M6pr binding compounds and conjugates

A cell surface mannose-6-phosphate receptor (M6PR) binding compound of formula (XIa):

• or a prodrug thereof, or a salt thereof,
• wherein:
• W is a non-hydrolyzable hydrophilic head group;
• Z1 is selected from optionally substituted (C1-C3)alkylene and optionally substituted ethenylene;
• Z2 is selected from O, S, NR21 and C(R22)2, wherein R21 is independently selected from H, and optionally substituted (C1-C6)alkyl, and each R22 is independently selected from H, halogen (e.g., F) and optionally substituted (C1-C6)alkyl;
• A is an optionally substituted cyclic group (e.g., optionally substituted aryl, optionally substituted heteroaryl, optionally substituted heterocycle, or optionally substituted cycloalkyl);
• each Z3 is independently a linking moiety;
• n is 1 to 500;
• m is 1 to 100;
• L is a linker;
• and
• Y is a moiety of interest.

A cell surface M6PR binding compound of formula (XV):

• or a prodrug thereof, or a salt thereof,
• wherein:
• W is a non-hydrolyzable hydrophilic head group;
• Z1 is selected from optionally substituted (C1-C3)alkylene and optionally substituted ethenylene;
• Z4 is selected from —Z14—, —Z14-A-, -A-, and —CH2—Z14—,
• Z14 is selected from O, S, NR21, and C(R22)2, wherein R21 is independently selected from H, and optionally substituted (C1-C6)alkyl, and each R22 is independently selected from H, halogen (e.g., F) and optionally substituted (C1-C6)alkyl;
• A is an optionally substituted cyclic group (e.g., optionally substituted aryl, optionally substituted heteroaryl, optionally substituted heterocycle, optionally substituted cycloalkyl);
• n is 1 to 500;
• m is 1 to 100;
• L is a linker;
• and
• Y is a moiety of interest.

A target protein degrading conjugate of formula (XXI):

• or a prodrug thereof, or pharmaceutically acceptable salt thereof,
• wherein:
• n is 1 to 3;
• m is an average loading of 1 to 10;
• L is a linker;
• P is a biomolecule that specifically binds the target protein;
• Z5 is a residual linking moiety resulting from the covalent linkage of a chemoselective ligation group of the linker L to a compatible group of P;
• W is a non-hydrolyzable hydrophilic head group;
• Z1 is selected from optionally substituted (C1-C3)alkylene and optionally substituted ethenylene;
• Z2 is selected from O, S, NR21 and C(R22)2, wherein R21 is independently selected from H, and optionally substituted (C1-C6)alkyl, and each R22 is independently selected from H, halogen (e.g., F) and optionally substituted (C1-C6)alkyl;
• A is an optionally substituted cyclic group;
• and
• Z3 is a linking moiety.