Table 1. Inhibitory Concentration of Phosphonamidates (1–2) (IC₅₀) against the Purified Enzymes NDM-1, GIM-1, and VIM-2^a.

	IC50 (μM)
enzyme	1a	1b	1c	1d	2	1e	1f	1g	1h
NDM-1	N.I.	356	N.I	430	N.I.	N.I.	P.	P.	P.
GIM-1	86	109	N.I.	N.I.	N.I.	2700	P.	P.	P.
VIM-2	N.I.	1417	500	N.I.	N.I.	N.I.	P.	P.	P.

^aIC₅₀ = appK_i + (E_t/2), where appK_i is the apparent K_i, and E_t is the enzyme concentration. Accordingly, when the observed IC₅₀ is much greater than the enzyme concentration, it is determined by the apparent K_i and not by the enzyme concentration.²¹ In the measurements mentioned above, the enzyme concentration has been at least 3 orders of magnitude below the observed IC₅₀ values, and hence, the reported IC₅₀s are in no mean affected by the NDM-1, GIM-1, and VIM-2 concentrations.