Solid phase synthesis of gastrin I. Comparison of methods utilizing strong acid for deprotection and cleavage

A successful synthesis of human gastrin I in 60% overall yield based on the first residue attached to a benzhydrylamine-resin was achieved by the stepwise solidphase method. The synthesis was carried out on a 1% crosslinked polystyrene support, using conventional benzyl-based side chain protecting groups and final deprotection with different acidic protocols. Several improvements in this general approach were applied, including new scavengers, new resin attachment and especially a new technique that allows the strong acid reactions to occur by an SN2 mechanism.