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Treatment of all-trans-retinal with one and two equivalents of NBS in a mixture of CH3CN-CH2Cl2-H2O provide 4-hydroxyretinal and 4-oxoretinal, respectively, in good yields.

A method of treating an ocular disorder in a subject associated with increased all-trans-retinal in an ocular tissue includes administering to the subject a therapeutically effective amount of a primary amine compound of formula (I); and pharmaceutically acceptable salts thereof.

All-trans-retinal, a retinoid metabolite naturally produced upon photoreceptor light activation, is cytotoxic when present at elevated levels in the retina. To lower its toxicity, two experimentally validated methods have been developed involving inhibition of the retinoid cycle and sequestration of excess of all-trans-retinal by drugs containing a primary amine group. We identified the first-in-class drug candidates that transiently sequester this metabolite or slow down its production by inhibiting regeneration of the visual chromophore, 11-cis-retinal. Two enzymes are critical for retinoid recycling in the eye. Lecithin:retinol acyltransferase (LRAT) is the enzyme that traps vitamin A (all-trans-retinol) from the circulation and photoreceptor cells to produce the esterified substrate for retinoid isomerase (RPE65), which converts all-trans-retinyl ester into 11-cis-retinol. Here we investigated retinylamine and its derivatives to assess their inhibitor/substrate specificities for RPE65 and LRAT, mechanisms of action, potency, retention in the eye, and protection against acute light-induced retinal degeneration in mice. We correlated levels of visual cycle inhibition with retinal protective effects and outlined chemical boundaries for LRAT substrates and RPE65 inhibitors to obtain critical insights into therapeutic properties needed for retinal preservation.

The involvement of a series of microsomal cytochrome P450 (P450) isozymes in all-trans-retinoid metabolism, including the conversion of all-trans- retinal to all-trans-retinoic acid, was previously described. In the current study, we examined the role of seven liver microsomal P450 isozymes in the oxidation of three isomers of retinal. P450 1A1, which was not tested previously, is by far the most active in the conversion of all-trans-, 9- cis-, and 13-cis-retinal to the corresponding acids, as well as in the 4- hydroxylation of all-trans- and 13-cis retinal. In contrast, P450s 2B4 and 2C3 are the most active in the 4-hydroxylation of 9-cis-retinal, with turnover numbers ~7 times as great as that of P450 1A1. The inclusion of cytochrome b5 in the reconstituted enzyme system is without effect or inhibitory in most cases but stimulates the 4-hydroxylation of 9-cis-retinal by P450 2B4, giving a turnover of 3.7 nmol of product/min/nmol of this isozyme, the highest for any of the retinoid conversions we have studied. Evidence was obtained for two additional catalytic reactions not previously attributed to P450 oxygenases: the oxidation of all-trans- and 9-cis-retinal to the corresponding 4-oxo derivatives by isoform 1A2, and the oxidative cleavage of the acetyl ester of vitamin A (retinyl acetate) to all-trans- retinal, also by isoform 1A2. The physiological significance of the latter reaction, with a K(m) for the ester of 32 μM and a V(max) of 18 pmol/min/nmol of P450, remains to be established. We also examined the effect on P450 of citral, a terpenoid α,β-unsaturated aldehyde and a known inhibitor of cytosolic retinoid dehydrogenases. Evidence was obtained that citral is an effective mechanism-based inactivator of isozyme 2B4, with a K1 of 44 μM as determined by the oxidation of 1-phenylethanol to acetophenone, and by isozyme 1A2 in the oxidation of all-trans-retinal to the corresponding acid and by isozyme 2B4 in the 4-hydroxylation of all-trans-retinol and retinoic acid. Thus, citral is not suitable for use in attempts to distinguish between retinoid conversions catalyzed by dehydrogenases in the cytoplasm and by P450 cytochromes in the endoplasmic reticulum.

The reaction of hydrogen peroxide with all-(E)-retinol (1) catalyzed by (meso-tetraphenylporphinato)iron(III) led to the formation of 4-hydroxyretinol (2), 4-oxoretinol (3), 5,8-epoxyretinol (4), 5,6-epoxyretinol (5), 3-dehydroretinol (6), all-(E)- and 12-(Z)-retroretinol (7/7a) as well as all-(E)- and 12-(Z)-anhydroretinol (8/8a) as major non-volatile products.The conversion products were characterized by comparison of their chromatographic (HPLC) and spectroscopic data (UV; MS; 1H and 13C NMR) with those of synthesized reference compounds.The observed product formation supports the hypothesis of a C4 centered radical as the key intermediate of all-(E)-retinol conversion. - Keywords: 5,6- and 5,8-Epoxyretinol, 4-Hydroxyretinol, 4-Oxoretinol, Retinol Conversion

Reaction of all-trans retinal with NBS in acetic acid gives 4-acetoxyretinal which hydrolyses in the presence of 1percent K2CO3-MeOH to give 4-hydroxyretinal.Oxidation of 4-hydroxyretinal with PCC gives 4-oxo-retinal.Isomerization of 13-trans to 13-cis do

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