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. 2021 Dec 7;49(22):12644–12660. doi: 10.1093/nar/gkab1166

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© The Author(s) 2021. Published by Oxford University Press on behalf of Nucleic Acids Research.

This is an Open Access article distributed under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited.

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Scheme 1. — Synthesis of copper-catalyzed alkyne-azide cycloaddition (CuAAC) PDC precursors: PDC-4,2-Alk, PDC-4,3-Alk and PDC-4,PEG-N3. Route A reagents and conditions: (i) 1,4-diaminobutane (100 equiv), NEt₃ (5 equiv), 95°C, 16 h, 90%; (ii) Carboxylic acid (1.5 equiv), EDCI (1.5 equiv), HOBt (0.15 equiv), DMF, rt, 16 h; R₁= 4-pentynoic acid, 77%; R₂ = 5-hexynoic acid, 70%; R₃ = 11-azido-3,6,9-trioxaundecanoic acid, 61%; (iii) CH₃I (235 equiv), DMF, 40°C, 16 h, R₁ = 95%; R₂ = 93%; R₃ = 76%. DMF = N,N-dimethylformamide; EDCI = 1-Ethyl-3-(3-dimethylaminopropyl)carbodiimide; HOBt = Hydroxybenzotriazole. Route B reagents and conditions: (i) 4-amino-1-butanol (18.7 equiv), NEt₃ (2.7 equiv), 90°C, 16 h, 66%; (ii) MsCl (4.5 equiv), NEt₃ (9.0 equiv), DCM, 0°C to rt, 1 h 30 min, 67%; (iii) NaN₃ (10 equiv), DMF, 110°C, 2 h, 77%; (iv) CH₃I (250 equiv), DMF, 40°C, 16 h, 87%. MsCl = Methanesulfonyl chloride.