Investigation of the Best Conditions to Obtain c(RGDfK) Peptide on Solid Phase

The cyclic pentapeptide c(RGDfK) is a high affinity ligand of alphaVbeta3 integrin. It was an analog of Cilengitide (EMD 121974) developed to be employed as tracer for cancer diagnosis and therapy by functionalisation of its Lys side-chain. Solution-phase and solid-phase synthetic approaches were previously reported. In the attempt to improve solid-phase synthesis of the cyclopeptide circumventing cyclodimerisation reactions, a systematic study of the synthetic conditions was performed, evaluating and optimising parameters directly involved in the ring closure step. The three-dimensional orthogonal solid-phase strategy developed in this study yields the desired c(RGDfK) peptide with no cyclodimerisation by-products. The protocols described allow the modification of the peptide directly on the solid support in order to obtain novel derivatives for biomedical applications.