L-Proline-Catalyzed Synthesis of Novel 5-(1H-Indol-3-yl-methylene)-thiazolidine-2,4-dione Derivatives as Potential Antihyperglycemic Agents

Knoevenagel condensation between indole-3-aldehyde 1 and an active methylene group containing 2,4-thiazolidinedione 2 in refluxing toluene using L-proline as a catalyst yielded 3, which on alkylation using 2 equivalents of alkylating agent under phase-transfer-catalyzed (PTC) conditions using K₂CO₃ as a base in dimethylformamide gave N,N^I-symmetrically disubstituted 5-(1H-indol-3ylmethylene)-thiazolidine-2,4-diones 4. Alternately, 4 can be synthesized by condensing 5 and 6 in a single step. Using this synthetic strategy, N,N^I-unsymmetricallydisubstituted derivatives 9a–f were prepared either by condensing 6 with N-substituted-2,4-thiazolidinedione 5 to obtain 7 followed by alkylation under PTC conditions or condensing 6 with N-unsubstituted- 2,4-thiazolidinedione 2 to yield 8 followed by alkylation under PTC conditions. The latter are the dehydro analogs of the dihydro-N-substituted-5-(1H-indol-3-yl-methylene)-thiazolidine-2,4-diones, which are potential antihyperglycemic agents.

Keywords: Indole-3-aldehyde, L-proline, N,N^I-symmetrically/unsymmetrically disubstituted 5-(1H-indol-3ylmethylene)-thiazolidine-2,4-diones, 2,4-thiazolidinedione (TZD)

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ACKNOWLEDGMENTS

The authors are thankful to the authorities of Jawaharlal Nehru Technological University, Hyderabad (A.P.), for providing laboratory facilities. They are also indebted to the University Grants Commission, government of India, New Delhi, for providing financial support.