Design, synthesis and evaluation of racemic 1-(4-hydroxyphenyl)-2-[3-(substituted phenoxy)-2-hydroxy-1-propyl]amino-1-propanol hydrochlorides as novel uterine relaxants

Drug discovery strategies for the identification of novel regulators of uterine contractility

Preterm birth and postpartum hemorrhage are the leading causes of neonatal and maternal morbidities worldwide, respectively. Current clinically utilized tocolytics and uterotonics to manage these obstetric conditions are limited due to their off-target effects and/or lack of efficacy. Thus, an ideal tocolytic or uterotonic would be uterine-selective with rapid onset and long-duration efficacy. Here, we discuss strategies for the discovery of new therapeutic targets and compounds that regulate uterine contractility with the aforementioned properties.

In vitro bioactivation of bazedoxifene and 2-(4-hydroxyphenyl)-3-methyl-1H-indol-5-ol in human liver microsomes

Bazedoxifene is a selective estrogen receptor modulator (SERM) that has been developed for use in post-menopausal osteoporosis. However, it contains a potentially toxic 5-hydroxy-3-methylindole moiety. Previous studies on the 5-hydroxyindole and the 3-alkylindole-containing drugs indometacine, zafirlukast and MK-0524 structural analogs have shown that they are bioactivated by cytochrome P450s through a dehydrogenation process to form quinoneimine or 3-methyleneindolenine electrophilic species. In the present study, bazedoxifene was synthesized and then evaluated, together with raloxifene and 2-(4-hydroxyphenyl)-3-methyl-1H-indol-5-ol (13), a 3-methyl-5-hydroxyindole-based structural fragment of bazedoxifene, for its ability to form reactive electrophilic species when incubated with human liver microsomes (HLMs) or recombinant CYP isozymes. We showed that bazedoxifene was bioactivated only in trace amounts with recombinant CYP isozymes. In contrast, the N-dealkylated fragment of bazedoxifene (2-(4-hydroxyphenyl)-3-methyl-1H-indol-5-ol) was bioactivated in considerable amounts to an electrophilic intermediate, which was trapped with glutathione and identified by LC-MS/MS. This suggests that bazedoxifene would require initial N-dealkylation, which could subsequently lead to the formation of the reactive intermediate. However, such an N-dealkylated metabolite of bazedoxifene was not detected after the incubation of bazedoxifene in HLM or recombinant CYP isozymes.

Synthesis and evaluation of uterine relaxant activity for a novel series of substituted p-hydroxyphenylethanolamines

Novel racemic 1-(4-hydroxyphenyl)-2-[3-(substituted phenoxy)-2-hydroxy-1-propyl]aminopropan-1-ol hydrochlorides (9a-h) were synthesized by condensing racemic 1-(p-hydroxyphenyl)-2-aminopropan-1-ol hydrochloride (6) with substituted aryloxymethyloxiranes (8a-h) in DMF in presence of anhydrous potassium carbonate and then reacting with dry hydrogen chloride gas. They were evaluated for uterine relaxant activity in vitro on isolated rat uterus and in vivo in pregnant rats. Their cAMP releasing potential was studied using rat uterus tissue homogenates by cAMP [3H] assay and cardiac stimulant potential was evaluated in dog. All compounds exhibited potent uterine relaxant activity in vitro and produced a significant delay in the onset of labour in pregnant rats; their cAMP releasing potential was higher than isoxsuprine hydrochloride except for 9b and 9c. Finally insignificant cardiac stimulant potential was noted for these compounds when compared to isoxsuprine hydrochloride.