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Synthesis of the boc-protected derivatives (14–16) and their transformation to the deprotected chromophores as chloride salts (1–3); conditions: (a) DCM, boc-protected amine (11, 12, or 13), NEt3, RT, 5 h; (b) DCM, TFA, RT, 4 h; (c) ion exchanger Amberlite IRA958, water.
