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

Phytosulfokine-alpha (PSK-alpha), a sulfated growth factor of structure H-Tyr(SO3H)-Ile-Tyr(SO3H)-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-alpha 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 H-3-labelled PSK-alpha according to the test of Matsubayashi et al. Among these peptide analogues, [H-Phe(4-Cl)(1)]-PSK-alpha (IV), [H-Phe(4-1)(1)]-PSK-alpha (VII), and [lPhe(4-Cl)(3)-]-PSK-alpha (XI) retained 30% PSK-alpha activity. Analogue [Tyr(PO3H2)(3)]-PSK-alpha (IX) showed 10% of PSK-alpha activity. Copyright (c) 2005 European Peptide Society and John Wiley & Sons, Ltd.