Retinoic acid derivatives naming

The stmcture of vitamin A [11103-57-4] and some of the important derivatives are shown in Figure 1. The parent stmcture is aH-Zra/ j -retinol [68-26-8] and its lUPAC name is (all-E)-3,7-dimethyl-9-(2,6,6-trimethyl-l-cyclohexen-l-yl)-2,4,6,8-nonatetraen-l-ol (1). The numbering system for vitamin A derivatives parallels the system used for the carotenoids. In older Hterature, vitamin A compounds are named as derivatives of trimethyl cyclohexene and the side chain is named as a substituent. For retinoic acid derivatives, the carboxyl group is denoted as C-1 and the trimethyl cyclohexane ring as a substituent on C-9. The stmctures of vitamin A and -carotene were elucidated by Karrer in 1930 and several derivatives of the vitamin were prepared by this group (5,6). In 1935, Wald isolated a substance found in the visual pigments of the eye and was able to show that this material was identical with Karrer s retinaldehyde [116-31-4] (5) (7). 

Derivatives of retinoic acids are named as carboxylic acid derivatives, e.g., ethyl retinoate (24) and A -ethylretinamide (25). 

Also based on the nomenclature rules for carotenoids is the use of the prefix nor for those retinoids that, compared with a standard structure, lack carbon atoms. The retinoic acid derivative (32) below is accordingly named 19,20-dinorretinoic acid methyl ester and retinoid (28) 5-acetyl-4,18-dinorretinoic acid. 

In 1960, lUPAC drew up a number of recommendations and rules for the nomenclature of vitamin A derivatives, and only recently lUPAC-IUB published new rules on the nomenclature of retinoids (lUPAC-lUB, 1982), which we follow in this book in naming retinoids. The basic structures are called retinol (1), retinaldehyde (2), and retinoic acid (3), and these names always refer to the... 

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