The invention provides a compound which is a peptide derivative of formula (1) as defined in the claims or a salt thereof: RG is H, -CH2-RGA or C1-12 hydrocarbyl optionally substituted with 1 to 4 substituents selected from -OR, -NO2, -CN, halogen and 5-6 membered heterocyclyl or RG and RN1 together form a 5-6 membered heterocyclic ring which is optionally substituted with 1 to 3 substituents selected from Ra, -OR and halogen RGA is C1-11 hydrocarbyl optionally substituted with 1 to 4 substituents selected from -NRR", -OR, -NO2, -CN, halogen and 5-6 membered heterocyclyl RSis C1-16 hydrocarbyl, a 5-10 membered heterocyclyl or heteroaryl group, -(C1-4 alkylene)-RSA or -(C1-4 alkylene)-L-RSA RSA is C1-16 hydrocarbyl, or a 5-10 membered heterocyclyl or heteroaryl group L is -SO2- and wherein RS and RSA are optionally substituted with a group Rb and/or from 1 to 5 substituents selected from Ra, -NRR", -OR, -NO2, -CN, -C(O)R, -C(O)OR, -C(O)NRR", -0-C(0)R, -N(R)-C(0)R", -SR, -S(O)R, -S(O)2R, -S(O)2OR, -P(O)(OR)(OR"), =O, -SiRR"R" and halogen or Rs and an RC1 together form a 5-6 membered heterocyclyl ring which is optionally substituted with 1 to 3 substituents selected from Ra, -OR and halogen Rb is phenyl, benzyl, C3-6 cycloalkyl or 5-6 membered heterocyclyl Q is -C(O)-N(RN2)-, -C(O)-C(RR")-, -C(O)-O- -N(RN2)-C(O)-, -C(RR")- C(O)-, -O-C(O)-, -C(RR")-C(R"R")-, -C(RR")-O- -O-C(RR")-, -C(RR")-N(RN2)-, -N(RN2)-C(RR")- or -C(R)=C(R")- Z is a group selected from -C(O)-O-RO and -CN4R (tetrazolyl) RO is H or C1-12 hydrocarbyl optionally substituted with 1 to 4 substituents selected from -NRR", -OR, -NO2, -CN, -C(O)R, -C(O)OR, -C(O)NRR", -O-C(O)R, -N(R)- C(O)R", -SR, -S(O)R, -S(O)2R, -S(O)2OR, -P(O)(OR)(OR"), =O, halogen and 5-6 membered heterocyclyl or RO and an RC2 together form a 5-6 membered heterocyclyl ring which is optionally substituted with 1 to 3 substituents selected from Ra, -OR and halogen each RN1 and RN2 is independently H or C1-4 alkyl each RC1, RC2, R, R", R" an
