Alzheimer's disease is an irreversible, degenerative and age-related disease which is growing more and more with the increase in life expectancy. Kaurane diterpenes are a class of natural products available in large amounts in nature and isolated from plants grown worldwide. In the present work¸ twenty-seven kaurane diterpenes of natural origin and some readily available derivatives were assayed for acetylcholinesterase inhibition and the structure-activity relationship was analyzed. The kaurenoic acid derivatives screened showed to be promising inhibitors of AChE, which could provide new leads for drugs to fight Alzheimer's disease symptoms. Among them, eleven compounds showed activities comparable or higher than the positive control galantamine. Existence of an allylic hydroxyl group showed to be an important structural feature for AChE inhibition. In addition, presence of free hydroxyl groups at C-17 and C-19, furnished a diol especially active, able to completely inhibit AChE.

A systematic investigation on the trypanocidal effect of several natural products isolated from Brazilian plant species has been carried out. In this paper we report on the results obtained from the screening of 26 diterpenes from natural sources or of synthetic/microbial transformations origin (mainly derivatives of kaurenoic acid) against trypomastigote forms of Trypanosoma cruzi, the causative agent of Chagas'disease. In the in vitro assays, kaurenoic acid, kaurenol, acutifloric acid and stemodin showed a complete elimination of parasites from the blood. Therefore, such diterpenoids can be considered as starting materials for molecular modification in the search for lead compounds for clearance of infected blood to be used in transfusions. Blood previously treated with active compounds was submitted to an infectivity test. Samples proceeded from treatment with kaurenol and kaurenoic acid showed to be completly clean from T. cruzi as no infection was observed in mice inoculated with contaminated blood treated by these compounds.