Synthesis of cyclic RGD derivatives via solid phase macrocyclization using the Heck reaction

A novel intramolecular macrocyclization reaction on a solid support using the Heck reaction has been achieved. For head to tail cyclization on a solid support, the linear precursor was anchored to a chlorotrityl chloride resin via an ester linkage using the β-carboxyl group of Asp. The Heck coupling of acrylic acid amide to 3-iodobenzylamine on the solid support proceeds smoothly to yield a cyclic tetrapeptide derivative, which contains a new 3-substituted cinnamic acid template and Arg-Gly-Asp sequence. The macrocyclization reaction takes place considerably more rapidly on a solid support than in solution. The solid phase procedure was successfully used for the construction of cyclic RGD libraries having diverse side chain structures, combined with a variety of ring sizes.