Effects of Alkyl Substitutions of Xanthine Skeleton on Bronchodilation

Article abstract of DOI:10.1021/jm00100a008

Structure-activity relationships in a series of 1,3,7-trialkyl-xanthine were studied with guinea pigs.Relaxant actions in the tracheal muscle were increased with alkyl chain length at the 1- and 3-positions of the xanthine skeleton, but decreased by alkylation at the 7-position.Positive chronotropic actions in the right atrium were potentiated with 3-alkyl chain length but tended to decrease with 1-alkylation and diminish by 7-substitution.Consequently, while the 1- and 3-substitutions were equally important for the tracheal smooth muscle relaxation, the substitution at the 1-position was more important than the 3-substitution for bronchoselectivity.The 7-alkylation may be significant to cancel heart stimulation.There were good correlations between the smooth muscle relexant action and the cyclic AMP-PDE inhibitory activity in 3-substituents and the affinity for adenosine (A₁)receptors in 1-,3-, and 7-substituents.This suggests that not only the cyclic AMP-PDE inhibitory activity but also the adenosine antagonistic activity is important in the bronchodilatory effects of alkylxanthines.Among these xanthine derivatives, 1-butyl-3-propylxanthine and its 7-methylated derivative showed high bronchoselectivity in the in vitro and in vivo experiments compared to theophylline and enprofylline and may be new candidates for bronchodilator.