Ether type lipid a 1-carboxylic acid analogs

A compound of formula (I)

• 5
• wherein:
• R1 and R3 may be the same or different and each is selected from the group consisting of a C1-C20 alkanoyl group which may optionally be substituted with one or more substituent groups selected from substituent group A, a C3-C20 alkenoyl group which may optionally be substituted with one or more substituent groups selected from substituent group A and a C3-C20 alkynoyl group which may optionally be substituted with one or more substituent groups selected from substituent group A;
• R2 and R4 may be the same or different and each is selected from the group consisting of a C1-C20 alkyl group which may optionally be substituted with one or more substituent groups selected from substituent group A, a C2-C20 alkenyl group which may optionally be substituted with one or more substituent groups selected from substituent group A and a C2-C20 alkynyl group which may optionally be substituted with one or more substituent groups selected from substituent group A;
• R5 is selected from the group consisting of a hydrogen atom, a halogen atom, a hydroxy group, a C1-C6 alkoxy group which may optionally be substituted with an oxo group, a C2-C6 alkenyloxy group which may optionally be substituted with an oxo group, and a C2-C6 alkynyloxy group which may optionally be substituted with an oxo group;
• Substituent group A is a halogen atom, a hydroxy group, an oxo group, a C1-C20 alkoxy group which may optionally be substituted with an oxo group, a C2-C20 alkenyloxy group which may optionally be substituted with an oxo group, a C2-C20 alkynyloxy group which may optionally be substituted with an oxo group, a C1-C20 alkanoyloxy group which may optionally be substituted with an oxo group, a C3-C20 alkenoyloxy which may optionally be substituted with an oxo group or a C3-C20 alkynoyloxy group which may optionally be substituted with an oxo group;
• or a pharmaceutically acceptable salt or ester thereof.