Lipid A is one of the core structures of bacterial
lipopolysaccharides (LPSs), and it is mainly responsible for the strong immunostimulatory activities of LPS through interactions with the
Toll-like receptors and other molecules in the human immune system. To obtain structurally homogeneous and well-defined
lipid As and its derivatives in quantities meaningful for various biological studies and applications, their chemical synthesis has become a focal point. This review has provided a survey of significant progresses made in the synthesis of
lipid A, and its derivatives that carry diverse saturated and unsaturated
lipids, have the
phosphate group at its reducing end replaced with a more stable
phosphate or carboxyl group, or lack the reducing end
phosphate or both
phosphate groups, as well as progresses in the synthesis of LPS analogs and other
lipid A conjugates. These synthetic molecules have facilitated the elucidation of the structure-activity relationships of
lipid A useful for the design and development of
lipid A based
therapeutics, such as those utilized to treat
sepsis, and other medical applications, for example the use of
monophosphoryl lipid A as a carrier molecule for the study of fully synthetic self-adjuvanting
conjugate vaccines. These topics are also briefly covered in the current review.