A method for preparing a peptide comprising at least one amino acid residue that carries an, optionally protected, thiol-group; the method comprising reacting a thiol-protected amino acid derivative with an amino acid or with an amino acid residue of a precursor peptide under coupling conditions, thus obtaining a peptide comprising at least one thiol-protected amino acid residue wherein the thiol-protected amino acid derivative is a compound of formula or formula wherein n is 1 or 2; R 1 is H, C 1 -C 4 -alkyl, C 2 -C 4 -alkenyl or C 2 -C 4 -alkynyl; and R 2 is a group of formula or formula wherein m is 1, 2, 3, 4 or 5, and each R 3 is independently selected from halogen, nitro, cyano and C 1 -C 4 -alkanoyl; preferably m is 1, 2, 3, 4 or 5, and each R 3 is independently selected from fluoro, chloro and bromo; more preferably m is 5, and R 3 is chloro, or m is 1, 2 or 3, and R 3 is fluoro; R 4 is selected from R a -C 1 -C 16 -alkyl, R a, C 1 -C 16 -alkyl, C 2 -C 16 -alkenyl and C 2 -C 16 -alkynyl, wherein the C 1 -C 16 -alkyl, C 2 -C 16 -alkenyl or C 2 -C 16 -alkynyl are unsubstituted or carry 1, 2 or 3 substituents R b; preferably R 4 is selected from C 1 -C 16 -alkyl, R a -C 1 -C 16 -alkyl, R a, unsubstituted C 2 -C 16 -alkenyl and partly or completely halogenated C 2 -C 16 -alkenyl; more preferably R 4 is selected from ethyl, butyl, hexyl and benzyl, wherein the benzyl is unsubstituted or carries 1, 2, 3 or 4 substituents R c; R b is independently selected from halogeno, cyano, nitro, hydroxyl and thiol; R a is selected from: (i) phenyl, (ii) 5- or 6-membered heteroaromatic monocyclic radicals having 1, 2, 3 or 4 heteroatoms as ring members which are independently selected from O, S and N, (iii) 8- to 10-membered heteroaromatic bicarbocyclic radicals having 1, 2, 3 or 4 heteroatoms as ring members which are independently selected from O, S and N, and (iv) 8- to 10-membered aromatic bicarbocyclic radicals, wherein said radicals (i) to (iv) are unsubstituted or carry 1, 2, 3 or 4 substituents R c; and R c is independently selected from halogeno, cyano, nitro, hydroxyl, C 1 -C 4 -alkyl, C 1 -C 4 -alkoxy, C 2 -C 4 -alkenyl, C 2 -C 4 -alkynyl and C 1 -C 4 -alkanoyl. n is 1 or 2; R 1 is H, C 1 -C 4 -alkyl, C 2 -C 4 -alkenyl or C 2 -C 4 -alkynyl; and R 2 is a group of formula or formula wherein m is 1, 2, 3, 4 or 5, and each R 3 is independently selected from halogen, nitro, cyano and C 1 -C 4 -alkanoyl; preferably m is 1, 2, 3, 4 or 5, and each R 3 is independently selected from fluoro, chloro and bromo; more preferably m is 5, and R 3 is chloro, or m is 1, 2 or 3, and R 3 is fluoro; R 4 is selected from R a -C 1 -C 16 -alkyl, R a, C 1 -C 16 -alkyl, C 2 -C 16 -alkenyl and C 2 -C 16 -alkynyl, wherein the C 1 -C 16 -alkyl, C 2 -C 16 -alkenyl or C 2 -C 16 -alkynyl are unsubstituted or carry 1, 2 or 3 substituents R b; preferably R 4 is selected from C 1 -C 16 -alkyl, R a -C 1 -C 16 -alkyl, R a, unsubstituted C 2 -C 16 -alkenyl and partly or completely halogenated C 2 -C 16 -alkenyl; more preferably R 4 is selected from ethyl, butyl, hexyl and benzyl, wherein the benzyl is unsubstituted or carries 1, 2, 3 or 4 substituents R c; m is 1, 2, 3, 4 or 5, and each R 3 is independently selected from halogen, nitro, cyano and C 1 -C 4 -alkanoyl; preferably m is 1, 2, 3, 4 or 5, and each R 3 is independently selected from fluoro, chloro and bromo; more preferably m is 5, and R 3 is chloro, or m is 1, 2 or 3, and R 3 is fluoro; preferably m is 1, 2, 3, 4 or 5, and each R 3 is independently selected from fluoro, chloro and bromo; more preferably m is 5, and R 3 is chloro, or m is 1, 2 or 3, and R 3 is fluoro; R 4 is selected from R a -C 1 -C 16 -alkyl, R a, C 1 -C 16 -alkyl, C 2 -C 16 -alkenyl and C 2 -C 16 -alkynyl, wherein the C 1 -C 16 -alkyl, C 2 -C 16 -alkenyl or C 2 -C 16 -alkynyl are unsubstituted or carry 1, 2 or 3 substituents R b; preferably R 4 is selected from C 1 -C 16 -alkyl, R a -C 1 -C 16 -alkyl, R a, unsubstituted C 2 -C 16 -alkenyl and partly or completely halogenated C 2 -C 16 -alkenyl; more preferably R 4 is selected from ethyl, butyl, hexyl and benzyl, wherein the benzyl is unsubstituted or carries 1, 2, 3 or 4 substituents R c; preferably R 4 is selected from C 1 -C 16 -alkyl, R a -C 1 -C 16 -alkyl, R a, unsubstituted C 2 -C 16 -alkenyl and partly or completely halogenated C 2 -C 16 -alkenyl; more preferably R 4 is selected from ethyl, butyl, hexyl and benzyl, wherein the benzyl is unsubstituted or carries 1, 2, 3 or 4 substituents R c; R b is independently selected from halogeno, cyano, nitro, hydroxyl and thiol; R a is selected from: (i) phenyl, (ii) 5- or 6-membered heteroaromatic monocyclic radicals having 1, 2, 3 or 4 heteroatoms as ring members which are independently selected from O, S and N, (iii) 8- to 10-membered heteroaromatic bicarbocyclic radicals having 1, 2, 3 or 4 heteroatoms as ring members which are independently selected from O, S and N, and (iv) 8- to 10-membered aromatic bicarbocyclic radicals, wherein said radicals (i) to (iv) are unsubstituted or carry 1, 2, 3 or 4 substituents R c; and (i) phenyl, (ii) 5- or 6-membered heteroaromatic monocyclic radicals having 1, 2, 3 or 4 heteroatoms as ring members which are independently selected from O, S and N, (iii) 8- to 10-membered heteroaromatic bicarbocyclic radicals having 1, 2, 3 or 4 heteroatoms as ring members which are independently selected from O, S and N, and (iv) 8- to 10-membered aromatic bicarbocyclic radicals, R c is independently selected from halogeno, cyano, nitro, hydroxyl, C 1 -C 4 -alkyl, C 1 -C 4 -alkoxy, C 2 -C 4 -alkenyl, C 2 -C 4 -alkynyl and C 1 -C 4 -alkanoyl.