Synthesis of Vitamin A

Early Organic Chemistry in Kyiv: Serhii Mykolayovych Reformatskyi (1860-1934) and his Name Reaction

Serhiy Mykolayovych Reformatskyi, [Ukrainian: Рeφopмaтcьκий, Cepгiй Mиκoлaйoвич; Russian: Sergei Nikolaevich Reformatskii, РeΦopмaтcκий, Cepгeй Hиκoлaeвич (1860-1934)] was a product of Zaitsev's laboratory in Kazan Imperial University in Russia and one of the founding fathers of organic chemistry in Ukraine. He discovered his eponymous reaction while a graduate student in Kazan under Zaitsev, studying the synthesis of homoallylic alcohols. He modified this reaction by replacing the olefinic π bond of an allyl halide with a carbonyl group. In the prototype reaction, he treated ethyl haloacetates with zinc and aldehydes or ketones. The reaction gave the corresponding β-hydroxyesters and remains an important synthetic method. Work on the reaction over the ensuing century and a quarter has led to the discovery of analogous reactions using a wide range of metals, and even permitting the use of water as a solvent.

Synthesis of Polyene Bioactive Natural Products: FR252921 and Vitamin A

A formal synthesis of FR252921, a potent macrocyclic immunosuppressive agent, and a six-step synthesis of vitamin A have been demonstrated. The application of a ruthenium-catalyzed step-economic and environmentally benign strategy for the highly stereo- and chemoselective construction of valuable polyene motifs of FR252921 and vitamin A highlights the syntheses. The key features for the synthesis FR252921 include preparation of the triene moiety followed by two consecutive peptide couplings of the three fragments.

First total synthesis of quiquesetinerviusin A

The first total synthesis of the dihydrobenzofuran neolignan quiquesetinerviusin A and its related structure have been described. Phenolic coupling is the key step to constructing the dihydrobenzofuran skeleton with vanillin as the raw material. The hydroxyl group was protected with dihydropyran (DHP) and the ester group was reduced with diisobutylaluminium hydride (DIBAL-H) in order to obtain the crucial intermediate diol, which was then condensed with an acid ligand to give the desired compounds following removal of the protecting groups.

Kinetic mechanism of lecithin retinol acyl transferase

Lecithin retinol acyl transferase transfers acyl groups regiospecifically from the 1-position of lecithins to all-trans-retinol (vitamin A) and similar retinoids. LRAT is essential for the biosynthesis of 11-cis-retinal, the visual pigment chromophore, and is also required for the general dietary mobilization of vitamin A. The kinetic mechanism of this enzyme is described here, KM and Vmax values were determined for the substrates dipalmitoylphosphatidylcholine (DPPC) [1.38 microM and 0.17 microM/(min-mg), respectively] and for all-trans-retinol [0.243 microM and 0.199 microM/(min-mg), respectively]. In order to distinguish between a ping-pong bi-bi mechanism and a rapid equilibrium random or ordered bi-bi mechanism, the velocity of product formation as a function of one of the substrates at different fixed concentrations of the other substrate was measured. The parallel lines generated are entirely consistent with a ping-pong bi-bi mechanism in which DPPC first binds to LRAT and acylates it and rule out both simple random binding and ordered kinetic mechanisms. Further evidence for a ping-pong bi-bi mechanism comes from partial exchange reaction studies which show that LRAT can catalyze acyl group interchange between two different lecithin derivatives. Finally, the ping-pong reaction was established as being ordered, using the potent and reversible dead-end inhibitor 13-desmethyl-13,14-dihydro-all-trans-retinyl trifluoroacetate. This compound proved to be competitive with respect to DPPC, with a KI = 11.4 microM, and uncompetitive with respect to all-trans-retinol.

Vitamin A in human skin: I. detection and identification of retinoids in normal epidermis

In an attempt to identify vitamin A and derivatives (retinoids) specimens of breast skin epidermis (0.5 g) were homogenized, freeze-dried and extracted with chloroform/methanol. The evaporated extract was partitioned repeatedly between petroleum ether and a mixture of ethanol and pH-adjusted water. This yielded 3 fractions of partially purified retinoids. High-pressure liquid chromatography (HPLC) of these fractions revealed the presence of the following retinoids given in order to their abundance in the epidermis: retinyl acyl esters, retinol, 3-dehydroretinyl acyl esters and retinoic acid. Small amounts of other retinoids may also be present. In order to obtain quantitative data it was essential to add internal retinoid standards and to completely hydrolyze the skin in KOH-ethanol before extraction. The retinoids were deconjugated by this procedure but, with the exception of retinaldehyde, were otherwise unchanged. The recoveries of the endogenous retinoids at HPLC were identical to those of the internal standards. The technique was reproducible and could be applied to the analysis of nanograms of retinol and dehydroretinol in small (10-30 mg) skin specimens. The amounts of acidic retinoids were usually below the detection limit of the method (less than 10 ng/g) but the approach may be useful at the higher levels attained during retinoid therapy.