The general procedure for the synthesis of 3,3'-(3,8,13,17-tetramethyl-7,12-divinylporphyrin-2,18-diyl)dipropionic acid from methyl 3,3'-(3,8,13,17-tetramethyl-8,13-divinyl-2,18-porphyrin) dipropionate is as follows: referring to the method of Smith (1999), dimethyl protoporphyrin IX ( 100 mg, 0.169 mmol) was dissolved in a methanol solution (35 mL) containing potassium hydroxide (3.02 g, 53.8 mmol) and heated to reflux overnight under nitrogen protection from light. After completion of the reaction, it was cooled to room temperature and extracted with ethyl acetate. The ethyl acetate layers were combined and back-extracted with 3M hydrochloric acid solution (2 x 50 mL). The aqueous phase was collected and the pH was adjusted to 4 with 3M sodium hydroxide solution, followed by extraction with ethyl acetate (3 x 100 mL). The organic phase was dried over anhydrous sodium sulfate, filtered and concentrated under reduced pressure to afford pure protoporphyrin IX (72.8 mg, 76.6% yield) in the form of a purple-red solid with a melting point of 205 °C (decomposition temperature >300 °C). The 1H NMR spectrum of the product was consistent with the literature reports. UV-Vis absorption spectrum (CHCl3/TFA) λmax/nm: 413 (logε 5.24), 525 (3.25), 556 (3.99), 578 (3.75), 600 (3.63).1H NMR (200 MHz, CDCl3, TMS as internal standard) δ: -3.33 (2H, s, internal NH). 3.19-3.26 (4H, t, J=6.6 Hz, -CH2CH2CO2H), 3.63 (3H, s, -CH3), 3.67 (3H, s, -CH3), 3.69 (3H, s, -CH3), 3.72 (3H, s, -CH3), 4.48 (4H, t, J=5.1 Hz, -CH2CH2CO2H) ), 6.30 (2H, dd, J=17.8 Hz and 10.0 Hz, -CH=CHAHB), 6.47 (2H, dd, J=11.4 Hz and 3.1 Hz, -CH=CHAHB), 8.09-8.27 (2H, m, -CH=CHAHB), 10.63 (1H, s, γ-H), 10.65 (1H, s, δ -H), 10.90 (1H, s, α-H), 10.92 (1H, s, β-H). Mass spectrum (MALDI-TOF) m/z: 563.4 [M+H]+ (calculated value 563.7).
