3.1.3. Synthesis of (3*S*,4*S*)-5,8-dihydroxy-7-isopentyl-4-methoxy-3-pentylisochroman-1-one (**6**)

To a solution of eurotiumide A (**1**) (1.6 mg, 4.6 μmol) in MeOH (0.23 mL) was added Pd/C (1.6 mg, 100 w/w%) at room temperature. After stirring for 1.5 h under hydrogen atmosphere (balloon), the reaction mixture was passed through Celite and the organic solvent was removed under reduced pressure. The residue was purified with flash column chromatography (EtOAc:*n*-hexane = 2:3) to give isopentyl derivative **6** (1.4 mg, 88%) as a white wax. 1H-NMR (500 MHz, CDCl3) δ 10.91 (1H, s), 6.93 (1H, s), 5.62 (1H, br-s), 4.74 (1H, d, *J* = 2.5 Hz), 4.48 (1H, ddd, *J* = 2.6, 5.4, 8.6 Hz), 3.38 (3H, s), 2.62 (2H, m), 1.95 (1H, m), 1.85 (1H, m), 1.65–1.50 (2H, overlapped), 1.50–1.40 (3H, overlapped), 1.40–1.30 (4H, overlapped), 0.95 (6H, d, *J* = 6.3 Hz), 0.90 (3H, *J* = 6.9 Hz); 13C-NMR (125 MHz, CDCl3) δ 169.4, 154.7, 145.0, 133.6, 124.8, 118.6, 106.8, 81.4, 69.9, 56.6, 38.4, 31.6, 29.8, 29.7, 27.9, 27.5, 14.9, 22.5, 14.0.; IR (KBr) 3290, 2956, 2927, 2870, 1761, 1445, 1171, 807 cm−1; HRMS (ESI) *m*/*z* (M + H)<sup>+</sup> calculated for (C20H31O5) <sup>+</sup> 351.2171, found 351.2177.
