A solanesol-derived scaffold for multimerization of bioactive peptides

A flexible molecular scaffold bearing varying numbers of terminal alkyne groups was synthesized in five steps from solanesol. R(CO)-MSH(4)-NH₂ ligands, which have a relatively low affinity for binding at the human melanocortin 4 receptor (hMC4R), were prepared by solid phase synthesis and were N-terminally acylated with 6-azidohexanoic acid. Multiple copies of the azide N₃(CH₂)₅(CO)-MSH(4)-NH₂ were attached to the alkyne-bearing, solanesol-derived molecular scaffold via the copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) reaction. Control studies showed that the binding affinity of the triazole-containing ligand, CH ₃(CH₂)₃(C₂N₃)(CH ₂)₅(CO)-MSH(4)-NH₂, was not significantly diminished relative to the corresponding parental ligand, CH₃(CO)- MSH(4)-NH₂. In a competitive binding assay with a Eu-labeled probe based on the superpotent ligand NDP-α-MSH, the monovalent and multivalent constructs appear to bind to hMC4R as monovalent species. In a similar assay with a Eu-labeled probe based on MSH(4), modest increases in binding potency with increased MSH(4) content per scaffold were observed.