3-Carboxy-2,3,4,9-tetrahydro-1H-pyrido[3,4-b]indole-1-propanoic acid is found in alcoholic beverages. 3-Carboxy-2,3,4,9-tetrahydro-1H-pyrido[3,4-b]indole-1-propanoic acid is present in soy and worcester sauces, yeast extract and wine as the (3S)-diastereoisomers. 3-Carboxy-2,3,4,9-tetrahydro-1H-pyrido[3,4-b]indole-1-propanoic acid is formed by Pictet-Spengler condensation of tryptophan with 4-oxobutanoic acid to give predominantly the cis-isomer
Ramirez-Gaona M, Marcu A, Pon A, Guo AC, Sajed T, Wishart NA, Karu N, Djoumbou Feunang Y, Arndt D, Wishart DS: YMDB 2.0: a significantly expanded version of the yeast metabolome database. Nucleic Acids Res. 2017 Jan 4;45(D1):D440-D445. doi: 10.1093/nar/gkw1058. Epub 2016 Nov 28. [PubMed:27899612 ]
Yannai, Shmuel (2004). Yannai, Shmuel. (2004) Dictionary of food compounds with CD-ROM: Additives, flavors, and ingredients. Boca Raton: Chapman & Hall/CRC.. Boca Raton: Chapman & Hall/CRC..