Raquel G. Soengas

Synthesis of polyhydroxylated α-nitrocyclohexane carboxylic acids derived from D-glucose: a striking case of racemization

The first total synthesis of polyhydroxylated α-nitrocyclohexane carboxylic acids from sugars is reported. A salient aspect of the synthesis is an unexpected Henry-mediated racemization of this new class of highly functionalized cyclohexanes.

Total synthesis of (-)-dysithiazolamide.

The tetrachlorinated natural product (-)-dysithiazolamide was synthesized from l-glutamic acid in a convergent way, confirming the previously proposed (2S,4S,6S,8S) absolute stereochemistry.

Synthesis of enantiopure 2-C-glycosyl-3-nitrochromenes.

A novel methodology has been developed to obtain enantiopure 2-C-glycosyl-3-nitrochromenes. First, (Z)-1-bromo-1-nitroalkenes were prepared from the corresponding sugar aldehydes through a sodium iodide-catalyzed Henry reaction with bromonitromethane followed by elimination of the resulting 1-bromo-1-nitroalkan-2-ols. In the next step, reaction of the sugar-derived (Z)-1-bromo-1-nitroalkenes with o-hydroxybenzaldehydes afforded enantiopure (2S,3S,4S)-3-bromo-3,4-dihydro-4-hydroxy-3-nitro-2H-1-benzopyrans, which, upon SmI2-promoted β-elimination, yielded chiral enantiopure 2-C-glycosyl-3-nitrochromenes.

Iron(III) complexation by Vanchrobactin, a siderophore of the bacterial fish pathogen Vibrio anguillarum

The bacterial fish pathogen Vibrio anguillarum serotype O2 strain RV22 produces the mono catecholate siderophore Vanchrobactin (Vb) under conditions of iron deficiency. Vb contains two potential bidentate coordination sites: catecholate and salicylate groups. The iron(III) coordination properties of Vb is investigated in aqueous solutions using spectrophotometric and potentiometric methods. The stepwise equilibrium constants (log K) for successive addition of Vb dianion to a ferric ion are 19.9; 13.3, and 9.5, respectively, for an overall association constant of 42.7. Based on the previous results, we estimated the equilibrium concentration of free iron(III) under physiological conditions for pH 7.4 solution containing 10(-6) M total iron and 10(-5) M total Vb as pFe = 20 (=-log[Fe(3+)]). The Vb model compounds catechol (Cat) and 2,4-dihydroxy-N-(2-hydroxyethyl)benzamide (Dhb) have also been examined, and the obtained results show that the interaction of the whole system of Vb that contains the ferric-chelating groups of both Dhb and Cat, is synergically greater than the separate parts; i.e. Vb is the best chelating agent either in acid or basic media. In summary, bacteria employing Vb-mediated iron transport thus are able to compete effectively for iron with other microorganisms within which they live.

Indium-mediated allylation and Reformatsky reaction on glyoxylic oximes under ultrasound irradiation

A novel and more convenient method for the indium-promoted allylation of glyoxylic oximes based on the use of ultrasonic waves is reported. A similar procedure was used to develop the first example reported in the literature of an indium-mediated Reformatsky reaction on oxime ethers.

Spirocyclic nucleosides in medicinal chemistry: an overview.

This review describes some spiro- and pseudospironucleoside derivatives as well as their biological and pharmacological applications.

An overview of key routes for the transformation of sugars into carbasugars and related compounds

This chapter reports an overview of the most relevant routes developed for the transformation of sugars into carbasugars and related compounds.

Two new examples of the rare C→O migration of ethoxycarbonyl groups

Abstract Two new examples of a carbon→oxygen ethoxycarbonyl group shift are described. Treatment of 3-ethoxycarbonylnitromethyl-1,2- O -isopropylidene-6- O - p -toluenesulfonyl-α- d -allofuranose ( 4 ) with Bu 4 NF leads to a rearrangement to 5- O -ethoxycarbonyl-1,2- O -isopropylidene-3-nitromethyl-6- O - p -toluenesulfonyl-α- d -allofuranose ( 8 ). Similar treatment of ethyl-3- O -benzyl-6-deoxy-6-nitro- d , l -glycero- d -glucoheptofuronate ( 12 ) gives 3- O -benzyl-4- O -ethoxycarbonyl-6-deoxy-6-nitro- d -glucopyranose ( 16 ).

3-O-tert-Butyldimethylsilyl-2,2′:5,6-di-O-isopropylidene-2-C-hydroxymethyl-d-1,4-gluconolactone

The title compound, C19H34O7Si, is derived from the minor component of a Kiliani reaction on d-fructose. Its crystal structure has been determined in order to confirm its structure and stereochemistry.

Chromium-mediated stereoselective synthesis of carbohydrate-derived (E)-α,β-unsaturated esters or amides.

A chromium-mediated novel synthesis of carbohydrate-derived di- and trisubstituted (E)-α,β-unsaturated esters or amides from a range of dichloroesters or amides and a variety of sugar aldehydes is reported. The process took place with total stereoselectivity and in high yields. A mechanism based on a sequential chromium-promoted aldol-type reaction and a completely stereoselective β-elimination reaction is proposed to explain these results.