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.

Opioid analgesics, such as morphine, oxycodone, and fentanyl, are the cornerstones for treating moderate to severe pain. However, on chronic administration, their efficiency is limited by prominent side effects such as analgesic tolerance and dependence liability. Neuropeptide FF (NPFF) and its receptors (NPFF1R and NPFF2R) are recognized as an important pronociceptive system involved in opioid-induced hyperalgesia and analgesic tolerance. In this article, we report the design of multitarget peptidomimetic compounds that show high-affinity binding to the mu-opioid receptor (MOPr) and NPFFRs. In vitro characterization of these compounds led to identification of KGFF03 and KGFF09 as G-protein-biased MOPr agonists with full agonist or antagonist activity at NPFFRs, respectively. In agreement with their biased MOPr agonism, KGFF03/09 showed reduced respiratory depression in mice, as compared to the unbiased parent opioid agonist KGOP01. Chronic subcutaneous administration of KGOP01 and KGFF03 in mice rapidly induced hyperalgesia and analgesic tolerance, effects that were not observed on chronic treatment with KGFF09. This favorable profile was further confirmed in a model of persistent inflammatory pain. In addition, we showed that KGFF09 induced less physical dependence compared with KGOP01 and KGFF03. Altogether, our data establish that combining, within a single molecule, the G-protein-biased MOPr agonism and NPFFR antagonism have beneficial effects on both acute and chronic side effects of conventional opioid analgesics. This strategy can lead to the development of novel and potent antinociceptive drugs with limited side effects on acute and chronic administration.

Abstract:The (site-selective) derivatization of amino acids and peptides represents an attractive field with potential applications in the establishment of structure-activity relationships and labeling of bioactive compounds. In this respect, bioorthogonal cross-coupling reactions provide valuable means for ready access to peptide analogues with diversified structure and function. Due to the complex and chiral nature of peptides, mild reaction conditions are preferred; hence, a suitable cross-coupling reaction is required for the chemical modification of these challenging substrates. The Suzuki reaction, involving organoboron species, is appropriate given the stability and environmentally benign nature of these reactants and their amenability to be applied in (partial) aqueous reaction conditions, an expected requirement upon the derivatization of peptides. Concerning the halogenated reaction partner, residues bearing halogen moieties can either be introduced directly as halogenated amino acids during solid-phase peptide synthesis (SPPS) or genetically encoded into larger proteins. A reversed approach building in boron in the peptidic backbone is also possible. Furthermore, based on this complementarity, cyclic peptides can be prepared by halogenation, and borylation of two amino acid side chains present within the same peptidic substrate. Here, the Suzuki-Miyaura reaction is a tool to induce the desired cyclization. In this review, we discuss diverse amino acid and peptide-based applications explored by means of this extremely versatile cross-coupling reaction. With the advent of peptide-based drugs, versatile bioorthogonal conversions on these substrates have become highly valuable.

The Suzuki-Miyaura derivatisation of free amino acids, peptides and proteins is an attractive area with much potential utility for medicinal chemistry and chemical biology. Here we report the modification of unprotected and Boc-protected aromatic amino acids and dipeptides in aqueous media, enabling heteroarylation and vinylation. We systematically investigate the impact of the peptide backbone and adjacent amino acid residues upon the reaction. Our studies reveal that whilst asparagine and histidine hinder the reaction, by utilising dppf, a ferrocene-based bidentate phosphine ligand, cross-coupling of halophenylalanine or halotryptophan adjacent to such a residue could be enabled. Our studies reveal dppf to have good compatibility with all unprotected, proteinogenic amino acid side chains.

While revisiting biologically active natural peptides, the importance of the tryptophan residue became clear. In this article, the incorporation of this amino acid, brominated at different positions of the indole ring, into cyclic peptides was successfully achieved. These products demonstrated improved properties in terms of passive diffusion, permeability across membranes, biostability in human serum and cytotoxicity. Moreover, these brominated tryptophans at positions 5, 6, or 7 proved to be compatible as building blocks to prepare bicyclic stapled peptides by performing on-resin Suzuki-Miyaura cross-coupling reactions.

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In this study, affinities and activities of derivatized analogues of Dmt-dermorphin[1–4] (i.e. Dmt-D-Ala-Phe-GlyNH2, Dmt = 2′,6′-dimethyl-(S)-tyrosine) for the μ opioid receptor (MOP) and δ opioid receptor (DOP) were evaluated using radioligand binding studies, functional cell-based assays and isolated organ bath experiments. By means of solid-phase or solution-phase Suzuki-Miyaura cross-couplings, various substituted regioisomers of the phenylalanine moiety in position 3 of the sequence were prepared. An 18-membered library of opioid tetrapeptides was generated via screening of the chemical space around the Phe3 side chain. These substitutions modulated bioactivity, receptor subtype selectivity and highly effective ligands with subnanomolar binding affinities, contributed to higher functional activities and potent analgesic actions. In search of selective peptidic ligands, we show here that the Suzuki-Miyaura reaction is a versatile and robust tool which could also be deployed elsewhere.

The First One-Pot Synthesis of L-7-Iodotryptophan (IIIe) from 7-Iodoindole and Serine, and an Improved Synthesis of Other L-7-Halotryptophans. -A bacterial cell lysate containing tryptophan synthase is developed to enable a scalable one-pot biotransformation of indoles to the corresponding tryptophans with serine as coupling partner. -(SMITH, D. R. M.; WILLEMSE, T.; GKOTSI, D. S.; SCHEPENS, W.; MAES, B. U. W.; BALLET, S.; GOSS*, R. J. M.; Org. Lett. 16 (2014) 10, 2622-2625, http://dx.doi.org/10.1021/ol5007746 ; Sch. Chem., Univ. St. Andrews, St. Andrews, Fife KY16 9ST, UK; Eng.) -Mais 42-224