Retinyl acetate

Fig. 1. Vitamin A and derivatives retinol (1), retinyl acetate [127-47-9] (2), retinyl palmitate [79-81-2] (3), and retinyl propionate [7069-42-3] (4).

Property Retinol Retinyl acetate Retinyl palmitate Retinyl propionate o p-carotene... 

Spectroscopic methods such as uv and fluorescence have rehed on the polyene chromophore of vitamin A as a basis for analysis. Indirectly, the classical Carr-Price colorimetric test also exploits this feature and measures the amount of a transient blue complex at 620 nm which is formed when vitamin A is dehydrated in the presence of Lewis acids. For uv measurements of retinol, retinyl acetate, and retinyl palmitate, analysis is done at 325 nm. More sensitive measurements can be obtained by fluorescence. Excitation is done at 325 nm and emission at 470 nm. Although useful, all of these methods suffer from the fact that the method is not specific and any compound which has spectral characteristics similar to vitamin A will assay like the vitamin... 

Retinyl acetate [127-47-9] M 328.5, m 57". Separated from retinol by column chromatography, then crystd from MeOH. See Kofler and Rubin [Vitamins and Hormones (NY) 18 315 1960] for review of purification methods. Stored in the dark, under N2 or Ar, at 0°. See Vitamin A acetate p. 574 in Chapter 6. 

Retinal (Vitamin A aldehyde). Retinoic acid (Vitamin A acid), Retinyl acetate, Retinyl palmitate see entries in Chapter 4. 

Retinoids are needed for cellular differentiation and skin growth. Some retinoids even exert a prophylactic effect on preneoplastic and malignant skin lesions. Fenretlnide (54) is somewhat more selective and less toxic than retinyl acetate (vitamin A acetate) for this purpose. It is synthesized by reaction of all trans-retinoic acid (53), via its acid chloride, with g-aminophe-nol to give ester 54 (13). 

Figure 10.9 Cliromatogi ams of foitified coconut oil obtained by using (a) normal-phase HPLC and (b) GPC/noimal-phase HPLC. Peak identification is as follows 1 (a,b), DL-a-toco-pheryl acetate, 2 (b), 2,6-di-tert-butyl-4-methylphenol 2 (a) and 3 (b), retinyl acetate 3 (a) and 4 (b), tocol 4 (a) and 5 (b), ergocalciferol. Reprinted from Analytical Chemistry, 60, J. M. Brown-Thomas et al., Determination of fat-soluble vitamins in oil matrices by multidimensional liigh-peiformance liquid cliromatography , pp. 1929-1933, copyright 1988, with permission from the American Chemical Society.

Ramipril, 84, 85 Ranitidine, 89,112,114 Recainam, 37 Reelazepam, 153 Remoxipride, 42 Reserpine, 139,209 Retinoids, 7 Retinyl acetate, 7 Ritneazole, 201 Riodipine, 107 Rioprostil, 12, 13 Ristianol, 102 Rolgamidine, 80... 

Some conversion into the anhydrovitamin (112) occurs during silica gel t.l.c. of retinyl palmitate in non-polar solvents. Some new colour reactions of vitamin A are reported to be better than the Carr-Price reaction. The kinetics and mechanism of acid-catalysed isomerization of retinyl acetate into the trans-retro-derivative (113) have been studied. Oppenauer oxidation of kitol (39) results in specific cyclopentanol-cyclopentanone oxidation. ... 

Similar processes were related. TiCl4 was added to a solution of the diol to give a crude mixture of isomers in which the 5-chlorosulfone was the main compound in 95% yield. The mixture was treated with MeOK to produce crude retinol. Acetylation with acetic anhydride (AC2O) in pyridine, in the presence of DMAP, provided the retinyl acetate in 70% from the diol [38,39], Fig. (15). 

In a similar fashion, the retinyl acetate (76%) could be synthezised quantitative borohydride reduction of phenylthioretinal to the alcohol, followed by its acetylation gave the acetate, which was oxidized to the sulfoxide by MCPBA and then eliminated by heating in CCI4, Fig. (49). 

Rezabek MS, Sleight SD, Jensen RK, et al. 1989. Effects of dietary retinyl acetate on the promotion of hepatic enzyme-altered foci by polybrominated biphenyls in initiated rats. Food Chem Toxicol 27(8) 539-544. 

Retinyl acetate [127-49-9] M 328.5, m 57 . Separated from retinol by column chromatography, then... 

The vitamin A value of foods has traditionally been expressed in international units (IU). One IU is defined as the amount of vitamin A activity contained in 0.334 fig of all-trans-retinyl acetate, which is equivalent to 0.300 fig of alRran.v-retinol. In 1965, an expert committee decided to abandon the IU for vitamin A, proposing instead that the vitamin A value be designated in terms of retinol equivalents (RE), expressed in micrograms of retinol. The RE is defined as the amount of retinol present plus the equivalent amount of retinol that can be obtained from the provitamins. It is purely a dietary concept and is not an equivalency in the usual chemical sense ... 

Fig. 7 Comparative HPLC separations of a standard solution of six vitamins using (A) 250 X 4.0-mm-ID standard-bore and (B) 250 X 2.0-mm-ID narrow-bore columns. Stationary phase (both columns), 5-/tm Nu-cleosil-120-5 C8 (octyl) mobile phase, methanol/water (92 8). Flow rate (A) 0.7 ml/min, (B) 0.2 ml/min. Injection volume, 1 fi 1. Wavelength-programmed absorbance detection. Peaks (1) retinol (2) retinyl acetate (3) vitamin D3 (4) a-tocopherol (5) a-tocopheryl acetate (6) retinyl palmitate. (From Ref. 108.)...

Retinol and its esters and unesterified tocopherols and tocotrienols possess strong native fluorescence, but neither vitamin D nor vitamin K fluoresce. The carotenoids commonly associated with foods do not fluoresce to any significant extent, except notably phytofluene, which is found in considerable amounts in tomatoes (22) and in smaller amounts in carrots (130) and which fluoresces six times more intensely than retinyl acetate (131). 

Several different quantification procedures for vitamin A have been described in the literature, some using retinol directly as a standard and some using retinyl acetate, which is converted to retinol by saponification. The latter approach is generally preferred, because crystalline all-trans-retinyl acetate is commercially available in high purity and is free from cis isomers. Commercial sources of retinol are oily preparations and are at best only about 70% pure. There are two ways of preparing a retinol standard from retinyl acetate. 

A relatively large amount (typically 25 mg) of retinyl acetate is saponified and extracted, and the residue is dissolved in 2-propanol to give a stock solution of retinol,... 

Margarine Dissolve sample in heptane containing 500 mg BHT and 200 mg a-tocopherol per L. Pass emulsion through glass column containing 10 g Na2S04 and 20 g NaCl. LiChrosorb Si-60 5 pm 250 X 4.6 mm Heptane/ diisopropyl ether, 95 5 Retinyl palmi-tate or retinyl acetate UV 325 nm 144... 

An accurately prepared standard solution of retinyl acetate (i.e., a solution of known concentration) is taken through the saponification and extraction procedure along with each batch of samples, and the resultant retinol solution is used as an external standard without spectrophotometric standardization. This technique, which is recommended by COST 91 (149), compensates for losses of vitamin A incurred during the saponification and subsequent manipulations (i.e., the calculated vitamin A value is recovery-corrected). 

For the determination of supplemental vitamin E in infant formulas, Woollard and Blott (222) employed a radially compressed Radial-PAK cartridge. This enabled lipid material to be rapidly cleared by stepping up the mobile-phase flow rate from 2 ml/min to 10 ml/min after elution of the a-tocopheryl acetate. Fluorescence detection, using a filter-type fluorometer, allowed the indigenous a-tocopherol to be conveniently estimated, while UV absorbance detection was used to quantify the a-tocopheryl acetate. Supplemental retinyl acetate could be assayed simultaneously with either added or indigenous vitamin E using the appropriate detection mode. With the aid of a dual-monochromator spectrofluorometer, a-tocopheryl acetate and a-tocopherol could be determined simultaneously with wavelengths of 280 nm (excitation) and 335 nm (emission), but the increased selectivity eliminated detection of the vitamin A esters (233). 

Figure 2. General structure of retinoic acid (all trans-retinoic acid). Of the many derivatives tested (e.g., retinol, retinyl acetate), none has the "anti-tumor promoter efficacy, in vivo, as retinoic acid.

Dietary Retinyl Acetate No. Rats at Tumor Incidence (%) ... 

Enhancement of Mutagenicity by Retinol or Retinyl Acetate. We initially examined the effect of vitamin A alcohol (retinol) on 2-fluorenamine-induced mutagenesis in S. typhimurium (TA98) (23). 

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