Reaction Steps
Intermediate 204 (191 mg, 0.350 mmol) was dissolved in anhydrous THF (2 mL). TBAF (1 M, 0.7 mL) was added dropwise. The solution was stirred at room temperature overnight. The mixture was extracted with EtOAc. The organic phase was combined and washed with water and brine. The organic layer was dried over Na2SO4 then solvent removed under vacuum. The resulting 3-(3-hydroxy-6-hydroxymethyl-4-oxo-4H-pyran-2-yl)-7-(3-methyl-but-2-enyl)-indole-1-carboxylic acid tert-butyl ester (211) was directly protected as following. KOH (85%, 15 mg, 0.23 mmol) was powdered and dissolved in anhydrous MeOH (3 mL). Then crude 211 was added, followed by p-methoxybenzyl chloride (47 mg, 0.30 mmol). The resulting solution was stirred at room temperature overnight. The mixture was diluted with EtOAc then washed with water and brine. The organic layer was dried over Na2SO4 then solvent removed under vacuum. After flash column chromatography, the desired product was obtained as a yellow oil (70 mg, 43%). 1H NMR (CDCl3): δ 1.61 (9H, s), 1.71 (3H, s), 1.73 (3H, s), 3.71 (3H, s), 3.75 (2H, d, J=6.6 Hz), 4.28 (2H, s), 5.24 (2H, s), 5.25 (1H, m), 6.57 (1H, s), 6.70 (2H, m), 7.08 (2H, m), 7.2-7.3 (2H, m), 7.86 (1H, m), 8.11 (1H, s). 13C NMR (CDCl3): δ 19.1, 22.6, 28.6, 31.3, 33.7, 56.0, 61.9, 73.3, 85.1, 111.4, 114.3, 119.3, 123.1, 124.5, 126.7, 127.3, 129.2, 129.5, 130.9, 133.2, 133.6, 134.5, 137.7, 141.2, 149.4, 149.8, 160.9, 165.1, 175.5. IR (KBr): 3167, 2871, 1554, 1233, 1105 cm−1. HRMS (El): m/z Calcd. for C32H35NO7 [M+] 545.2414, found 545.2429.
