Natural diterpene β-lactone derivative as photosystem II inhibitor on spinach chloroplasts

Abstract α,7β-Dihydroxyvouacapan-17β-oic acid ( 1 ) was isolated from Pterodon polygalaeflorus Benth. Then, ( 1 ) was modified to obtain 6α-hydroxyvouacapan-7β,17β-lactone ( 2 ). Inhibition properties of both ( 1 ) and ( 2 ) were evaluated in spinach chloroplasts. Only compound ( 2 ) inhibited non-cyclic electron transport and ATP synthesis, i.e., ( 2 ) behaved as a Hill reaction inhibitor. Compound ( 2 ) did not affect photosystem I (PSI) activity but it did inhibit electron flow through PSII. Analysis of the partial PSII reactions from water to DCPIP ox , water to silicomolybdate, and diphenylcarbazide to DCPIP ox allowed locating inhibition sites at (i) the oxygen-evolving complex (OEC) and (ii) the redox enzymes of the electron transport chain, in the span of P 680 to Q A . Chlorophyll a fluorescence measurements confirmed the action site for ( 2 ).