Discovery, structure-activity relationship, and pharmacological evaluation of (5-substituted-pyrrolidinyl-2-carbonyl)-2-cyanopyrrolidines as potent dipeptidyl peptidase IV inhibitors

Enantio- and Diastereoselective Variations on α-Iminonitriles: Harnessing Chiral Cyclopropenimine-Thiourea Organocatalysts

Chiral 1-pyrrolines containing a nitrile motif serve as crucial structural scaffolds in biologically active molecules and exhibit diversity as building blocks owing to their valuable functional groups; however, the asymmetric synthesis of such compounds remains largely unexplored. Herein, we present an enantio- and diastereoselective method for the synthesis of α-chiral nitrile-containing 1-pyrroline derivatives bearing vicinal stereocenters through the design and introduction of chiral cyclopropenimine-based bifunctional catalysts featuring a thiourea moiety. This synthesis entails a highly stereoselective conjugate addition of α-iminonitriles to a wide array of enones, followed by cyclocondensation, thereby affording a series of cyanopyrroline derivatives, some of which contain all-carbon quaternary centers. Moreover, we demonstrate the synthetic utility of this strategy by performing a gram-scale reaction with 1% catalyst loading, along with a variety of chemoselective transformations of the product, including the synthesis of a vildagliptin analogue. Finally, we showcase the selective synthesis of all four stereoisomers of the cyanopyrroline products through trans-to-cis isomerization, highlighting the versatility of our approach.

Isolation and In silico Study of Curcumin from Curcuma longa and Its Anti-Diabetic Activity

Natural products have been widely used for the management of various diseases that affect human health. Natural products are chemical substances that can be extracted with solvents and isolated by column chromatography techniques from the plant source. The development of new drugs from natural products is still challenging, and the most extensively studied plant material is turmeric, Curcuma longa, which is the chief source of curcumin. Curcumin is a bright yellow solid. In our present study, we have taken Curcuma longa, which is defatted with hexane, followed by being extracted with methanol as a solvent. The turmeric methanolic extract is taken for the isolation of curcumin. This was carried out and confirmed by spectroscopy techniques including ¹H NMR, ¹³C NMR, ESI-HRMS, and FT-IR. The compound in silico ADME properties estimate falls within an acceptable range, and a molecular docking analysis shows that it has a higher binding affinity than reference standards. Based on the findings, it can be said that curcumin, a natural substance, has good therapeutic qualities when it is isolated.

Therapeutic Effect of Novel Cyanopyrrolidine-Based Prolyl Oligopeptidase Inhibitors in Rat Models of Amnesia

Prolyl oligopeptidase (POP) is a large cytosolic serine peptidase that is altered in patients with Alzheimer’s disease, Parkinsonian syndrome, muscular dystrophies, and other denervating diseases. Thus, POP may represent a relevant therapeutic target for treatment of neuropsychiatric disorders and neurodegenerative diseases. Here, we report the characterization of five novel cyanopyrrolidine-based compounds (BocTrpPrdN, BocGlyPrdN, CbzMetPrdN, CbzGlnPrdN, and CbzAlaPrdN) and show that they are potent inhibitors of POP and are predicted to penetrate the blood-brain barrier (BBB). Indeed, we show that CbzMetPrdN penetrates the rat BBB and effectively inhibits POP in the brain when administered intraperitoneally. Furthermore, molecular modeling confirmed these compounds likely inhibit POP via interaction with the POP catalytic site. We evaluated protective effects of the cyanopyrrolidine-based POP inhibitors using scopolamine- and maximal electroshock-induced models of amnesia in rats and showed that BocTrpPrdN, BocGlyPrdN, CbzMetPrdN, and CbzGlnPrdN significantly prolonged conditioned passive avoidance reflex (CPAR) retention time when administered intraperitoneally (1 and 2 mg/kg) before evaluation in both models of amnesia, although CbzAlaPrdN was not effective in scopolamine-induced amnesia. Our data support previous reports on the antiamnesic effects of prolinal-based POP inhibitors and indicate an important role of POP in the regulation of learning and memory processes in the CNS.

Research Progress on Dipeptidyl Peptidase Family: Structure, Function and Xenobiotic Metabolism

Prolyl-specific peptidases or proteases, including Dipeptidyl Peptidase 2, 4, 6, 8, 9, 10, Fibroblast Activation Protein, prolyl endopeptidase and prolyl carboxypeptidase, belong to the dipeptidyl peptidase family. In human physiology and anatomy, they have homology amino acid sequences, similarities in structure, but play distinct functions and roles. Some of them also play important roles in the metabolism of drugs containing endogenous peptides, xenobiotics containing peptides, and exogenous peptides. The major functions of these peptidases in both the metabolism of human health and bioactive peptides are of significant importance in the development of effective inhibitors to control the metabolism of endogenous bioactive peptides. The structural characteristics, distribution of tissue, endogenous substrates, and biological functions were summarized in this review. Furthermore, the xenobiotics metabolism of the dipeptidyl peptidase family is illustrated. All the evidence and information summarized in this review would be very useful for researchers to extend the understanding of the proteins of these families and offer advice and assistance in physiology and pathology studies.

Structure-activity relationship and biochemical evaluation of novel fibroblast activation protein and prolyl endopeptidase inhibitors with α-ketoamide warheads

Peptidomimetic inhibitors of fibroblast activation protein (FAP) are regarded as promising tools for tumor targeting in vivo. Even though several peptidomimetic compounds with nanomolar potency have been described, broad chemical space for further modification remained unexplored. Therefore, we set to analyze the structure-activity relationship (SAR) of pseudopeptide compound series with α-ketoamide warheads in order to explore the contributions of the P1' and P2' moieties to the inhibitory potency. A series of novel inhibitors bearing varied P1' and/or P2' moieties was synthesized by combining a Passerini reaction-Amine Deprotection-Acyl Migration (PADAM) approach with peptide coupling and subsequent oxidation. The resulting compounds inhibited FAP and the related prolyl endopeptidase (PREP) with potencies in the nanomolar to sub-nanomolar range. The most potent FAP inhibitor IOCB22-AP446 (6d, IC₅₀ = 89 pM) had about 36-fold higher inhibition potency than the most potent inhibitor published to date. The compounds were selective over FAP's closest homolog DPP-IV, were stable in human and mouse plasma and in mouse microsomes, and displayed minimal cytotoxicity in tissue cultures.

The reaction of prop-2-ynylsulfonium salts and sulfonyl-protected β-amino ketones to epoxide-fused 2-methylenepyrrolidines and S-containing pyrroles

A novel divergent domino annulation reaction of prop-2-ynylsulfonium salts with sulfonyl-protected β-amino ketones has been developed, affording various epoxide-fused 2-methylenepyrrolidines and S-containing pyrroles in moderate to excellent yields. Prop-2-ynylsulfonium salts act as C₂ synthons in the reactions providing a promising epoxide-fused skeleton in a single operation with readily accessible starting materials.

Structure-based virtual screening of dipeptidyl peptidase 4 inhibitors and their in vitro analysis

Type 2 diabetes mellitus (T2DM) is one of the most widely prevalent metabolic disorders with no cure to date thus remains the most challenging task in the current drug discovery. Therefore, the only strategy to control diabetes prevalence is to develop novel efficacious therapeutics. Dipeptidyl Peptidase 4 (DPP-4) inhibitors are currently used as anti-diabetic drugs for the inhibition of incretins. This study aims to construct the chemical feature based on pharmacophore models for dipeptidyl peptidase IV. The structure-based pharmacophore modeling has been employed to evaluate new inhibitors of DPP-4. A four-featured pharmacophore model was developed from crystal structure of DPP-4 enzyme with 4-(2-aminoethyl) benzenesulfonyl fluoride in its active site via pharmacophore constructing tool of Molecular Operating Environment (MOE) consisting F1 Hyd (hydrophobic region), F2 Hyd|Cat|Don (hydrophobic cationic and donor region), F3 Acc (acceptor region) and F4 Hyd (hydrophobic region). The generated pharmacophore model was used for virtual screening of in-house compound library (the available compounds which were used for initial screening to get the few compounds for the current studies). The resultant selected compounds, after virtual screening were further validated using in vitro assay. Furthermore, structure-activity relationship was carried out for the compounds possessing significant inhibition potential after docking studies. The binding free energy of analogs was evaluated via molecular mechanics generalized Born surface area (MM-GBSA) and Poisson-Boltzmann surface area (MM-PBSA) methods using AMBER 16 as a molecular dynamics (MD) simulation package. Based on potential findings, we report that selected candidates are more likely to be used as DPP-4 inhibitors or as starting leads for the development of novel and potent DPP-4 inhibitors.

Integrated Protocol to Design Potential Inhibitors of Dipeptidyl Peptidase- 4 (DPP-4)

BACKGROUND

A strategy for the treatment of type II diabetes mellitus is the inhibition of the enzyme known as dipeptidyl peptidase-4 (DPP-4).

AIMS

This study aims to investigate the main interactions between DPP-4 and a set of inhibitors, as well as proposing potential candidates to inhibit this enzyme.

METHODS

We performed molecular docking studies followed by the construction and validation of CoMFA and CoMSIA models. The information provided from these models was used to aid in the search for new candidates to inhibit DPP-4 and the design of new bioactive ligands from structural modifications in the most active molecule of the studied series.

RESULTS

We were able to propose a set of analogues with biological activity predicted by the CoMFA and CoMSIA models, suggesting that our protocol can be used to guide the design of new DPP-4 inhibitors as drug candidates to treat diabetes.

CONCLUSION

Once the integration of the techniques mentioned in this article was effective, our strategy can be applied to design possible new DPP-4 inhibitors as candidates to treat diabetes.

Rational Design of Multitarget-Directed Ligands: Strategies and Emerging Paradigms

Due to the complexity of multifactorial diseases, single-target drugs do not always exhibit satisfactory efficacy. Recently, increasing evidence indicates that simultaneous modulation of multiple targets may improve both therapeutic safety and efficacy, compared with single-target drugs. However, few multitarget drugs are on market or in clinical trials, despite the best efforts of medicinal chemists. This article discusses the systematic establishment of target combination, lead generation, and optimization of multitarget-directed ligands (MTDLs). Moreover, we analyze some MTDLs research cases for several complex diseases in recent years and the physicochemical properties of 117 clinical multitarget drugs, with the aim to reveal the trends and insights of the potential use of MTDLs.

Predictive Power of Different Types of Experimental Restraints in Small Molecule Docking: A Review

Incorporating experimental restraints is a powerful method of increasing accuracy in computational protein small molecule docking simulations. Different algorithms integrate distinct forms of biochemical data during the docking and/or scoring stages. These so-called hybrid methods make use of receptor-based information such as nuclear magnetic resonance (NMR) restraints or small molecule-based information such as structure-activity relationships (SARs). A third class of methods directly interrogates contacts between the protein receptor and the small molecule. This work reviews the current state of using such restraints in docking simulations, evaluates their feasibility across broad systems, and identifies potential areas of algorithm development.

Exploration of DPP-IV inhibitors with a novel scaffold by multistep in silico screening

Dipeptidyl peptidase-IV (DPP-IV), an enzyme that degrades incretins-hormones that promote insulin secretion-is a therapeutic target for type 2 diabetes, with a number of its inhibitors having been launched as therapies for diabetes. Since adverse effects of these inhibitors have recently been reported, the development of novel DPP-IV inhibitors with higher efficacy and safety is required. We, therefore, screened for novel DPP-IV inhibitors using the combination of an in silico drug discovery technique and a DPP-IV assay system. We initially selected seven candidate compounds as DPP-IV inhibitors from a database consisting of four million compounds by a multistep in silico screening procedure combining pharmacophore-based screening, docking calculation and the analysis of three-dimensional quantitative structure-activity relationship. We then measured the inhibitory activity of the selected compounds and identified a hit compound. In addition, we discuss the structure-activity relationship between the binding mode model and inhibitory activity of the hit compound.

Effects of activated carbon N-acetylcysteine sustained-release microcapsule on dipeptidyl peptidase IV expression in young rats with non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) in children has become the most common liver disease influencing adolescent health and one of the most influencing chronic liver diseases among children in Chinese wealthy families, particularly in coastal regions. However, the medicine available for the treatment of NAFLD is deficient. In order to solve this problem, our team studied the activated carbon N-acetylcysteine (NAC) sustained-release microcapsule, which improves the oxidation resistance, bioavailability and drug stability of acetylcysteine and reduces toxic and side effects. In addition, it accords with the characteristics of medication in infants and children. The present study mainly discusses whether the activated carbon NAC sustained-release microcapsule has effects on dipeptidyl peptidase IV (DPPIV) activity and protein in young rats with NAFLD, and whether it has the effect of an DPPIV inhibitor, hoping to provide new thoughts and methods with respect of basic studies on young rats with NAFLD/non-alcoholic steatohepatitis.

Approaches towards the development of chimeric DPP4/ACE inhibitors for treating metabolic syndrome

Designing drug candidates exhibiting polypharmacology is one of the strategies adopted by medicinal chemists to address multifactorial diseases. Metabolic disease is one such multifactorial disorder characterized by hyperglycaemia, hypertension and dyslipidaemia among others. In this paper we report a new class of molecular framework combining the pharmacophoric features of DPP4 inhibitors with those of ACE inhibitors to afford potent dual inhibitors of DPP4 and ACE.

Comprehensive analysis of the Co-structures of dipeptidyl peptidase IV and its inhibitor

Background

We comprehensively analyzed X-ray cocrystal structures of dipeptidyl peptidase IV (DPP-4) and its inhibitor to clarify whether DPP-4 alters its general or partial structure according to the inhibitor used and whether DPP-4 has a common rule for inhibitor binding.

Results

All the main and side chains in the inhibitor binding area were minimally altered, except for a few side chains, despite binding to inhibitors of various shapes. Some residues (Arg125, Glu205, Glu206, Tyr662 and Asn710) in the area had binding modes to fix a specific atom of inhibitor to a particular spatial position in DPP-4. We found two specific water molecules that were common to 92 DPP-4 structures. The two water molecules were close to many inhibitors, and seemed to play two roles: maintaining the orientation of the Glu205 and Glu206 side chains through a network via the water molecules, and arranging the inhibitor appropriately at the S2 subsite.

Conclusions

Our study based on high-quality resources may provide a necessary minimum consensus to help in the discovery of a novel DPP-4 inhibitor that is commercially useful.

Electronic supplementary material

The online version of this article (doi:10.1186/s12900-016-0062-8) contains supplementary material, which is available to authorized users.

Mutant cycle analysis with modified saxitoxins reveals specific interactions critical to attaining high-affinity inhibition of hNaV1.7

Improper function of voltage-gated sodium channels (NaVs), obligatory membrane proteins for bioelectrical signaling, has been linked to a number of human pathologies. Small-molecule agents that target NaVs hold considerable promise for treatment of chronic disease. Absent a comprehensive understanding of channel structure, the challenge of designing selective agents to modulate the activity of NaV subtypes is formidable. We have endeavored to gain insight into the 3D architecture of the outer vestibule of NaV through a systematic structure-activity relationship (SAR) study involving the bis-guanidinium toxin saxitoxin (STX), modified saxitoxins, and protein mutagenesis. Mutant cycle analysis has led to the identification of an acetylated variant of STX with unprecedented, low-nanomolar affinity for human NaV1.7 (hNaV1.7), a channel subtype that has been implicated in pain perception. A revised toxin-receptor binding model is presented, which is consistent with the large body of SAR data that we have obtained. This new model is expected to facilitate subsequent efforts to design isoform-selective NaV inhibitors.

Design, Synthesis, and Pharmacological Evaluation of Fused β-Homophenylalanine Derivatives as Potent DPP-4 Inhibitors

Dipeptidyl peptidase-4 (DPP-4) inhibitors are accepted as a favorable class of agents for the treatment of type 2 diabetes. Herein, a series of fused β-homophenylalanine derivatives as novel DPP-4 inhibitors were designed, synthesized, and evaluated for their inhibitory activities against DPP-4. Most of them displayed excellent DPP-4 inhibitory activities and good selectivity. Among them, 9aa, 18a, and 18m also showed good efficacy in an oral glucose tolerance test (OGTT) in ICR mice. Moreover, when dosed 8 h prior to glucose challenge, 18m showed significantly greater potency than sitagliptin. It thus provides potential candidates for the further development into potent drugs targeting DPP-4.

Design, synthesis, and pharmacological evaluation of highly potent and selective dipeptidyl peptidase-4 inhibitors

The optimization of a series of fused β-homophenylalanine inhibitors of dipeptidyl peptidase-4 (DPP-4) is described. Modification on the P2-binding moiety of 6 (IC50 = 10 nM) led to the discovery of β-homophenylalanine derivatives containing pyrrolidin-2-ylmethyl amides. The introduction of a sulfamine in the meta position of the phenyl ring improved the potency against DPP-4 (6-12-fold increase). Compound 14k showed DPP-4 inhibitory activity with an IC50 value of 0.87 nM. Meanwhile, in vivo experiments exhibited that 14h had an efficiency comparable to sitagliptin at the dose of 10 mg/kg.

Facile access to unnatural dipeptide-alcohols based on cis-2,5-disubstituted pyrrolidines

Well-defined unnatural dipeptide-alcohols based on a cis-2,5-disubstitued pyrrolidine backbone were synthesized from commercially available starting materials meso-diethyl-2,5-dibromoadipate, (S)-(−)-1-phenylethylamine, and phenylalaninol. The structures of these unnatural dipeptide-alcohols are supported by HRMS, ¹H- and ¹³C-NMR spectroscopy. These unnatural dipeptide-alcohols can act as building blocks for peptidomimetics.

Synthesis of enantiomerically pure δ-benzylproline derivatives

The methodology allows for the preparation of enantiopure δ-substituted l-proline analogues bearing the side chain of proteinogenic residues.

Indium(iii)-catalyzed tandem synthesis of 2-alkynyl-3,3-dichloropyrrolidines and their conversion to 3-chloropyrroles

A convenient route to 2-alkynyl-3,3-dichloropyrrolidines was described by addition of terminal acetylenes to 2,2,4-trichloroaldimines using In(OTf)₃ as a catalyst. In the presence of a base these pyrrolidines were transformed into 3-chloropyrroles.

Recent approaches to medicinal chemistry and therapeutic potential of dipeptidyl peptidase-4 (DPP-4) inhibitors

Dipeptidyl peptidase-4 (DPP-4) is one of the widely explored novel targets for Type 2 diabetes mellitus (T2DM) currently. Research has been focused on the strategy to preserve the endogenous glucagon like peptide (GLP)-1 activity by inhibiting the DPP-4 action. The DPP-4 inhibitors are weight neutral, well tolerated and give better glycaemic control over a longer duration of time compared to existing conventional therapies. The journey of DPP-4 inhibitors in the market started from the launch of sitagliptin in 2006 to latest drug teneligliptin in 2012. This review is mainly focusing on the recent medicinal aspects and advancements in the designing of DPP-4 inhibitors with the therapeutic potential of DPP-4 as a target to convey more clarity in the diffused data.

New leads for DPP IV inhibition: structure-based pharmacophore mapping and virtual screening study

Dipeptidyl peptidase IV (DPP IV) is an attractive target for the development of new antidiabetic drugs. DPP IV inhibitors improve glycemic control by preventing the rapid inactivation of the incretin hormones; glucagon-like peptide 1 (GLP-1) and glucose-dependent insulinotropic peptide. In the current study, virtual screening, using 2D and 3D filters implemented in a hierarchical cascade, was employed to identify new DPP IV inhibitors. Co-crystallized ligands, with potent DPP IV-inhibitory activities, were utilized to generate structure-based pharmacophore models using DS Visualizer software. The derived pharmacophore maps were validated using in-house built database containing active and inactive DPP IV inhibitors. Subsequently, the optimum validated pharmacophore model was used as a search query against two 3D-databases (NCI and in-house built drug databases). Further hit filtration was carried out employing 2D virtual filters based on Lipinski's rule of 5; number of rotatable bonds and other physicochemical filters. 3D filter using high-throughput molecular docking was also applied. As a result, 5 novel DPP IV inhibitors were discovered as potential lead compounds and later confirmed via in vitro bioassay.

The importance of plasma protein binding in drug discovery

Plasma protein binding of drugs is a well-recognised phenomena, but it is only recently that the implications for drug action in vivo have been fully appreciated. Plasma proteins, by virtue of their high concentration, control the free drug concentration in plasma and in compartments in equilibrium with plasma, thereby, effectively attenuating drug potency in vivo. The historical background and thermodynamic basis for the 'Free Drug Principle' is presented, along with special considerations for intracellular targets, deep compartments and α1-acid glycoprotein binding. Real and apparent exceptions to the principle are discussed along with a survey of citations from the recent medicinal chemistry literature.

Perspective: Alchemical free energy calculations for drug discovery

Computational techniques see widespread use in pharmaceutical drug discovery, but typically prove unreliable in predicting trends in protein-ligand binding. Alchemical free energy calculations seek to change that by providing rigorous binding free energies from molecular simulations. Given adequate sampling and an accurate enough force field, these techniques yield accurate free energy estimates. Recent innovations in alchemical techniques have sparked a resurgence of interest in these calculations. Still, many obstacles stand in the way of their routine application in a drug discovery context, including the one we focus on here, sampling. Sampling of binding modes poses a particular challenge as binding modes are often separated by large energy barriers, leading to slow transitions. Binding modes are difficult to predict, and in some cases multiple binding modes may contribute to binding. In view of these hurdles, we present a framework for dealing carefully with uncertainty in binding mode or conformation in the context of free energy calculations. With careful sampling, free energy techniques show considerable promise for aiding drug discovery.

Inhibition of dipeptidyl peptidase IV (DPP IV) is one of the mechanisms explaining the hypoglycemic effect of berberine

Berberine was investigated as an inhibitor of human dipeptidyl peptidase IV (DPP IV) in an attempt to explain its anti-hyperglycemic activities. The investigation included simulated docking experiments to fit berberine within the binding pocket of DPP IV. Berberine was found to readily fit within the binding pocket of DPP IV in a low energy orientation characterized with optimal electrostatic attractive interactions bridging the isoquinolinium positively charged nitrogen atom (berberine) and the negatively charged acidic residue of glutamic acid-205 (GLU205) of DPP IV. Experimentally, berberine was found to inhibit human recombinant DPP IV in vitro with IC(50) = 13.3 microM. Our findings suggest that DPP IV inhibition is, at least, one of the mechanisms that explain the anti-hyperglycemic activity of berberine. The fact that berberine was recently reported to potently inhibit the pro-diabetic target human protein tyrosine phosphatase 1B (h-PTP 1B) discloses a novel dual natural h-PTP 1B/DPP IV inhibitor.

Discovery of DPP IV inhibitors by pharmacophore modeling and QSAR analysis followed by in silico screening

Dipeptidyl peptidase IV (DPP IV) deactivates the natural hypoglycemic incretin hormones. Inhibition of this enzyme should restore glucose homeostasis in diabetic patients making it an attractive target for the development of new antidiabetic drugs. With this in mind, the pharmacophoric space of DPP IV was explored using a set of 358 known inhibitors. Thereafter, genetic algorithm and multiple linear regression analysis were employed to select an optimal combination of pharmacophoric models and physicochemical descriptors that yield selfconsistent and predictive quantitative structure-activity relationships (QSAR) (r(2) (287)=0.74, F-statistic=44.5, r(2) (BS)=0.74, r(2) (LOO)=0.69, r(2) (PRESS) against 71 external testing inhibitors=0.51). Two orthogonal pharmacophores (of cross-correlation r(2)=0.23) emerged in the QSAR equation suggesting the existence of at least two distinct binding modes accessible to ligands within the DPP IV binding pocket. Docking experiments supported the binding modes suggested by QSAR/pharmacophore analyses. The validity of the QSAR equation and the associated pharmacophore models were established by the identification of new low-micromolar anti-DPP IV leads retrieved by in silico screening. One of our interesting potent anti-DPP IV hits is the fluoroquinolone gemifloxacin (IC(50)=1.12 muM). The fact that gemifloxacin was recently reported to potently inhibit the prodiabetic target glycogen synthase kinase 3beta (GSK-3beta) suggests that gemifloxacin is an excellent lead for the development of novel dual antidiabetic inhibitors against DPP IV and GSK-3beta.

Binding of small-molecule ligands to proteins: "what you see" is not always "what you get"

We review insights from computational studies of affinities of ligands binding to proteins. The power of structural biology is in translating knowledge of protein structures into insights about their forces, binding, and mechanisms. However, the complementary power of computer modeling is in showing "the rest of the story" (i.e., how motions and ensembles and alternative conformers and the entropies and forces that cannot be seen in single molecular structures also contribute to binding affinities). Upon binding to a protein, a ligand can bind in multiple orientations; the protein or ligand can be deformed by the binding event; waters, ions, or cofactors can have unexpected involvement; and conformational or solvation entropies can sometimes play large and otherwise unpredictable roles. Computer modeling is helping to elucidate these factors.

Facile synthetic route to enantiopure unsymmetriccis-2,5-disubstituted pyrrolidines

The (+/-)-cis-5-arylcarbamoyl-2-ethoxycarbonylpyrrolidines 6a-g were firstly synthesized in 53-64% yields by using meso-diethyl-2,5-dibromoadipate 3 and (S)-(-)-1-phenylethylamine in three steps. The diastereomeric mixture (S;2S,5R)-(-)-7 and (S;2R,5S)-(+)-8 were prepared by the Grignard reaction and separated by a flash column chromatography in 29 and 52% yields. The absolute configurations of (+)-8 was confirmed by X-ray crystallographic analysis and the enantiopure pyrrolidines (2S,5R)-(-)-9/(2R,5S)-(+)-9 and (2S,5R)-(-)-10/(2R,5S)-(+)-10 were obtained in good yields.