Evaluation and synthesis of 7-arylhydroxymethyltriazolopyridines as potential cardiovascular agents

7-Arylhydroxymethyltriazolopyridines 3a-c and 4a-d were synthesized by regioselective lithiation of [1,2,3]triazolo[1,5-a ]pyridines 1 and 2 and subsequent trapping of the 7-lithio-derivatives formed using aryl aldehydes as electrophiles. The structural relationship between compounds 3a-c and 4a-d and arylethanolamines suggested their consideration as potential cardiovascular agents. A preliminary evaluation as vascular smooth muscle relaxants was carried out. These compounds did not act as α 1 -adrenoceptor antagonists and were unable to block calcium entry through voltage-dependent calcium channels.


Introduction
Phenylalkylamines and phenylethanolamines are well known cardiovascular agents.Related compounds such as benzyltetrahydroisoquinoline and bisbenzyltetrahydroisoquinoline alkaloids have the ability to block calcium channels and/or antagonize α 1 -adrenoceptors, and may have applications in the treatment of cardiovascular disorders.2][3][4] The search for new compounds with activity in vascular pathologies is an interesting challenge, considering that these conditions are the major cause of death in the European Community.The idea that 7-arylhydroxymethyltriazolopyridines might be considered as structural analogues of the above mentioned compounds led us to synthesize a series of these triazolopyridine derivatives and to carry out a preliminary evaluation of them as cardiovascular agents.

A. Chemistry
In the context of our work on synthesis and reactivity of [1,2,3]triazolo [1,5-a]pyridines 1 and 2, 5 we have studied lithiation reactions that are regioselective at the 7 position.The 7-lithio derivatives are formed at -40ºC and can be trapped by electrophiles.We have now used aryl aldehydes as electrophiles and have synthesized the new 7-arylhydroxymethyltriazolopyridines 4a-d in addition to the previously known 3a-c. 6

B. Biology
The activity of compounds 3a-c and 4a-d as relaxants of vascular smooth muscle was tested in isolated aortic rings precontracted by noradrenaline in order to determinate whether any of the compounds show activity as antagonists of the α 1 -adrenoceptors present in this tissue and stimulated by the noradrenaline.Addition of 10 µM noradrenaline in Krebs solution induced a sustained contractile response in the intact rat aortic rings (753.8 ± 78.5 mg; n= 28).Compounds 3a-c and 4a-d were added in cumulative concentrations (0.0001 µM -100 µM) to the contracted tissue, but changes in the tone were not observed (n = 4 for each compound).The lack of a relaxant action excludes the possibility that these compounds act as α 1 -adrenoceptor antagonists.
In another set of experiments, addition of depolarising solution (KCl 80mM) to aortic rings induced a sustained contractile response in the absence of endothelium (658.8 ± 66.7 mg; n=28).In these conditions, opening of voltage-sensitive calcium channels and calcium entry promotes this contractile response.Subsequent addition of compounds 3a-c or 4a-d in cumulative concentrations (0.0001 µM -100 µM), once the contractile plateau induced by depolarising solution had been reached, did not modify the tone (n = 4 for each compound), thus suggesting that none of the compounds tested can block calcium entry through voltage-dependent calcium channels.

B. Biological Evaluation
Wistar rats of both sexes, weighing 200-220g were decapitated and the thoracic aorta was isolated.The connective tissue was removed and the vessels were cut into rings of about 5 mm in length which were suspended in a 10 ml organ bath containing Krebs-bicarbonate solution (KBS), maintained at 37ºC and gassed with 95% O 2 and 5% CO 2 .An initial load of 1 g was applied and maintained throughout a 75-90 min equilibration period.Tension was recorded isometrically on a polygraph (Grass M7) via force-displacement transducers (Grass FT03).KBS had the following composition (mM): NaCl 118, KCl 4.75, CaCl 2 1.8, MgCl 2 1.2, KH 2 PO 4 1.2, NaHCO 3 25 and glucose 11.For experiments with Ca 2+ -free solution CaCl 2 was omitted and EDTA (0.1 mM) was added.Depolarizing solution, 80mM, was prepared by equimolar substitution of NaCl by KCl in the Krebs solution.Endothelium-denuded aortic rings were prepared by rubbing the entire intimal surface.To test for the presence of vascular endothelium, acetylcholine (100 µM) was added to preparations pre-contracted with noradrenaline (1 µM). 7Acetylcholine-induced-relaxation was expressed as a percentage of the maximum increase in tension obtained by NA addition.Segments with relaxant responses lower than 20% were considered as endothelium-denuded preparations.Concentration-response relaxation curves were obtained by addition of cumulative concentrations of each compound to vascular rings precontracted by noradrenaline (1 µM) or depolarizing solution. 1-)-Noradrenaline bitartrate was from Sigma, St. Louis MO, U.S.A.; other reagents were of analytical grade.Compounds 3a-c and 4a-d were dissolved in ethanol and diluted in deionized water.The other drugs were dissolved in deionized water.All solutions were prepared daily and the pH was adjusted to 7.0.