Tibouchina pulchra

The quinones are generally skin irritants. Some compounds have both toxic and dermatological actions. For example, juglone was known to be toxic as well as to cause dermatitis (170). Other examples were reviewed most recently by Hausen (75). Jones et al. (89) showed that 2,6-dimethoxybenzoquinone, a cytotoxic constituent of the woody stems of Tibouchina pulchra, has an LD50 of 2.5 pg/ml in KB cell culture. 

Jones E, Ekundayo O, Kingston D G I 1981 Plant anticancer agents. XI. 2,6-dimethoxybenzo-quinone as a cytotoxic constituent of Tibouchina pulchra. J Nat Prod 44 493-494... 

---