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Lchemical and Physic Characteristics I LChemical and physic 1. 1.2 Structural and molecular formulae and characteristics i relative molecular mass The general characteristics of retinol, retinyl 20H acetate, retinyl palmitate and fl-retinal have J been obtained from the following: Beilstein __L 11 (Boit, 1966); Directory of Chemical Producers (MDL Information Systems, 1998); Kirk-Othmer C20H300. Encyclopedia of Chemical Technology, 4th ed. (Kroschwitz, 1998); Keiloff et al. (1994a); Relative molecular mass: 286.46 Martindale. The Extra Pharmacopoeia (Reynolds, 1989); The Merck Index, 12th ed. (Budavari, 1.1.3 Physical and chemical properties 1996); and the Physicians'Desk Reference (1997). Description 1.1 Retinol Pale yellow prisms 1.1.1 Name Melting-point Chemical Abstracts Services Registry Number 62-64°C (yellow prisms from ethyl formate, 68-26-8 petroleum ether, propylene oxide) Chemical Abstracts Primary Name Solubility Retinol Soluble in most organic solvents (acetone, chlo- roform, dimethyl sulfoxide, ether, ethanol, IUPAC Systematic Name hexane, isopropanol, methanol) and in fats and (Ail-E) -3, 7-Dimethyl-9- (2,6, 6-trimethyl- 1 -cyclo- mineral oils (2.5 mol/L) (Boit, 1966); practically hexen- 1 -yl)-2, 4,6, 8-nonatetraen- 1-01 insoluble in water (0.06 pmol/L) (Szuts & Harosi, 1991) and glycerol. Synonyms Ali-trans-retinol; anti-infective vitamin; anti- Spectroscopy xerophthalmic vitamin; 15 -apo-13-caroten-1 5-ol; Double-bond isomers of retinol do not show axerol; axerophthol; axerophtholum; biosterol; differences in their infrared spectra, which are (E) -3, 7-dimethyl-9- (2,6, 6-trimethylcyclohex- briefly mentioned in the review by Frickel enyl) -2,4,6, 8-nonatetraenol; (E) -3, 7-dimethyl- (1984) and more extensively covered in that by 9-(2, 6, 6-trimethylcyclohexen- 1 -yl)-2, 4,6,8- Isler et al. (1971). The ultraviolet (UV) absorp- nonatetraenol; fat-soluble A (obsolete); (E)-9- tion spectrum in ethanol has 2max at 325 nm; hydroxy-3, 7-dimethyl-9'- (2,6, 6-trimethylcyclo- E = 1835 (Tee, 1992). Retinol exhibits 1 CM hexenyl)- 1,3,5, 7-nonatetraene; lard factor; yellow-green fluorescence at 510 nm after excita- oleovitamin A; ophthalamin (obsolete); trans- tion at 327 nm and at 470 nm after excitation retinol; 2-trans,4-trans,6- trans, 8-trans-retinol; at 325 nm. The infrared (IR) and proton vitamin A; vitamin Al; vitamin A1 alcohol; vit- magnetic resonance ('H-NMR) spectra of amin A alcohol; vitaminum A. retinol can be found in the relevant Aldrich Library volumes (Pouchert, 1985; Pouchert & Behnke, 1993). 23 IARC Handbooks of Cancer Prevention Stability (E)-9-Acetoyl-3, 7-dimethyl-9- (2,6, 6-trimethyl- Photo-induced bond isomerization from trans cyclohexenyl)-2,4, 6, 8-nonatetraenol to cis gives the other known retinol isomers: 11- cis (neo b), 13-cis (neo a), 9,13-di-cis (iso b), 9- Synonyms cis (iso a), and 11,13-di-cis (neo c) (Tee, 1992). Acetic acid (E) -3, 7-dimethyl-9-(2, 6, 6-trimethyl- Particularly in oil solution, retinol can be pro- cyclohexenyl) -2,4,6,8 -non atetraenyl ester; tected from isomerization by preventing expo- acetic acid retinyl ester; all-trans-retinyl acetate; sure to UV and sunlight. Bond isomerization all-trans-retinol acetate; Q-acetoxy-all-trans- can also be caused by heat and iodine. High lev- retinol; 0-acetyl-all-trans-retinol; retinyl els of illumination can induce polymerization.' acetate; 2- trans, 4- trans, 6-trans,8-trans-retino.l Retinol is sensitive to oxygen and is optimally acetate; 2- trans, 4- trans, 6-trans,8-trans-retinyl stored at below 4°C under an inert gas (argon or acetate; vitamin A acetate. nitrogen) or in the presence of an antioxidant, such as butylated hydroxytoluene. Heat and 1.2.2 Structural and molecular formulae and trace metals accelerate retinol decomposition relative molecular mass by oxygen and light (Kroschwitz, 1998). Retinol is unstable to acids, which cause bond rearrange- CH2000CH3 ment to retrovitamin A, isomerization, and dehydration to anhydrovitamin A; sometimes followed by solvent addition; it is also unstable C22H3202 to alkali in the presence of oxygen (Tee, 1992). Unlike the palmitate ester, the alcohol and its acetate can bind strongly to polyvinyl chloride in plastics used for administration. Relative molecular mass: 328.5 1:1.4 Technical products 1.2.3 Physical and chemical properties Commercial preparations of retinol may con- tain antioxidants (low levels of butylated Description hydroxyanisole and butylated hydroxytoluene, Pale yellow prisms or yellow supercooled, viscous dispersants and antimicrobial agents when liquid diluted with edible oils or solid dispersants (Polysorbate 20). One international unit (TU) of Melting point vitamin A is defined as 0.3 ig of pure all-trans- 57-58°C retinol. The major producers of vitamin A are BASF Solubility AG (Germany), BASF Corp. (USA), BASF Soluble in most organic solvents (acetone, Mexicana (Mexico), Bayer AG (Germany), chloroform, ethanol, isopropanol) and in fats Gaveteco S.A.I.C.I. e I. (Argentina), Hoffmann- and oils (750 g/100 mL); insoluble in water and La Roche AG (Germany) and Rhone-Poulenc glycerol. Animal Nutrition (France). Spectroscopy 1.2 Retinyl acetate UV-visible: kmax 326 nm (in ethanol); 1.2.1 Name E'1 cm 1550. Chemical Abstracts Services Registry Number Fluorescence 127-47-9 Emission max at 470 nm for excitation at 325 nm Chemical Abstracts Primary Name Stability Retinol acetate More stable than retinol. For stability in IUPAC Systematic Name crystalline form and in solution, see Guerrant 24 Vitamin A et al. (1948); for stability to hydrolysis in 1.3.2 Structural and molecular formulae and ethanolic sodium hydroxide at 400 and 60°C, relative molecular mass see Isler et al. (1949). Store at below 4°C. 1.2.4 Technical products CH200(0)(CH2)14CH3 Activity is based on high-performance liquid chromatographic comparison with the interna- tional standard. The international unit (TU) was defined by the WHO Expert Committee on C36H6002 Biological Standardization as the activity of 0.344 ig of pure all-trans-retinyl acetate. Relative molecular mass: 524.8 Synthetic material may be sold dispersed in a corn starch--gelatin matrix (Sigma, USA) or in gelatin, sucrose, peanut oil, and calcium phosphate-containing butylated hydroxy- Description anisole and butylated hydroxytoluene (USB, Yellow, crystalline or amorphous powder, USA), and in pure form (2 800 000 IU/g, Sigma). n ° 1.5558 (Tee, 1992) Major producers are BASF AG (Germany), F. Hoffman-La Roche AG (Germany) and Roche Melting-point AG (Switzerland). In one pharmaceutical source 27-29°C (Tee, 1992) (Materna prenatal tablets; Lederle, USA), retinyl acetate is combined with 13-carotene and Solubility vitamins D, E, B11 B21 B6, B12, biotin, panto- Soluble in most organic solvents (ethanol, iso- thenic acid and minerals. propanol, chloroform, acetone) and in fats and oils insoluble in water and glycerol. 1.3 Retinyl palmitate 1.3.1 Name Spectroscopy UV-visible: Xmax 325-328 nm (in ethanol); Chemical Abstracts Services Registry Number E101 "cm 940-975 79-81-2 Fluorescence Chemical Abstracts Primary Name Emission Xm at 470 nm for excitation at 325 nm Retinol hexadecanoate Stability IUPAC Systematic Name More stable than retinol to oxidation in air; rate (E)-3, 7-Dimethyl-9-O-palmitoyl-9-(2, 6,6-tri- of hydrolysis in ethanolic sodium hydroxide methylcyclohexenyl)-2,4, 6,8-nonatetraenol was reported by Isler et al. (1949). Store at below 4°C. Synonyms Palmitic acid (E)-3, 7-dimethyl-9-(2, 6, 6-trimethyl- 1.3.4 Technical products cyclohexenyl)-2,4, 6,8-nonatetraenyl ester; pal- One TU of vitamin A is contained in 0.55 pg mitic acid retinyl ester; O-palmitoyl-all-trans- of pure all-trans-retinyl palmitate. Major retinol; O-palmitoyl-retinol; O-palmitoyl-retinol; producers of retinyl palmitate are BASF AG retinyl palmitate; 2-trans,4-trans, 6-trans, 8-trans- (Germany), BASF Mexicana, S.A. de C.V. retinyl palmitate; 2-trans,4-trans, 6-trcins, 8-trans- (Mexico), F. Hoffman-La Roche AG (Switzer- retinol palmitate; trans-refinol palmitate; trans- land) and Piramal Health-care Limited (India). retinyl palmitate; vitamin A palmitate. A pharmaceutical source is Aquasol A (cap- sules or the parental form is water-miscible by solubilization in polysorbate 80; Carlson 25 IARC Handbooks of Cancer Prevention 2 2 222 - = = 2TtSZ2 Laboratories, USA). Retinyl palmitate is also petroleum ether and oils; virtually insoluble in available in a corn starch-gelatin matrix con- water. taining butylated hydroxyanisole and butylated hydroxytoluene, in a water-dispersible starch- Spectroscopy gelatin matrix containing butylated hydroxy- JR (Rockley et al., 1986); NMR (Patel, 1969) anisole and butylated hydroxytoluene, in a mixture of acacia, lactose, coconut oil, butylat- UV-visible ed hydroxytoluene, sodium benzoate, sorbic max 383 urn (E 4.288 x 10 in ethanol); max acid, and silicon dioxide, or in corn oil (USB, 368 nm (E 4.88 x 104 in hexane) (Hubbard et al., USA). 1971) 1.4 Retinal Stability 124.1 Name Sensitive to light and oxygen. Store under an inert gas (argon or nitrogen) at < 4°C. Chemical Abstracts Service Registry Number 116-31-4 Commercial sources Retinal can be obtained from the following Chemical Abstracts Primary Name suppliers: Sigma (USA), Crescent Chemical Co. Retinal (USA), Nacalia Tesque, Inc. (Japan) and Kanto Chemicals Co. (Japan). IUPAC Systematic Name (All-E) -3, 7-Dimethyl-2-(2, 6, 6-trimethyl-1 -cyclo- 1.5 Retinoic acid hexen- l-yl)2, 4,6, 8-nonatetraenol 1.521 Name Synonyms Chemical Abstracts Services Registry Number All-trans-retinal, axerophthal, retinaldehyde, 302-79-4 retinene, vitamin A aldehyde Chemical Abstracts Primary Name 1.4.2 Structural and molecular formulae and Retinoic acid relative molecular mass IUPAC Systematic Name CHO All-trans-retinoic acid Synonyms (All-E)-3, 7-dimethyl-9-(2,2,6-trimethylcyclohex- C20H280 enyl)nona-2, 4,6, 8-tetraenoic acid, trans-retinoic acid, tretinoin, vitamin A acid, vitamin Al acid.
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