Concepción López Rodríguez

An efficient and highly stereoselective synthesis of nucleoside derivatives from furanoid 1,2=diols

Abstract Reaction between suitably protected furanoid glycals 1b–4b , readily obtained from furanoid 1,2-diols ( 1a–4a ), and different silylated pyrimidine bases, gave the corresponding 3′,5′- and 3′,5′,6′- O -protected 2′-deoxy-2′-β- d - xylo -pentofuranosyl 5–10 and β- d - gluco -hexofuranosyl 11 nucleosides, respectively. Compound 5 has been transformed into its 2′-deoxy 12 and 2′,3′- anhydro 14 derivatives. The high stereoselectivity of the reaction is discussed.

4-Octulose Derivatives as Key Intermediates in a New and Short Synthesis of Polyhydroxyindolizidines

Reaction of 3 with (cyanomethylene)triphenylphosphorane in refluxing dichloromethane or methanol gave mixtures of 4a and 4b in ratios of about 3:1 and 1:3, respectively. The same reaction performed with the furanoid isomer 5 afforded 6a and 6b in (E)/(Z) ratios of approximately 9:1 and 1:2, respectively. Catalytic hydrogenation of the α,β-unsaturated nitriles 4 and 6 with either 10% Pd-C or Raney nickel afforded the saturated nitriles 7 and 9, or the 1-amino-1,2,3-trideoxy-4-octulose derivatives 8 and 10, respectively. In an attempt to transform 6a into the appropriate polyhydroxylated branched-chain pyrrolidine 15, (5R,8S,9R,10S)-8,9,10-trihydroxy-1-aza-6-oxaspiro[4.5]decane, which was identified as its peracylated derivative 16, was isolated. Following an alternative synthetic strategy, partial hydrolysis of compound 9 afforded 17 which was regioselectively transformed into the corresponding derivative 22 via its 8-O-p-toluenesulfonyl derivative 18. Removal of the 4,5-O-isopropylidene group in 22 with aqueous trifluroacetic acid gave the free octulose 23, which was hydrogenated in the presence of 10% Pd-C, to afford the expected (6S,7R,8R,8aR)-6,7,8-trihydroxyindolizidine (1-deoxycasta-nospermine, 11).

Preparation of 2,2′-anhydronucleosides: regio- and stereoselective modifications of the base and sugar moieties

Abstract 2′-Deoxy-2′-iodonucleosides 4 – 9 , obtained from suitably protected furanoid glycals 1 and 2 with different silylated pyrimidine bases, were transformed into the corresponding 2,2′-anhydronucleosides 10 – 15 with inversion of the configuration at C-2′, by heating in DMF with n -dibutyltin oxide. Regio- and stereospecific opening at C-2′ of the 2,2′-ring in compounds 10 , 11 , and 12 with sodium azide afforded the related 2′-azido-2′-deoxynucleosides 16 , 17 and 18 , respectively. Action of sodium hydroxide on 12 caused the regioselective opening of the above-mentioned ring at C-2 with retention of the configuration at C-2′ giving 19 . Compound 19 could be transformed straightforwardly into 18 by well-established methodology. On the other hand, compound 15 could be transformed into the related 2′,3′-anhydronucleoside 23 by a regio- and stereoselective addition at N-3–C-2′ of allyl bromide concomitant with 2,2′-ring opening and inversion of the configuration at C-2′ to afford the intermediate 2′-bromo-2′-deoxynucleoside 21 , which was subsequently treated with sodium methoxide giving 23 .

A highly diastereoselective synthesis of 4-octulose and 2-deoxy-4-octulose from a d-fructose derivative

Abstract Bishydroxylation of methyl (Z)-2,3- dideoxy -4,5:6,7- di -O- isopropylidene -β- d -arabino- oct-2-ene-4-ulo-4,8-pyranosonate 1 with osmium tetraoxide proceeded with extremed high diastereoselectivity to give only methyl 4,5:6,7- di -O- isopropylidene -β- d -arabino- l -erythro- oct-4-ulo-4,8- pyranosonate 2 . Configurations of the new stereogenic centers (C-2,3) in 2 were determined by degradation of the C-5,6,7,8 fragment to the well-known methyl 2,3,4- tri -O- methyl- d -(+)-erythronate 7 . Transformation of 2 into the required d -arabino- l -erythro- oct-4-ulosa 10 , was achieved by a methodology that implied, protection to 8 , reduction of the ester group in 8 to a hydroxymethyl group in 9 , and finally deprotection to the free d -arabino- l -erythro- oct-4-ulosa 10 . On the other hand, epoxidation reaction on (E)-2,3- dideoxy-4,5:6,7-di -O- isopropylidene -β- d -arabino- oct-2-ene-4-ulo- 4,8-pyranose 11 afforded only the corresponding 2,3- anhydro derivative 12 with β- d -arabino- d -threo configuration, as could be demonstrated by degradation to ( S )-1,2,4-trimetoxybutane 16 , which synthesis is reported herein.

Synthesis of nucleosides from 4-methylidenefuranoses: a non-classical electrophilic addition

Abstract The reaction of persilylated bases (thymine, uracil, cytosine, and 5-fluorouracil) with either 3-O-benzoyl-5-deoxy-1,2-O-isopropylidene-α- d -erythro-pent-4-enofuranose 6 or its 3-O-benzyl analogue 7 in the presence of N-iodosuccinimide (NIS) afforded two types of product with high stereoselectivity; either (1′S,2′R,3′S)-3′-O-benzoyl- 8–10 or -3′-O-benzyl-5′-deoxy-5′-iodo-1′,2′-O-isopropylidene-4′-oxo-1′-yl-pyrimidines 11–13, respectively, from 1,4-addition with participation of the oxygen atom at the furanoid ring, and either 3′-O-benzoyl- 14–16, or 3′-O-benzyl-5′-deoxy-5′-iodo-1′,2′-O-isopropylidene-β- l -lyxo-4′-yl-pyrimidine and 17–19 resulting from normal electrophilic addition at the exocyclic methylene group. A third compound was isolated from the reaction of 7 with persilylated uracil/NIS and identified as the doubly N,N′-glycosylated pyrimidine 20.

Una lectura del mito de Narciso en Luis Cernuda: Luis de Baviera escucha Lohengrin

Resumen : Luis Cernuda destaco siempre la capacidad expresiva implicita en los mitos griegos y a ellos recurrio en su obra poetica. El mas importante sin duda es el mito de Narciso, que constituye no un mero ejemplo sino la base estructural de su poesia. En este trabajo presento un analisis de la presencia del mito de Narciso en el poema “Luis de Baviera escucha Lohengrin”, perteneciente a la ultima seccion de La realidad y el deseo , la titulada Desolacion de la Quimera . Tras exponer algunos ejemplos en obras precedentes, llego a la conclusion de que en este poema, Luis de Baviera, Luis Cernuda y Narciso son el mismo personaje, y que la musica discurre como sonora corriente de agua donde se reflejan la imagen del rey y del poeta, espejo donde ambos hallan la culminacion del deseo de si mismos. Palabra s clave: Narciso; Luis Cernuda; Luis de Baviera; poesia; musica. Abstract : Luis Cernuda always stressed the expressive potential implicit in Greek myths, and made a constant use of them in his poetic work. Without a doubt the most important of these myths to his work is the myth of Narcissus, which becomes not only a mere example but also the structural base of his poetry. In this article I present an analysis about the presence of the myth of Narcissus in the poem “Luis de Baviera escucha Lohengrin” (Ludwig of Bavaria listens to Lohengrin), which belongs to the last section of Cernuda’s work La Realidad y el Deseo , called Desolacion de la Quimera . After showing some examples from some of his previous work, I get to the conclusion that in this poem, Ludwig of Bavaria, Luis Cernuda and Narcissus are the same character. I also verify that the poem’s music flows as a sounding current where the images of both the king and the poet are reflected, a mirror where they both find the culmination of their own desire. Keywords : Narcissus; Luis Cernuda; Ludwig of Bavaria; poetry; music.

La 'Argumentatio' en el tratado "Sobre la tisana" de Galeno

The role of Argumentatio in the Peri ptisanēs is studied in the present paper, considering basically Galen’s logical and rhetorical procedures in order to conform an exact example of dietetic logos. http://dx.doi.org/10.14195/2183-1718_66_8

Tradición clásica y voluntad política en el Setenario de Alfonso X El Sabio

The Castilian King, Alphonso X the Wise, wrote the Setenario following different classical traditions that have given to the seven number one symbolical meaning. This value comes from many Greek and Latin authors; one of them, perhaps the most important, is Ptolemy. But Alphonso found out how to fit perfectly that traditional symbol to his proper work providing it with a religious and political content; furthermore he made of this number the emblem of his proper name: in Spanish language, in fact, A-l-f-o-n-s-o has seven letters. On the other hand, these letters summarize his personal excellence. But, mainly, his final purpose is essentially political: he aims to unify his kingdom which was scattered into different local laws after the Reconquest.