Abstract: The present invention relates to new synthetic molecules with agonist activity of human Toll-like Receptor 4 (TLR4), compositions comprising them and uses thereof for the treatment of diseases in which it is useful to induce or increase an immune response. These new syntethic molecules differ from other similar agonists due to the simplicity of the formula, the ease and cheapness of preparation and the possibility of further chemical processing to modify the physicochemical properties and allow conjugation to other molecules (for example protein antigens).