Table 1. SAR on the bottom ring of 1 (ring A).

Compound	Ring A	K d a (μM)	LE b	PDB	Compound	Ring A	K d a (μ M)	LE b	PDB
1		267	0.33	5CSH	7		375	0.30	5OSL
2		41	0.38	5ORH	8		>500	—	n.a
3		17	0.39	5ORJ	9		>500	—	5OUL
4		205	0.29	5OS7	10		>500	—	n.a
5		244	0.30	5OQU	11		105	0.33	5OS8
6		234	0.32	5ORK	12		250	0.27	n.a
					13		>500	—	n.a

^aMeasured by ITC.

^bLE = ligand efficiency*. *Ligand efficiency is defined as the ratio of the Gibbs free energy of binding of a ligand divided by the number of heavy (non-hydrogen) atoms in the molecule (LE = ΔG/[number of heavy atoms]).20