Reverse thioether ligation route to multimeric peptide antigens

Multimeric presentation, a rather effective way of enhancing peptide immunogenicity, is best exemplified by MAP (multiple antigenic peptide) dendrimers consisting of a branched Lys core on which several copies of the peptide epitope are displayed. While accessible by solid-phase synthesis, MAPs can also be conveniently made in solution, e.g., by linking the epitope (N-acetylated and with a C-terminal Cys) through a thioether bond onto the α and ε (haloacetyl-activated) positions of the Lys core. We now report the reverse version of this approach, whereby a chloroacetyl-derivatised epitope is tethered to a thiol-functionalised form of a Lys dendron core. This convergent approach can be carried out either in solution or in the solid phase and is advantageous because (i) in situ tris(2-carboxyethyl)phosphine (TCEP)-mediated reduction of disulfide bonds maintains the thiol platform reactive throughout the ligation process; (ii) the low amounts of TCEP used pose minimal risk to chloroacetyl groups in the peptide, resulting in (iii) significantly reduced byproduct formation, hence cleaner products. For the solid phase version of the method, an optimised procedure has been devised to convert the Lys core into a tetrathiol dendron.