C(OC([C:6]1[O:17][C:16]2[C:15]3[CH:14]=[CH:13][CH:12]=[CH:11][C:10]=3[N:9]([CH3:18])[C:8]=2[C:7]=1[OH:19])=O)C.[OH-].[Na+].Cl>C(O)C>[CH3:18][N:9]1[C:10]2[CH:11]=[CH:12][CH:13]=[CH:14][C:15]=2[C:16]2[O:17][CH2:6][C:7](=[O:19])[C:8]1=2A mixture of 47.0 g (0.18 mole) of 3-hydroxy-4-methyl-4H-furo[3,2-b]indole-2-carboxylic ethyl ester (Prep. described in U.S. patent application Ser. No. 369,448) in 450 ml of 95% ethanol was treated with 450 ml of 30% aqueous sodium hydroxide. The mixture was stirred at reflux for two hours, cooled, added to 3.0 kg ice/water, and acidified with 6.0 N hydrochloric acid. The product was filtered, washed with water, and recrystallized from ethanol-water to yield 17.9 g (53% yield) of the product, mp 113°-116° C. An additional recrystallization as above raised the mp to 115.5°-118° C.
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