Peak AAA fatty acid homolog contaminants present in the dietary supplement L-Tryptophan associated with the onset of eosinophilia-myalgia syndrome

The eosinophilia-myalgia syndrome (EMS) outbreak that occurred in the USA and elsewhere in 1989 was caused by the ingestion of Showa Denko K.K. (SD) L-tryptophan (L-Trp). Six compounds detected in the L-Trp were reported as case-associated contaminants. Recently the final and most statistically significant contaminant, Peak AAA was structurally characterized. The compound was actually shown to be two structural isomers resulting from condensation reactions of L-Trp with fatty acids derived from the bacterial cell membrane. They were identified as the indole C-2 anteiso (AAA(1)-343) and linear (AAA(2)-343) aliphatic chain isomers. Based on those findings, we utilized a combination of on-line HPLC-electrospray ionization mass spectrometry (LC-MS), as well as both precursor and product ion tandem mass spectrometry (MS/MS) to facilitate identification of a homologous family of condensation products related to AAA(1)-343 and AAA(2)-343. We structurally characterized eight new AAA(1)-XXX/AAA(2)-XXX contaminants, where XXX represents the integer molecular ions of all the related homologs, differing by aliphatic chain length and isomer configuration. The contaminants were derived from the following fatty acids of the bacterial cell membrane, 5-methylheptanoic acid (anteiso-C8:0) for AAA(1)-315; n-octanoic acid (n-C8:0) for AAA(2)-315; 6-methyloctanoic acid (anteiso-C9:0) for AAA(1)-329; n-nonanoic acid (n-C9:0) for AAA(2)-329; 10-methyldodecanoic acid (anteiso-C13:0) for AAA(1)-385; n-tridecanoic acid (n-C13:0) for AAA(2)-385; 11-methyltridecanoic acid (anteiso-C14:0) for AAA(1)-399; and n-tetradecanoic acid (n-C14:0) for AAA(2)-399. The concentration levels for these contaminants were estimated to be 0.1-7.9 mu g / 500 mg of an individual SD L-Trp tablet or capsule The structural similarity of these homologs to case-related contaminants of Spanish Toxic Oil Syndrome (TOS) is discussed.