Antineoplastic agents. 42. The butterfly, Prioneris thestylis

Isoguanine (2) was found to be an antineoplastic constituent of Prioneris thestylis Dbldy. wings. Three other purine components of the butterfly wings were identified as hypoxanthine (3), uric acid (4) and xanthine (5). Isolation of urocanic acid (6) from the same wing material represented the first detection of this interesting histidine derivative in an arthropod.