6-Chloro-D-tryptophan

A highly sweet amino acid, monatin (83), was isolated from an African plant, Schlerochiton ilicifolius A. Meeuse (Acanthaceae) [101]. Monatin (83) was rated as being comparable to the synthetic amino acid, 6-chloro-D-tryptophan, which showed a sweetness intensity of 1,300 times that of sucrose. Monatin (83) appears to be the only native plant amino acid with a highly sweet taste to have been discovered. 

One of the first explanations to be put forward for the cause of the sweetness of carbohydrates involved the presence of several hydroxyl groups whose specific stereochemistry elicited a sweet taste [1]. But it was also recognized that certain compounds other than carbohydrates were sweet, sometimes more so than carbohydrates. Compounds such as chloroform, L-alanine, saccharin, 2-amino-4-nitro-benzene, and 6-chloro-D-tryptophan are sweet, and most of these do not have any hydroxyl groups or at most have only one. 

Saito K, Markey SP, Heyes MP (1994) 6-Chloro-D, L-tryptophan, 4-chloro-3-hydroxyyan-thranilate and dexamethasone attenuate quinolinic acid accumulation in brain and bllod following systemic immune activation. Neurosci Lett 178 211-215... 

L-Tryptophan was used for the synthesis of octahydroindolo[2,3-a]quinol-izines 147 (64CB2463 74CPB2614 81JOC4914), and the tetracyclic system 148 was obtained from a-AAs and 4-chloro-6,7-dihydro-5//-pyrimido[5,4-d][l]benzazepine (93JHC233). 

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