This thesis divided into four chapters and each chapter includes its own number of derivatives and references. Due to great biological significance of heterocyclic compounds, here in this dissertation we have described synthesis and bioactivities of benzothiazole, thiadiazole and isatin analogs in search of important therapeutic agents. Variety of benzothiazole, thiadiazole and isatin analogs were synthesized, characterized by 1HNMR, 13CNMR and HR-EIMS and screened for enzyme inhibition studies (α-glucosidase, α-amylase and thymidine phosphorylase activities). The results are separately discussed in the forthcoming chapter 1, 2 and 3. In first chapter, Benzothiazole based oxadiazole derivatives (122-144) have been synthesized and evaluated for α-glucosidase inhibition. All analogs exhibited a varying degree of α-glucosidase inhibitory potential with IC50 values ranging in between 0.5 ± 0.01 - 30.90 ± 0.70 μM when compared with the standard acarbose (IC50 = 866.30 ± 3.20 μM). In second chapter, two series of thiadiazole are described. In first series, thiadiazole quinoline analogs (180-209) were synthesized and screened for α-amylase inhibitory potential. Thirteen analogs 180, 181, 182, 183, 184, 185, 201, 202, 204, 205, 206, 207 and 209 showed outstanding α-amylase activity with IC50 values ranges between (0.002 ± 0.60 to 42.31 ± 0.17 μM) which is many folds better than standard acarbose having IC50 value 53.02 ± 0.12 μM. Eleven analogs 190, 192, 193, 194, 195, 197, 198, 200, 201, 202 and xxx 207 showed good to moderate inhibitory potential while seven analogs 187, 192, 195, 199, 200 and 208 were found inactive. In second series, 2-amino-thiadiazole based Schiff bases (211–219) were synthesized and screened for α-glucosidase inhibitory activity. All compounds showed outstanding α-glucosidase inhibition ranging between 2.30 ± 0.1μM to 25.30 ± 0.5μM when compared with the standard inhibitor acarbose having IC50 value 39.60 ± 0.70μM. Among the series, analogs 211, 214, 216 and 217 showed potent α-glucosidase activity which was more active than standard acarbose. The remaining analogs also showed excellent α-glucosidase inhibition. In third chapter, a new class of exceptionally potent isatin based oxadiazole (88-117) has been synthesized and evaluated for thymidine phosphorylase inhibitory potential. All analogs showed potent thymidine phosphorylase inhibition when compared with standard 7-Deazaxanthine, 7DX (IC50 = 38.68 ± 1.12 μM). In chapter four, procedures for different biological assay are described.