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. The compounds have general formula (1), wherein R1 is a saturated C8-C16 aliphatic chain having a ?0 on C1, said chain being free from —OH substituents on C3, wherein R2 is a saturated C8-C16 aliphatic chain having a ?O on C1, said chain being free from —OH substituents on C3, wherein R3 is a saturated C8-C16 aliphatic chain having a ?O on C1, said chain being free from —OH substituents on C3; wherein R4 is a hydrogen atom (H) or a phosphate group (PO42?).