Trifluoromethyl ketones and methyl fluorophosphonates as inhibitors of group IV and VI phospholipases A(2): structure-function studies with vesicle, micelle, and membrane assays

A series of fatty alkyl trifluoromethyl ketones and methyl fluorophosphonat es have been prepared and tested as inhibitors and inactivators of human gr oups IV and VI phospholipases A(2) (cPLA(2) and iPLA(2)). Compounds were an alyzed with phospholipid vesicle-, detergent-phospholipid mixed-micelle-, a nd natural membrane-based assays, and, with few exceptions, the relative in hibitor potencies measured with the three assays were similar. Ph(CH2)(4)CO CF3 and Ph(CH2)(4)PO(OMe)F emerged as a potent inhibitor and inactivator, r espectively, of iPLA(2), and both are poorly effective against cPLA(2). Of all 13 fatty alkyl trifluoromethyl ketones tested, the trifluoromethyl keto ne analog of arachidonic acid is the most potent cPLA(2) inhibitor, and str ucturally similar compounds including the trifluoromethyl ketone analog of docosahexenoic acid are much poorer cPLA(2) inhibitors. Inactivation of cPL A(2) by fatty alkyl fluoromethylphosphonates is greatly promoted by binding of enzyme to the interface. The use of both vesicles and mixed micelles to assay phospholipase A? inhibitors and inactivators present at low mol frac tion in the interface provides reliable rank order potencies of a series of compounds that correlate with their behavior in a natural membrane assay. (C) 1999 Elsevier Science B.V. All rights reserved.