Design, Synthesis, and Evaluation of Water-Soluble Phospholipid Analogues as Inhibitors of Phospholipase C from Bacillus cereus

The rate of hydrolysis of natural phospholipids by the phosphatidylcholine-preferring phospholipase C from Bacillus cereus (PLCBc) follows the order phosphatidylcholine > phosphatidylethanolamine ≫ phosphatidyl-l-serine. To probe the structural basis for this substrate specificity, a series of water-soluble, nonhydrolyzable substrate analogues were needed so their complexes with the enzyme could be studied via X-ray crystallography and isothermal titration calorimetry (ITC). Accordingly the water-soluble dithiophospholipids 2−10 having choline, ethanolamine, and l-serine headgroups were synthesized, and the inhibitory activity of each was determined in an assay using 1,2-dihexanoyl-sn-glycero-3-phosphocholine (C6PC) as the monomeric substrate. The 1,2-dibutanoyl dithiophosphocholine 2 was a weak inhibitor, whereas the related 1,2-dipentanoyl dithiophosphocholine 3 and the ethylene glycol dithiophosphocholines 4 and 5 were moderate inhibitors. The 1,2-ω-hydroxydiacyl dithiophosphocholines 6 and 7 were pote...