Pathway indoxyl

Scheme I. Major pathway for the transformation of natural colorless precursors obtained from banded dye-murex to hyacinthine purple (tekhelet ). J, 6,6 -dibromoindigotin 11 y potassium indoxyl sulfate 111, potassium 6-bromoindoxyl sulfate IV, indigotin E, enzymatic or acidic hydrolysis, and [0], aerobic oxidation. (Reproduced with permission from Ref. 7.

In addition to enolates, Grignard reagents add to 3-nitroindoles 6 to produce the tra s-2-aIkyl-3-nitroindolines 7 in moderate yields [8]. In these examples, the stereochemistry was confirmed by both NMR coupling constants and X-ray crystallography. Indoxyls, which are the result of an in situ Nef reaction, are also isolated in low yields which can be increased to moderate levels (38% of 8 (R = /-Pr, PG = S02Ph) if reagents such as Ceric Ammonium Nitrate (CAN) are employed to maximize this pathway (Table 2). 

Figure 9. Proposed pathway for the degradation of indole by A niger. Indoxyl is a proposed intermediate [87].

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