The present invention provides a peptide of formula (I), or a pharmaceutically acceptable salt thereof, wherein the N-terminal group of the peptide is a monoradical of formula - NHR1； the C-terminal group of the peptide is a monoradical of formula -C(O)-R2； R1 is a monoradical selected from hydrogen and -C(O)-(C1-C20)alkyl； R2 is a monoradical selected from -OH and -NR3R4 radical； R3 and R4 are independently selected from hydrogen and (C1-C10)alkyl； "a" to "j" are integers from 0 to 1, provided that at least one of "a" to "j" is 1； and X1 represents any amino acid. The present invention also provides conjugates and compositions comprising the peptide of formula (I).
