Synthesis of substrates of cyclic AMP-dependent protein kinase and use of their protected precursors for the convenient preparation of phosphoserine peptides

Abstract

The synthesis of protected hexa- to nona-peptide precursors of substrates of cyclic AMP-dependent protein kinase, based on a partial amino acid sequence from rat liver pyruvate kinase, as well as of related phosphoserine peptides has been explored. A convenient scheme has been developed which furnishes both N-terminally elongated peptides of variable lengths and intermediates suitable for chemical phosphorylation. The use of adamantyloxycarbonyl as a protecting group for the two important guanidine functions involved, gave rise to the highly lipophilic intermediates (9), (21), (22), (28), and (31), which could easily be purified. Treatment of these with anhydrous hydrogen fluoride [or trifluoroacetic acid in the case of compound (31)] afforded the pure substrate peptides (10), (23), (24), (29), and (32) in high overall yield. All of the free peptides obtained could be phosphorylated by cyclic AMP-dependent protein kinase at a significant rate. The chemical synthesis of two phosphoserine peptides (12) and (14) and their purification by preparative reversed-phase ion-pair chromatography are also reported.