Acid-cleavable and clickable affinity capture probe

A compound of the Formula:

• Q-L1-X2—X3—R2—R3-L2-Y I
• wherein,
• X1, X2 and X3 are independently absent, a bond, C(R1)2, NR1, O, S, or CO;
• each R1 is the same or different and is H, or (C1-C10) alkyl;
• L1 is a bond, (C2-C50 alkyl), polyethylene glycol of the formula CH2CH2—(O—CH2CH2)n, wherein n is 1-30, a polypeptide of 1-15 amino acids of the formula AA1-AAn1, or a polypeptide of 1-15 amino acids of the formula:
• AAm-AA1;
• each AA is the same or different amino acid,
• m and n1 are independently 0-14.
• R2 is C1-C30 alkyl, disubstitued aryl, disubstituted arylalkyl, or
• polyethylene glycol of the formula CH2CH2—(O—CH2CH2)n2 wherein n2 is 1-30;
• R3 is
• L2 is a bond, X4-T-X5, wherein T is an alkyl group of C2-C50, or a polyethylene glycol of the formula X4—CH2—CH2—(O—CH2—CH2)n-X5
• X4 is C(R5)(R6), CO;
• X5 is N(R7), O, or S or a polypeptide of the formula AA1-AAn3
• n3 is 0-14
• R5, R6, and R7 and are independently H or C1-C10 alkyl,
• or an affinity tag peptide,
• with the proviso that there can be no two adjacent oxygen, sulfur, nitrogen or carbonyl atoms, and when L1 is a polypeptide of the formula AA1-AAn1, then X2 is a bond and AA1 is bonded to X1 and AAn1 is bonded to X3 or when L1 is a polypeptide of the formula:
• AAm-AA1, then X2 is absent and AA1 is bonded to X1 and AAm is bonded to X3.