Structural requirements for inducing in vitro B lymphocyte activation by chemically synthesized derivatives related to the nonreducing D‐glucosamine subunit of lipid A

AbstractMitogenic and polyclonal B cell activation (PBA) activities of 16 synthetic compounds related to the nonreducing D‐glucosamine (GlcN‐II) subunit of lipid A were investigated. Among compounds possessing the GlcN backbone, a 4‐O‐phosphorylated GlcN derivative carrying N‐linked 3‐tetradecanoyloxytetradecanoyl [C14‐O‐(C14)] and 3‐O‐linked tetradecanoyl (C14) groups, GLA‐27, expressed the highest degree of both activities. Omission of the 3‐O‐linked C14 group from GLA‐27 and transfer of the C14group to the C‐6 position induced critical changes in expression of activities. Both 4‐ O‐phosphorylated compounds carrying an N‐linked C14 or 3‐hydroxytetradecanoyl (C14OH) group instead of the C14‐O‐(C14) group in GLA‐27 showed no detectable activity. Substituting a 3‐O‐linked C14 group in GLA‐27 for the C14‐O‐(C14) group also markedly decreased mitogenic and PBA activities. Change of phosphorylation site from the C‐4 to the C‐6 position and bisphosphorylation at the C‐4 and C‐6 positions induced somewhat weak depression. Much weaker activities were observed in a compound carrying N‐linked 3‐dodecanoyloxydodecanoyl [C12‐O‐(C12)] and 3‐O‐ dodecanoyl (C12) as fatty acid substituents. No detectable activity was seen in a compound carrying N‐linked 3‐hexadecanoyloxyhexadecanoyl [C16‐O‐(C16)] and 3‐O‐ hexadecanoyl (C16), indicating that the most suitable carbon chain length for expressing the activities is C14. Regarding structural change of the GlcN backbone, a 1‐deoxy derivative of GLA‐27 exhibited stronger activity than did GLA‐27 itself. Mitogenic and PBA activity of GLA‐27 were stronger than those of lipid X, which corresponds to the reducing D‐GlcN (GlcN‐I) subunit of Escherichia coli lipid A and is a 1‐O‐phosphorylated GlcN derivative carrying N‐ and 3‐O‐linked C14OH groups. These results indicate that N‐linked acyloxyacyl and 3‐O‐linked acyl groups and phosphorylation are critical for expressing both mitogenic and PBA activities.