Structural investigations have shown that lipid A constitutes the active principle of lipopoly saccharide (LPS, endotoxin), a complex amphipathic molecule located on the cell surface of Gram-negative bacteria.1Lipid A elicits not only the typical endotoxic reactions such as fever and lethal shock but also adjuvant, antitumor and other beneficial effects.1As a result, there has been a great deal of interest in the synthesis of lipid A derivatives possessing low toxicity.1,2