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

Abstract

Mitogenic 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.