3.4. Acid Hydrolysis of Compounds 1–6

A solution of compound (3.0 mg) dissolved in dioxane (0.5 mL) and in 1 N H₂SO₄ (0.5 mL) was refluxed (4 h), cooled, and extracted with CH₂Cl₂ (3 × 2 mL). The CH₂Cl₂ layer was condensed and washed with 5% NaHCO₃ and H₂O five times respectively, and then purified on Si gel preparative thin layer chromatography [petroleum ether/EtOAc, 30:1, v/v] to give a diterpene aldehyde (for 1, 4–6) or diterpene alcohol (for 2 and 3). The aqueous layer was neutralized with 5% NaOH to pH 7 and then condensed as white solids to yield D-glucose. The D-glucose product and L-cysteine methyl ester hydrochloride (5 mg) was dissolved in pyridine (0.5 mL) and heated at 60 °C for 60 min, and then phenylisothiocyanate (5 µL) was added to the mixture and heated at 60 °C for 60 min. The reaction mixture was analyzed by UPLC and detected at 250 nm, 25 °C, using a Waters BEH C₁₈ (1.7 μm, 2.1 × 100 mm) column, eluting with MeCN/H₂O (from 10:90 to 0:100, v/v, 0–10 min). Peaks of the glucose derivatives were detected by comparison with retention time. Standard d-glucose was treated in the same way as the sample.