Table 3.

Structure Activity Relationships on the Ansamycin Scaffold

NSC Number	Structure	EC50 (nM)a
		T. brucei	L1210	Selectivityb
330500 Macbecin II		240	47	0.2c
265481		>80 000	>80 000	NA

Abbreviations: EC₅₀, half maximal effective concentration; NA, not applicable; T. brucei, Trypanosoma brucei.

^a Values are mean of at least 3 independent determinations. Coefficients of variation for EC₅₀ values were all ≤35%. r² values for dose-response curves all exceeded 0.98; within an assay, the coefficients of variation for quadruplicate determinations were ≤10% and averaged 2.6%.

^b Defined as the ratio of the L1210 EC₅₀ to the T. brucei EC₅₀; large numbers are favorable.

^c P < .05, by a 2-tailed t test.