Indolylpyruvic acid

Tryptophan and its relative indolylpyruvic acid (3.42) have been shown to precursors of hinnuliquinone (3.41), which is a pigment of Nodulisporium hin-nuleum. Typical of many fungal indoles in which alkylation by a dimethylallyl or isopentenyl group has occurred, mevalonate was also a precursor. However, the stage at which prenylation of a monomer or a dimer took place was unclear. Asterriquinone (3.43) from Aspergillus terreus and cochliodinol (3.44) from Chaetomium cochliodes are similar metabolites. Fission of the hydroxyquinone in the latter followed by lactonization leads to cochliodinone (3.45) in a sequence that is similar to that which inter-relates the terphenyls and pulvinic acids described in Chapter 7. 

Both tryptophan and tyrosine fiamished melanin. Similar results were also obtained by Allegri et al. (3), who studied melanin synthesis from tryptophan and tyrosine spectrophotometrically. From tyrosine, p-hydro-xyphenylpyruvic acid (15), 4,4-dihydroxybiphenyl (16), 5,6-dihydroxy-indole (17), and 3,5,6-trihydroxyindole (18) were obtained in addition to melanin and from tryptophan, 5,6-dihydroxyindole (17), indole (19), anthranilic acid (20), 3-hydroxyanthranilic acid (21), indolylpyruvic acid (22), 3-hydroxypyrrol-4,5-dicarboxylic acid (23), and isatin (24). 

Further, owing to deamination, p-hydroxyphenylpyruvic acid (15), a well-known inhibitor of tyrosinase, was produced from tyrosine. This product underwent further transformation to yield biphenyl 16 while indolylpyruvic acid (22) and subsequently indole (19) were formed from tryptophan. Hence, in biological systems, the loss of the starting material, i.e. tyrosine, for melanin synthesis due to the formation of 15, 16 and 18 may be counteracted by tryptophan, as an alternative substrate in the pathway of melanogenesis through 22 and 19. However, such a replacement of substrate for melanin by tryptophan is not possible in... 

These workers observed that in these feeding experiments a significant amount of the N-label from the (2Si )-tryptophan is lost under the conditions of the feeding experiment. This was attributed to the conversion of the (2k)-tryptophan into indolylpyruvic acid and then to (2S)-tryptophan. 

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