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

Abstract

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 µM, whereas the standard inhibitor of xanthine oxidase (allopurinol) had an IC₅₀ value of 7.4 ± 0.07 µM. Compounds 1 (IC₅₀ 7.21 ± 0.05 µM), 2 (IC₅₀ 9.40 ± 0.03 µM), 3 (IC₅₀ 11.51 ± 0.07 µM), 4 (IC₅₀ 12.53 ± 0.06 µM), 5 (IC₅₀ 14.29 ± 0.09 µM), and 6 (IC₅₀ 17.34 ± 0.04 µM) exhibited pronounced activities when compared with the standard tyrosinase inhibitor l-mimosine (IC₅₀ 3.70 ± 0.03 µM), along with DPPH radical scavenging activity with IC₅₀ 226, 270, 300, 320, 401, and 431 µM, 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.

Keywords::

• Isatis costata
• brassicaseae
• oxindole alkaloids
• xanthine oxidase
• tyrosinase
• antioxidant
• antifungal activity