Further analogues of plant peptide hormone phytosulfokine‐α (PSK‐α) and their biological evaluation

Phytosulfokine‐α (PSK‐α), a sulfated growth factor of structure H‐Tyr(SO 3 H)‐Ile‐Tyr(SO 3 H)‐Thr‐Gln‐OH universally found in both monocotyledons and dicotyledons, strongly promotes proliferation of plant cells in culture. In studies on the structure/activity relationship of PSK‐α the synthesis was performed of a series of a further 23 analogues modified in position 1, 3 or 4 as well as simultaneously in positions 1 and 3 of the peptide chain. Peptides were synthesized by the solid phase method according to the Fmoc procedure on a Wang‐resin. Free peptides were released from the resin by 95% TFA in the presence of EDT. All peptides were tested by competitive binding assay to the carrot membrane using 3 H‐labelled PSK‐α according to the test of Matsubayashi et al . Among these peptide analogues, [H‐Phe(4‐Cl) 1 ]‐PSK‐α ( IV ), [H‐Phe(4‐I) 1 ]‐PSK‐α ( VII ), and [Phe(4‐Cl) 3 ]‐PSK‐α ( XI ) retained 30% PSK‐α activity. Analogue [Tyr(PO 3 H 2 ) 3 ]‐PSK‐α ( IX ) showed 10% of PSK‐α activity. Copyright © 2005 European Peptide Society and John Wiley & Sons, Ltd.