Unnatural amino acids comprising a cyclooctynyl or trans-cyclooctenyl analog group and uses thereof

A compound of formula I

• wherein:
• X1 has formula
• wherein:
• Y1, Y2, Y3, Y5, Y6 independently are —CH2—, —NH—, —S— or —O— provided that at least 4 of Y1, Y2, Y3, Y4, Y5, Y6 are —CH2—;
• R2 is hydrogen, halogen, C1-C4-alkyl, CF3, CN, C1-C4-alkoxy, —O—CF3, C2-C5-alkanoyloxy, C1-C4-alkylaminocarbonyloxy or C1-C4-alkylthio;
• X2 is —CH2—, —O—, —S—, —NH—, —C(O)—, —OC(O)—, —C(O)O—, —NH—C(O)— or —C(O)—NH—, or
• X2 is >CH— or >N— wherein the carbon or the nitrogen atom together with two adjacent ring atoms of X1 forms a 3-membered ring, or
• X2 is —CH2—CH<, —NH—CH< or —CH2—N< wherein the two carbon atoms or the carbon and the nitrogen atom together with two adjacent ring atoms of X1 form a 4-membered ring, or
• X2 is —CH2—CH2—CH<, —NH—CH2—CH<, —CH2—NH—CH<, —CH2—CH2—N<,
• wherein the three carbon atoms or the two carbon atoms and the nitrogen atom together with two adjacent ring atoms of X1 form a 5-membered ring;
• X3 is C1-C6-alkylene, —(CH2—CH2—O)m—, —(CH2—O)p— or a single bond;
• X4 is —NH—, —C(O)—NH—, —NH—C(O)—, —NH—CH(NH2)—, —CH(NH2)—NH—, —NH—C(NH)—NH—, —C(O)—NH—CH(NH2)—, —C(O)—NH—C(NH)—NH—, NH—CH(NH2)—C(O)— or —NH—C(NH)—NH—C(O)—;
• X5 is hydrogen, C1-C6-alkyl, C1-C6-alkoxy-C1-C2-alkyl, C2-C7-alkanoyloxy-C1-C2-alkyl or C2-C7-alkanoylsulfanyl-C1-C2-alkyl;
• R1 is —OH or —NH2;
• n is an integer from 1 to 4;
• m is an integer from 1 to 6;
• and
• p is an integer from 1 to 6,
• or an acid or base addition salt thereof.