A Compound of structure (IX) or (X) or a pharmaceutically acceptable salt thereof, wherein: X is —C(═O)N(R
10
)— or —CH(OPr
3
)—; R
7
, R
9
and R
10
are the same or different and represent hydrogen or an amino acid side chain moiety from either a natural or an unnatural amino acid; Pr
1
and Pr
2
are the same or different and represent hydrogen or a thiol protecting group; Pr
3
is hydrogen or an alcohol protecting group; R
1
, R
2
, R
5
and R
6
are the same or different and represent hydrogen or an amino acid side chain moiety from either a natural or an unnatural amino acid, or R
1
and R
2
and/or R
5
and R
6
, taken together with the carbon atom to which they are attached, form a spirocyclic moiety, with the proviso that: each of R
1
and R
2
is not hydrogen, or each of R
5
and R
6
is not hydrogen.
一种结构化合物(IX)或(X)或其药学上可接受的盐,其中:X为—C(═O)N(R10)—或—CH(OPr3)—;R7、R9和R10相同或不同,代表
氢或来自
天然或非
天然氨基酸的
氨基酸侧链基团;Pr1和Pr2相同或不同,代表
氢或巯基保护基团;Pr3为
氢或醇保护基团;R1、R2、R5和R6相同或不同,代表
氢或来自
天然或非
天然氨基酸的
氨基酸侧链基团,或R1和R2和/或R5和R6,与它们连接的
碳原子一起形成螺环基团,条件是:R1和R2中的每一个都不是
氢,或R5和R6中的每一个都不是
氢。