Method for preparing cyclopeptide

A method for preparing a cyclopeptide, comprising the following steps:

• (A) providing a compound represented by formulas (I′-1) and (II-2):
• wherein, Ra is alkyl, cycloalkyl, aryl, or heteroaryl;
• Rc is a protection group;
• and
• R1 is
• in which each of R2 and R3 independently is H or C1-6 alkyl;
• X is O, S, CH2 or N—R4, in which R4 is H, C1-6 alkyl, (CH2CH2O)nH, —C(═O)—C1-10 alkyl, or C(═O)(C2H4)2C(═O)O(C2H4O)nH, in which n=1-3;
• (B) performing a reaction between the compounds of formula (II′-1) and (II-2), to obtain a compound represented by the following formula (II′-3):
• (C) performing a reaction between the compound of formula (II′-3) and a compound represented by the following formula (II′-4):
• to obtain a compound represented by the following formula (II′-5):
• wherein each Rd and Re is a protection group:
• (D) performing a cyclization reaction of the compound of formula (II′-5) with a catalyst of formula (III);
• wherein M is a metal selected from the group consisting of IVB, VB, VIB and actinide groups;
• L1 and L2 respectively is a ligand;
• m and y are integers of greater than or equal to 1;
• and
• Z is an integer of greater than or equal to zero;
• to obtain a compound represented by the following formula (I′):
• and thereby produce a compound represented by any one of the following formulas (I′-1) to (I′-4):