Solid phase synthesis without repetitive acidolysis. Preparation of leucyl-alanyl-glycyl-valine using 9-fluorenylmethyloxycarbonylamino acids.

The utility of repetitive nonhydrolytic base cleavage of alpha-amino protective groups in solid phase peptide synthesis is shown by a preparation of the model tetrapeptide leucyl-alanyl-glycyl-valine on a p-benzyloxybenzyl ester polystyrene--1% divinylbenzene resin support. Nalpha-9-Fluorenylmethyloxycarbonyl (Fmoc: Carpino & Han, 1970, 1972) amino acids were coupled by the symmetrical anhydride procedure, followed by Fmoc group cleavage using 50% piperidine in methylene chloride. Quantitative removal of the Fmoc-tetrapeptide from the solid support was effected by treatment with 55% trifluoroacetic acid in methylene chloride. Homogeneous free tetrapeptide was obtained in 87% overall yield. The procedure is proposed to offer advantages over present solid phase methods which use acidolysis for repetitive alpha-amino group deblocking.