Preparation of racemic 2r-carboxy-trans, trans-3,4-dideutero-pyrrolidine (DL-trans, trans-3,4-dideutero-proline) and unambiguous assignment of protons in the 1H n.m.r. spectrum of proline

Racemic trans-3,4-dideutero proline has been prepared by catalytic deuteration of 3-pyrroline-2-carboxylic acid. The stereospecificity of the reduction (i.e. trans to the carboxylic group) was ascertained after transformation of the dideutero compound into the diketopiperazide c/Pro, Aib/, for which unambiguous proton assignments in the 1H n.m.r. spectrum had been obtained previously. The identification of the configuration of the dideuteroproline allows for the affirmation of the correctness of proton assignments as previously proposed in literature.

Improved protocol for asymmetric, intramolecular heteroatom Michael addition using organocatalysis: enantioselective syntheses of homoproline, pelletierine, and homopipecolic acid

An improved protocol for the construction of enantioenriched pyrrolidine, indoline, and piperidine rings using an organocatalyzed, intramolecular heteroatom Michael addition is described. Application to the enantioselective synthesis of homoproline, homopipecolic acid, and pelletierine has been accomplished.

4-chloroprolines: synthesis, conformational analysis, and effect on the collagen triple helix

Collagen is an abundant, triple-helical protein comprising three strands of the repeating sequence: Xaa-Yaa-Gly. (2S)-Proline and (2S,4R)-4-hydroxyproline (Hyp) are common in the primary structure of collagen. Here, we use nonnatural proline derivatives to reveal determinants of collagen stability. Specifically, we report high-yielding syntheses of (2S,4S)-4-chloroproline (clp) and (2S,4R)-4-chloroproline (Clp). We find that the molecular structure of Ac-Clp-OMe in the solid state is virtually identical to that of Ac-Hyp-OMe. In contrast, the conformational properties of Ac-clp-OMe are similar to those of Ac-Pro-OMe. Ac-Clp-OMe has a stronger preference for a trans amide bond than does Ac-Pro-OMe, whereas Ac-clp-OMe has a weaker preference. (Pro-Clp-Gly)(10) forms triple helices that are significantly more stable than those of (Pro-Pro-Gly)(10). Triple helices of (clp-Pro-Gly)(10) have stability similar to those of (Pro-Pro-Gly)(10). Unlike (Pro-Clp-Gly)(10) and (clp-Pro-Gly)(10), (clp-Clp-Gly)(10) does not form a stable triple helix, presumably due to a deleterious steric interaction between proximal chlorines on different strands. These data, which are consistent with previous work on 4-fluoroprolines and 4-methylprolines, support the importance of stereoelectronic and steric effects in the stability of the collagen triple helix and provide another means to modulate that stability. (

Concise, stereoselective route to the four diastereoisomers of 4-methylproline

The full stereochemical characterization of 4-methylproline, a rare amino acid found in a number of peptidic secondary metabolites, has often been hindered by long reaction sequences or low stereoselectivity in the synthesis leading to reference samples. The preparation of the four diastereoisomers of 4-methylproline by a concise and stereoselective route is presented and features a six-step route with late-stage stereodivergence, good stereoselectivity for both cis- and trans-series (75% and 88% de, respectively), and good overall yields (cumulative yields of 30-40%). Additional data on the Marfey's derivatives of the stereoisomers are also presented.

A comparative study of different glycosylation methods for the synthesis of d-mannopyranosides of Nα-fluorenylmethoxycarbonyl-trans-4-hydroxy-l-proline allyl ester

The synthesis of Nalpha-fluorenylmethoxycarbonyl-trans-4-hydroxy-4-O-[(2,3,4,6-tetra-O-acetyl)-alpha-d-mannopyranosyl]-l-proline allyl ester and Nalpha-fluorenylmethoxycarbonyl-trans-4-hydroxy-4-O-[(2,3,4,6-tetra-O-benzoyl)-alpha-d-mannopyranosyl]-l-proline allyl ester is described. Glycosylation using Königs-Knorr conditions with a benzoyl protected glycosyl donor provided the optimum method. Removal of the allyl ester gave two mannosylated building blocks suitable for solid phase glycopeptide synthesis.

Small molecule inhibitors of integrin alpha2beta1

Interactions between the integrin, alpha2beta1, and extracellular matrix (ECM), particularly collagen, play a pivotal role in platelet adhesion and thrombus formation. Platelets interact with collagen in the subendothelial matrix that is exposed by vascular damage. To evaluate the potential of alpha2beta1 inhibitors for anticancer and antithrombotic applications, we have developed a series of small molecule inhibitors of this integrin based on a prolyl-2,3-diaminopropionic acid (DAP) scaffold using solid-phase parallel synthesis. A benzenesulfonamide substituent at the N-terminus of the dipepetide and a benzyl urea at the DAP side chain resulted in tight and highly selective inhibition of alpha2beta1-mediated adhesion of human platelets and other cells to collagen.

Selective Defluorination Approach to N-Cbz-3,3-difluoro-2-difluoromethylenepyrrolidine and Its Application to 3,3-Difluoroproline Dipeptide Synthesis

Mg-promoted defluorination of N-(p-methoxyphenyl)bis(trifluoromethyl)imine 1 gave perfluoroenamine 2, which was readily transformed to N-Cbz-2-trifluoromethyl-3,3-difluoropyrrolidine 10. Chemoselective defluorination from the trifluoromethyl group of 10 by LHMDS-promoted dehydrofluorination in THF provided 3,3-difluoro-2-difluoromethylenepyrrolidine 11. The product 11 was converted to 3,3-difluoroproline dipeptides 16 upon treatment with aminoesters.

V-PROLI/NO, a prodrug of the nitric oxide donor, PROLI/NO

The sensitivity to decomposition of the nitric oxide (NO) donor ion, 1-[2-(carboxylato)pyrrolidin-1-yl]diazen-1-ium-1,2-diolate (PROLI/NO), complicates direct electrophilic substitution to form useful prodrug derivatives. A modified general synthetic approach involving 1-[2-(hydroxymethyl)pyrrolidin-1-yl]diazen-1-ium-1,2-diolate ion (structure A, above) was used to prepare several PROLI/NO prodrugs including the previously inaccessible O2-vinyl derivative, V-PROLI/NO. Metabolism of V-PROLI/NO by liver microsomes enriched in human cytochrome P450 isoforms was demonstrated.

A Memory of Chirality Approach to the Stereoselective Synthesis of 4-Hydroxy-α-methylprolines

To extend the memory of chirality (MOC) methodology to structurally more diverse compounds, the synthesis of 4-hydroxy-alpha-methylprolines was undertaken. Yield and selectivity were very good, with an unexpected reversal in selectivity observed for the cyclization of one adduct with an unprotected hydroxyl.

Synthesis and DNA Binding/Cleavage of Mononuclear Copper(II) Phenanthroline/Bipyridine Proline Complexes

The complexes [Cu(II)(phen)(L-Pro)(H2O)]+ ClO4(-) (1; phen = 1,10-phenanthroline) and [Cu(II)(bipy)(L-Pro)(H2O)]+ ClO4(-) (2; bipy = 2,2'-bipyridine) were synthesized and characterized by IR, magnetic susceptibility, UV/VIS, EPR, ESI-MS, elemental analysis, and theoretical calculations. The metal center was found in a square-pyramidal geometry. UV/VIS, thermal-denaturation, and fluorescence-spectroscopic studies were conducted to assess the interaction of the complexes with CT-DNA. An intercalative mode of binding was found, with intrinsic binding constants (Kb) of 3.86x10(3) and 4.6x10(3) M(-1) and Stern-Volmer quenching constants (K) of 0.15 and 0.11 for 1 and 2, respectively. Interestingly, none of the Cu(II) complexes was able to cleave pUC-19 DNA, which is attributed to the absence of a Pro amide H-atom and inhibition of the formation of an OH radical from the axially coordinated H2O molecule.

Design and Synthesis of a 3,4-Dehydroproline Amide Discovery Library

The synthesis of a discovery library of 80 3,4-dehydroproline amides was achieved in a four-step reaction sequence from easily accessible 3-aminoallene-3-carboxylate methyl esters. Diversification of these proline mimics was introduced at five different sites: the substituents at the 3-pyrroline unit (R1, R2, R3), at the nitrogen (R4), and the C-terminus (R5). The 3-pyrroline scaffold was synthesized in excellent yields by a silver-catalyzed intramolecular cyclization of aminoallenes, followed by N-functionalization reactions. Maximum diversity was introduced in the final step of the reaction sequence by taking advantage of the carboxylic acid handle of the 3-pyrroline subunit. Amide coupling reactions using polystyrene-carbodiimide (PS-carbodiimide) and 1-hydroxybenzotriazole (HOBt) under microwave irradiation led to 3,4-dehydroproline amides that were obtained in purities greater than 85% by LC/MS/ESLD after scavenging the excess HOBt on a silica-bound carbonate SPE cartridge.

Discovery of the HCV NS3/4A Protease Inhibitor (1R,5S)-N-[3-Amino-1-(cyclobutylmethyl)-2,3-dioxopropyl]-3- [2(S)-[[[(1,1-dimethylethyl)amino]carbonyl]amino]-3,3-dimethyl-1-oxobutyl]- 6,6-dimethyl-3-azabicyclo[3.1.0]hexan-2(S)-carboxamide (Sch 503034) II. Key Steps in Structure-Based Optimization

The structures of both the native holo-HCV NS3/4A protease domain and the protease domain with a serine 139 to alanine (S139A) mutation were solved to high resolution. Subsequently, structures were determined for a series of ketoamide inhibitors in complex with the protease. The changes in the inhibitor potency were correlated with changes in the buried surface area upon binding the inhibitor to the active site. The largest contribution to the binding energy arises from the hydrophobic interactions of the P1 and P2 groups as they bind to the S1 and S2 pockets [the numbering of the subsites is as defined in Berger, A.; Schechter, I. Philos. Trans. R. Soc. London, Ser. B 1970, 257, 249-264]. This correlation of the changes in potency with increased buried surface area contributed directly to the design of a potent tripeptide inhibitor of the HCV NS3/4A protease that is currently in clinical trials.

Diastereoselective synthesis of glycosylated prolines as α-glucosidase inhibitors and organocatalyst in asymmetric aldol reaction

1,3-Dipolar cycloaddition of azomethine ylides and glycosyl E-olefins in presence of LDA led to diastereoselective formation of C-glycosylated proline esters. The selected esters on regioselective hydrolysis with LiOH gave C-glycosyl prolines. Few of the proline esters exhibited very good alpha-glucosidase inhibitory activity. The organocatalytic activity of the proline derivatives in a prototype Aldol reaction has also been investigated.

Diastereoselective synthesis of 4,5'-bis-proline compounds via reductive dimerization of N-acyloxyiminium ions

A short, practical synthesis of novel, unsymmetrical 4,5'-bis-proline compounds has been achieved, highlighted by the application of an unprecedented samarium diiodide-driven regio- and diastereocontrolled reductive dimerization of N-acyloxyiminium ions generated from readily available 2-methoxy-5-silyloxymethyl-N-Boc pyrrolidines. The title proline dimers proved to be pertinent metal-free catalysts in aldol and Mannich reactions.

An Efficient Synthesis of Enantiomerically Pure (R)-Pipecolic Acid, (S)-Proline, and Their N-Alkylated Derivatives

Enantiomerically pure (R)-(+)-pipecolic acid was synthesized in four steps and 42% overall yield starting from dihydropyran and (R)-alpha-methylbenzylamine. A general short strategy is also described for preparing (S)-proline (47.5% overall yield) and derivatives.

Diastereocontrolled Synthesis of Enantioenriched 3,4-Disubstituted β-Prolines

Enantioenriched 3,4-disubstituted beta-prolines have been prepared with a high diastereocontrol through a carbometalation reaction or through a domino Michael addition/carbometalation reaction.

Conformationally restricted dipeptide amides as potent and selective neuronal nitric oxide synthase inhibitors

Four new conformationally restricted analogues of a potent and selective neuronal nitric oxide synthase inhibitor, l-nitroargininyl-l-2,4-diaminobutyramide (1), have been synthesized. N(alpha)-Methyl and N(alpha)-benzyl derivatives (3 and 4, respectively) of 4-N-(l-Arg(NO(2))-trans-4-amino-l-prolineamide (2) are also selective inhibitors, but the potency and selectivity of 3 are weak. Analogue 4 has only one-third the potency and one-half to one-third the selectivity of 2 against iNOS (inducible nitric oxide synthase) and eNOS (endothelial nitric oxide synthase), respectively. 3-N-(l-Arg(NO)(2))-trans-3-amino-l-prolineamide (6) is as potent an inhibitor of nNOS (neuronal nitric oxide synthase) as 2; selectivity for nNOS over iNOS is half of that for 2, but the selectivity for nNOS over eNOS is almost double that for 2. The corresponding cis-isomer (5) is a weak inhibitor of nNOS. These results are supported by computer modeling.

A Spiroisoxazolinoproline-Based Amino Acid Scaffold for Solid Phase and One-Bead−One-Compound Library Synthesis

An efficient, multigram synthesis of a spiroisoxazolinoproline-based amino acid, 7, requiring minimal purification, delivering good cis:trans diastereoselectivity (approximately 1:4), and providing good yields is reported. Surface-bound studies of the reduction of an arylnitro group in the presence of an isoxazoline ring with tin(II) dichloride dihydrate were undertaken to confirm the stability of the isoxazoline ring. Full derivitization of this spiroisoxazolinoproline-based amino acid scaffold was performed during the synthesis of a sample library with high yields and high purity that validated the efficiency of the chemistry that was employed in resin-bound library synthesis. A 129,600 member one-bead-one-compound (OBOC) library based on the scaffold 7 was synthesized utilizing a dual amino acid encoding method and bifunctionalization of TentaGel resin.

Discovery of (1R,5S)-N-[3-amino-1-(cyclobutylmethyl)-2,3-dioxopropyl]- 3-[2(S)-[[[(1,1-dimethylethyl)amino]carbonyl]amino]-3,3-dimethyl-1-oxobutyl]- 6,6-dimethyl-3-azabicyclo[3.1.0]hexan-2(S)-carboxamide (SCH 503034), a selective, potent, orally bioavailable hepatitis C virus NS3 protease inhibitor: a potential therapeutic agent for the treatment of hepatitis C infection

Hepatitis C virus (HCV) infection is the major cause of chronic liver disease, leading to cirrhosis and hepatocellular carcinoma, which affects more than 170 million people worldwide. Currently the only therapeutic regimens are subcutaneous interferon-alpha or polyethylene glycol (PEG)-interferon-alpha alone or in combination with oral ribavirin. Although combination therapy is reasonably successful with the majority of genotypes, its efficacy against the predominant genotype (genotype 1) is moderate at best, with only about 40% of the patients showing sustained virological response. Herein, the SAR leading to the discovery of 70 (SCH 503034), a novel, potent, selective, orally bioavailable NS3 protease inhibitor that has been advanced to clinical trials in human beings for the treatment of hepatitis C viral infections is described. X-ray structure of inhibitor 70 complexed with the NS3 protease and biological data are also discussed.

Efficient Preparation of Proline N-Carboxyanhydride Using Polymer-Supported Bases

[Structure: see text] A procedure for the preparation of proline N-carboxyanhydride in high yield and purity is described using polymer-supported tertiary amines. The polymer-supported amine can be recycled with a basic wash and filtration of the resin. The procedure facilitates the access to the efficient preparation of the polyproline polymer with potential therapeutic interest.

Divergent Chemical Synthesis of Prolines Bearing Fluorinated One-Carbon Units at the 4-Position via Nucleophilic 5-Endo-Trig Cyclizations

N-[3-(Trifluoromethyl)homoallyl]sulfonamides, prepared via ring opening of (S)-glycidyl ethers or 2-aryloxiranes with 1-(trifluoromethyl)vinyllithium, underwent intramolecular addition or S(N)2'-type reaction in the normally disfavored 5-endo-trig fashion, leading to 2-substituted 4-(trifluoromethyl)- or 4-(difluoromethylene)pyrrolidines. Both alpha- and beta-face-selective hydrogenation of the 4-difluoromethylene group afforded syn- and anti-4-(difluoromethyl)pyrrolidines, respectively. These sequences, followed by the oxidation of a 2-hydroxymethyl or 2-aryl group, successfully provided prolines with a trifluoromethyl, difluoromethylene, or difluoromethyl group at the 4-position, including optically active prolines.

Design, synthesis, and evaluation of proline and pyrrolidine based melanocortin receptor agonists. A conformationally restricted dipeptide mimic approach

The design, synthesis, and structure-activity relationships (SAR) of a series of novel proline and pyrrolidine based melanocortin receptor (MCR) agonists are described. To validate a conformationally constrained Arg-Nal dipeptide analogue strategy, we first synthesized and evaluated a test set of cis-(2R,4R)-proline analogues (21a-g). All of these compounds showed significant binding and agonist potency at the hMC1R, hMC3R, and hMC4R. Potent cis-(2S,4R)-pyrrolidine based MCR agonists (35a-g) were subsequently developed by means of this design approach. A SAR study directed toward probing the effect of the two chiral centers in the pyrrolidine ring on biological activity revealed the importance of the (S) absolute configuration at the 2-position for binding affinity, agonist potency, and receptor selectivity. Among the four sets of the pyrrolidine diastereomers investigated, analogues with the (2S,4R) configuration were the most potent agonists across the three receptors, followed by those possessing the (2S,4S) configuration.

Discovery of proline sulfonamides as potent and selective hepatitis C virus NS5b polymerase inhibitors. Evidence for a new NS5b polymerase binding site

Through high throughput screening, substituted proline sulfonamide 6 was identified as HCV NS5b RNA-dependent RNA polymerase inhibitor. Optimization of various regions of the lead molecule resulted in compounds that displayed good potency and selectivity. The crystal structure of 6 and NS5b polymerase complex confirmed the binding near the active site region. The optimization approach and SAR are discussed in detail.