Success in discovering bioactive peptide mimetics is often limited by the difficulties in correctly transposing known binding elements of the active peptide onto a small and metabolically more stable scaffold while maintaining bioactivity. Here we describe a scanning approach using a library of pyranose-based peptidomimetics that is structurally diverse in a systematic manner, designed to cover all possible conformations of tripeptide motifs containing two aromatic groups and one positive charge. Structural diversity was achieved by efficient selection of various chemoforms, characterized by a choice of pyranose scaffold of defined chirality and substitution pattern. A systematic scanning library of 490 compounds was thus designed, produced, and screened in vitro for activity at the somatostatin (sst(1-5)) and melanin-concentrating hormone (MCH(1)) receptors. Bioactive compounds were found for each target, with specific chemoform preferences identified in each case, which can be used to guide follow-on drug discovery projects without the need for scaffold hopping.

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Keywords: 5(4H)-Oxazolone / β-Carboline / Cyclopenta [b]indolone / Cyclization / BischlerϪNapieralski reaction / Canthine / Synthesis design 4-(1H-Indol-3-ylmethyl)-2-trichloromethyl-1,3-oxazol-5(4H)-one (4) was shown to undergo an intramolecular reaction in the presence of TFA, to afford a β-carboline 5 and a cyclopenta[b]indolone 6 by nucleophilic addition at C-2 and C-5, respectively. The distribution of these two products was found to be dependent on the reaction temperature, with lower temperatures favouring the formation of the β-carboline 5. Subsequent reactions performed on the β-carboline 5 led to the formation of canthine and canthin-6-one derivatives.

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The pyranose scaffold is unique in its ability to position pharmacophore substituents in various ways in 3D space, and unique pharmacophore scanning libraries could be envisaged that focus on scanning topography rather than diversity in the type of substituents. Approaches have been described that make use of amine and acid functionalities on the pyranose scaffolds to append substituents, and this has enabled the generation of libraries of significant structural diversity. Our general aim was to generate libraries of pyranose-based drug-like mimetics, where the substituents are held close to the scaffold, in order to obtain molecules with better defined positions for the pharmacophore substituents. Here we describe the development of a versatile synthetic route toward peptide mimetics build on 2-amino pyranose scaffolds. The method allows introduction of a wide range of substituent types, it is regio- and stereospecific, and the later diversity steps are performed on solid phase. Further, the same process was applied on glucose and allose scaffolds, in the exemplified cases, and is likely adaptable to other pyranose building blocks. The methods developed in this work give access to molecules that position the three selected binding elements in various 3D orientations on a pyranose scaffold and have been applied for the production of a systematically diverse library of several hundred monosaccharide-based mimetics.