Photosynthetic inhibitory activity of dihydro-beta-agarofurans sesquiterpenes from Maytenus disticha and Maytenus boaria (Celastraceae)

The effects of 9 beta-benzoyloxy-1 alpha,2 alpha,6 beta,8 alpha,15-pentaace toxy-dihydro-beta-agarofuran and 9 beta-furoyloxy-1 alpha,6 beta,8 alpha-tr iacetoxy-dihydro-beta-agarofuran, major phytogrowth inhibitors isolated fro m the aerial parts of Maytenus disticha (Celastraceae) and seeds of Maytenu s boaria (Celastaraceae), respectively, on different photosynthetic activit ies of isolated spinach chloroplasts have been investigated. Photophosphory lation and electron transport (basal, phosphorylating and uncoupled) were i nhibited in a concentration dependent manner by both compounds, therefore a cting as Hill reaction inhibitors. The site of action of these natural comp ounds was located in the span from P-680 to Q(A). 9 beta-benzoyloxy-1,2,6,8 ,15-pentaacetoxydihydro-beta-agarofuran was one order of magnitude more pot ent (I-50 = 2.6 mu M) than 9 beta-furoyloxy-1,6,8,-triacetoxydihydro-beta-a garofuran, suggesting that the substitution at C-9 and the acetoxy groups a t carbons 2 and 15 are important structural requirements for the displayed inhibitory activity.