3.4. Acid Hydrolysis of Compounds

Compounds 1–4 (1 mg each) were dissolved in 2 M HCl (5.0 mL) and stirred at 90°C for 4 h. The reaction solution was neutralized with NH₄OH and partitioned between EtOAc and H₂O. The residue was obtained from the water layer under vacuum distillation and dissolved in pyridine (1 mL), which was added to 0.1 M l-cysteine methyl ester hydrochloride in pyridine (1 mL). After being heated to 60 °C for 1 h, the mixture was added to phenyl isothiocynate in pyridine (1 mL) and stirred at 60 °C for an additional 1 h. After removal of the solvent, the residue was dissolved in MeOH and analyzed by HPLC, with the mobile phase CH₃CN-H₂O (30:80, v/v) containing 0.1% formic acid; the flow rate was 1 mL/min. The standard d-glucose derivative was prepared in the same way. We then compared the retention times of sugar derivatives obtained from compounds with standard d-glucose derivatives (d-glucose: 19.5 min).