Synthesis of 5- and 7-hydroxy indolizidin-2-one prostaglandin-F modulators and activity on myometrial contractility towards development of agents for delaying preterm birth.

In pursuit of more effective-labor delaying tocolytic agents, the prostaglandin F2α (PGF2α) receptor (FP) modulator PDC113.824 [(6S)-2] represents a potent lead for developing therapy to treat preterm birth. Derivatives of FP modulator (6S)-2 were synthesized, possessing respectively 5- and 7-hydroxyl groups on the indolizidin-2-one amino acid (I aa) residue. The effects of the alcohol substituents were examined in a PGF2α-induced myometrial contraction assay. Based on knowledge of dihedral angle values of model I aa peptides from X-ray analyses, the results of the study indicate respectively encouraging and limited potential for creating improved tocolytic agents by modifications at the 5- and 7-positions.