Retinol synthesis from carotene

In 1937 Holmes and Corbet (1937) were able to crystallize pure retinol from fish liver. A decade later, Arens and Van Dorp (1946) and Isler and his associates (Isler et aL, 1947) succeeded in achieving the chemical synthesis of pure retinoic acid and retinol. Shortly thereafter, the total synthesis of -carotene was also reported (Karrer and Eugster, 1950). 

Napoli, J. L. (1990) Quantification and characteristics of retinoid synthesis from retinol and b-carotene in tissue fractions and established cell lines. Methods in Enzymol. 189,470-482. 

Apo-jS-carotenal, ethyl 8 -apo- -carotenoate and citranaxanthin are readily accessible by this modular synthesis. The central building block is ll -apo- -carotenal, which itself may be synthesised in diverse ways by Wittig reactions from the intermediates mentioned above. Of particular appeal is a synthesis, wh ich starts from retinol. First, the retinol is oxidised to retinal by an Oppenau-er or TEMPO oxidation. Successive reactions of retinal with Cs-phosphonium salts or phosphonate esters, followed by isomerisation, lead to 8 - po-)8-carotenal and ethyl 8 -apo-yS-carotenoate. Citranaxanthin is obtained by an aldol condensation of 8 -flpo-yS-carotenal with acetone. [55]... 

The conversion of P-carotene to retinol (vitamin A) is an important biosynthetic process since it converts the plant product p-carotene to a product necessary for the growth and life of the animal organism. Throughout the course of evolution most, if not all, of the vitamin A utilized by animals was ultimately derived from this process. In recent years, however, retinol has been synthesized chemically by several procedures and chemical synthesis is now the main commercial source of vitamin A. 

Both RALDHl and RALDH2 also catalyze the conversion of 9-cw-retinal into 9-cis-RA [72, 73]. Therefore, they could also serve as partners with the ci s-retinoid RDH in a pathway that generates 9-cis-RA from 9-cw-retinol. Alternatively, they could catalyze synthesis of 9-cis-RA from 9-cw-retinal produced by central cleavage of 9-cw-p-carotene [74]. 

---