Shikonin

Shikonin was purchased from Chengdu Biopurify Phytochemicals Ltd. (Chengdu, China). Reagents and solvents were acquired from commercial suppliers. Solvents were dried and purified using standard techniques. Under argon atmosphere, a solution of Shikonin (29 mg, 0.1 mmol) and dimethyl acrylic acid (20 mg, 0.2 mmol) in abs. THF (0.83 mL) was cooled to 0 °C. PPh₃ (105 mg, 0.4 mmol) was added and the solution was stirred for 15 min, followed by addition of DIAD (0.13 mL, 0.75 mmol) in 0.22 mL THF. After stirring for 30 min at 0 °C, cyclohexane was added (1 mL) and the mixture was concentrated in vacuo. The residue was filtered over silica and celite^® (2 mm layer each), the products containing fractions were combined, concentrated in vacuo, and submitted to flash chromatography (silica, cyclohexane cyclohexane/CH₂Cl₂ = 1:0 to 1:2). PTLC of the raw product (silica, developed three times with cyclohexane/CH₂Cl₂ = 2:1 and twice with cyclohexane /CH₂Cl₂ = 1:1) resulted in 6.5 mg (24%) SK119.

Shikonin was obtained from Chengdu Biopurify Phytochemicals Ltd. (Chengdu, China). Reagents and solvents were obtained from commercial suppliers. Solvents were dried and purified using standard techniques.

Shikonin was purchased from Chengdu Biopurify Phytochemicals Ltd. (Chengdu, China). β,β-DimethylacrylShikonin (2) was isolated from dried roots of Onosma paniculata Bureau & Franchet (Boraginaceae) and identified as reported previously [14 (link)].