Table 1. Antiproliferative Activities of Compounds 4–6 and 15 in KB Cells.

	% inhibition of KB cell growth
compound no.	10 μM	1 μM	ITPc (μM)
4	100	100a	1.8
5	81	63	5.3
6	100	27	4.2
15	100	100b	4.1

^aThe IC₅₀ of 4 was determined to be 35 nM.

^bThe IC₅₀ of 15 was determined to be 2 nM.

^cInhibition of tubulin polymerization.