Selective, high affinity α4β1 (Very Late Antigen 4; VLA-4) inhibitor; displays 200-fold selectivity for the activated form of α4β1 (KD = 70 pM; IC50 = 0.004 μM). Selective for α4β1 over a range of other integrins (IC50 >100 μM for α1β1, α5β1 and α6β1). MW (observed): 708.8.