Structures of isamic acid and methylisatoid
Abstract
Isamic acid, a red crystalline product from the reaction of isatin with ammonia, is proved to be 1,2-dihydro-2-oxospiro-[3H-indole-3,2′(1′H)-quinazoline]-4′-carboxylic acid, as suggested by G. F. Field. The colour and lack of basicity appear to be due in part to spiroconjugation. Methylisatoid, from O-methylisatin and moist air or aqueous acetic acid, is shown by rational synthesis and degradation to be methyl 6,12-dihydro-12-hydroxy-6-oxoindolo-[2,1-b]quinazoline-12-carboxylate.