Oxidative esterification of retinal and 3-dehydroretinal to methyl esters of retinoic acid and 3-dehydroretinoic acid.

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Oxidative esterification of retinal and 3-dehydroretinal to methyl esters of retinoic acid and 3-dehydroretinoic acid.

Publication Date
Jun 01, 1969
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PMC
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Abstract

Biochem. J. (1969) 113, 447 447 Printed in Great Britain Oxidative Esterification of Retinal and 3-Dehydroretinal to Methyl Esters of Retinoic Acid and 3-Dehydroretinoic Acid By A. B. BARUA, M. C. GHOSH and K. GOSWAMI Department of Chemi8try, Gauhati Univeraity, Gauhati 14, India (Received 2 April 1969) A method for the preparation of retinoic acid and 3-dehydroretinoic acid was reported from this laboratory (Barua & Barua, 1964; Barua & Nayar, 1968). Although the method is simple and yields are good, the method has two disadvantages: the high cost of AgNO3 and the occasionally explosive nature of Tollens reagent. Recently a new method for oxidation of aldehydes to carboxylic acids and esters has been reported (Corey, Gilman & Ganem, 1968), but has not hitherto been utilized for the conversion ofretinal, with a long chain ofconjugated double bonds, into retinoic acid. This communica- tion describes the conversion of retinal and de- hydroretinal by this new procedure, into the methyl esters of retinoic acid (yield > 90%) and dehydro- retinoic acid (yield > 90%) respectively. A 110mg. sample ofretinal (prepared from retinol by the method of Ball, Goodwin & Morton, 1948) was stirred in the dark with a mixture of 198mg. of NaCN, 0 06ml. of acetic acid and 1-5g. of MnO2 (British Drug Houses Ltd., Poole, Dorset) in 50ml. of methanol for l9hr. at 20-25°. The solution was filtered, water was added and the product was extracted with ether. The extract was dried over anhydrous Na2SO4 and the solvent was removed in vacuo. The residue was dissolved in light petroleum and chromatographed on a column of water-deactivated (7%, v/w) alumina. The main zone containing retinoic acid methyl ester was eluted with light petroleum. The methyl ester (98mg.) was crystallized from methanol-water (6:1, v/v), m.p. 54550, Ama.. 350nm. (light petroleum), SbCl3 product Amax. 570nm. The methyl ester was saponified with ethanolic KOH, the solution was acidified with HCI and the product was extracted with ether. The extract

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