Interferon-inducing, Pyrogenic and Proclotting Enzyme of Horseshoe Crab Activation Activities of Chemically Synthesized Lipid A Analogues

Interferon-inducing, pyrogenic and proclotting enzyme of horseshoe crab activation activities of chemically synthesized lipid A analogues were investigated and compared with the same activities of a natural lipid A. These analogues are nonphosphorylated, C-1 or C-4' monophosphorylated and C-1,4' bisphosphorylated derivatives of beta-1,6-linked D-glucosamine disaccharide possessing both ester-bound and amide-bound fatty acid substituents. Fatty acid substituents of the analogues are tetradecanoyl (C14), (R)-3-hydroxytetradecanoyl (C14-OH) or (R)-3-tetradecanoyloxytetradecanoyl [C14-O-(C14)] groups. The biological activities of the samples were assayed after solubilization with triethylamine and complexing with bovine serum albumin. Interferon-inducing activity was exhibited by both the C-1 monophosphorylated compounds examined. Ester-bound and amide-bound fatty acid substituents of these compounds are both C14 or C14 and C14-OH, respectively. Nonphosphorylated, C-4' monophosphorylated and C-1,4' bisphosphorylated compounds possessing the same fatty acid substituents as those of the C-1 monophosphorylated compounds showed no detectable interferon-inducing activity. C-4' monophosphorylated compounds possessing C14-OH as ester-bound and C14-OH or C14-O-(C14) as amide-bound fatty acid substituents exhibited interferon-inducing activity, but nonphosphorylated compounds possessing the same fatty acid substituents did not. None of the analogues exhibited significant pyrogenicity nor proclotting enzyme of horseshoe crab activation activity under the conditions employed in this study.