Author(s):

Rajesh S. Gavit* and K. S. Laddha

Abstract: Rhein and several analogues thereof, are particularly important from commercial point of view and are known for their use in the treatment of degenerative diseases of the joints, for example osteoarthritis, osteoporosis and rheumatoid arthritis. Rhein occurs in nature in plant families such as Cassia, Rheum and Rhamnus, but in a very less concentration. Aloin, a natural substance isolated from various species of aloe, consist almost exclusively of barbaloin (10-β-glucopyranosyl-1, 8-dihydroxy-3-hydroxymethyl-anthracen-9-one). Barbaloin, the C-glycoside of aloe-emodin anthrone, localizes in the outer rind of the aloe vera leaf, has been reported to constitute upto 30% of aloe plants dried leaf exudate and proposed as a part of defense mechanism against herbivores. In this paper, an attempt has been made to prepare rhein from barbaloin via formation of aloe-emodin and its chemical modification using benzyl alcohol to prepare its benzyl carboxylate ester.

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