Table 2. Inhibitory Concentration (IC₅₀, μM) against Isolated DHFR^a and Selectivity Ratios^b.

cmpd	P. carinii	rat liver	rl/pcb	M. avium	rl/mab
3	0.00311	0.06	19.3	0.000737	81.4
4	0.0048	0.186	38.8	0.000391	475.7
5	37.3	4.57	0.12	0.7	6.5
6	14.6	7.8	0.5	0.1	78
7	21.8	5.6	0.3	0.88	6.36
8	6.04	4.05	0.7	0.1043	38.8
11	5.35	5.95	1.1	12.3	0.5
12	5.32	2.43	0.5	10.4	0.23
13	4.21	1.25	0.3	1.31	1.0
14	4.21	1.25	0.3	0.63	2.0
15	10.4	8.9	0.9	0.6	14.8
16	8.45	3.45	0.4	0.21	16.4
17	8.6	6.5	0.8	4.1	1.59
18	3.5(16%)c	3.8	ND	7.8	0.5
19	22(14%)	2.4	NDd	2.7	0.9
20	27.2	14.8	0.5	28.6	0.52
21	11.2	2	0.2	0.3687	5.42
22	ND	1.9	ND	ND	ND
23	35.6	50.3	1.4	2.1	24
24	28.2	4.6	0.2	3.4	1.3
25	0.68	0.91	1.3	0.24	3.8
26	7.1	2.1	0.3	2.54	0.83
27	10.9	13.5	1.2	1.14	11.84
TMQ	0.042	0.003	0.07	0.0015	2.0
TMP	12	180	15	0.3	600

^aThese assays were carried out at 37 °C under conditions of substrate (90 μM dihydrofolic acid) and cofactor (119 μM NADPH) in the presence of 150 mM KCl.

^bSelectivity ratios, rl/pc = IC₅₀ rat liver dihydrofolate reductase/IC₅₀P. carinii dihydrofolate reductase; rl/ma = IC₅₀ rat liver dihydrofolate reductase/IC₅₀M. aνium dihydrofolate reductase.

^cNumber in parenthesis indicate the percentage inhibition at the given concentration.

^dND = not determined.