Compound, conjugate, composition, and uses thereof

A compound represented by formula (Ia), a stereoisomer, a pharmaceutically acceptable salt, or a prodrug thereof,

• in formula (Ia), R1 represents a hydroxyl protecting group,
• R2 is selected from the group consisting of:
• wherein
• represents a solid phase support, and R2′ is a covalent linking group connected to the solid phase support,
• n is selected from the group consisting of 0, 1, 2 and 3,
• each Z is independently selected from the group consisting of hydroxyl and mercapto,
• each p is independently selected from the group consisting of 1, 2 and 3,
• each q is independently selected from the group consisting of 1, 2 and 3,
• each A is independently an unsubstituted or substituted 4- to 10-membered aliphatic ring,
• each X is independently selected from the group consisting of NH, O and S,
• each L1 is independently selected from the group consisting of
• wherein j is selected from the group consisting of 1, 2, 3, 4, 5, 6, 7, 8, 9 and 10,
• each R3 is independently selected from the group consisting of H, C1-C6 alkyl, C1-C6 haloalkyl, and C1-C6 alkoxy,
• each L2 is independently selected from the group consisting of C1-C30 alkylidene and
• wherein each RL2a is independently C1-C10 alkylidene, each RL2b is independently selected from the group consisting of O, S, NH, and —NH—C(O)—, and k is selected from the group consisting of 1, 2, 3, 4, 5, 6, 7, 8, 9, and 10,
• each Y is independently selected from the group consisting of NH, O and S, and
• each R4 is independently selected from the group consisting of: