Steven Ballet

Structural basis for bifunctional peptide recognition at human δ-opioid receptor

Bifunctional μ- and δ-opioid receptor (OR) ligands are potential therapeutic alternatives, with diminished side effects, to alkaloid opiate analgesics. We solved the structure of human δ-OR bound to the bifunctional δ-OR antagonist and μ-OR agonist tetrapeptide H-Dmt-Tic-Phe-Phe-NH2 (DIPP-NH2) by serial femtosecond crystallography, revealing a cis-peptide bond between H-Dmt and Tic. The observed receptor-peptide interactions are critical for understanding of the pharmacological profiles of opioid peptides and for development of improved analgesics.

The First One-Pot Synthesis of l-7-Iodotryptophan from 7-Iodoindole and Serine, and an Improved Synthesis of Other l-7-Halotryptophans

A simple and scalable one-pot biotransformation enables direct access to L-halotryptophans, including L-7-iodotryptophan, from the corresponding haloindoles. The biotransformation utilizes an easy to prepare bacterial cell lysate that may be stored as the lyophilizate for several months and utilized as a catalyst as and when required.

Amino Triazolo Diazepines (Ata) as Constrained Histidine Mimics

Two synthetic routes for the synthesis of amino-triazolodiazepine (Ata) scaffolds are presented. The scope of both of these proceeding through key intra- and intermolecular Huisgen cycloaddition reactions is discussed. The replacement of the His-Pro dipeptide segment in angiotensin IV by the dipeptide mimetic Ata-Gly and subsequent biological evaluation in two inhibitory enzyme assays validated the use of the Ata moiety as a His mimic given the equipotency of both peptidic analogs.

Blood-Brain Barrier Penetration by Two Dermorphin Tetrapeptide Analogues : Role of Lipophilicity vs Structural Flexibility

Two dermorphin analogues having an almost identical structure but different structural flexibility were compared for opioid activity. In 1 the aromatic side chains were incorporated into a lactam structure, while in 2 N-amide alkylation was retained but the side chains were flexible. Both compounds produced comparable antinociceptive effects in the mouse tail flick test after peripheral administration. This indicates that lipophilicity, rather than side chain flexibility, is the key determinant for blood-CNS barrier penetration.

Hybrid opioid/non-opioid ligands in pain research.

To address the different types of pain (e.g. acute, chronic, neuropathic) different classes of medications, mainly non-steroidal anti-inflammatory drugs and narcotics (opioids), are used. More specifically, the alleviation or treatment of moderate to severe pain states commonly invokes the use of opioids. Unfortunately, their chronic administration induces various undesirable side effects, such as for example physical dependence and tolerance. One strategy to overcome these major side effects and to prolong the antinociceptive efficiency of the applied drugs involves the creation of multifunctional compounds which contain hybridized structures. Combination of opioid agonist and antagonist pharmacophores in a single chemical entity has been considered and extensively investigated, but opioids have also been combined with other bioactive neurotransmitters and peptide hormones that are involved in pain perception (e.g. substance P, neurotensin, cholecystokinin, cannabinoids, melanocortin ligands, etc.). Such novel chimeras (also called designed multiple ligands or twin/triplet drugs), may interact independently with their respective receptors and potentially result in more effective antinociceptive properties. The designed multiple ligands presented in this work include opioid-non-opioid peptide dimer analogs, mixed peptidic- non-peptidic bifunctional ligands and dual non-peptidic dimers. The main focus herein is placed on the design and biological evaluation of these multiple opioid compounds, rather than the synthetic approach and preparation.

Variation of the net charge, lipophilicity, and side chain flexibility in Dmt(1)-DALDA: Effect on Opioid Activity and Biodistribution.

The influence of the side chain charges of the second and fourth amino acid residues in the peptidic μ opioid lead agonist Dmt-d-Arg-Phe-Lys-NH(2) ([Dmt(1)]-DALDA) was examined. Additionally, to increase the overall lipophilicity of [Dmt(1)]-DALDA and to investigate the Phe(3) side chain flexibility, the final amide bond was N-methylated and Phe(3) was replaced by a constrained aminobenzazepine analogue. The in vitro receptor binding and activity of the peptides, as well as their in vivo transport (brain in- and efflux and tissue biodistribution) and antinociceptive properties after peripheral administration (ip and sc) in mice were determined. The structural modifications result in significant shifts of receptor binding, activity, and transport properties. Strikingly, while [Dmt(1)]-DALDA and its N-methyl analogue, Dmt-d-Arg-Phe-NMeLys-NH(2), showed a long-lasting antinociceptive effect (>7 h), the peptides with d-Cit(2) generate potent antinociception more rapidly (maximal effect at 1h postinjection) but also lose their analgesic activity faster when compared to [Dmt(1)]-DALDA and [Dmt(1),NMeLys(4)]-DALDA.

PK20, a new opioid-neurotensin hybrid peptide that exhibits central and peripheral antinociceptive effects

BackgroundThe clinical treatment of various types of pain relies upon the use of opioid analgesics. However most of them produce, in addition to the analgesic effect, several side effects such as the development of dependence and addiction as well as sedation, dysphoria, and constipation. One solution to these problems are chimeric compounds in which the opioid pharmacophore is hybridized with another type of compound to incease antinociceptive effects. Neurotensin-induced antinociception is not mediated through the opioid system. Therefore, hybridizing neurotensin with opioid elements may result in a potent synergistic antinociceptor.ResultsUsing the known structure-activity relationships of neurotensin we have synthesized a new chimeric opioid-neurotensin compound PK20 which is characterized by a very strong antinociceptive potency. The observation that the opioid antagonist naltrexone did not completely reverse the antinociceptive effect, indicates the partial involvement of the nonopioid component in PK20 in the produced analgesia.ConclusionsThe opioid-neurotensin hybrid analogue PK20, in which opioid and neurotensin pharmacophores overlap partially, expresses high antinociceptive tail-flick effects after central as well as peripheral applications.

Conformationally constrained opioid ligands: the Dmt-Aba and Dmt-Aia versus Dmt-Tic scaffold.

Replacement of the constrained phenylalanine analogue 1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid (Tic) in the opioid Dmt-Tic-Gly-NH-Bn scaffold by the 4-amino-1,2,4,5-tetrahydro-indolo[2,3-c]azepin-3-one (Aia) and 4-amino-1,2,4,5-tetrahydro-2-benzazepin-3-one (Aba) scaffolds has led to the discovery of novel potent mu-selective agonists (Structures 5 and 12) as well as potent and selective delta-opioid receptor antagonists (Structures 9 and 15). Both stereochemistry and N-terminal N,N-dimethylation proved to be crucial factors for opioid receptor selectivity and functional bioactivity in the investigated small peptidomimetic templates. In addition to the in vitro pharmacological evaluation, automated docking models of Dmt-Tic and Dmt-Aba analogues were constructed in order to rationalize the observed structure-activity data.

Rational design of a hexapeptide hydrogelator for controlled-release drug delivery

The amphiphilic peptide sequence H-Phe-Glu-Phe-Gln-Phe-Lys-OH (MBG-1) is developed as a novel hydrogelator for use in controlled-drug release administration, which is the smallest tunable ionic self-complementary hydrogelating peptide reported to date making it attractive for larger scale preparation. Hydrogelation is demonstrated to result from self-assembly of the peptide into beta-sheet nanofibers that are physically cross-linked by intertwining as well as larger bundle formation. Finally, the release of two small molecule cargos, fluorescein sodium and ciprofloxacin hydrochloride, is demonstrated revealing a two-stage zero-order sustained release profile up to 80% cumulative release over eight days.

Synthesis of Fused 3-Aminoazepinones via Trapping of a New Class of Cyclic Seven-Membered Allenamides with Furan

Novel tricyclic tetrahydroazepinones were synthesized via an in situ Diels-Alder reaction of furan with cyclic allenamides. These reactive intermediates are the first examples of cyclic seven-membered allenamides and were prepared starting from N-(2-chloroallyl)-2-allylglycine derivatives via ring-closing metathesis followed by dehydrochlorination. The trapping of the intermediate cycloallene with furan occurred endo- and regioselectively and provided a convenient entry into new building blocks for medicinal chemistry. The diastereoselectivity of the cycloaddition was confirmed using quantum chemical computations.