L-Tyrosine is an efficient catalyst for the condensation of substituted indole-3-aldehydes 1(a–d), Nmethyl indole-3-aldehydes 4(a–d), and N-ethyl indole-3 aldehydes 6(a–d) with meldrum's acid (2) containing a cyclic active methylene group to produce 3(a–d), 5(a–d), and 7(a–d), respectively, in water at room temperature for 30 min. The antimicrobial activities of 3(a–d), 5(a–d), and 7(a–d) have been studied.