Journal or Scientific & Industri al Research Yol.60, Jan uary 200 I, j:Jp 1-9 Chemistry and Pharmacology of Rhubarb (Rheum species)- A Review Santosh K Agarwal *, Sudhir S Singh, Vijai Lakshmi+, Sushma Verma and Sushi! Kumar Central Institute of Medicinal and Aromatic Plants (('SIR), Lucknow 226 015, India +Central Drug Research Institute (CSIR), Luck now 226 00 I, India Vari ous chemical constituents iso lated from rhubarb (Rheum ) species in clude an thraquinones, di anthrones, stilbencs. anth ocyanins, navonoids, anthragl ycos icles , polyphenols, organic acids, essential oi ls, vitamins, chromenes, chromanone and chromone glycosides. Notable biological ac ti viti es reported rro111 ,, ,l. va ri ous parts or th e plant and its iso lates arc cath arti c. an tibacteri al, fatal poisOfling, antiviral, anti inllammatory, mollu sciudal, anticoagulant , spas molyti c, cytotoxicity. chronic rcn;ll failure, chemiluminescence quencing and an ti -p latelet acti vities. Introduction (R-28), R. webbianum (R-29), /?. willrockii (R-30) and R. qinlingense (R-31 ). About ten species are found in Rheum Linn (family polygonaceae; English name: India. rhubarb), a large genus of perennial, stout herbs and dis­ tributed in the temperate and sub-tropical regions of the Indian rhubarb, which is official in Indian Phar­ world, chiefly in Asian countries, viz. India (Kashmir, macopoeia, consists of the dried rhizomes of R. enwdi Assam, Sikkim), Nepal, Bhutan, China, Pak istan, Ko­ and R. webbian um and other species of Rheum. Rhizomes rea, Turkey, Russia and Tibet. Several species of this and roots of R. moorcroftianum and R. spicifonne are plant are used in medicine, some for culinary purposes also reported to be mixed with th e drug. The plant grows and few others are grown as ornamental plants. There wild at an altitude of about 4000 to 12000 feet. Rhubarb are three main types of rhubarb, viz. the Chinese Rhu­ has been successfully grown in certa in parts of Assam barb, the Indian or Himalayan Rhubarb and the Rhapontic also. Indian rhubarb occurs in sub-cylindrical or irregu­ Rhubarb u. Some known species of Rheum are R. lar pieces, rangin g from 2 to 20 em in length and 1.5 to acuminatum (R-1 ), R. alexandrae (R-2), R. altai cum (R- 2.0 em in diameter, much shrunken, li g ht in we ight. It is 3), R. australe (R-4), R. compactum (R-5), R. coreanum some what dark in colour, almost odourl ess or some­ (R-6), R.corodatum (R-7), R. delavayi (R-8), R. emodi what fragrant with a bitter and astringe nt taste. It con­ (R-9), R. franzenbachii (R- 10), R. hotaoense (R-11 ), R. tains anthraquinone derivatives and y ie ld s about 25-30 hybridium (R-1 2), R. kialense (R-1 3), R. /hasaense (R- per cent of ~·x tra c t soluble in 50 pe r cent aqueous alco­ 14), R. maximoviczii (R-15), R. moorcro.fiianum (R-16), hol'. In ayurvedic preparations, rhubarb has long been R. nobile (R-17), /?. offlcina/e (R-1 8), /?. pa/aestinwn used as an ingredient of purgatives, laxatives and sto­ (R-19), R. palmatum (R-20), /?. pami/um (R-2 1), /?. ribes machic-tonics ·' · ~. It is hoped th at the review would be (R-22), /?. rhabarbamm (R-23), R. rhaponricwn (R-24), useful to th ose workin g in th e fi e ld of phytochemical (R-13), R. lhasaense (R-14 ), R. maxim oviczii (R- 15 ), /( investigations of rhubarb. moorcrojtianum (R- 16), /?. nobile (R- 17), /?. oJficina/e (R-1 8), R. palaestinum (R- 19), R. pa/matuiii (R-20), /?. pamilwn (R-21 ), R. ribes (R-22), R. rhabarbarwn (R- Chemistry 23), R. rhaponticum (R-24), R. spiciforme (R-25), R. A variety of const ituents have been isolated fro m tanguticum (R-26), R. tataricum (R-27), R. undu/atum Rheum species and the ir structures e lu c id ated. They be­ long to such classes as anthraquinones, clianthroncs, stil­ *Author for correspondence benes, anthocynins, rlavono icl s, anthrag lycosides, CIMAP Publi cat ion No.: 99 -11 R polyphenols, essenti al oi l. organic acid s, chromcnc, 2 J SCI IND RES VOL.60 JANUARY 2001 chromanone, chromone glycos id es and vitamins. Analy­ analyzed the rhubarb extract ( I 00 g) whi ch cont ained sis of samples of th e rhubarb contain ed (in percent ) ash, acet ic ac id (8 .5 -39.4), formi c ac id (9.'2-37. 1), oxa li c acid 9.3-4.9; protein , 1.1; fibre, 1.3-0.8; catha rti c acid , 3.5- ( 100-638), mali c ac id (3 05-1200) and citri c acid (207- 3.2; organi c acid s, 3.3-2.2 ; and su gar, 1.4- l. l ; res pec­ 340 mg). Trace amounts of lac ti c, succ in ic and fumari c tively' . acids were also detected' . Palmitic ac id content was found to be 49.3 1 per cent in the volatil e oil II of R. Essential Oil.\· tangu ti cu m. The essential oil s (0.05 per cent) obtain ed fro m rhi zomes of R. cmodi have charac teri sti c odour due to Stilbelles the presence of eugenol and meth yl heptyl k e ton e~ . The Rhubarb had many stilbene derivatives such as vo latil e oil from rhi zomes of R. polnw lun1 contain ed I 08 rhaponti ci n, deox yrhapo nt ic in , rh apon t ic i n-~ -D- g I uco­ vola til e components of whi ch 27.3 per cent we re terpe­ sid , desoxyrh aponti genin , rh apon ti genin, piceatann ol, noid s. The main constituent s were (per cent): palmitic 4'-0-meth y Ipic e id , rh apon t ige n in -3'-0- ~ -n-gl ucop­ aciu (22. 5) , pa eono l ( 16. 2), a -copa ene (9.8), met hyl yranoside, piceatannol- 3 '-0 - ~ - n -g i ucopy ran os idc (Table stearate (9.3), 8-cadinene (5.4), and meth yl-eugenol I). Rhapontin wh en ad ministered to ca~t r ated female rats (5. 4)('. (dose 600 ~L g) has been reported to restore the oestrous An 1h raquinones cycle. Also, tab lets containing 5 mg rhapontin and 90 mg of hops-extract ex hibited an ac tion sim ilar to th at of Many an thraq uin ones have been iso lated from dif­ the fo lli cular honnone in th e treatment of am enorrh oea, ferent spec ies of rhu ba rb. A few of th em are physcion, dysmenotTh oea and endomet ritis and in inh ibiting lacta­ ch rysophanol (c hrysophanic acid or chrysophan) , rh ein , tion 1. emodi n, aloe-emodin, rh einal , hydroxy-meth yl an ­ th raq uin one and Jst izin. Out of these anthraquinone de­ Flo vonnids 7 rivatives, most of th e rhubarb spec it.:s contain ph ysc ion, Mainl y two spec ies, R. laWricum and R. \l'il/mckii. chr y ~op h anol, emodi n, al oe-emodin and rh ein as shown of rhubarb gave fl avono id s such as qu e rcetin, in Tab le I. Indian rhubarb (R. cmodi) was found to con­ isoguercetin , meratin, rutin (0.32 per ct: nt) and querce­ 13 tain free rhein (0.48), free chrysophanol (0.50) and gly­ tin-3 ,7-glu coarbinosides12· . Rutin ha s been iso lated cosidic rhein ( 1.52) and glycosidi c chrysophanol (0.4 1 from th e foll ow ing Rheum species (per cent ): R. cnwdi 1 pe r cent) . The antimicrobial acti vit y of rh ein was al so (0.32), R. officinale ( 1.30), R. rhapol/(icttlll (0.6 1) and observ ed again st Escherichia coli, Bacillus suhtiles, N. undulatum (0 . 7 0 ) 1 ~ . Alyukina ct a/.·1 found th at the Micrococcus luleus, Candida albicons. Clostrirliulil ground part of rhubarb (R. \l 'illmckii) conta ined 18 ph e­ 1 pe1ji-ingr'il.\' and Fusofacleriu/11 voriwn . We have also noli c compounds, seven of whi ch were flav onoids. The isolated a new anthraquin one deri vative rh einal (0.008 maximum amount of flav onoids was in th e fl owers and p,c r cent) from th e rh izomes of R. c n wd i ·~ . the immature fruit s (6.57 per cent) . fo ll owed by ripe fruits and buds (4.60 and4.1 8 per cent, respecti vely). Dianthrones Rh eidin A is a heterodianthrone co mposed of one mole of emodin and one mole of rhein anthrone, obt ai ned from 1<. palmatwnx. Simil arl y, three other di anthrones Anthocycutins se nnidin C (o ne mole of aloe-emodin and one mole of rhcin ), rhci din B (one mole of rhein and one mole of R. rh aponlicun1 and R. tawricum gave anth ocya­ chrysophanol), and rheidi n C (o ne mole of rhein <llld one nin and th eir deri va ti ves such as cyaniclin-3-g lu coside. mole of physc ion) we re isolated from rhubarb roots') . cyanidin -3-rutin os id e, chrysanth emin , ;t nd cyanin 1' 1x. Organic Acids Vi to 111 in s Some orga ni c acids obtained from rhu barb spec ies arc: oxalic, pa lmitic, acetic, succ ini c, lacti c, ma li c, cit ­ Vit amin B. vitami n C (ascorbic acid) and vit am in ric , fumaric an d form ic (Table I). The oxa li c acid con­ D have been reported from rhubarb·1·1') Its juice proved a tent in In dian rhubarb 1 w;:s 1.3-t per ce nt.