This disclosure relates to flavour modification and to compounds of formula (I) wherein R1 is selected from C6-C20 alkyl, and C9-C25 alkenyl, and i) R3 and R4 are hydrogen and R2 the residue of a proteinogenic amino acid; ii) R2 and R3 are methyl and R4 is hydrogen; or R4 is hydrogen and R2 and R3 form together with the carbon atom to which they are attached cyclopropyl; iii) R2 is hydrogen, and R3 and R4 together are —CH2—CH2—CH2—, useful in modifying flavours.