Abstract
Four phenylglycine enamines were synthesized by reacting sodium phenylglycinate and β-diketones, ethyl acetoacetate, and diethyl ethoxymethylenemalonate, ethoxyethyl acetoacetate, and 3-acetylbutyrolactone (abbreviated as PG-EtAA Na, PG-DEMM Na, PG-EthoxyEtAA Na, and PG-AcBu Na, respectively). Increase in the immunoreactive serum insulin levels and decrease in the serum glucose levels were observed in rabbits and dogs following the rectal administration of insulin suppositories in the presence of most PG-enamines. However, PG-AcBu Na failed to promote the rectal absorption of insulin or inulin. The ability of PG-enamines to interact with Ca2+ was found to be closely correlated with their promoting efficacies on the rectal absorption of insulin in terms of the maximum response to glucose levels and on the rectal absorption of inulin in terms of the AUC value of serum levels. The lack of promoting efficacy of PG-AcBu Na was explained on the basis of its poor ability to interact with Ca2+.
