STUDIES ON CHINESE RHUBARB——Ⅰ.PRELIMINARY STUDY ON THE ANTIBACTERIAL ACTIVITY OF ANTHRAQUINONE DERIVATIVES OF CHINESE RHUBARB(RHEUM PALMATUM L.)

Pure crystalline anthraquinone derivatives have been isolated from Chinese rhubarb (Rheum palmatum L.), and their antibacterial activity on 26 different species of pathogenic bacteria is investigated. From the preliminary result, it is observed that the antibacterial effect of rhubarb is mainly, though not exclusively, due to anthraquinone derivatives, among which rhein, emodin and aloe-emodin are more active. These derivatives are active against Staphylococci, Streptococci, Cory. diphtheriae, B. substilis, B. anthracis, Sal. paratyphi, Shigella dysenteriae, and Sal. typhi (the last one sensitive to rhein only). The staphylococci and streptococci are highly sensitive, being inhibited even at a concentration of 1.5--25 Υ/ml. Other derivatives such as emodin monomethyl ether plus chrysophanol are less effective: they show bacteriostatic action only on Sh. dysenteriae at a concentration of 25 Υ/ml., and require much higher concentration (100—600 Υ/ml.) for other pathogens. As to non-anthraquinone derivatives, such as trihydroxy-dihydroanthracene, gallic acid, cinnamic acid, etc., the bacteriostatic activity is much inferior. For example, a concentration higher than 100 Υ/ml. is required to inhibit the anthraquinone-derivative-scnsitive staphylococci. The antibacterial effect of anthraquinone derivatives of Chinese rhubarb is related to their chemical structure. 1,9-Dihydroxyanthraquinone is the prerequisite of the fundamental structure. If acidic groups such as carboxyl group, hydroxyl group or methyl hydroxyl group are added at position 7 or 3, the bacteriostatic activity is much enhanced. On the other hand, if such groups are absent from position 1, 3, 7, or 9 or anthraquinone derivatives become anthracene derivatives, the inhibitory effect is much reduced.