All-tranj-Retinol

Figure 12.8 Vitamin Ar All-tranj-retinol (Vitamin A alcohol) is usually referred to as Vitamin A,.

A series of 14 retinoids, carotenoids, and tocopherols from very polar (e.g., all-rranj-4-oxo-retinoyl /J-glucuronide, all-rranj-4 oxo-retinoic acid, all-rrans-5,6-epox-yretinoic acid) to slightly polar (e.g., all-tranj-retinol, all-trans-retinoic acid) to nonpolar (e.g., all-fra 5-lycopene, all-rrans-jS-carotene) were resolved on a Micro-sorb-MV column (A = 330nm) using a 100/0->0/100 (at 15 min hold 19 min) (3/1 methanol/water with 10mM ammonium acetate)/(4/l methanol/chloroform) gradient [350]. 

All-tra/w-retinol, 11-cw-retinol (A2) and 11-m-retinaldehyde are found in the 1PM (Liou et al., 1982c). At present, it is not clear which retinoid, or which isomer, is in transit from the RPE to the ROS. With regard to carrier proteins, the evidence suggests that CRBP and CRAIBP are present in the 1PM (Liou et al., 1982c), but it is probable that they have leached from the RPE and retina cytosols where both proteins occur. On the other hand, interstitial retinol-binding protein is believed to be a true IPM protein because it is absent from the RPE and retina cytosols. This conclusion has been confirmed by immunocytochemical observations in the author s laboratory (Fong et al., 1984) and by Bunt-Milam and Saari (1983). Although IRBP binds the all-tranj-retinol that is released when rhodop-sin is bleached, it also carries some 11-cis isomer, and it has not been established whether it may be implicated in the two-way transport of retinoids. 

Figure 1. Formulas of major retinoids and of P-carotene. A, all-tranj retinol B, all-tranj retinal C, all-rran retinoic acid D, 11-cw retinal E, 13-cw retinoic acid F, all-tran retinyl palmtate G, ai -trans retinoyl p-glu-curonide H, the trimethyl methoxyphenol analog of all-rra 5 retinoic acid (etretin, acitretin) I, all-rra 5 p-carotene. From [5], p. 110, reprinted with the permission of the International Life Sciences Institute, Washington DC 20036-4810, Copyright 1996.

Photoisomerization of tranj-13-demethylretinal (115) gave a mixture of C-7, C-9, C-11, and C-13 stereoisomers which were separated by h.p.I.c. and identified by 400 MHz n.m.r. The photochemistry of (115) and of 14-methylretinal (116) in polar and non-polar solvents has been examined. Conditions for the photoisomerization of methyl retinoate (117) to various ci5-isomers have been studied.Photoisomerization studies of the all-tran -isomers of 3,4-dehydroretinal (118), 10-fluororetinal (119), and 14-fluororetinal (120) suggest Zwitterion intermediates, e.g. (121), the stability of which is influenced by the fluorine substituent or the extra double bond. Conditions have been optimized for reduction of the retinal-hydroquinone complex to retinol by aluminium isopropylate. The electrodimerization of retinal in the presence of electron donors has been studied. ... 

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