A series of novel benzamide appended heterocyclic thiadiazole were synthesized and evaluated for their angiotensin-I-converting enzyme (ACE-I) inhibitory activity. Furthermore their antioxidant activity by DPPH assay, lipid peroxidation assay and super radical scavenging activity is described. The reaction of compounds (6a-i) in the presence of conc. H2SO4 proceeded efficiently to give the respective benzamide embedded thiadizole in very good yields. Screening of all the new compounds using ACE-I inhibition assay, when compared to the standard lisinophril resulted the following. Among the compounds, 7i was the marginally active ACE-I inhibitor with IC50 of 40.98 μg/μl and compounds 7b-f were moderate ACE-I inhibitors when compared to standard lisinopril (IC50 value = 40.40 μg/μl). Antioxidant activity, by DPPH assay revealed that compounds 7b-7g were moderate radical scavengers with IC50 value in the range of 31.5-35 μg/μl when compared to standard Ascorbic acid (IC50 value = 24.0 μg/μl). The compounds 7a-7g showed moderate anti-lipid peroxidation activity when compared to standard α-Tocopherol (% activity 49.82) with % activity in the range of 40-45%. By Superoxide radical scavenging assay, compounds 7a-7g were found to be moderate superoxide radical scavengers with % activity in the range of 38-49% when compared to standard Butylated hydroxyanisole (23.55%). Compound 7h exhibited better antioxidant properties by DPPH assay, anti-lipid peroxidation activity and Superoxide radical scavenging assay.
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