Pyridine-3/4-thiocarboxamide derivatives were used as starting materials for the synthesis of the target compounds. The pyridine-3/4-thiocarboxamide derivatives were reacted with ethyl 2-chloroacetoacetate in ethanol to give the thiazole derivatives (1, 2). The two ethyl thiazole-carboxylate derivatives (1, 2) thus obtained were treated with sodium hydroxide solution and ethanol and converted to carboxylic acids (3, 4). The carboxylic acid derivatives (3, 4) were reacted with thiosemicarbazide in phosphoroxy trichloride and aminothiadiazole rings (5, 6) were formed. Thus, two thiazolyl-thiadiazole amine derivatives (5, 6) were obtained. These two derivatives (5, 6) were converted into two chloroacetamidothiadiazole derivatives (7, 8) by reaction with chloroacetylchloride over the amino group in the presence of triethylamine in acetone. After all these steps, the starting materials (7, 8) needed to reach the target compounds were obtained. With the two derivatives (7, 8) obtained in this last step, phenol and thiophenol derivatives were reacted in acetone in the presence of potassium carbonate. The target compounds, thiazolyl-thiadiazole derivatives (TDA$_{\mathbf{1-16}})$, are completely unique and their structure has been elucidated by elemental analysis, IR, NMR, and MS spectral data. After all these synthesis steps, telomerase activity studies were performed on the target compounds obtained. For this purpose, a PCR ELISA-based TRAP method was used on the heart of zebrafish. According to the enzyme assay results, derivative TDA$_{\mathbf{8}}$ has shown an increase of telomerase enzyme activity.