Xanthine oxidase/tyrosinase inhibiting, antioxidant, and antifungal oxindole alkaloids from Isatis costata.

Phytochemical investigations on the ethyl acetate soluble fraction of the whole plant of Isatis costata Linn. (Brassicaseae) led to the isolation of the oxindole alkaloids costinones A (1), B (2), isatinones A (3), B (4), indirubin (5), and trisindoline (6). Compounds 1-6 displayed significant to moderate inhibition against xanthine oxidase enzyme with IC50 values ranging from 90.3+/-0.06 to 179.6+/-0.04 microM, whereas the standard inhibitor of xanthine oxidase (allopurinol) had an IC(50) value of 7.4+/-0.07 microM. Compounds 1 (IC50 7.21+/-0.05 microM), 2 (IC50 9.40+/-0.03 microM), 3 (IC50 11.51+/-0.07 microM), 4 (IC50 12.53+/-0.06 microM), 5 (IC50 14.29+/-0.09 microM), and 6 (IC50 17.34+/-0.04 microM) exhibited pronounced activities when compared with the standard tyrosinase inhibitor L-mimosine (IC50 3.70+/-0.03 microM), along with DPPH radical scavenging activity with IC50 226, 270, 300, 320, 401, and 431 microM, respectively. The crude extract and compounds 1, 2, 5, and 6 showed significant antifungal activity against Trichophyton schoen leinii, Aspergillus niger, Candida albicans, Trichophyton simii, and Macrophomina phaseolina.