Heterocyclic ortho-quinones, a novel type of Photosystem II inhibitors

Members of the new chemical class of 7-substituted 6-bromo-benzo[4,5]imidaz o[1,2 alpha ]pyridin-8,9-diones were found to be excellent inhibitors at th e Q(B) site of the photosystem II D1 reaction center protein. The best inhi bitors with pI(50)-values of > 7 are: dimethyl-propyl, 7.05; i-pentyl, 7.36 ; t. butyl, 7.47; and i-propyl, 7.51. Displacement experiments with [C-14]a trazine revealed that the 8,9-diones behave non-competitively in respect of Photosystem II herbicides and, hence, have to be considered as a new type of Photosystem II inhibitors. This notion is further corroborated by their inhibitory activity in D1 mutants of Chlamydomonas reinhardtii. (C) 2001 El sevier Science B.V. All rights reserved.