Retro-retinol

Unlike many retinol dehydrogenases, the enzyme that catalyzes the conversion of retinol to anhydroretinol, retinol dehydratase, does not use CRBP-retinol as a substrate rather, it uses free retinol (49-51). However, the enzyme responsible for biosynthesis of 14-hydroxy-4,14-retro-retinol has not yet been isolated. 

Arnhold, T., Tzimas, G., Wittfoht, W., Plonait, S. and Nau, H. (1996) Identification of 9-cis-retinoic acid, 9,13-di-cis-retinoic acid, and 14-hydroxy-4,14-retro-retinol in human plasma after liver consumption. Life Sciences, 59, PL169-177. 

Buck, J., Derguini, F., Levi, E., Nakanishi, K., and Hammerling, U (1991) Intracellular signaling by 14-hydroxy-4,4-retro-retinol. Science 254, 1654-1656. 

Interestingly a new class of intracellular messenger molecules, the retro-retinoids were recently identified [43-45]. Both the growth supportive 14-hydroxyl-retro-retinol (14-HHR) pathway and the growth suppressive anhydroretinol (AR) pathway have been described. The AR-producing enzyme ARase has been purified to homogeneity. It is not yet known whether... 

Derguini F, Nakanishi K, Haemmerling U (1994) Synthesis and intracellular signalling activity of (14R), (14S) and 14RS)-14-Hydroxy-4,14-Retro-Retinol (14-HRR). Biochemistry 33 623—628... 

Because of the presence of an extended polyene chain, the chemical and physical properties of the retinoids and carotenoids are dominated by this feature. Vitamin A and related substances are yellow compounds which are unstable in the presence of oxygen and light. This decay can be accelerated by heat and trace metals. Retinol is stable to base but is subject to acid-cataly2ed dehydration in the presence of dilute acids to yield anhydrovitamin A [1224-18-8] (16). Retro-vitamin A [16729-22-9] (17) is obtained by treatment of retinol in the presence of concentrated hydrobromic acid. In the case of retinoic acid and retinal, reisomerization is possible after conversion to appropriate derivatives such as the acid chloride or the hydroquinone adduct. Table 1 Hsts the physical properties of -carotene [7235-40-7] and vitamin A. 

MYVPACK OLEOVITAMIN A OPHTHALAMIN PREPALIN RETINOL aU-trans RETINOL RETRO-VITAMIN A TESTAVOL VAFLOL VI-ALPHA VITAMIN A1 VITAMIN A1 ALCOHOL aU-trans-VITAMIN A ALCOHOL VITAVEL-A VITPEX VOGAN VOGAN-NEU... 

Retinal pigment epithelium (RPE), 3925, 3927-3929, 3937, 3939 3941, 3943-3947 Retinoids, 2675, 2695 Retinol, 3369 Retinopathy, 1450 Retroaldol-aldol mechanism, 2700 Retrochalcones, 1869, 1874, 1875 Retrograde amnesia, 292 Retronecine, 1058, 1064 Retro-Prince reaction, 3075, 3076 Retrorsine, 1061, 1063, 1385 Reversed phase... 

The C20 triphenylphosphonium salt (276), which has a 4,6-retro structure, was prepared from the corresponding bromide and triphenylphosphine (Stem, 1960). Retinol (1) underwent acid-catalyzed dehydration to give anhydrovitamin A (58) (Henbest et al., 1955 Reppe, 1972 Christensen and Kohler, 1973 Auerbach et al, 1979). The enol acetate (277) of retinaldehyde (2) likewise has a retro structure. 

The Ci5 acetylene compound (425) was also used as a starting material for the synthesis of retro-18,14-retinol (435) via the acetylene alcohol (431), which was obtained from (425) and oligomeric formaldehyde by a Grignard reaction (Chauhan et al., 1982). 

Two methods were developed to stabilize retinol during GLC analysis, namely formation of the trimethylsilyl ethers (Vecchi et al., 1967, 1973) and formation of perhydro derivatives of retinol by catalytic hydrogenation (Fenton et al., 1973). Trimethylsilyl ethers of retinol were separated on columns of Chromosorb W-HP coated with 7% Silicone QF-1 and conditioned by repeated injections of V,0-bis(trimethylsilyl)acetamide. Some separation of isomers of retinol, i.e., all-rran5-retinol from 13-cw-retinol, was also possible. The retention times of various isomers, relative to the trimethylsilyl ether of all-fran -retinol (1.00), were 13-cw (0.64), 11,13-di-cw (0.28), and retro (0.72 and 1.00) (Vecchi etal., 1967). 

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