Synthesis of halogenated trimetoquinol derivatives and evaluation of their beta-agonist and thromboxane A2 (TXA2) antagonist activities.
Markovich KM, Tantishaiyakul V, Hamada A, Miller DD, Romstedt KJ, Shams G, Shin Y, Fraundorfer PF, Doyle K, Feller DR.
The 5,8-difluoro (4), 5-iodo (5), 8-iodo (6), and 5-trifluoromethyl (7) derivatives of trimetoquinol (TMQ, 1) have been synthesized and evaluated for their ability to stimulate beta 1 (guinea pig atria) and beta 2 (guinea pig trachea) adrenoceptors as well as for their inhibitory activity against U46619 [a thromboxane A2 (TXA2) mimetic]-mediated contraction of rat thoracic aorta and human platelet aggregation. Both 5 and 6 were considerably less active than TMQ on both beta-adrenergic systems and gave a rank order of stimulatory potency of 1 much greater than 6 greater than or equal to 5. Similarly, iodine substitution at either position also caused a reduction in TXA2 antagonist activity with a rank order potency of 1 greater than 6 much greater than 5. Compared to 1, however, 5-iodo-TMQ (5) showed a marked selectivity for blockade of U46619 responses in rat aorta over human platelets. On beta-systems, 4 had reduced potency compared to TMQ and was similarly nonselective. Introduction of a trifluoromethyl group at the 5-position of TMQ completely abolished both beta 1- and beta 2-adrenergic agonist activities while imparting weak antagonist activity on beta 1 receptors. On TXA2 systems, both 4 and 7 possessed significantly decreased inhibitory activity compared to TMQ. The synthetic approaches to the synthesis of 8-(trifluoromethyl)-TMQ (8) are also described. The enantiomers of the 8-fluoro derivative (3) of TMQ were separated on a preparative Chiralcel OD column and evaluated on beta-adrenergic systems and TXA2 systems. On beta-adrenergic systems, (S)-(+)-8-fluoro-TMQ was at least 10-fold more potent than (R)-(-)-8-fluoro-TMQ. Conversely, (R)-(-)-8-fluoro-TMQ was approximately 14-fold more potent as an antagonist of TXA2-mediated aggregation in human platelets than (S)-(+)-8-fluoro-TMQ. In contrast to platelets, (S)-(+)-8-fluoro-TMQ was an agonist in rat aorta whereas (R)-(-)-8-fluoro-TMQ was an antagonist.