*3.1. Synthesis of* **6a–j**

The synthetic pathway of the compounds (**6**) is illustrated in Scheme 1. *N*-benzylisatin (**3**) was prepared using our previously reported method [31] by heating same equivalent of isatin (**1**) and benzyl bromide (**2**) at 80 ◦C in dimethylformamide (DMF) for 12 h. *N*-benzylisatin monohydrazone (**4**) also was prepared using previously reported hydrazone formation method [27,32,33,37] using 1.2 equivalent of hydrazine hydrate and *N-*benzylisatin (**3**) at refluxing condition for 3–4 h in alcoholic solution (MeOH/EtOH). Designed *N-*benzylisatin-aryl hydrazones (**6a**–**j**) were synthesized by reacting compound **4** with substituted aryl aldehydes (**5a**–**j**) in absolute ethanol in presence of catalytic amount of glacial acetic acid [27]. The choice of the substituents and its positions on the aromatic ring of benzaldehyde is to offer various electron withdrawal and donation on the aromatic ring which will, in turn, give different degrees of electron density on the biologically active parts of isatin molecule.

**Scheme 1.** Synthesis of *N*-benzylisatin-aryl hydrazones (**6a**–**j**).
