Anthraquinone 2 carboxylic acid

Based on antimicrobial and antiparasitic properties reported in the literature for Rheum spp. [16 (link), 17 (link), 18 (link), 19 (link), 20 ], we tested the Chinese rhubarb “rhein extract” (from leaves) for potential anti-amebic effects. A commercial powder containing >90% rhein, “rhein extract”, was purchased from Natural-Field Bio-Technique Co. (Xi'an, China). Relying on the chemical structure of rhein (i.e. the anthraquinone present in R. palmatum [17 (link), 18 (link)] and main component of the commercial “rhein extract”), we selected ten isolated/synthetic anthraquinone analogs, which we suspected could inhibit amebic growth, for additional testing, as follows: AHDDAC (1-amino-4-hydroxy-9, 10-dioxo-9, 10-dihydro-anthracene-2-carboxylic acid); unisol blue AS; anthraquinone-2-carboxylic acid; 2,3-bis-bromomethyl-1, 4-dihydroxy-anthraquinone; and quinalizarin (these five were purchased from Sigma Aldrich, St. Louis, MO); as well as rhein, sennoside B, diacetyl rhein, sennoside A, and carminic acid (these five were purchased from CromaDex, Irvine, CA). All compounds were stored in dimethyl sulfoxide (DMSO) at -20 °C prior to inhibition assays (below).