Aminoalkyl glucosaminide 4-phosphates or AGPs are a class of lipid A mimetics in which the reducing sugar of lipid A has been replaced with an N-acylated aminoalkyl aglycon unit (54) . The AGPs contain an L-serine-based aglycon unit as well as three (R)-3-n-alkanoyloxytetradecanoyl residues comprised of even-numbered normal fatty acyl chains between 6 and 14 carbon atoms in length. All members of this family have 14 carbon atoms in the "primary" fatty acid, which is the -hydroxy fatty acid attached directly to the AGP backbone. -Hydroxymyristic acid is the most common of the primary fatty acids present in lipid A. These compounds were used in a variety of cell-based and an in vivo model to determine structure-activity relationships related to AGP acyl chain length and stimulation via TLR4 (54) . Figure 4 shows the chemical structure of two AGPs: MPL and CRX-526. The structure of CRX-526 differs significantly from monophosphoryl lipid A (MPL) and other TLR4-agonist AGP in the length of its secondary fatty acyl chains (SAC): for instance CRX-526 contains 3 SAC of 6 carbons in length, whereas MPL and other AGP, which signal through the TLR4 complex, contain SAC of >10 carbons in length (55) .