Table 4. Cytotoxic Activity of 2 and 3 against Human Cancer Cells and Normal Cells (IC₅₀, μM) and Their Selective Indexes^a.

	IC50 (μM)
compounds	HL-60	A549	MRC-5	SIc
2a	0.36 ± 0.023	0.38 ± 0.003	0.68 ± 0.013	1.79
2b	0.27 ± 0.017	0.73 ± 0.015	0.60 ± 0.008	0.82
2c	0.23 ± 0.013	0.75 ± 0.006	0.37 ± 0.019	0.49
3a	2.59 ± 0.195	0.88 ± 0.023	0.87 ± 0.063	0.99
3b	0.67 ± 0.038	0.33 ± 0.010	0.54 ± 0.009	1.64
3c	2.20 ± 0.070	0.66 ± 0.016	0.66 ± 0.041	1.00
SN-38b	0.056 ± 0.002	0.052 ± 0.003	0.092 ± 0.001	1.77

^aThe concentration of the compound needed to reduce cell viability by 50% (IC₅₀) was determined using the WST-8 assay. IC₅₀ values are expressed as the mean ± SD of triplicate experiments.

^bSN-38 was used as a positive control.

^cThe SI is defined as the IC₅₀ value against normal MRC-5 cells divided by the IC₅₀ value against A549 cells.