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The regioselective Z-isomerization of thermodynamically stable all-trans retinoids remains challenging, and ultimately limits the availability of much needed therapeutics for the treatment of human diseases. We present here a novel, straightforward approach for the catalytic Z-isomerization of retinoids using conventional heat treatment or microwave irradiation. A screen of 20 transition metal-based catalysts identified an optimal approach for the regioselective production of Z-retinoids. The most effective catalytic system was comprised of a palladium complex with labile ligands. Several mechanistic studies, including isotopic H/D exchange and state-of-the-art quantum chemical calculations using coupled cluster methods indicate that the isomerization is initiated by catalyst dimerization followed by the formation of a cyclic, six-membered chloropalladate catalyst-substrate adduct, which eventually opens to produce the desired Z-isomer. The synthetic development described here, combined with thorough mechanistic analysis of the underlying chemistry, highlights the use of readily available transition metal-based catalysts in straightforward formats for gram-scale drug synthesis.

Ring-oxidized retinoids have been synthesized stereoselectively using the Stille cross-coupling reaction. Kinetic constants of mouse class I alcohol dehydrogenase (ADH1) with these retinoids were determined.

A method of simultaneous one-stage synthesis of three retinal derivatives (5,6-dioxo-5,6-seco-, 5,6-dihydro-5,6-epoxy-, and 4-oxoretinal) was proposed, with the yield of the first derivative being ～50%. These compounds are useful tools for studying the an

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.

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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

Photoaffinity mapping can be used to help clarify the tertiary structures of the retinal proteins bacteriorhodopsin (bR) and rhodopsin (Rh). An efficient photoaffinity labeled retinal analogue, [l5-3H]-all-trans-3-diazo-4-ketoretinal (specific

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

The title compound (C20H26O2) crystallizes in the monoclinic space group P21/n with a = 14.761(2), b = 8.292(1), c = 15.210(2) Angstroem, β = 102.40(1) deg, Z = 4.The structure was solved by direct methods and refined by least squares to a final R-value of 0.038 for 1211 observed reflections.The crystal structure is isomorphous with that of all-trans-retinal.The cyclohexenone ring shows a half-boat conformation.The connection of the cyclohexenone ring and the conjugated polyene chain via a formal single C-C bond is s-cis.The torsion angle C(5)-C(6)-C(7)-C(8) amounts to 56 deg.For the polyene side chain the typical curvature is evident.A comparison with analogous compounds shows that details in conformation, especially at the ring side-chain connection, are induced by crystal matrix.It seems that the differences in biological activity between retinal analogous compounds are not reflected by conformational differences of the free molecules. - Key words: X-ray, Retinal, Conformation

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