Syringaldehyde

Vanillin, 4-hydroxybenzaldehyde, syringaldehyde, NaBH₄, TBAI, tetrabutylammonium bromide (TBAB), SC, and anhydrous pyridine were purchased from MilliporeSigma Canada in Oakville, ON. Ethylene carbonate and 1,3-dibromopropane were purchased from Alfa Aesar in Ward Hill, MA. MDI, PDI, 1,4-diazabicyclo[2.2.2]octane (DABCO 33LV), SA, PDO, titanium (IV) triethanolaminato isopropoxide (8.2 Ti wt%) (Organotix TC-400), triethyl citrate (TEC), Tegostab B4113, and orange dye paste (Dye 2012C) were supplied by Evoco Ltd in Toronto, ON. Anhydrous THF was dried using an SPS solvent purification solvent. All other solvents were reagent grade and used as received. All reactions carried out in a nitrogen environment were performed using standard Schlenk line techniques.

Methanol and water (LC-MS grade) were purchased from HiPerSolv CHROMANORM, VWR Chemicals BDH (Amsterdam, The Netherlands). Formic acid 98–100% was purchased from Merck (Darmstadt, Germany). For the determination of phenolic compounds, apigenin 98%, caffeic acid 98%, catechin 97%, cinnamiccinnamic acid 97%, chrysin 98%, diosmin 97%, epicatechin, epigallocatechin 97%, ferulic acid 98%, epicatechin gallate 98%, hesperidin 98% (internal standard), kaempferol 98%, luteolin 98%, myritecin 97%, myricitrin 97%, naringin 98%, p-coumaric acid 98%, quercetin 98%, quercitrin 99%, rosmarinic acid 98%, protocatechuic acid 97%, rutin 98%, sinapic acid 98%, syringaldehyde 97%, syringic acid 98%, taxifolin 98%, vanillic acid 98%, and vanillin 98% were used and were purchased from Sigma-Aldrich (Stenheim, Germany). Stock standard solutions of all the analytical standard compounds were prepared with LC-MS-grade methanol at 1000 mg/L and were afterward stored in dark brown glass bottles at −20 °C.

Alkaline nitrobenzene oxidation (NBO) was carried out in a stainless-steel bomb using the modified method of Kačíková et al. [34 (link)]. NBO products were analyzed using high-performance liquid chromatography (HPLC) in an Agilent 1260 Infinity II Prime LC (Agilent, Santa Clara, CA, USA) apparatus equipped with a diode array detector at 210 nm, a Luna Omega column of 1.6 µm C18 (100 × 4.6 mm) (Phenomenex, Torrance, CA, USA), mobile phase water/methanol/propionic acid (88/4/8/0.1), a flow rate of 0.4 mL·min⁻¹, and a temperature of 35 °C. The quantification was performed with the external calibration using standards (p-hydroxybenzaldehyde, p-hydroxybenzoic acid, vanillin, vanillic acid, syringaldehyde, and syringic acid) purchased from Sigma-Aldrich (St. Louis, MO, USA). NBO was performed in duplicate, and each sample was analyzed twice. Identification was made using a comparison of the retention times and UV spectra with the standards.