Photosynlhetic Inhibitory Activity of Dihydro-β-agarofurans Sesquiterpenes from Maytenus dislicha and Maytenus boaria (Celastraceae)

Abstract

The effects of 9β-benzoyloxy-la, 2α, 6β, 8α, 15-pentaacetoxy-dihydro-β-agarofuran and 9β furoyloxy-1α, 6β, 8α-triacetoxy-dihydro-β-agarofuran, major phytogrowth inhibitors isolated from the aerial parts of Maytenus disticha (Celastraceae) and seeds of Maytenus boaria (Celastaraceae), respectively, on different photosynthetic activities of isolated spinach chloroplasts have been investigated. Photophosphorylation and electron transport (basal, phosphorylating and uncoupled) were inhibited in a concentration dependent manner by both compounds, therefore acting as Hill reaction inhibitors. The site of action of these natural compounds was located in the span from P₆₈₀ to Q_A. 9β-benzoyloxy-1,2,6,8,15-pentaacetoxydihydro-β-agarofuran was one order of magnitude more potent (I₅₀ = 2.6 μм) than 9β-furoyloxy-1,6,8,-triacetoxydihydro-β-agarofuran, suggesting that the substitution at C-9 and the acetoxy groups at carbons 2 and 15 are important structural requirements for the displayed inhibitory activity.