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Information Retrieval focuses on finding documents whose content matches with a user query from a large document collection. As formulating well-designed queries is difficult for most users, it is necessary to use query expansion to retrieve relevant information. Query expansion techniques are widely applied for improving the efficiency of the textual information retrieval systems. These techniques help to overcome vocabulary mismatch issues by expanding the original query with additional relevant terms and reweighting the terms in the expanded query. In this paper, different text preprocessing and query expansion approaches are combined to improve the documents initially retrieved by a query in a scientific documental database. A corpus belonging to MEDLINE, called Cystic Fibrosis, is used as a knowledge source. Experimental results show that the proposed combinations of techniques greatly enhance the efficiency obtained by traditional queries.

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Vitamin A is a family of derivatives synthesized from carotenoids acquired from the diet and can be converted in animals to bioactive forms essential for life. Vitamin A1 (all-trans-retinol/ATROL) and provitamin A1 (all-trans-β,β-carotene/ATBC) are precursors of all-trans-retinoic acid acting as a ligand for the retinoic acid receptors. The contribution of ATROL and ATBC to formation of 9-cis-13,14-dihydroretinoic acid (9CDHRA), the only endogenous retinoid acting as retinoid X receptor (RXR) ligand, remains unknown. To address this point novel and already known retinoids and carotenoids were stereoselectively synthesized and administered in vitro to oligodendrocyte cell culture and supplemented in vivo (orally) to mice with a following high-performance liquid chromatography-mass spectrometry (HPLC-MS)/UV-Vis based metabolic profiling. In this study, we show that ATROL and ATBC are at best only weak and non-selective precursors of 9CDHRA. Instead, we identify 9-cis-13,14-dihydroretinol (9CDHROL) and 9-cis-13,14-dihydro-β,β-carotene (9CDHBC) as novel direct nutritional precursors of 9CDHRA, which are present endogenously in humans and the human food chain matrix. Furthermore, 9CDHROL displayed RXR-dependent promnemonic activity in working memory test similar to that reported for 9CDHRA. We also propose that the endogenous carotenoid 9-cis-β,β-carotene (9CBC) can act as weak, indirect precursor of 9CDHRA via hydrogenation to 9CDHBC and further metabolism to 9CDHROL and/or 9CDHRA. In summary, since classical vitamin A1 is not an efficient 9CDHRA precursor, we conclude that this group of molecules constitutes a new class of vitamin or a new independent member of the vitamin A family, named “Vitamin A5/X”.

The construction of the carotenoid skeleton by Pd-catalyzed Csp 2 ÀCsp 2 cross-coupling reactions of symmetrical and non-symmetrical1 ,10-bissilyldeca-1,3,5,7,9-pentaenes andt he corresponding complementary alkenyl iodides has been developed. Reaction conditions for these bidirectionala nd orthogonal Hiyama-Denmark cross-coupling reactions of bisfunctionalized pentaenes are mild andt he carotenoid products preserve the stereochemical information of the corresponding oligoenep artners. The carotenoids synthesized in this manner include b,b-carotenea nd (3R,3'R)-zeaxanthin (symmetrical)a sw ell as 9-cis-b,b-carotene, 7,8-dihydro-b,b-carotenea nd b-cryptoxanthin (nonsymmetrical).Scheme3.To tal synthesis of symmetrical carotenoids (7, 8)byH iyama-Denmark cross-coupling of symmetrical pentaenylbissilane (5)and trienyliodides (1 and 22).

Bifunctional unsaturated reagents designed to undergo palladium‐catalyzed cross‐coupling reactions with complementary polyenyl connective fragments are highly useful for the undoubtedly challenging synthesis of polyenes. The current toolkit of building blocks for the bidirectional formation of Csp2−Csp2 single bonds of polyenes includes homo‐bisfunctionalized reagents with equal or unequal reactivity (due to steric and/or electronic factors), and hetero‐bisfunctionalized counterparts containing either two different nucleophiles, two electrophiles or one of these functionalities and a latent nucleophile that can be unmasked when desired. The combination of these bifunctional linchpin reagents using tactics that modulate the reactivity of each terminus in order to achieve the required connection have streamlined the synthesis of polyenes of great complexity using (iterative) cross‐coupling methods for Csp2−Csp2 bond formation. Reaction conditions for the Pd‐catalyzed cross‐coupling reactions are mild and functional‐group‐tolerant, and therefore these protocols allow to construct the polyene structures using shorter unsaturated reactants with the desired geometries, since in general the products preserve the stereochemical information of the connected cross‐coupling partners.

Mono‐ and difunctionalized alkenyl linchpins are continuously being developed with the purpose of connecting components of complementary reactivity as a general strategy for the synthesis of polyenes by Csp2−Csp2 single‐bond construction. In their Review on page 13543 ff., A. R. de Lera et al. outline some of the recent strategies and protocols for fragment cross‐coupling for the stereoselective construction of a range of polyunsaturated products.

Human aldo-keto reductases (AKRs) are enzymes involved in the reduction, among other substrates, of all-trans-retinal to all-trans-retinol (vitamin A), thus contributing to the control of the levels of retinoids in organisms.