Solid-phase synthesis of chiral bicyclic guanidinium oligomers.

Vera Martos, Pilar Castreño, Miriam Royo, Fernando Albericio, Javier de Mendoza

Index: J. Comb. Chem. 11(3) , 410-21, (2009)

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Abstract

A simple solid-phase synthesis of thioether-linked chiral bicyclic guanidinium oligomers for cell internalization purposes has been developed. The approach is based on a Merrifield-like peptide synthesis on Rinkamide-p-methylbenzhydrylamine resin functionalized with Cys(methoxytrityl). A difunctionalized bicyclic guanidinium synthon, bearing both electrophile (O-mesyl) and protected nucleophile (S-methoxytrityl) group, is repeatedly grafted via a nucleophilic substitution. The sequence requires removal of methoxytrityl, reduction with 1,4-dithiothreitol to cleave any adventitious disulfides, coupling and capping with benzyl bromide. Moreover, Alloc protection of the alpha-amino group of the initial cysteine, provides a potential handle for cargo attachment after oligomer elongation to the desired internalizing agent and prior to cleaving it from the resin. Finally, a bicyclic guanidinium monomer containing an amino group and a carboxylic acid function has been evaluated as an alternative building block for novel amide-bridged oligomers or peptidomimetics.