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Advances in the field of shuttle-mediated drug delivery have been made in the last decade; however, the treatment of brain disorders still remains a great challenge because of the presence of the blood-brain barrier (BBB), a structure that limits the access of drugs to their site of action in the central nervous system. Several strategies have been proposed to enhance the transport of drugs across the BBB. In this Review, we focus on the vector-mediated approach, in which a drug is coupled to a molecule (shuttle) that has the ability to cross the BBB and deliver the drug to the brain.

Open and closed: The characterization of protein mobility is crucial for the understanding of biological functions. We have applied NMR spectroscopy to study the conformational dynamics of the 80 kDa enzyme prolyl oligopeptidase (POP). Our results revealed that POP is highly dynamic and that inhibition of catalytic activity shifts this conformational equilibrium towards a less dynamic state.

At present, colistin is among the few antibiotics effective against Acinetobacter baumannii clinical isolates. However, in the last few years, colistin-resistant A. baumannii strains have been isolated. Therefore, antibiotics effective against these usually pan-resistant colistin-resistant A. baumannii strains are required. The main objective of this study was to analyse the activity of 15 peptides against colistin-susceptible and colistin-resistant A. baumannii. The MICs were determined by microdilution. Among these 15 antimicrobial peptides (AMPs), melittin, indolicidin and mastoparan showed good activity against both colistin-susceptible and colistin-resistant A. baumannii. Further studies of mastoparan with time-killing curves showed bactericidal activity at MIC x8 for both colistin-susceptible and colistin-resistant A. baumannii. In conclusion, mastoparan may be a potential alternative for the treatment of colistin-resistant A. baumannii infections.

The recognition of protein surfaces by designed ligands has become an attractive approach in drug discovery. However, the variable nature and irregular behavior of protein surfaces defy this new area of research. The easy to understand "lock-and-key" model is far from being the ideal paradigm in biomolecular interactions and, hence, any new finding on how proteins and ligands behave in recognition events paves a step of the way. Herein, we illustrate a clear example on how an increase in flexibility of both protein and ligand can result in an increase in the stability of the macromolecular complex. The biophysical study of the interaction between a designed flexible tetraguanidinium-calix[4]arene and the tetramerization domain of protein p53 (p53TD) and its natural mutant p53TD-R337H shows how the floppy mutant domain interacts more tightly with the ligand than the well-packed wild-type protein. Moreover, the flexible calixarene ligand interacts with higher affinity to both wild-type and mutated protein domains than a conformationally rigid calixarene analog previously reported. These findings underscore the crucial role of flexibility in molecular recognition processes, for both small ligands and large biomolecular surfaces.

Prolyl Oligopeptidase (POP) is a serine peptidase that cleaves post-proline bonds in short peptides. Besides the direct hydrolytic regulation function over peptides, neuropeptides and peptide hormones, POP is probably involved in the regulation of the inositol pathway and participates in protein-protein interactions. Experimental data show that POP inhibitors have neuroprotective, anti-amnesic and cognition-enhancing properties. These compounds are considered therapeutic agents of interest for the treatment of cognitive deficits related to neuropsychiatric and neurodegenerative diseases, such as Alzheimer's disease and Parkinson's disease. Recent findings pointed to the involvement of POP in angiogenesis, although the exact mechanism is still under study.This review comprises patents and patent applications involving POP inhibitors patented between 2003 and 2010, classified as peptidomimetics, heteroaryl ketones and alkaloids. The binding processes and the mechanisms of inhibition of these inhibitors are also discussed, together with their in vivo effects.The major part of the repertory of POP inhibitors derived from systematical modification of the canonical compound benzyloxycarbonyl-prolyl-prolinal (ZPP). Nevertheless, only two of them have progressed into the clinical trials. One possible reason for this failure is the lack of studies concerning pharmacodynamics, pharmacokinetics and toxicity, together with the absence of suitable animal models. Moreover, POP is still not a well-defined therapeutic target. Further studies are required for the elucidation of the biological role of POP and to validate the therapeutic action of inhibitors in cognitive processes. In contrast, the involvement of POP in protein-protein interactions together with the recent evidences in angiogenesis opens alternative approaches to the traditional active site-directed inhibitors, as well as new therapeutic applications.

A critical aspect to understanding the molecular basis of Alzheimer's disease (AD) is the characterization of the kinetics of interconversion between the different species present during amyloid-β protein (Aβ) aggregation. By monitoring hydrogen/deuterium exchange in Aβ fibrils using electrospray ionization mass spectrometry, we demonstrate that the Aβ molecules comprising the fibril continuously dissociate and reassociate, resulting in molecular recycling within the fibril population. Investigations on Aβ40 and Aβ42 amyloid fibrils reveal that molecules making up Aβ40 fibrils recycle to a much greater extent than those of Aβ42. By examining factors that could influence molecular recycling and by running simulations, we show that the rate constant for dissociation of molecules from the fibril (k(off)) is much greater for Aβ40 than that for Aβ42. Importantly, the k(off) values obtained for Aβ40 and Aβ42 reveal that recycling occurs on biologically relevant time scales. These results have implications for understanding the role of Aβ fibrils in neurotoxicity and for designing therapeutic strategies against AD.

Heterotrimeric guanine nucleotide-binding proteins (G proteins) composed of three subunits α, β, γ mediate activation of multiple intracellular signaling cascades initiated by G protein-coupled receptors (GPCRs). Previously our laboratory identified small molecules that bind to Gβγ and interfere with or enhance binding of select effectors with Gβγ. To understand the molecular mechanisms of selectivity and assess binding of compounds to Gβγ, we used biophysical and biochemical approaches to directly monitor small molecule binding to Gβγ. Surface plasmon resonance (SPR) analysis indicated that multiple compounds bound directly to Gβγ with affinities in the high nanomolar to low micromolar range but with surprisingly slow on and off rate kinetics. While the k(off) was slow for most of the compounds in physiological buffers, they could be removed from Gβγ with mild chaotropic salts or mildly dissociating collision energy in a mass-spectrometer indicating that compound-Gβγ interactions were non-covalent. Finally, at concentrations used to observe maximal biological effects the stoichiometry of binding was 1:1. The results from this study show that small molecule modulation of Gβγ-effector interactions is by specific direct non-covalent and reversible binding of small molecules to Gβγ. This is highly relevant to development of Gβγ targeting as a therapeutic approach since reversible, direct binding is a prerequisite for drug development and important for specificity.

Summary Fluoroquinolones are an important class of wide‐spectrum antibacterial agents. The first quinolone described was nalidixic acid, which showed a narrow spectrum of activity. The evolution of quinolones to more potent molecules was based on changes at positions 1, 6, 7 and 8 of the chemical structure of nalidixic acid. Quinolones inhibit DNA gyrase and topoisomerase IV activities, two enzymes essential for bacteria viability. The acquisition of quinolone resistance is frequently related to (i) chromosomal mutations such as those in the genes encoding the A and B subunits of the protein targets (gyrA, gyrB, parC and parE), or mutations causing reduced drug accumulation, either by a decreased uptake or by an increased efflux, and (ii) quinolone resistance genes associated with plasmids have been also described, i.e. the qnr gene that encodes a pentapeptide, which blocks the action of quinolones on the DNA gyrase and topoisomerase IV; the aac(6′)‐Ib‐cr gene that encodes an acetylase that modifies the amino group of the piperazin ring of the fluoroquinolones and efflux pump encoded by the qepA gene that decreases intracellular drug levels. These plasmid‐mediated mechanisms of resistance confer low levels of resistance but provide a favourable background in which selection of additional chromosomally encoded quinolone resistance mechanisms can occur.

6 páginas, 3 figuras., The use of square wave voltammetry to monitor the cellular uptake, in HeLa cells, of quantum dots (QD) decorated with sweet arrow peptide (SAP) is reported. A SAP derivative containing an additional N-terminal cysteine residue (C-SAP) was synthesized using the solid-phase method and conjugated to QDs. The obtained results show that QDs-SAP either interact with the extracellular cell membrane matrix or translocate the bilayer. The first situation, membrane adsorption, is probably a transient state before cellular uptake. Both confocal microscopy and SWV results support the detection of this cellular internalization process. The developed electrochemical investigation technique can provide valuable insights into the study of peptide-mediated delivery, as well as the design and development of nanoparticle probes for intracellular imaging, diagnostic, and therapeutic applications. In addition, the described electrochemical interrogation is low cost, is easy to use, and offers future interest for diagnostics including cell analysis., This work was supported by MAT2008-03079/NAN (MEC, Madrid); MCI-FEDER (Bio2008-00799, NAN2004-09159-C04- 02 and NANOBIOMED-CONSOLIDER) and the Generalitat de Catalunya (CeRBa and 2005SGR-00663). S. Pujals is supported by a FPU grant from the Ministerio de Ciencia e Innovación of Spain.

Background: The capacity of a polypeptide chain to engage in an amyloid formation process and cause a conformational disease is contained in its sequence. Some of the sequences undergoing fibrillation contain critical methionine (Met) residues which in vivo can be synthetically substituted by selenomethionine (SeM) and alter their properties. Methodology/Principal Findings: Using peptide synthesis, biophysical techniques and cell viability determinations we have studied the effect of the substitution of methionine (Met) by selenomethionine (SeM) on the fibrillogenesis and toxic properties of Aβ40 and HuPrP(106-140). We have found that the effects display site-specificity and vary from inhibition of fibrillation and decreased toxicity ([SeM35]Aβ40, [SeM129]HuPrP(106-140) and [SeM134]HuPrP(106-140)), retarded assembly, modulation of polymer shape and retention of toxicity ([SeM112]HuPrP(106-140) to absence of effects ([SeM109]HuPrP(106-140)). Conclusions/Significance: This work provides direct evidence that the substitution of Met by SeM in proamyloid sequences has a major impact on their self-assembly and toxic properties, suggesting that the SeM pool can play a major role in dictating the allowance and efficiency of a polypeptide chain to undergo toxic polymerization. © 2011 Martínez et al., Spanish Ministry of Science and Innovation, from the Fundación Cien-Fundación Reina Sofia, and from Generalitat de Catalunya (XRB and Grups Consolidats).

This paper shows Gel-phase 31 P-NMR spectra of synthetic intermediates obtained during solid-phase oligonucleotide synthesis on polystyrene for the first time. We have demonstrated the application of this technique using the phosphotriester, H-phosphonate and phosphite triester approaches. The use of Gel-phase 31 P-NMR for monitoring solid phase oligonucleotide synthesis is discussed.

A cyclic disulfide peptide representing antigenic site A of foot-and-mouth-disease virus (FMDV) strain C-S8cl (residues 134 to 155 of viral protein l (VP1) with Tyr136 and Arg153 replaced by cystine; TTCTASARGDLAHLTTTHACHL) was synthesized by solid phase methods. Formation of the cyclic disulfide was carried out by air oxidation of the fully deprotected and reduced bis-cysteine precursor, under high dilution conditions. The identity of the cyclic peptide was confirmed by both physical and enzymatic methods. A conformational study of the cyclic peptide and of its linear parent structure (YTASARGDLAHLTTTHARHLP, residues 136–156 of VP1 of FMDV C-S8cl) by circular dichroism in the presence of a structure-inducing solvent showed the cyclic disulfide analog to adopt lower levels of α-helix than its linear counterpart. In competitive ELISA assays both peptides reacted with similar affinity against a representative panel of neutralizing monoclonal antibodies directed towards antigenic site A. Thus, a high inherent flexibility of this loop may preclude a conformational restriction strong enough to alter recognition by anti-virus antibodies.

Protected peptide segments corresponding to the 1–4, 5–11, 19–30, 39–49 and 50–58 segments of the Uteroglobin monomer have been synthesised on a solid support using the photolabile ortho -nitrobenzyl unit as a handle. Photolytic detachment of the peptides from the solid support occurred in good yields. The 50–58 protected peptide segment has also been synthesised using the base-labile NPE handle, and detached from the solid support in excellent yield by treatment with a 20% solution of piperidine in DMF. The protected peptide segments were purified by MPLC and/or preparative HPLC, using solvents containing DMF.

The reduction of methionine sulfoxide with Bu4NBr in TFA is reported. The use of this reagent in conjunction with Fmoc chemistry-based acidolytic cocktails and the short reaction times that are needed for sulfoxide reduction (5 min) are the main advantages of this method, which is compatible with peptides containing aromatic amino acids. Cysteine is also stable under these conditions although, if desired, simultaneous disulfide formation can be achieved in the absence of thiols.

A general method for the solid phase synthesis of type 2 3,4,5-trihydroxypiperidin-2-ones is described. Amination of d- ribonolactone 4 was accomplished using a Mitsunobu reaction, and type 7 aminolactone underwent direct lactamisation upon treatment with NaOAc. For the solid phase synthesis, the aminoacid was anchored directly to a TentaGel® resin, and the lactamisation step was concomitant with the cleavage from the resin.

Preface. List of Contributors. PART I PRINCIPLES. 1 The Discovery and Characterization of Protein-Protein Interactions (C.W. Bertoncini, A. Higueruelo, and X. Salvatella). 1.1 Introduction. 1.2 Techniques to Identify Protein-Protein Interactions. 1.3 Techniques to Characterize Protein-Protein Interactions. 1.4 Structure and Dynamics of Protein Complexes. 1.5 Protein-Protein Complexes as Therapeutic Targets. 1.6 Conclusions. References. 2 Biophysics of Protein-Protein Interactions (Irene Luque). 2.1 Introduction. 2.2 Intermolecular Forces in Protein Recognition. 2.3 Basic Binding Thermodynamics. 2.4 Thermodynamically Driven Drug Design. 2.5 Measurement of Binding Energetics. 2.6 Structure-based Calculation of Protein Binding Energetics. 2.7 Interfacial Water Molecules in Protein Recognition. 2.8 The Linkage Between Binding and Conformational Equilibrium in Proteins. References. PART II APPROACHES. 3 On the Logic of Natural Product Binding in Protein-Protein Interactivity (James J. La Clair). 3.1 Introduction. 3.2 Structural Logic. 3.3 Functional Logic. 3.4 The Need for Programmers. 3.5 Compiling the NPPI Mapper. References. 4 Interface peptide inhibitors of PPIs (Mark W. Peczuh, and Richard T. Desmond). 4.1 Interface Peptides Defined. 4.2 Unmodified Peptides. 4.3 Modified Peptides. 4.4 Summary/Perspective. References. 5 Inhibition of Protein-Protein Interactions by Peptide Mimics (Jorge Becerril, Johanna M. Rodriguez, Pauline N. Wyrembak, and Andrew D. Hamilton). 5.1 Introduction. 5.2 Inhibition of Calmodulin. 5.3 Inhibition of HIV-1 Fusion. 5.4 Inhibition of the Nuclear Estrogen Receptor. 5.5 Inhibition of the Bcl-x /Bak Interaction. 5.6 Inhibition of the p53/MDM2 Interaction. 5.7 Miscellaneous Protein Targets. 5.8 Conclusion. References. 6 Discovery of Inhibitors of Protein-Protein Interactions by Screening Chemical Libraries (Carlos Garcia-Echeverria). 6.1 Introduction. 6.2 Screening Strategies to Identify and Develop Antagonists of Protein-Protein Interactions. 6.3 Mimetics of Common Protein Structure Motifs and Structure-based Design of Peptidomimetics. 6.4 Conclusions and Outlook. References. PART III TECHNIQUES. 7 High-throughput Methods of Chemical Synthesis Applied to the Preparation of Inhibitors of Protein-Protein Interactions (Annaliese K. Franz, Jared T. Shaw, and Yuchen Tang). 7.1 Introduction. 7.2 Survey of High-throughput Organic Synthesis. 7.3 Synthesis of 'Peptide-Inspired' Compounds and Libraries. 7.4 Synthesis of 'Natural Product-Inspired' Compounds and Libraries. 7.5 Diversity Oriented Synthesis (DOS) in the Discovery of PPI Inhibitors. 7.6 Summary and Outlook. References. 8 In Silico screening (F.J. Luque, and Xavier Barril). 8.1 Introduction. 8.2 Methods for Virtual Ligand Screening. 8.3 Binding Site Characterization. 8.4 Case Studies. 8.5 Outlook and Conclusions. References. 9.1 In Vitro Screening: Screening by Nuclear Magnetic Resonance (Ernest Giralt). 9.1.1 Saturation Transfer Difference (STD). 9.1.2 STD in Fragment-based Drug Design. 9.1.3 Chemical Shift Perturbation (CSP). 9.1.4 19F-NMR in Molecular Recognition Studies. References. 9.2 In Vitro Screening: Methods of High-throughput Screening (Wenjiao Song and Qing Lin). 9.2.1 Introduction. 9.2.2 Statistical Evaluation of the HTS Assay Performance. 9.2.3 Biochemical Assays. 9.2.4 Cell-based Assays. 9.2.5 Conclusion. References. PART IV CASE STUDIES. 10 Case Study: Inhibitors of the MDM2-p53 Protein-Protein Interaction (Sanjeev Shangary, Denzil Bernard, and Shaomeng Wang). 10.1 MDM2-p53 Protein-Protein Interaction: A Case Study. 10.2 Regulation of p53 by the MDM2-p53 Protein-Protein Interaction. 10.3 Structural Basis of the MDM2-p53 Interaction. 10.4 Design of p53-based Peptides. 10.5 Design of Nonpeptidic Small-Molecule Inhibitors of the MDM2-p53 Interaction. 10.6 Challenges in the Design of Small Molecule Inhibitors of the MDM2-p53 Interaction. 10.7 Reactivation of p53 by Inhibitors of the MDM2-p53 Interaction. 10.8 Development of MDM2 Inhibitors and New Anticancer Drugs. 10.9 Concluding Remarks. References. 11 Case Study: The Discovery of Potent LFA-1 Antagonists (Tom Gadek). 11.1 Introduction. 11.2 Structural, Molecular and Cellular Biologies of LFA-1. 11.3 The Search for Small Molecule LFA-1 Antagonists. 11.4 Screening Assays. 11.5 Lead Identification and Optimization. 11.6 Protein and Small Molecule Structure Activity Relationships (PSAR) in the LFA-1/ICAM-1 Interaction. 11.7 Summary. References. Index.

The objective of this project was to study the interaction between HR1 and HR2, the stability of the complex formed, and to characterize the antibodies produced against monomeric HR1 and HR2 peptides as well as the HR1-HR2 complex. In this work, HR1 was mimicked by peptide N36, and HR2 was mimicked by peptide C34L and its analogues C34M2, C34M3, and C34D. Whereas C34M2 and C34M3 are partially composed of D-amino acids, C34D has same sequence as C34L, but is assembled entirely of D-amino acids. Using CD analysis, SPR assays, and gel filtration chromatography, we demonstrate the physical interaction between N36 and C34L and its analogues C34M2 and C34M3, but not C34D. We show that the HR1-HR2 complex is formed rapidly (

Introduction A new cytotoxic cyclodepsipeptide IB-01212 was isolated from the mycelium extract of Chlonostachys pitirodes (Fig. 1) [1]. The novo cyclodepsipeptide is a symmetric cyclic peptide formed by the condensation of two chains of the tetrapeptide L-N,NMe2Leu-L-Ser-L-NMeLeu-L-NMePhe. The absolute configuration was determined by our group and it was confirmed that all amino acids were in the L-configuration. Herein we describe several strategies of synthesis on solid phase such as i) dimerization of heterodetic fragment, ii) linear synthesis, and iii) convergent synthesis. All syntheses were performed using Fmoc/tBu chemistry and ester bond resin. A comparison of the yield and quality of the synthetic processes showed that the convergent synthesis that combines fragments synthesized on two different resins gave the best results. Thus, this strategy is particularly suitable for the large-scale synthesis of IB-01212 and other peptides containing the same motifs.

Attempts of synthesis of oligonucleotides containing 2-aza-2′-deoxyinosine protected with the N,N-diphenylcarbamoyl group are described. An unexpected behaviour of the protected nucleoside can be used for the introduction of dAICA in synthetic oligonucleotides.

Disulfide-containing peptides may be obtained in good yields and purities when oxidations are carried out on peptide chains anchored to polymeric supports used for solid-phase synthesis. Such approaches take advantage of the pseudo-dilution phenomenon which favors intramolecular processes. A variety of procedures have been demonstrated using the related model peptides Ac-Cys-Pro-D Val-Cys-NH2 and Ac-Pen-Pro-D Val-Cys-NH2 (which both readily assume a type II beta-turn conformation that becomes stabilized by a 14-membered disulfide-containing intramolecular ring), and oxytocin (conformationally mobile 20-membered disulfide ring). Both Boc and Fmoc were used for N alpha-amino protection, the beta-thiols of cysteine or penicillamine were blocked by S-acetamidomethyl (Acm), S-9-fluorenylmethyl (Fm), or S-trityl (Trt), and compatible anchoring linkages included HF-labile 4-methylbenzhydrylamide (MBHA), TFA-labile tris (alkoxy)benzylamide (PAL), and photolabile o-nitrobenzylamide (Nonb). Assemblies of linear sequences proceeded smoothly, and polymer-supported oxidations were carried out in a variety of ways either directly or after deblocking to the resin-bound dithiol. Chains were released from the support without substantial damage to the disulfide bridges, and overall yields were as high as 60-90%.

The use of the α-(4-hydroxymethyl-3-nitrobenzamido)benzylpolystyrene (4-hydroxymethyl-Nbb resin) 1 to obtain peptide esters and amides is reported. The lability of the peptide-resin bond to methanol, methylamine, dimethylamine and hexylamine has been tested on three peptidyl-resin models with encouraging results.

A new acid stable protecting group for the sulfhydryl function of cystein is described. The S-2-(2,4-dinitrophenyl)ethyl-L-cysteine derivative is fully compatible with the Boc/Bzl solid phase peptide synyhesis strategy and can be smoothly and quantitatively removed to give the free thiol or a disulfide bridge.

The reliability of the S-phenylacetamidomethyl-L-cysteine Cys(Phacm), a versatile derivative compatible with both Boc and Fmoc protection schemes, has been examined for solid-phase peptide synthesis. The Phacm group has the same properties as acetamidomethyl (Acm) and in addition is cleaved by the action of the enzyme penicillin amidohydrolase. Thus, Phacm is orthogonal with the common cysteine-protecting groups, such as 4-methylbenzyl (p-MeBzl), trityl (Trt) and fluorenylmethyl (Fm).

The N-terminal domain of maize gamma-zein has a repetitive structure (Val-His-Leu-Pro-Pro-Pro)(8) that has recently been shown to adopt an amphipathic polyproline II type conformation in aqueous solution. We report here the synthesis and conformational analysis of three model peptides (Val-X-Leu-Pro-Pro-Pro)(8) (X = Ala (1), Glu (2), Lys (3)). The three compounds have been synthesized in a very efficient way using a convergent solid-phase strategy. Circular dichroism shows unequivocally that the three model peptides adopt polyproline II (PPII) type conformations under a variety of experimental conditions and that neither the presence of histidine nor amphipathicity of the peptide is an absolute requirement for adopting the native conformation. These results open the door for the de novo design of compounds with PPII conformations and must be taken into account in the structure prediction of protein structures from sequence data banks.

The {Trp-phenylglycinol} pseudodipeptide (αR,3R∗,4R∗)-N-(2-acetoxy-1-phenylethyl)-3-amino-4-indolyl-2-piperidone 33 has been synthezised by condensation of the 3-amino-substituted anhydride 30 with (R)-(-)-phenylglycinol followed by reduction of the resulting imide.

New total syntheses of didemnin A and of dehydrodidemnin B are described. The latter didemnin has the highest antiproliferative activity of all members of this family of macrocyclic depsipeptides. It was produced on coupling the side chain Pyr-Pro-OH to didemnin A, which was itself synthesized by two novel routes. One of these was based on the elaboration of a linear heptadepsipeptide incorporating the first amino acid of the didemnin side chain, (R)-N(Me)-Leu. Deprotection of the amino and carboxyl terminii of this linear precursor followed by macrocyclization gave a protected derivative of didemnin A. The second route involved synthesis of the Boc-protected didemnin macrocycle from a linear hexadepsipeptide lacking (R)-N(Me)-Leu. Removal of the Boc group from the macrocycle followed by its coupling with Boc-(R)-N(Me)-Leu-OH then gave Boc-didemnin A. The overall yield was much higher for the second strategy (27% compared to 4% for the first synthesis), but both allowed synthetic didemnin A, identical wit...

The use of N-Fmoc-N-(Hmb)amino acids for the introduction of the Hmb backbone protection into peptides during solid-phase synthesis is described. An efficient two step synthesis of these derivatives is reported and their coupling to the peptide chain is studied.

N-Acetylated threonine derivatives, having tert-butyl or benzyl-based side-chain protection, form isolable 5(4H)-oxazolones on treatment with N-ethyl-N′-3-dimethylaminopropyl carbodiimide. N-chloroacetylated threonine derivatives, on the other hand, do not form oxazolones so readily. The N-acetylated oxazolones are easily epimerized and lead to diastereoisomeric mixtures of threonine derivatives on hydrolysis with dilute aqueous acid. The components of these mixtures can be separated chromatographically, but a useful alternative for the O-benzylated mixture is selective enzymatic hydrolysis using hog kidney acylase. These chemical transformations provide the basis for practical syntheses of protected derivatives of the non-proteinogenic allo-threonines, suitable for use in peptide synthesis.

A new synthesis of 9-hydroxy- and 9-(alkylamino)thiazolo[5,4-b]quinolines by cyclization of 4-(ethoxycarbonyl)-5-(arylamino)thiazoles and 5-(arylamino)-4-carbamoylthiazoles, respectively, is described. In vitro cytotoxicity of a large number of derivatives of these compounds has been tested against several cell lines. The highest activities observed are associated with the presence of a 2-[[(N,N-diethylamino)ethyl]amino] substituent at C-2 and a fluorine atom at the C-7 position of the tricyclic planar heteroaromatic framework. Three structural features seem to be essential for antitumor activities: a positive charge density at carbon C-7, a side chain at position C-2 or C-9 of the thiazoloquinoline skeleton with two basic nitrogens and a pKa value of 7.5−10 in the most basic center, and a conformational flexibility of this basic side chain. These structural requirements must be simultaneously satisfied in order to ensure a significant antitumor activity.

Herein we present the design, synthesis, and evaluation of a structurally novel library of 20 peptidyl 3-aryl vinyl sulfones as inhibitors of cathepsins L and B. The building blocks, described here for the first time, were synthesized in a highly efficient and enantioselective manner, starting from 3-aryl-substituted allyl alcohols. The corresponding vinyl sulfones were prepared by a new approach, based on a combination of solid-phase peptide synthesis using the Fmoc/tBu strategy, followed by solution-phase coupling to the corresponding (R)-3-amino-3-aryl vinyl sulfones as trifluoroacetate salts. The inhibitory activity of the resulting compounds against cathepsins L and B was evaluated, and the compound exhibiting the best activity was selected for enzymatic characterization. Finally, docking studies were performed in order to identify key structural features of the aryl substituent.

We describe a stereoselective preparation of 3-amino-2-piperidone 1 , a new conformationally constrained Ser-Leu surrogate. The key steps of the synthesis of compound 1 are the lactamisation of the secondary aminolactone 4 and the amination of the 3-position via the sulfite 2 .