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International audience; Metallo-β-lactamases (MBLs) contribute to the resistance of Gram-negative bacteria to carbapenems, last-resort antibiotics at hospital, and MBL inhibitors are urgently needed to preserve these important antibacterial drugs. Here, we describe a series of 1,2,4-triazole-3-thione-based inhibitors displaying an α-amino acid substituent, which amine was mono- or disubstituted by (hetero)aryl groups. Compounds disubstituted by certain nitrogen-containing heterocycles showed submicromolar activities against VIM-type enzymes and strong NDM-1 inhibition (Ki = 10-30 nM). Equilibrium dialysis, native mass spectrometry, isothermal calorimetry (ITC), and X-ray crystallography showed that the compounds inhibited both VIM-2 and NDM-1 at least partially by stripping the catalytic zinc ions. These inhibitors also displayed a very potent synergistic activity with meropenem (16- to 1000-fold minimum inhibitory concentration (MIC) reduction) against VIM-type- and NDM-1-producing ultraresistant clinical isolates, including Enterobacterales and Pseudomonas aeruginosa. Furthermore, selected compounds exhibited no or moderate toxicity toward HeLa cells, favorable absorption, distribution, metabolism, excretion (ADME) properties, and no or modest inhibition of several mammalian metalloenzymes.

International audience; Metallo-β-lactamases (MBLs) represent an increasingly serious threat to public health because of their increased prevalence worldwide in relevant opportunistic Gram-negative pathogens. MBLs efficiently inactivate widely used and most valuable β-lactam antibiotics, such as oxyiminocephalosporins (ceftriaxone, ceftazidime) and the last-resort carbapenems. To date, no MBL inhibitor has been approved for therapeutic applications. We are developing inhibitors characterized by a 1,2,4-triazole-3-thione scaffold as an original zinc ligand and few promising series were already reported. Here, we present the synthesis and evaluation of a new series of compounds characterized by the presence of an arylalkyl substituent at position 4 of the triazole ring. The alkyl link was mainly an ethylene, but a few compounds without alkyl or with an alkyl group of various lengths up to a butyl chain were also synthesized. Some compounds in both sub-series were micromolar to submicromolar inhibitors of tested VIM-type MBLs. A few of them were broad-spectrum inhibitors, as they showed significant inhibitory activity on NDM-1 and, to a lesser extent, IMP-1. Among these, several inhibitors were able to significantly reduce the meropenem MIC on VIM-1- and VIM-4- producing clinical isolates by up to 16-fold. In addition, ACE inhibition was absent or moderate and one promising compound did not show toxicity toward HeLa cells at concentrations up to 250 μM. This series represents a promising basis for further exploration. Finally, molecular modelling of representative compounds in complex with VIM-2 was performed to study their binding mode.

International audience; Metallo-β-lactamases (MBLs) are increasingly involved as a major mechanism of resistance to carbapenems in relevant opportunistic Gram-negative pathogens. Unfortunately, clinically efficient MBL inhibitors still represent an unmet medical need. We previously reported several series of compounds based on the 1,2,4-triazole-3-thione scaffold. In particular, Schiff bases formed between diversely 5-substituted-4-amino compounds and 2-carboxybenzaldehyde were broad-spectrum inhibitors of VIM-type, NDM-1 and IMP-1 MBLs. Unfortunately, these compounds were unable to restore antibiotic susceptibility of MBL-producing bacteria, probably because of poor penetration and/or susceptibility to hydrolysis. To improve their microbiological activity, we synthesized and characterized compounds where the hydrazone-like bond of the Schiff base analogues was replaced by a stable ethyl link. This small change resulted in a narrower inhibition spectrum, as all compounds were poorly or not inhibiting NDM-1 and IMP-1, but showed a significantly better activity on VIM-type enzymes, with K i values in the μM to sub-μM range. The resolution of the crystallographic structure of VIM-2 in complex with one of the best inhibitors yielded valuable information about their binding mode. Interestingly, several compounds were shown to restore the β-lactam susceptibility of VIM-type-producing E. coli laboratory strains and also of K. pneumoniae clinical isolates. In addition, selected compounds were found to be devoid of toxicity toward human cancer cells at high concentration, thus showing promising safety.

In Gram-negative bacteria, the major mechanism of resistance to β-lactam antibiotics is the production of one or several β-lactamases (BLs), including the highly worrying carbapenemases. Whereas inhibitors of these enzymes were recently marketed, they only target serine-carbapenemases (e.g. KPC-type), and no clinically useful inhibitor is available yet to neutralize the class of metallo-β-lactamases (MBLs). We are developing compounds based on the 1,2,4-triazole-3-thione scaffold, which binds to the di-zinc catalytic site of MBLs in an original fashion, and we previously reported its promising potential to yield broad-spectrum inhibitors. However, up to now only moderate antibiotic potentiation could be observed in microbiological assays and further exploration was needed to improve outer membrane penetration. Here, we synthesized and characterized a series of compounds possessing a diversely functionalized alkyl chain at the 4-position of the heterocycle. We found that the presence of a carboxylic group at the extremity of an alkyl chain yielded potent inhibitors of VIM-type enzymes with Ki values in the μM to sub-μM range, and that this alkyl chain had to be longer or equal to a propyl chain. This result confirmed the importance of a carboxylic function on the 4-substituent of 1,2,4-triazole-3-thione heterocycle. As observed in previous series, active compounds also preferentially contained phenyl, 2-hydroxy-5-methoxyphenyl, naphth-2-yl or m-biphenyl at position 5. However, none efficiently inhibited NDM-1 or IMP-1. Microbiological study on VIM-2-producing E. coli strains and on VIM-1/VIM-4-producing multidrug-resistant K. pneumoniae clinical isolates gave promising results, suggesting that the 1,2,4-triazole-3-thione scaffold worth continuing exploration to further improve penetration. Finally, docking experiments were performed to study the binding mode of alkanoic analogues in the active site of VIM-2.

International audience; Molecular dynamics on the complexes of inhibitors with Zn-metalloproteins are a privileged area of applications of polarizable molecular mechanics potentials. With which accuracy could these reproduce the QC intermolecular interaction energies in the two mono-zinc cores and in the dizinc core, toward full-fledged MD simulations on the entire protein complexes? We considered the complexes of the extended recognition site of a Zn-dependent metallo-β-lactamase, VIM-2, produced by bacteria responsible for nosocomial infections, with five newly synthesized inhibitors sharing an original dizinc binding group, 1,2,4-triazole-3-thione (TZT). We considered the energy-minimized structures of each of the five VIM-2 complexes obtained with the SIBFA potential. Energy decomposition analyses (EDA) at the HF level enabled to compare the QC and the SIBFA ΔE values and their contributions in the zinc cores, with and without TZT, totaling 30 complexes. With one exception, the ΔE(QC) values were reproduced with relative errors

To fight the increasingly worrying bacterial resistance to antibiotics, the discovery and development of new therapeutics is urgently needed. Here, we report on a new series of 1,2,4-triazole-3-thione compounds as inhibitors of metallo-&beta, lactamases (MBLs), which represent major resistance determinants to &beta, lactams, and especially carbapenems, in Gram-negative bacteria. These molecules are stable analogs of 4-amino-1,2,4-triazole-derived Schiff bases, where the hydrazone-like bond has been reduced (hydrazine series) or the 4-amino group has been acylated (hydrazide series), the synthesis and physicochemical properties thereof are described. The inhibitory potency was determined on the most clinically relevant acquired MBLs (IMP-, VIM-, and NDM-types subclass B1 MBLs). When compared with the previously reported hydrazone series, hydrazine but not hydrazide analogs showed similarly potent inhibitory activity on VIM-type enzymes, especially VIM-2 and VIM-4, with Ki values in the micromolar to submicromolar range. One of these showed broad-spectrum inhibition as it also significantly inhibited VIM-1 and NDM-1. Restoration of &beta, lactam activity in microbiological assays was observed for one selected compound. Finally, the binding to the VIM-2 active site was evaluated by isothermal titration calorimetry and a modeling study explored the effect of the linker structure on the mode of binding with this MBL.

Resistance to β-lactam antibiotics in Gram-negatives producing metallo-β-lactamases (MBLs) represents a major medical threat and there is an extremely urgent need to develop clinically useful inhibitors. We previously reported the original binding mode of 5-substituted-4-amino/H-1,2,4-triazole-3-thione compounds in the catalytic site of an MBL. Moreover, we showed that, although moderately potent, they represented a promising basis for the development of broad-spectrum MBL inhibitors. Here, we synthesized and characterized a large number of 4-amino-1,2,4-triazole-3-thione-derived Schiff bases. Compared to the previous series, the presence of an aryl moiety at position 4 afforded an average 10-fold increase in potency. Among 90 synthetic compounds, more than half inhibited at least one of the six tested MBLs (L1, VIM-4, VIM-2, NDM-1, IMP-1, CphA) with Ki values in the μM to sub-μM range. Several were broad-spectrum inhibitors, also inhibiting the most clinically relevant VIM-2 and NDM-1. Active compounds generally contained halogenated, bicyclic aryl or phenolic moieties at position 5, and one substituent among o-benzoic, 2,4-dihydroxyphenyl, p-benzyloxyphenyl or 3-(m-benzoyl)-phenyl at position 4. The crystallographic structure of VIM-2 in complex with an inhibitor showed the expected binding between the triazole-thione moiety and the dinuclear centre and also revealed a network of interactions involving Phe61, Tyr67, Trp87 and the conserved Asn233. Microbiological analysis suggested that the potentiation activity of the compounds was limited by poor outer membrane penetration or efflux. This was supported by the ability of one compound to restore the susceptibility of an NDM-1-producing E. coli clinical strain toward several β-lactams in the presence only of a sub-inhibitory concentration of colistin, a permeabilizing agent. Finally, some compounds were tested against the structurally similar di-zinc human glyoxalase II and found weaker inhibitors of the latter enzyme, thus showing a promising selectivity towards MBLs.

Metallo-β-lactamases (MBLs) are important contributors of Gram-negative bacteria resistance to β-lactam antibiotics. MBLs are highly worrying because of their carbapenemase activity, their rapid spread in major human opportunistic pathogens while no clinically useful inhibitor is available yet. In this context, we are exploring the potential of compounds based on the 1,2,4-triazole-3-thione scaffold as an original ligand of the di-zinc active sites of MBLs, and diversely substituted at its positions 4 and 5. Here, we present a new series of compounds substituted at the 4-position by a thioether-containing alkyl chain with a carboxylic and/or an aryl group at its extremity. Several compounds showed broad-spectrum inhibition with Ki values in the μM to sub-μM range against VIM-type enzymes, NDM-1 and IMP-1. The presence of the sulfur and of the aryl group was important for the inhibitory activity and the binding mode of a few compounds in VIM-2 was revealed by X-ray crystallography. Importantly, in vitro antibacterial susceptibility assays showed that several inhibitors were able to potentiate the activity of meropenem on Klebsiella pneumoniae clinical isolates producing VIM-1 or VIM-4, with a potentiation effect of up to 16-fold. Finally, a selected compound was found to only moderately inhibit the di-zinc human glyoxalase II, and several showed no or only moderate toxicity toward several human cells, thus favourably completing a promising behaviour.

Ghrelin plays a central role in controlling major biological processes. As for other G protein-coupled receptor (GPCR) peptide agonists, the structure and dynamics of ghrelin bound to its receptor remain obscure. Using a combination of solution-state NMR and molecular modeling, we demonstrate that binding to the growth hormone secretagogue receptor is accompanied by a conformational change in ghrelin that structures its central region, involving the formation of a well-defined hydrophobic core. By comparing its acylated and nonacylated forms, we conclude that the ghrelin octanoyl chain is essential to form the hydrophobic core and promote access of ghrelin to the receptor ligand-binding pocket. The combination of coarse-grained molecular dynamics studies and NMR should prove useful in improving our mechanistic understanding of the complex conformational space explored by a natural peptide agonist when binding to its GPCR. Such information should also facilitate the design of new ghrelin receptor-selective drugs.

Pyrophosphate analogues are of great importance especially for the design of biologically active molecules. The phospha-Claisen condensation allows for the rapid synthesis of (phosphonomethyl)phosphinate pyrophosphate analogues and building blocks that can be employed in numerous applications.

In the context of the SIBFA polarizable molecular mechanics/dynamics (PMM/PMD) procedure, we report the calibration and a series of validation tests for the 1,2,4-triazole-3-thione (TZT) heterocycle. TZT acts as the chelating group of inhibitors of dizinc metallo-β-lactamases (MBL), an emerging class of Zn-dependent bacterial enzymes, which by cleaving the β-lactam bond of most β-lactam antibiotics are responsible for the acquired resistance of bacteria to these drugs. Such a study is indispensable prior to performing PMD simulations of complexes of TZT-based inhibitors with MBL's, on account of the anchoring role of TZT in the dizinc MBL recognition site. Calibration was done by comparisons to energy decomposition analyses (EDA) of high-level ab initio QC computations of the TZT complexes with two probes: Zn(II), representative of "soft" dications, and water, representative of dipolar molecules. We performed distance variations of the approach of each probe to each of the two TZT atoms involved in Zn ligation, the S atom and the N atom ortho to it, so that each SIBFA contribution matches its QC counterpart. Validations were obtained by performing in- and out-of-plane angular variations of Zn(II) binding in monoligated Zn(II)-TZT complexes. The most demanding part of this study was then addressed. How well does ΔE(SIBFA) and its individual contributions compare to their QC counterparts in the dizinc binding site of one MBL, L1, whose structure is known from high-resolution X-ray crystallography? Six distinct complexes were considered, namely each separate monozinc site, and the dizinc site, whether ligated or unligated by TZT. Despite the large magnitude of the interaction energies, in all six complexes ΔE(SIBFA) can match ΔE(QC) with relative errors2% and the proper balance of individual energy contributions. The computations were extended to the dizinc site of another MBL, VIM-2, and its complexes with two other TZT analogues. ΔE(SIBFA) faithfully reproduced ΔE(QC) in terms of magnitude, ranking of the three ligands, and trends of the separate energy contributions. A preliminary extension to correlated calculations is finally presented. All these validations should enable a secure design of a diversity of TZT-containing MBL inhibitors: a structurally and energetically correct anchoring of TZT should enable all other inhibitor groups to in turn optimize their interactions with the other target MBL residues.

52nd International Conference on Medicinal Chemistry (RICT) of the French-Medicinal-Chemistry-Society (SCT) - Interfacing Chemical Biology and Drug Discovery -- JUL 06-08, 2016 -- Caen, FRANCE, WOS: 000403905300014, PubMed ID: 28505394, Metallo-beta-lactamases (MBLs) cause resistance of Gram-negative bacteria to beta-lactam antibiotics and are of serious concern, because they can inactivate the last-resort carbapenems and because MBL inhibitors of clinical value are still lacking. We previously identified the original binding mode of 4-amino-2,4-dihydro-5-(2-methylphenyl)-3H-1,2,4-triazole-3-thione (compound IIIA) within the dizinc active site of the L1 MBL. Herein we present the crystallographic structure of a complex of L1 with the corresponding non-amino compound IIIB (1,2-dihydro-5-(2-methylphenyl)-3H-1,2,4-triazole-3-thione). Unexpectedly, the binding mode of IIIB was similar but reverse to that of IIIA. The 3D structures suggested that the triazolethione scaffold was suitable to bind to the catalytic site of dizinc metalloenzymes. On the basis of these results, we synthesized 54 analogues of IIIA or IIIB. Nineteen showed IC50 values in the micromolar range toward at least one of five representative MBLs (i.e., L1, VIM-4, VIM-2, NDM-1, and IMP-1). Five of these exhibited a significant inhibition of at least four enzymes, including NDM-1, VIM2, and IMP-1. Active compounds mainly featured either halogen or bulky bicyclic aryl substituents. Finally, some compounds were also tested on several microbial dinuclear zinc-dependent hydrolases belonging to the MBL-fold superfamily (i.e., endonucleases and glyoxalase II) to explore their activity toward structurally similar but functionally distinct enzymes. Whereas the bacterial tRNases were not inhibited, the best IC50 values toward plasmodial glyoxalase II were in the 10 mm range., French Med Chem Soc, Univ Caen, Agence Nationale de la Recherche ("ANTIMBL") [ANR-14-CE16-0028-01]; Deutsche Forschungsgemeinschaft [BE1540/15-2 within SPP 1710]; Agence Nationale de la Recherche [ANR-06-BLAN-0086], We thank Mr. Pierre Sanchez for mass spectrometry analyses and Wolfram Meyer-Klaucke for advice about tRNase Z. Part of this work was supported by the Agence Nationale de la Recherche ("ANTIMBL", ANR-14-CE16-0028-01, including a fellowship to L.S.), the Deutsche Forschungsgemeinschaft (BE1540/15-2 within SPP 1710 to K.B.), and Agence Nationale de la Recherche ("subtilRNA", ANR-06-BLAN-0086) to C.C.

International audience; A new series of nitro or amino substituted pyrazolo[4,3-a]phenanthridines was synthesized in 6 steps from 5-bromo-6-nitroindazole. The evaluation of their inhibitory potency toward Pim kinases demonstrated that the nitro series could be considered as an interesting starting point for the development of new Pim kinase inhibitors, especially Pim-3. A preferential binding mode was suggested by molecular modeling experiments for nitro series and Pim-1/Pim-3 ATP-binding sites. Moreover, the most active compounds exhibited antiproliferative activities toward PC3 cells in the micromolar range.

The alkylation of alkyl phosphinates and some H-phosphonate diesters is promoted by the base DBU. Only more reactive alkyl halides react in preparatively useful yields. However, the method provides easy access to important H-phosphinate building blocks, without the need for a protecting group strategy or metal catalysts. The reaction is conveniently conducted at, or below, room temperature. The preparation of methyl-H-phosphinate esters is particularly interesting as it avoids the heretofore more common use of methyldichlorophosphine MePCl2.

(Hydroxymethyl)phosphorus compounds are well-known and valuable compounds in general; however the use of (hydroxymethyl)phosphinates R(1)P(O)(OR(2))CH(2)OH in particular has been much more limited. The potential of this functionality has not yet been fully realized because the mild unmasking of the hydroxymethyl group was not available. The mild oxidative conversion of R(1)P(O)(OR(2))CH(2)OH into R(1)P(O)(OR(2))H using the Corey-Kim oxidation is described. Other reactions preserving the methylene carbon are also reported.

The synthesis of 1,6-dihydropyrrolo[2,3-g]indazole derivatives is described. The indolic ring system is constructed via a Larock palladium-catalyzed annulation using terminal and internal alkynes. Additionally, when using internal alkynes for this reaction, we found that a directing effect on regioselectivity was mediated by the ester group of alkyl 3-substituted propiolate derivatives.

The synthesis of thiodeoxyvasicinone and thioluotonin derivatives is described. The results obtained indicate that in these series, oxygen to sulfur replacement leads to absence of strong interaction with topoisomerase I-DNA.

The synthesis of a series of novel indazole-5,6-diamine derivatives is described. This indazole ring system was incorporated in an octahydropyrrolo[3,4-b]phenazine scaffold and was diversely and regioselectively substituted on the nitrogen atoms at the 5- and 10-positions. Thus, the nitrogen atom at the 5-position was found to be more reactive toward electrophiles than the one at the 10-position. This difference of reactivity could be attributed to the electronic effect of the pyrazole moiety. Moreover, an unexpected tetrahydropyran protecting group migration was observed from the N-1 atom to the C-11 position of the octahydropyrrolo[3,4-b]phenazine scaffold.

The synthesis of new pyrazolo[3,4-g]quinoxaline derivatives, as well as their Pim kinases (Pim-1, Pim-2, Pim-3) inhibitory potencies and in vitro antiproliferative activities toward a human fibroblast primary culture and three human solid cancer cell lines (PA1, PC3 and DU145) are described. The results obtained in this preliminary structure-activity relationship study have pointed out that most of the compounds in this series exhibited interesting in vitro Pim-3 kinase inhibitory potencies. Moreover, some of the tested compounds have demonstrated favorable antiproliferative potencies.

In the context of the preparation of camptothecin and luotonin A analogs, the synthesis of some key keto-precursors and their use in Friedlander condensation are described. This paper also focuses on the stability of these keto intermediates and emphasizes the major differences between indolizinones and pyrroloquinazolinones series. Noteworthy is also the report of some original structures isolated as by-products of some experiments.

The synthesis of potential precursors of ketones, which could be used to obtain camptothecin analogs, is described. Noteworthy is the difference of reactivity between indolizinone and pyrrolidinoquinazolinone heterocycle.

A mixture of iso-amyl nitrite/HBr is shown to be a mild and efficient reagent for electrophilic aromatic bromination. The reaction succeeds with slightly activated arenes and heterocyclic compounds. By using HCl instead of HBr, chlorination can also be performed in few cases. The i-amONO2/HBr mixture can also be utilized for bromination in the α-position of electron withdrawing groups. A possible mechanism is briefly discussed.

In the context of formation of new aza analogs of camptothecin, nitration then reduction of condensed pyridones was realized, leading to new derivatives of pyrrolo-aza-indoles. Treatment of these compounds with hydrobromic acid led to new structure rearrangements while oxidation of the α-position was unsuccessful. Mechanisms of formation of the new products are discussed.

International audience; How G protein-coupled receptor conformational dynamics control G protein coupling to trigger signaling is a key but still open question. We addressed this question with a model system composed of the purified ghrelin receptor assembled into lipid discs. Combining receptor labeling through genetic incorporation of unnatural amino acids, lanthanide resonance energy transfer, and normal mode analyses, we directly demonstrate the occurrence of two distinct receptor:Gq assemblies with different geometries whose relative populations parallel the activation state of the receptor. The first of these assemblies is a preassembled complex with the receptor in its basal conformation. This complex is specific of Gq and is not observed with Gi. The second one is an active assembly in which the receptor in its active conformation triggers G proteinactivation. The active complex is present even in the absence of agonist, in a direct relationship with the high constitutive activity of the ghrelin receptor. These data provide direct evidence of a mechanism for ghrelin receptor-mediated Gq signaling in which transition of the receptor from an inactive to an active conformation is accompanied by a rearrangement of a preassembled receptor: G protein complex, ultimately leading to G protein activation and signaling.

The title reaction between different phosphorus-stabilized carbanions and a phosphorus electrophile offers a convenient synthesis of 1,1-bisphosphorus compounds.

International audience; New 1,6-dihydropyrazolo[4,3-c]carbazoles and 3,6-dihydropyrazolo[3,4-c]carbazoles were prepared and evaluated for their Pim kinase inhibitory potencies as well as their antiproliferative activities toward two prostatic cancer cell lines. Pyrazolocarbazole 15a was found to be a potent Pim kinase modulator with inhibitory potency toward the three isoforms. Compound 6c strongly inhibited Pim-3 with weaker effect toward Pim-1 and Pim-2, and thus could be used as an interesting molecular tool to study Pim-3 biological functions.

International audience; The synthesis and Pim kinase inhibition potency of a new series of pyrrolo[2,3-g]indazole derivatives is described. The results obtained in this preliminary structure–activity relationship study pointed out that sub-micromolar Pim-1 and Pim-3 inhibitory potencies could be obtained in this series, more particularly for compounds 10 and 20, showing that pyrrolo[2,3-g]indazole scaffold could be used for the development of new potent Pim kinase inhibitors. Molecular modeling experiments were also performed to study the binding mode of these compounds in Pim-3 ATP-binding pocket.

The method avoids the use of Me-PCl2 and neither a metal catalyst nor a protecting group strategy are required.

It is found that (hydroxymethyl)phosphinates can smoothly be converted into several derivatives.

The synthesis of 1,6-dihydropyrrolo[2,3-g]indazole derivatives is described. The indolic ring system is constructed via a Larock palladium-catalyzed annulation using terminal and internal alkynes. Additionally, when using internal alkynes for this reaction, we found that a directing effect on regioselectivity was mediated by the ester group of alkyl 3-substituted propiolate derivatives.

A mixture of iso-amyl nitrite/HBr is shown to be a mild and efficient reagent for electrophilic aromatic bromination. The reaction succeeds with slightly activated arenes and heterocyclic compounds. By using HCl instead of HBr, chlorination can also be performed in few cases. The i-amONO2/HBr mixture can also be utilized for bromination in the α-position of electron withdrawing groups. A possible mechanism is briefly discussed.

International audience; Mainly synthesized in the stomach, ghrelin is a peptide hormone which stimulates growth hormone secretion and appetite, thus promoting food intake and body-weight gain. Historically, researchers started to work on the discovery of ghrelin receptor ligands several years before the discovery of the ghrelin receptor and the hormone itself. Indeed peptides able to stimulate growth hormone secretion (growth hormone releasing peptides, GHRPs) were found while the mechanism of action and the target receptor were still unknown. Non peptidic agonists were then described (growth hormone secretagogues, GHSs) and the receptor (GHS-R1a) identified in 1996. Three years later, the natural ligand of this receptor (ghrelin) was isolated from stomach and its chemical synthesis allowed to show the physiological role of ghrelin in energy balance. In this review, we present some pseudopeptide and peptidomimetic approaches used by researchers for the design of ghrelin receptor ligands. We will start by the pioneering work of Bowers et al. on enkephalin analogues, which was the starting point for the development of an impressive number of compounds, by several of the major worldwide pharma companies. We will also describe the work achieved starting from a substance P derivative, which was one of the first peptides identified as an antagonist of the newly discovered ghrelin receptor. Then we will review the structure activity relationship study starting from the peptide ghrelin, which started with the discovery of this peptide in 1999. We will also focus on a more recent work based on macrocyclic peptidic analogues for the development of ghrelin receptor ligands.