Biological effects of a new set 1,2,4-triazolo[1,5-a]quinazolines on heart rate and blood pressure

Background Several quinazoline and triazole derivatives are reported to possess a wide-range of interesting pharmacological effects. Although various triazoloquinazoline subclasses having been synthesized and studied, the preparation of 1,2,4-triazolo[1,5-a]quinazolines as antihypertensive agent is still relatively unexplored. In continuation of our earlier research, we aimed at the synthesis and development of various potent antihypertensive 1,2,4-triazoloquinazoline derivatives. Results A new series of 1,2,4-triazolo[1,5-a]quinazoline derivatives have been synthesized. Their structures were mainly established by spectroscopic methods of analysis (IR, MS, 1H and 13C NMR). Their in vivo antihypertensive activity was evaluated by tail cuff method using Muromachi Blood Pressure Monitor (Model MK 2000) for rats and mice. Some of the tested compounds were found to exhibit valuable effects in terms of heart rate and blood pressure. According to the biological results, some of tested derivatives have abolished completely the tachycardia of the parent compounds and may be studied and modified as potential adrenoblockers and cardiac stimulant. Conclusion New series of fifteen 1,2,4-triazolo[1,5-a]quinazolines were synthesized by convenient methodology from four key molecules, whereby their structures were established by advanced spectroscopic analyses. Some lead compounds have abolished completely the tachycardia of the parent compounds, that may be examined as potent adrenoblockers and some other compounds seem to be a cardiac stimulant or may be modified to enhance their hypotensive activity.


Background
Arterial diseases cause more premature deaths than all other disorders such as cancer and infections combined. High blood pressure has been identified as the most powerful one among the major risk factors for arterial diseases [1]. Now-a-days, several efforts have been made in search of potent anti-hypertensive drugs because hypertension was commonly proved to cause heart failure. Quinazolines and their condensed products are reported to possess several interesting pharmacological effects such as antihypertensive [2], antihistaminic [3,4], analgesic, anti-inflammatory [5,6], anticancer [7], and anti-HIV [8] activities. Prazocin, terazocin and doxazocin as quinazoline derived α-1 blockers, are reputed class of antihypertensive agents. In spite of various triazoloquinazoline systems having been synthesized and studied, the elaborating of 1,2,4-triazolo [1,5-a]quinazoline as antihypertensive agent is still relatively unexplored [1]. Moreover, Some of potent antihypertensive 1,2,4-triazoloquinazoline derivatives were reported [1]. In view of these facts and continuation to our earlier reported triazoloquinazolines researches [1,[9][10][11][12], we aimed at synthesis of various substituted 1,2,4-triazolo [1,5-a]quinazolines and evaluation their biological effects on heart rate and blood pressure.
Generally, uncorrected melting points of all compounds were recorded and their chemical structures primarily consistent with their IR and MS data (see experimental section) and confirmed by 1 H-and 13 C NMR spectroscopy (splitting pattern, δand J-values and comparison with literature of structural related compounds). In the tricyclic nucleus, the benzofused moiety was deduced from its own four one proton 1 H-signals as two dd (or br d) resonances with J ortho (7.5-8.5 Hz) and J meta (1-2 Hz) assignable for H-9 and H-6 and two td (or br t) resonances with  J ortho and J meta for H-8 and H-7, respectively. The exchangeable NH-proton was interpreted in 1 H NMR of 3 and 4 at δ > 13 ppm and were absent in all spectra of N-alkyl or 5-chloro-triazoloquinazolines. 13 C NMR spectra proved the main tricyclic moiety through characteristic nine resonances including the most downfield key signal of C-2 assigned at ≈ 165 ppm in 2-phenoxy derivatives (e.g. 3, 5-7) that was observed relatively upfield at ≈ 160 in case of 2-methylsulfonyl function (e.g. 4, 8-10) due to the stronger -R and -I (deshielding) effect of O-phenoxy than -SO 2 .

Antihypertensive activity
In vivo antihypertensive activity study of the title compounds 1-19 was performed by tail cuff method using Muromachi Blood Pressure Monitor for rats and mice (Model MK 2000). The obtained results, in Table 1, revealed that the nature of substituent and substitution pattern on the tricyclic systems 1-4 may have had a considerable impact on the heart rate and blood pressure in all synthesized derivatives (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19). Basically, the parent 1 was found to increase the heart rate, however it has not demonstrated any effect on blood pressure. Replacement of phenoxy group on position 2 by a sulfanyl group in case of compound 2 has been abolished effect on the heart rate. On the other hand, presence of sulfonyl group in 4 was found to induce the bradycardia, however no effect on blood pressure was noticed. Introduction of methyl group on the lead compound 1 to afford 3 did offer advantageous effect on reduction of blood pressure accomplished by suppressing effect on heart rate in regard to 3. Alkylation of lactam moiety in 1 furnished N-alkylated products 5-7, that did demonstrate remarkable effect. For instance, compound 5 was induced bradycardia, however great increasing in the heart rate showed by 6, whereas abolished in the tachycardia term and slightly induction on bradycardia was demonstrated by 7. Similarly, transformation of 4 into 9 has emerged more bradycardia effect accomplished by moderate decreasing on blood pressure. However the product 8 showed induction on bradycardia and 10 exhibited only bradycardia effect. Further transformation of 1 into 11 does not seem to offer any advantages effect on heart rate but a very slightly decrease in blood pressure was observed. Whereas, compound 12 showed more bradycardia and completely abolished in tachycardia effects together with a slightly increase on blood pressure. Moreover, decreasing on tachycardia profile was exhibited by compound 13. The replacement of the chlorine atom in 11 by ethoxide group gave 14, which has shown decrease on blood pressure and tachycardia effects. Thionation of 1 into 15 was accomplished by abolishing the tachycardia profile and induce on bradycardia term. The same behavior on tachycardia effect was observed by compound 16 but no influence on blood pressure profile has been recorded. Moreover, the transformation of 15 into 17 demonstrated almost the same behavior in the terms of the effects on heart rate and blood pressure. Whereas, compound 18 was exerted complete abolishing in tachycardia and slight induction on bradycardia profiles. However, induction on tachycardia and decreasing on blood pressure terms was demonstrated by compound 19.
Structure modifications on the lead compounds 1-4 have afforded derivatives with different effects on heart rate and blood pressure profiles. Variation in the substituted alkyl groups has demonstrated slightly remarkable activity in regards to the parents, such as increasing on heart rate emerged by 6, induction in bradycardia proved by 5 and slightly decreasing in blood pressure occurred with 9. This could be attributed to the characteristic features of their alkyl groups. Introduction of lipophilic group on position 5 of the parent was appeared to offer slightly decrease in blood pressure in case of compounds 11 and 12. Nevertheless, the slight effect on blood pressure of 11 and 12 bearing at the 5-position a chlorine atom indicates that, not only chloro lipophilic factor, but also the sterric effect are important for decrease on blood pressure as shown by 14. Thionation targets 15 and 16 showed remarkable attenuated on profiles activity, despite these compounds possess enhanced lipophilicity comparable to that parent compounds. However thioether products have almost emerged the same behavior on blood pressure and heart rate as in 17, and decreasing on blood pressure by 19. The actual explanation for these changes regarding SAR will await the elucidation of the mechanism(s) of action of the compounds.

Experimental General
Melting points were determined on open glass capillaries using a Mettler FP 62 apparatus and are uncorrected. The IR (KBr, ѵ, cm -1 ) spectra were recorded on a Perkin Elmer FT-IR Spectrum BX system. NMR spectra were recorded on a Bruker AMX 500 spectrometer in DMSO-d 6 and reported as δ ppm values relative to TMS at 500 and 125 MHz for 1 H-and 13 C NMR, respectively. Mass spectra were measured on an Agilent 6410 TSQ system connected to Agilent 1200 HPLC interface (samples were infused in MeOH). Follow up of the reactions and checking the purity of compounds was made by TLC on DC-Mikrokarten polygram SIL G/UV254, from the Macherey-Nagel Firm, Duren Thickness: 0.25 mm. Column chromatography was conducted on silica gel (ICN Silica 100-200, active 60 Å).

8-Methyl-2-phenoxy-4H-[1,2,4]triazolo[1,5-a]quinazolin-5one (3)
2-Hydrazino-5-methyl benzoic acid (10 mmol) was added portion wise to a stirred solution of diphenyl-N-cyanoimidocarabonate (10 mmol) in EtOH (20 mL) at 0°C. Afterwards, triethylamine (30 mmol) was added drop-wise over a period of 30 min. After the addition was complete, the reaction mixture was left to stirr overnight at room temperature. Acidification of the mixture was  To a solution of 1 or 4 (I mmol) in DMF (5 mL) was added potassium carbonate (1.2 mmol) portion wise over a period of 10 min at room temperature. After stirring for 20 min, the appropriate alkyl halide (1.5 mmol) was added drop wise, and the reaction mixture was stirred for 18 h at room temperature. The mixture was poured into ice/water, the precipitate was filtered off, washed with water and dried. Analytically pure products 5-10 were obtained after recrystallization from THF. Compound 1 (1 mmol) was refluxed with Phosphorous oxychloride (1 mL) in benzene (7 mL) for 2.5 h. The solvent was evaporated and the residue was treated with saturated solution of potassium carbonate. The solid was filtered, washed thoroughly with water, dried and recrystallized from THF to give pure compound as white solid, yield: 82%, m.p. 167-169°C; 1  General procedure for synthesis of 5-Alkyl(phenyl)sulfanyl-2-phenxy- [1,2,4]triazolo[1,5-a]-quinazolines (17)(18)(19) Compound 15 (1 mmol) was dissolved in 2 M sodium hydroxide solution (10 mL), alkyl halide (1.5 mmol) was added dropwise over a period 2 min, the mixture was left to stir for I h at room temperature, and the obtained solid was separated by filtration, washed thoroughly with water and dried. Recrystallization of the crude products from THF afforded 17-19 as colored pure solid.