Gamboge. Part IV. Scission of gambogic acid by alkali
Gambogic acid has been cleaved into two major fragments, together accounting for 33 of its 38 carbon atoms; the structures of the products, 2-isopropyl-5-methyl-2′,4′,6′-trihydroxybiphenyl (IIIa), a chroman (IVa), and 4-carboxy-α,1,1-trimethylphthalan-3-butyric acid (Va) have been established, and they support the structure (I) previously proposed for gambogic acid. New assignments have been made for the n.m.r. signals of two of the methyl groups of gambogic acid.
Improvements have been made in the preparation of p-nitrophenylazobenzoates and of 6-cyano-3,3-dimethyl-phthalide.