3.1.2. Synthesis of (3*S*,4*S*)-5,8-dihydroxy-4-methoxy-3-pentylisochroman-1-one (**4**)

To a solution of bromo compound **3** (10.0 mg, 30.8 μmol) in MeOH (2.3 mL) was added 6 M aqueous HCl (0.77 mL) at 0 ◦C. After stirring for 30 min at 40 ◦C, the reaction was quenched by adding saturated aqueous NaHCO3 at 0 ◦C. The mixture was extracted with EtOAc (×3) and the combined organic layers were washed with brine, dried over Na2SO4, filtered, and concentrated under reduced pressure. The residue was purified by preparative thin layer chromatography (PTLC) (EtOAc:*n*-hexane = 3:7) to give non-substituted derivative **4** (6.8 mg, 79%) as a white solid. m.p. 120–121 ◦C; 1H-NMR (400 MHz, CDCl3) δ 10.62 (1H, s), 7.06 (1H, d, *J* = 9.0 Hz), 6.91 (1H, d, *J* = 9.0 Hz), 5.89 (1H, br-s), 4.77 (1H, d, *J* = 2.7 Hz), 4.50 (1H, ddd, *J* = 2.7, 5.4, 8.3 Hz), 3.40 (3H, s), 1.95 (1H, m), 1.85 (1H, m), 1.70–1.50 (1H, overlapped), 1.46 (1H, m), 1.40–1.25 (4H, overlapped), 0.91 (3H, t, *J* = 6.8 Hz); 13C-NMR (100 MHz, CDCl3) δ 169.0, 156.2, 145.7, 125.1, 121.7, 118.8, 107.6, 81.4, 69.8, 56.8, 31.6, 29.8, 24.9, 22.5, 14.0.; IR (KBr) 3219, 2955, 2924, 2860, 1661, 1586, 1471, 1293, 1204, 905 cm<sup>−</sup>1; HRMS (ESI) *m*/*z* (M + Na)<sup>+</sup> calculated for (C15H20O5Na)<sup>+</sup> 303.1208, found 303.1200.
