Identification of Urea-Dialdehyde Adduct under Acidic Conditions

2,5-Dimethoxytetrahydrofuran (mixture of cis and trans) (0.5 mmol, 1.0 equiv) was dissolved in PBS, and the pH was adjusted with 1 M HCl to pH 2 and stirred for 30 min at RT. Urea (300.3 mg, 5 mmol, 10 equiv) was added, and the reaction mixture was heated to 50 °C and stirred for 5 h. The mixture was allowed to cool to RT and freeze-dried. The crude mixture was purified over silica (EtOAc/MeOH 19:1), and the ¹H NMR spectra of the isolated compound corresponded with 1H-pyrrole-1-carboxamide.³⁴