What are the details of the DCI-AC-NBS probe's synthesis?

DCI-AC-NBS is a near-infrared fluorescent probe designed for biothiol detection. Its synthesis involves multiple steps, including the preparation of intermediate compounds.

The synthesis of the DCI-AC-NBS probe involves the following steps:

Synthesis of DCI: Isophorone (3.80 g, 27 mmol) and malononitrile (6.00 g, 88 mmol) were dissolved in anhydrous ethanol (30 mL). Piperidine (200 µL) was added to this solution and stirred at 60 °C until the reaction was complete. The reaction mixture was then concentrated under vacuum, extracted with ethyl acetate (3 × 20 mL), washed with saturated sodium chloride (20 mL), dried over anhydrous sodium sulfate, and concentrated under vacuum to remove the solvent. The crude product was purified by flash column chromatography (V PE :V EA =30:1) to yield a white needle-like solid (3.58 g, 72%).
Synthesis of DCI-OH: 4-hydroxybenzaldehyde (0.12 g, 1 mmol) and compound DCI (0.19 g, 1 mmol) were dissolved in acetonitrile (6 mL). Ten drops of piperidine were added to the solution, which was then refluxed and stirred at 82 °C for 6 hours. After the reaction, the mixture was cooled to room temperature, concentrated under vacuum, and purified by flash column chromatography (V PE :V EA =15:1) to obtain an orange solid (0.17 g, 58%).
Synthesis of DCI-CHO-OH: Compound DCI-OH (0.58 g, 2 mmol) and HMTA (0.56 g, 4 mmol) were dissolved in TFA (10 mL) and refluxed and stirred at 73 °C for 3 hours. After the reaction, the mixture was cooled to room temperature, ice water (30 mL) was added, and the mixture was extracted with dichloromethane (3 × 20 mL), washed with saturated sodium chloride (20 mL), dried over anhydrous sodium sulfate, and concentrated under vacuum. The crude product was purified by flash column chromatography (V DCM :V EA =1:1) to yield a yellow solid (0.29 g, 46%).
Synthesis of DCI-AC-OH: Compound DCI-CHO-OH (0.16 g, 0.50 mmol) and (ethoxycarbonylmethylene)triphenylphosphorane (0.26 g, 0.75 mmol) were added to toluene (30 mL) and heated to 60 °C under argon protection, reacting in the dark for 4 hours. After the reaction, the mixture was cooled to room temperature, extracted with dichloromethane (3 × 20 mL), washed with saturated sodium chloride (20 mL), and the combined organic phases were concentrated under vacuum. The crude product was purified by flash column chromatography (V DCM :V PE =1:1) to obtain an orange solid (0.16 g, 83%).
Synthesis of DCI-AC-NBS: Compound DCI-AC-OH (0.10 g, 0.25 mmol) and TEA (0.18 g, 0.28 mmol) were dissolved in 15 mL of DMF and stirred at room temperature for 10 minutes. Then, 2,4-dinitrobenzenesulfonyl chloride (0.48 g, 1.65 mmol) was added dropwise, and the mixture was stirred at room temperature for 10 hours. Water (20 mL) was added to quench the reaction, followed by extraction with dichloromethane (3 × 20 mL) and washing with saturated sodium chloride (20 mL). The combined organic phases were dried over anhydrous sodium sulfate and concentrated under vacuum. The crude product was purified by flash column chromatography (V PE :V EA =5:1) to yield a yellow solid (0.07 g, 38%).