Structure-efficiency relationship of photoinduced electron transfer-triggered nitric oxide releasers

Spatiotemporally controllable nitric oxide (NO) releasers are required for biological studies and as candidate therapeutic agents. Here, we investigate the structure-efficiency relationship of a series of photoinduced electron transfer-triggered NO releasers based on our reported yellowish-green light-controllable NO releaser, NO-Rosa. The distance between the NO-releasing N-nitrosoaminophenol moiety and the rosamine antenna moiety was critical for efficient NO release. Notably, substitution at the phenolic hydroxyl group blocked NO release. We synthesized NO-Rosa-Gal bearing D-galactose (Gal) at this location, and showed that hydrolysis by β-galactosidase restored the photoresponse. This represents proof-of-concept of a strategy for highly specific control of NO release by using a double-lock system involving both enzymatic reactivation and photo-control.


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Preparation of S11: A solution of S7 (1.49 g, 6.11 mmol, 3.3 equiv.) in dry THF (30 mL) was stirred at -78 C under an argon balloon. To the solution was added dropwise a 1.04 M solution of sec-BuLi in n-hexane/cyclohexane (5.6 mL, 5.82 mmol, 3.1 equiv.), and stirring was continued for 1 hr. Then, a solution of S8 (673 mg, 1.86 mmol) in dry THF (10 mL×2) was added dropwise. The reaction mixture was stirred at room temperature for a further 2 hr, then the reaction was quenched with AcOH (1 mL), and the mixture was evaporated in vacuo. The residue was dissolved in THF (20 mL), and 2 N HCl (20 mL) was added. The reaction mixture was stirred at room temperature for 12 hr, then diluted with water (100 mL) and extracted with CH2Cl2 three times. The organic layer was dried over Na2SO4.
The reaction mixture was removed from the low-temperature bath and stirred at room temperature for 40 min. The reaction was confirmed to be complete by ESI-MS, and 2 N HCl (18 mL) was added. The mixture was stirred at room temperature for 20 min, then diluted with water (60 mL) and brine (30 mL), and extracted with CH2Cl2 three times. The organic layer was dried over Na2SO4. Filtration, evaporation in vacuo, and purification of the residue on a Yamazen  Preparation of S15: To a solution of S14 (143 mg, 0.640 mmol, 1.1 equiv.) in CH2Cl2 (4 mL) was added S11 (292 mg, 0.583 mmol), followed by AcOH (0.2 mL). The mixture was stirred at room temperature for 30 min, and NaBH(OAc)3 (371 mg, 1.75 mmol, 3.0 equiv.) was added. Stirring was continued for an hour, then the mixture was quenched with 0.1 N HCl (20 mL), and extracted with CH2Cl2 three times. The organic layer was dried over Na2SO4. Filtration, evaporation in vacuo and purification of the residue by silica gel flash chromatography (CH2Cl2/MeOH = 10/1 → 8/1) gave 243 mg (59%) of S15 as a purple solid: 1 H NMR (DMSO-d6, 500 MHz, δ; ppm) 7.51 (1H, s), 7.44 (1H, d, 6 Preparation of S16: To a solution of S12 (218 mg, 0.432 mmol) in CH2Cl2 (10 mL) was added S14 (111 μL, 0.474 mmol, 1.1 equiv.) and AcOH (1 mL). The mixture was stirred at room temperature for an hour, and NaBH(OAc)3 (261 mg, 1.23 mmol, 3.0 equiv.) was added. Stirring was continued for 15 min, then the mixture was quenched with 0.1 N HCl (40 mL) and extracted with CH2Cl2 three times.
The mixture was stirred at room temperature for 2.5 hr, then water (35 mL) and brine (35 mL) were added, and the whole was extracted with CH2Cl2 three times. The organic layer was dried over Na2SO4.
To a solution of S22 (70.5 mg, 0.144 mmol) and S28 (76.5 mg, 0.174 mmol, 1.2 equiv.) in CH2Cl2 (6 mL) was added AcOH (0.5 mL). The mixture was stirred for an hour at room temperature, then NaBH(OAc)3 (93.5 mg, 0.441 mmol, 3.1 equiv.) was added. Stirring was continued for 22.5 hr at room temperature. The reaction was confirmed to be complete by ESI-MS, then the mixture was quenched with 2 N HCl and brine, and extracted with CH2Cl2 three times. The organic layer was dried over A solution of S29 (103 mg, 0.113 mmol) and NaOMe (3.2 mg, 0.0592 mmol, 0.52 equiv.) in dry MeOH (10 mL) was stirred at room temperature under a N2 balloon. The mixture was stirred for 24 hr, then 20% NaOEt in EtOH (10 μL, 0.0232 mmol, 0.21 equiv.) was added. Stirring was continued for 3 hr.
The reaction was confirmed to be complete by ESI-MS, then the mixture was quenched with brine, and extracted with CH2Cl2 three times. The organic layer was dried over Na2SO4.    The amplitude-averaged lifetime (<F>) was calculated according to the following equation, where F1, F2, and A1, A2 are the fluorescence lifetimes and the pre-exponential factors, respectively.