A compound of formula (I) for use as an adjuvant in vaccination; wherein R is an optionally-substituted alkyl, alkenyl, alkynyl, aryl, arylalkyl or alkylaryl moiety having from 1 to 50 carbon atoms; R1 is an optionally-substituted alkyl, alkenyl, alkynyl, aryl, arylalkyl or alkylaryl moiety having from 1 to 40 carbon atoms; each of R2, R3 and R4 is independently selected from an optionally-substituted alkylene, alkenylene, alkynylene, arylene, arylalkylene or alkylarylene moiety having from 1 to 40 carbon atoms; each of X, Y and Z is independently selected from an optionally-substituted alkylene, alkenylene, alkynylene, arylene, alkylarylene or cycloalkylene, ketone, ester, amide, imide, imine, thioether, ether, thioester, thioketone; and P is selected from hydrogen, an alkyl group, a sugar residue, or a metal, phosphonium or ammonium species; wherein at least one of X, Y and Z includes a moiety selected from cyclopropyl, C=A, C-AH and C—OR5; wherein R5 is alkyl or haloalkyl, and A is S, O or NR6, wherein R6 maybe H or 20 alkyl.