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1-Benzoyl-2-alkyl piperazines are strong inhibitors of Group I and II secreted PLA2s. An improvement of their activity was obtained by replacing the amide function by a sulfamide and by introduction of electrodonor substituents on the para position of the benzenesulfonyl moiety. Neither the position on one of the carbon of the piperazine ring nor the absolute configuration of this carbon have an effect on the affinity for one or the other group of PLA2, but the lipophilicity remains for these series an essential parameter. In addition structure–activity relationships allow new hypothesis on interaction of these piperazine derivatives with the catalytic site of PLA2s.

Starting from a series of compounds which were known to be PAF antagonists, we have synthesized molecules that are good inhibitors of PLA2s of groups I or II, with IC50 in the micromolar range (Binisti et al., 1997). In this report we investigate the mechanism of inhibition of bovine and porcine pancreatic phospholipases A2 (group I), and platelet lysate phospholipase A2 (group II) by one of these compounds, 1-(4'-methoxybenzoyl)-2-n-tridecylpiperazine (PMS 832). We show that PMS 832 behaves as a reversible, competitive inhibitor, with Ki values of 4.1 +/- 1.2 and 1.5 +/- 0.4 microM for porcine pancreatic phospholipase A2 and platelet lysate phospholipase A2, respectively. PMS 832 failed to inhibit platelet activation induced by several agonists and was also found to be inactive towards phospholipase C from Bacillus cereus, indicating a high specificity for phospholipase A2 inactivation. Thus, PMS 832 and its derivatives could serve as interesting tools to investigate the role of extracellular phospholipases A2 in inflammatory processes, and may be useful in the development of new anti-inflammatory agents.

A series of 4-alkoxybenzamidines was synthesized, varying the number of carbons of the alkyl chain, and their potency as phospholipase A2 (PLA2) inhibitors was evaluated. The relationship between their capacity to inhibit PLA2 activity and their lipophilicity was examined. The optimum of the inhibitory effect against two extracellular PLA2S from rabbit platelets and bovine pancreas was observed with compounds bearing an alkyl chain of 12 and 14 carbons. These 4-dodecyl and tetradecyloxbenzamidines inhibited bovine pancreatic and rabbit platelet lysate PLA2S with IC50 values of 3 microM and 5-5.8 microM, respectively. The mechanism of inhibition was of the competitive type. In addition, 4-tetradecyloxbenzamidine was shown to exert an antiinflammatory effect in vivo on the carrageenan-induced rat paw oedema. These results show that 4-tetradecyloxybenzamidine will serve as an interesting tool to investigate the physiological role of mammalian-secreted PLA2, both in vitro and in vivo.