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Synthesis of lipid A and its analogues for investigation of the structural basis for their bioactivity

Department of Chemistry, Graduate School of Science, Osaka University, Toyonaka, Japan

Yo Adachi

Department of Chemistry, Graduate School of Science, Osaka University, Toyonaka, Japan

Masao Akamatsu

Department of Chemistry, Graduate School of Science, Osaka University, Toyonaka, Japan

Yoshiyuki Fukase

Department of Chemistry, Graduate School of Science, Osaka University, Toyonaka, Japan

Mikayo Kataoka

Department of Chemistry, Graduate School of Science, Osaka University, Toyonaka, Japan

Yasuo Suda

Department of Nanostructure and Advanced Materials, Graduate School of Science and Engineering, Kagoshima University, Kagoshima, Japan

Koichi Fukase

Department of Chemistry, Graduate School of Science, Osaka University, Toyonaka, Japan, koichi{at}chem.sci.osaka-u.ac.jp

Shoichi Kusumoto

Department of Chemistry, Graduate School of Science, Osaka University, Toyonaka, Japan

As a step to elucidate the structural requirements for the endotoxic and antagonistic activity of lipid A derivatives, we have focused, in the present study, on the effects of the acyl moieties and acidic groups at the 1- and 4'- positions. We synthesized a new analogue corresponding to Rubrivivax gelatinosus lipid A, which has a characteristic symmetrical distribution of acyl groups on the two glucosamine residues with shorter acyl groups (decanoyl groups [C₁₀] and lauryl groups [C₁₂]) than Escherichia coli lipid A. Carboxymethyl analogues in which one of the phosphates was replaced with a carboxymethyl group were also synthesized with different distribution of acyl groups. Biological tests revealed that the distribution of acyl groups strongly affected the bioactivity. The synthetic Ru. gelatinosus type lipid A showed potent antagonistic activity against LPS, whereas its 1-O-carboxymethyl analogue showed weak endotoxic activity. These results demonstrated that when the lipid A has shorter (C₁₀, C ₁₂) hexa-acyl groups, the bioactivity of lipid A is easily affected with small structural difference, such as the difference of acidic group or the distribution of acyl groups, and the bioactivity changes from endotoxic to agonistic or vice versa at this structural boundary for the bioactivity. We also designed, based on molecular mechanics calculations, and synthesized lipid A analogues possessing acidic amino acid residues in place of the non-reducing end phosphorylated glucosamine. Definite switching of the endotoxic or antagonistic activity was also observed depending on the difference of the acidic groups (phosphoric acid or carboxylic acid) in the lipid A analogues.

Key Words: Lipid A • Rubrivivax gelatinosus • conformation • IL-6 induction

Journal of Endotoxin Research, Vol. 11, No. 6, 341-347 (2005)
DOI: 10.1177/09680519050110060901


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