Two fluorophores, 7-(dimethylamino)-coumarin-4-acetic acid (DMACA, prepared according to literature procedures52 , 53 (link)) and 7-nitrobenzofurazan (NBD, Sigma–Aldrich), were functionalized with an alkyne substituent (Scheme 2 ) so that they could be coupled to the linezolid–azide analogue 9 by click chemistry. DMACA 23 was reacted with propargylamine in the presence of HATU as coupling agent to give DMACA linked alkyne 24 . NBD linked alkyne 26 was prepared by a substitution reaction from NBD-Cl (4-chloro-7-nitrobenzofurazan) 25 by an improved method based on that previously reported in the literature.54 The use of Cs2CO3 in THF for the substitution gave improved yields compared to aqueous NaHCO3 in MeOH.![]()
Synthesis of alkyne-functionalised fluorophores. Reagents and conditions: (i) propargylamine, HATU, DIPEA, DMF rt; (ii) propargylamine, Cs2CO3, THF.
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