Indian Journal of Chemistry Vol. 43B, July 2005, pp. 1494-1496 1,8-Dihydroxyanthraquinone derivatives from rhizomes of Rheum emodi Wall Sudhir S Singh 1 *, Satish C Pandey 1 , Rajesh Singh 2 & Santosh K Agarwal 2 1 Chembiotek Research International Block-BN, Plot-7, Sector-V, Salt Lake, Kolkata 700 091, India 2 Phytochemical Technology Division, Central Institute of Medicinal and Aromatic Plants, PO-CIMAP, Lucknow 226 015, India Email : singh_ss@hotmail.com Received 25 July 2003; accepted (revised) 17 January 2004 Two 1,8-dihydroxyanthraquinones isolated from rhizomes of Rheum emodi Wall. have been characterized as 6-methyl- rhein 1 and 6-methyl-aloe-emodin 2 by spectral data and chemical studies. Keywords: 1,8-Dihydroxyanthraquinone, rhizomes, Rheum emodi Wall, 6-methyl-rhein, emodin IPC: Int.Cl. 7 A 61 K 31/122 Rheum emodi Wall. (Fam : Polygonaceae, English Name Rhubarb) is a stout herb and distributed in the temperate and sub-tropical regions of Asian countries, viz. India (Kashmir, Assam, Sikkim), Nepal, Bhutan and China. Indian Rhubarb, which is official in Indian Pharmacopoeia, consists of the dried rhizomes of R. emodi 1,2 . In a recent study 3 the bioassay-guided chemical examination of the rhizomes of R. emodi resulted in the isolation of two new oxanthrone esters, revandchinone-1, revandchinone-2, a new anthrax- quinone ether revandchinone-3 and a new oxanthrone ether, revandchinone-4. The present communication describes the separation and identification of two new natural products as 6-methyl-rhein 1 and 6-methyl- aloe-emodin 2 from the methanolic extract of rhizomes of R. emodi. The compounds were isolated chromatographically and identified by their spectral data and chemical studies (Table I). In our previous reports, we have described the isolation and identification of two anthraquinones rheinal and rhein-11-O-β-D-glucoside in addition to known compounds rhein, emodin, aloe-emodin, physcion and chrysophanol from the rhizomes of the same plant 4-5 . Result and Discussion Silica gel column chromatography of the MeOH extract afforded compounds 1 and 2. Compound 1 OR C H 3 R 1 OR O O 1 2 3 4 5 6 7 8 9 10 4a 10a 9a 8a 12 1 R = H, R 1 = COOH 1a R = Ac, R 1 = COOH 2 R = H, R 1 = CH 2 OH 2a R = Ac, R 1 = CH 2 OAc Table I ⎯ 13 C NMR data of compounds 1, 1a, 2 and 2a (75 MHz), multiplicities were determined by DEPT Carbon 1 1a 2 2a C-1 161.6 s 157.6 s 160.8 s 156.2 s C-2 121.7 d 127.4 d 119.9 d 125.8 d C-3 136.4 s 135.6 s 143.7 s 142.4 s C-4 124.0 d 128.2 d 123.2 d 126.4 d C-5 123.5 d 127.8 d 124.1 d 128.2 d C-6 138.5 s 137.6 s 139.6 s 138.4 s C-7 120.8 d 126.4 d 121.6 d 127.8 d C-8 160.8 s 156.8 s 159.4 s 155.8 s C-9 187.8 s 184.6 s 188.2 s 184.4 s C-10 182.2 s 182.4 s 182.8 s 182.9 s C-11 171.6 s 171.8 s 70.2 t 74.5 t C-12 21.8 q 21.2 q 21.4 q 20.6 q C-4a 138.2 s 137.2 s 141.0 s 140.2 s C-8a 121.2 s 128.4 s 124.6 s 131.2 s C-9a 119.5 s 125.8 s 127.2 s 132.6 s C-10a 136.8 s 134.6 s 140.7 s 139.7 s Ar-OAc - 168.0 s - 169.2 s - 17.2 q - 16.2 q Aliph-OAc - - - 171.6 s - - - 17.9 q