Indoline

Reagents and solvents were purchased from Aldrich Chemical, Alfa Aesar, Chem Impex international or TCI America and used as received. Reactions were carried out under an argon atmosphere in oven-dried glassware using anhydrous solvents from commercial suppliers. Air and/or moisture sensitive reagents were transferred via syringe or cannula and were introduced into reaction vessels through rubber septa. Solvent removal was accomplished with a rotary evaporator at ∼10–50 Torr. Automated column chromatography was carried out using a Biotage SP1 system and silica gel cartridges from Biotage or Silicycle. Analytical TLC plates from EM Science (Silica Gel 60 F₂₅₄) were employed for TLC analyses. ¹H NMR spectra were recorded on a Varian INOVA-400 400 MHz spectrometer.
Analogs 1[43] (link), [44] , 3, 6, and 9 were synthesized in one step from commercially available N-benzyloxycarbonyl (Cbz) protected amino acids according to the following general procedure. A solution of the N-benzyloxycarbonyl protected L-amino acid (0.33 mmol) in 2 mL of DMF was treated with aminoacetonitrile bisulfate (0.37 mmol, 1.1 equiv.), 1-hydroxybenzotriazole (0.33 mmol, 1.0 equiv), N-(3-dimethylaminopropyl)-N′-ethylcarbodiimide hydrochloride (0.67 mmol, 2.0 equiv.), and N,N-diisopropylethylamine (2.0 mmol, 6.0 equiv.). The reaction was stirred at room temperature and monitored until judged complete by TLC or HPLC. The reaction mixture was then poured into ethyl acetate and the resulting organic solution washed in succession with aqueous 1 N HCl (for non-basic analogs only), 50% aqueous NaHCO₃, saturated aqueous NaCl, and then dried (MgSO₄), filtered, and concentrated. The crude product thus obtained was purified using automated silica gel flash chromatography (Biotage SP1, ethyl acetate-hexane) to afford the desired products.
Analogs 2, 4, 5, 7, and 10 were synthesized in two steps from N-(benzyloxycarbonyl)-L-serine lactone [45] according to the following procedure. A solution of N-(benzyloxycarbonyl)-L-serine lactone (0.45 mmol) in 2 mL of acetonitrile was added dropwise to a solution of the relevant amine or N-trimethylsilylamine (1–10 equivalents depending on the amine, see below) in ∼3 mL of acetonitrile. The reaction was monitored at room temperature or in some cases heated at 50°C, depending on the reactivity of the amine (see below). When the reaction was judged complete by TLC or HPLC, the reaction mixture was concentrated and the desired amino acid separated from undesired amide side product in one of the following ways. For the amino acid leading to 2, the crude product was partitioned between ethyl acetate and water and the water phase (containing the desired product) was then lyophilized. For the amino acids leading to 4 and 5, purification by automated silica gel flash chromatography (Biotage SP1, methanol-dichloromethane) afforded the desired amino acids. For intermediate amino acids leading to 7 and 10, the crude residue was partitioned between dichloromethane and 1 N aqueous NaOH, followed after phase separation by acidification of the aqueous phase with 1 N HCl to effect precipitation of the amino acid, which was collected on a filter, washed with cold water, and dried. The procedures described above provided the desired amino acids in sufficient purity for use in the subsequent coupling reaction with aminoacetonitrile, which was carried out according to the general coupling protocol described for analogs 1, 3, 6, and 9 above.
Analog 8 was prepared in three steps by reaction of indoline with N-(benzyloxycarbonyl)-L-serine lactone as described above, using automated silica gel flash chromatography (Biotage SP1, methanol-dichloromethane) to isolate the desired amino acid. The amino acid intermediate was coupled to aminoacetonitrile according to the general procedure and finally, the resulting indoline product was oxidized to the desired indole 8 by reaction with 1.05 equivalents of 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) in dichloromethane for 30 minutes. The final product was purified by automated silica gel flash chromatography (Biotage SP1, ethyl acetate-hexane).
Additional details and NMR data are provided in Supplementary Methods (Text S1).

13c (143 mg, 711 μmol, 85%, pale rose solid)
was prepared according to GP2 from indoline (100 mg, 839 μmol)
and purified by filtration over a silica plug (R_f = 0.45, EtOAc:n-hexane
= 1:6). Molecular formula (molecular mass): C₈H₈FNO₂S (201.22 g/mol). ¹H NMR (400 MHz, CDCl₃): δ 7.54–7.37 (m, 1H), 7.30–7.19 (m,
2H), 7.17–7.05 (m, 1H), 4.14 (td, J = 8.4,
2.5 Hz, 2H), 3.21 (t, J = 8.4 Hz, 2H). ¹³C{¹H} NMR (101 MHz, CDCl₃): δ 139.9,
131.0, 128.3, 125.6, 125.3, 114.7, 51.7, 28.1. ¹⁹F NMR
(376 MHz, CDCl₃): δ 39.12. HR-EI-MS m/z: [M]^•+ calcd for C₈H₈FNO₂S 201.0254; found, 201.0252.

A clean, oven-dried Schlenk tube with previously placed magnetic stir-bar was charged with nitrobenzene (184.7 mg, 1.5 mmol), ^tBuOK (224.5 mg, 2.0 mmol) in dry DMF (5 mL) solvent at room temperature under argon atmosphere. After the reaction mixture was stirred at −30 °C for 10 min, the reaction was evacuated and back filled with O₂ (1.0 atm) and this sequence was repeated for three additional times. After indoline (59.6 mg, 0.5 mmol) was added, the reaction stirred at −30 °C and monitored by TLC. After the complete consumption of indoline, the reaction mixture was quenched with water (5 mL), diluted with ethyl acetate, and extracted with ethyl acetate (25 mL × 3). The combined organic phases were washed with brine (5 mL), dried over Na₂SO₄ and concentrated in vacuo. The residue was purified by neutral Al₂O₃ column chromatography (PE: EtOAc = 40:1, v/v).

A mixture of carbohydrazide 4 (0.196 g, 1.0 mmol) and indoline-2,3-dione derivatives 5a–l (1.0 mmol) in EtOH (30 mL) and AcOH (0.3 mL) was refluxed for 4 h. Crystallization of the resulting solid from EtOH/DMF gave compounds 6a–l, respectively.