PHYTOCHEMICAL AND BIOCHEMICAL-CHARACTERIZATION OF EPIMERIC PHOTOGEDUNIN DERIVATIVES - THEIR DIFFERENT SITES OF INTERACTION ON THE REDOX ELECTRON-TRANSPORT CARRIER OF SPINACEA-OLERACEA L. CHLOROPLASTS

Bioactivity-directed fractionation of the dichloromethane extract of t he heartwood of Cedrela salvadorensis L. resulted in the isolation of two epimeric photogedunins and in the acquirement of two bioactive epi meric photagedunin acetates 3 (beta) and 4 (alpha) at the C-23 positio n. Compounds 3 and 4 inhibited photophosphorylation, H+-uptake, and no ncyclic electron flow from water to methyl viologen (basal, phosphoryl ating, and uncoupled). Inhibiton of all photosynthetic activities requ ire 3 min of preincubation in the light before inhibition is observed. The results indicate that compounds 3 and 4 behave as Hill reaction i nhibitors. alpha-Photogedunin acetate 3 inhibits PS II electron flow f rom H2O to DCBQ without affecting PS I electron transport from reduced DCPIP to MV and PSII from water to SiMo. Therefore, its target is loc alized at the Q(B) level. beta-Photogedunin acetate 4 inhibits PS I el ectron flow from reduced DCPIP to MV, PMSred to MV, and TMQH(2) to MV without affecting PS II electron flow, interacting at the b(6)f level and in the span of P-700 to F-x.