Source Naturals, Cat's Claw, 500 mg, 120 TabletsHerbal Supplement Una De Gato Standardized Extract 1. 5% Oxindole Alkaloids (7. 5 mg) Cat's claw (Uncaria tomentosa) is an herb that grows in the rain forests of the Peruvian Amazon where it has been used for centuries by the indigenous Peruvians. Recent research has discovered that its inner bark contains unique active alkaloid constituents known as oxindole alkaloids, that help support the body's immune system.