Figure 1

Synthesis of HYNIC-lys(Cy5.5)-PEG₄-biotin.

Reagents and conditions: (a) EDC, Sulfo-NHS, DMF:H₂O(1:1), 28 °C, 10 h, 52.1%; (b) 20% piperidine, DMF, rt, 0.5 h, 82.9%; (c) H₂O:DMF =1:1, DIPEA, pH 8.5, 28 °C, 10 h, 58.2%; (d) 5% Hydrazine, DMF, rt, 0.5 h, 87.0%; (e) 0.1 M Na₂B₄O₇, pH 8.5, dark, r.t, 10 h, 52.1%.