cyclized in the presence of triethylamine to afford the resulting protected pyrrolidines, which could be readily deprotected under standard conditions.

Discovery and Preclinical Profile of Saxagliptin (BMS-477118): A Highly Potent, Long-Acting, Orally Active Dipeptidyl Peptidase IV Inhibitor for the Treatment of Type 2 Diabetes

Efforts to further elucidate structure-activity relationships (SAR) within our previously disclosed series of beta-quaternary amino acid linked l-cis-4,5-methanoprolinenitrile dipeptidyl peptidase IV (DPP-IV) inhibitors led to the investigation of vinyl substitution at the beta-position of alpha-cycloalkyl-substituted glycines. Despite poor systemic exposure, vinyl-substituted compounds showed extended duration of action in acute rat ex vivo plasma DPP-IV inhibition models. Oxygenated putative metabolites were prepared and were shown to exhibit the potency and extended duration of action of their precursors in efficacy models measuring glucose clearance in Zucker(fa/fa) rats. Extension of this approach to adamantylglycine-derived inhibitors led to the discovery of highly potent inhibitors, including hydroxyadamantyl compound BMS-477118 (saxagliptin), a highly efficacious, stable, and long-acting DPP-IV inhibitor, which is currently undergoing clinical trials for treatment of type 2 diabetes.

Dicarboxylic Acid Azacycle l-Prolyl-pyrrolidine Amides as Prolyl Oligopeptidase Inhibitors and Three-Dimensional Quantitative Structure−Activity Relationship of the Enzyme−Inhibitor Interactions

A series of dicarboxylic acid azacycle l-prolyl-pyrrolidine amides was synthesized, and their inhibitory activity against prolyl oligopeptidase (POP) from porcine brain was tested. Three different azacycles were tested at the position beyond P3 and six different dicarboxylic acids at the P3 position. l-Prolyl-pyrrolidine and l-prolyl-2(S)-cyanopyrrolidine were used at the P2-P1 positions. The IC(50) values ranged from 0.39 to 19000 nM. The most potent inhibitor was the 3,3-dimethylglutaric acid azepane l-prolyl-2(S)-cyanopyrrolidine amide. Molecular docking (GOLD) was used to analyze binding interactions between different POP inhibitors of this type and the POP enzyme. The data set consisted of the novel inhibitors, inhibitors published previously by our group, and well-known reference compounds. The alignments were further analyzed using comparative molecular similarity indices analysis. The binding of the inhibitors was consistent at the P1-P3 positions. Beyond the P3 position, two different binding modes were found, one that favors lipophilic structures and one that favors nonhydrophobic structures.

A Highly Efficient Organocatalyst for Direct Aldol Reactions of Ketones with Aldedydes

L-proline amides derived from various chiral beta-amino alcohols that bear substituents with various electron natures at their stereogenic centers are prepared and evaluated for catalyzing the direct Aldol reaction of 4-nitrobenzaldehyde with acetone. Catalysts with strong electron-withdrawing groups are found to exhibit higher catalytic activity and enantioselectivity than their analogues with electron-donating groups. The presence of 2 mol % catalyst 4g significantly catalyzes the direct Aldol reactions of a wide range of aldehydes with acetone and butanone, to give the beta-hydroxy ketones with very high enantioselectivities ranging from 96% to >99% ee. High diastereoselectivity of 95/5 was observed for the anti Aldol product from the reaction of cyclohexanone, and excellent enantioselectivity of 93% ee was provided for anti Aldol product from the reaction of cyclopentanone.

A Fluorous Chiral Dirhodium(II) Complex as a Recyclable Asymmetric Catalyst

[reaction: see text] The chiral fluorous complex tetrakis-dirhodium(II)-(S)-N-(n-perfluorooctylsulfonyl)prolinate has been prepared and used as a catalyst in homogeneous or fluorous biphasic fashion. The catalyst displays good chemo- and enantioselectivity in intermolecular cyclopropanation and C-H bond activation reactions. The catalyst can be simply and thoroughly separated from the reaction mixture and is recyclable.

9-hydroxyazafluorenes and their use in thrombin inhibitors

Optimization of a previously reported thrombin inhibitor, 9-hydroxy-9-fluorenylcarbonyl-l-prolyl-trans-4-aminocyclohexylmethylamide (1), by replacing the aminocyclohexyl P1 group provided a new lead structure, 9-hydroxy-9-fluorenylcarbonyl-l-prolyl-2-aminomethyl-5-chlorobenzylamide (2), with improved potency (K(i) = 0.49 nM for human thrombin, 2x APTT = 0.37 microM in human plasma) and pharmacokinetic properties (F = 39%, iv T(1/2) = 13 h in dogs). An effective strategy for reducing plasma protein binding of 2 and improving efficacy in an in vivo thrombosis model in rats was to replace the lipophilic fluorenyl group in P3 with an azafluorenyl group. Systematic investigation of all possible azafluorenyl P3 isomers and azafluorenyl-N-oxide analogues of 2 led to the identification of an optimal compound, 3-aza-9-hydroxyfluoren-9(R)-ylcarbonyl-l-prolyl-2-aminomethyl-5-chlorobenzylamide (19b), with high potency (K(i) = 0.40 nM, 2x APTT = 0.18 microM), excellent pharmacokinetic properties (F = 55%, T(1/2) = 14 h in dogs), and complete efficacy in the in vivo thrombosis model in rats (inhibition of FeCl(3)-induced vessel occlusions in six of six rats receiving an intravenous infusion of 10 microg/kg/min of 19b). The stereochemistry of the azafluorenyl group in 19b was determined by X-ray crystallographic analysis of its N-oxide derivative (23b) bound in the active site of human thrombin.

Parallel solid-phase synthesis and characterization of new sulfonamide and carboxamide proline derivatives as potential CNS agents

A solid-phase synthesis of the 64-member library of novel sulfonamide and carboxamide proline derivatives, focused on the 5-HT7 receptor antagonist SB-258741, was described. The final compounds were obtained in good yields and high purity upon cleavage from SynPhase Lanterns, functionalized by a BAL linker. The library representatives were screened for 5-HT7, 5-HT1A and D2 receptors to explore the impact of a tertiary amine moiety, the length of an alkylene spacer and the aryl fragment on the receptor affinity. The preliminary biological results provided data for further investigation aimed at a search for 5-HT7 receptor agents, and permitted the identification of several compounds with significant 5-HT1A receptor affinity.

Succinct Synthesis of β-Amino Acids via Chiral Isoxazolines

beta-Amino acids are important synthetic targets due to their presence in a wide variety of natural products, pharmaceutical agents, and mimics of protein structural motifs. While beta-amino acids containing geminal substitution patterns have enormous potential for application in these contexts, synthetic challenges to the stereoselective preparation of this class of compound have thus far limited more complete studies. We present here a straightforward method employing chiral isoxazolines as key intermediates to access five different beta-amino acid structural types with excellent selectivity. Of particular note is the use of this approach to prepare highly substituted cis-beta-proline analogues. The ready access to these diversely substituted compounds is expected to facilitate future studies of the structure and function of this important class of molecules.

Synthesis of optically active trans 4-cyclohexyl-L-proline as an intermediate product in the preparation of fosinopril

A nine-step synthesis of trans 4-cyclohexyl-L-proline has been developed on a laboratory scale. The product is an intermediate in the preparation of fosinopril--an effective hypotensive drug. The total yield of the synthesis was 25%. The final product was 99.7% pure. Analytical methods were developed for each step of the synthesis (HPLC, TLC, IR, 1H-NMR, 13C-NMR, GC-MS, [alpha]D).

Cu(I)-Catalyzed Enantioselective [3 + 2] Cycloaddition Reaction of 1-Alkylallenylsilane with α-Imino Ester: Asymmetric Synthesis of Dehydroproline Derivatives

[reaction: see text] The catalytic, enantioselective [3 + 2] cycloaddition reaction of 1-alkyl-substituted allenylsilanes with alpha-imino ester has been achieved by means of [Cu(MeCN)(4)]BF(4)/(R)-DM-SEGPHOS catalyst to afford silyl-substituted dehydroproline derivatives in high yields and enantioselectivities.

Novel Approach to 5-Substituted Proline Derivatives Using a Silver-Catalyzed Cyclization as the Key Step

A novel synthetic approach to the synthesis of enantiomerically pure 2,5-disubstituted pyrrolines is described. The methodology involves a Ag-catalyzed 5-endo-dig cyclization of enantiopure aryl-substituted acetylene-containing amino acids. It has also been shown that the obtained pyrrolines can be efficiently transformed into the corresponding saturated 5-aryl-substituted proline derivatives.