M. Luisa Jimeno

Synthesis and characterization of a potential prebiotic trisaccharide from cheese whey permeate and sucrose by Leuconostoc mesenteroides dextransucrase.

The production of new bioactive oligosaccharides is currently garnering much attention for their potential use as functional ingredients. This work addresses the enzymatic synthesis and NMR structural characterization of 2-α-D-glucopyranosyl-lactose derived from sucrose:lactose and sucrose:cheese whey permeate mixtures by using a Leuconostoc mesenteroides B-512F dextransucrase. The effect of synthesis conditions, including concentration of substrates, molar ratio of donor/acceptor, enzyme concentration, reaction time, and temperature, on the formation of transfer products is evaluated. Results indicated that cheese whey permeate is a suitable material for the synthesis of 2-α-D-glucopyranosyl-lactose, giving rise to yields around 50% (in weight respect to the initial amount of lactose) under the optimum reaction conditions. According to its structure, this trisaccharide is an excellent candidate for a new prebiotic ingredient, due to the reported high resistance of α-(1→2) linkages to the digestive enzymes in humans and animals, as well as to its potential selective stimulation of beneficial bacteria in the large intestine mainly attributed to the two linked glucose units located at the reducing end that reflects the disaccharide kojibiose (2-α-D-glucopyranosyl-D-glucose). These findings could contribute to broadening the use of important agricultural raw materials, such as sucrose or cheese whey permeates, as renewable substrates for enzymatic synthesis of oligosaccharides of nutritional interest.

Efficient synthesis and characterization of lactulosucrose by leuconostoc mesenteroides B-512F dextransucrase

This work describes an efficient enzymatic synthesis and NMR structural characterization of the trisaccharide β-D-galactopyranosyl-(1→4)-β-D-fructofuranosyl-(2→1)-α-D-glucopyranoside, also termed as lactulosucrose. This oligosaccharide was formed by the Leuconostoc mesenteroides B-512F dextransucrase-catalyzed transfer of the glucosyl residue from sucrose to the 2-hydroxyl group of the reducing unit of lactulose. The enzymatic reaction was carried out under optimal conditions, i.e., at 30 °C in 20 mM sodium acetate buffer with 0.34 mM CaCl(2) at pH 5.2, and the effect of factors such as reaction time (0-48 h), enzyme charge (0.8, 1.6, and 2.4 U mL(-1)), and sucrose:lactulose concentration ratios (20:40, 30:30, and 40:20, expressed in g/100 mL) on the formation of transfer products were studied. The highest formation in lactulosucrose was attained at 8 and 24-32 h by using 20%:40% and 30%:30% sucrose:lactulose mixtures, respectively, with 1.6 or 2.4 U mL(-1) dextransucrase, leading to lactulosucrose yields of 27-35% in weight respect to the initial amount of lactulose. Furthermore, minor tetra- and pentasaccharide, both probably derived from lactulose, were also detected and quantified. Likewise, the capacity of lactulosucrose to act as D-glucosyl donor once the sucrose was consumed, could explain its decrease from 16 to 24 h when the highest charge of dextransucrase was used. Considering the chemical structure of the synthesized oligosaccharides, lactulosucrose and its derivatives could potentially be excellent candidates for an emerging prebiotic ingredient.

The reaction of pyranoside 2-uloses with DAST revised. Synthesis of 1-fluoro-ketofuranosyl fluorides and their reactivity with alcohols

Abstract We have reinvestigated the reaction of α-pyranosides-2-uloses 13 , 14 , 19 and 24 with DAST and shown that the 1,2-difluorinated compounds 17 , 18 and 25 are produced by a ring-contraction reaction. The reaction of 18 with benzyl alcohol gives the tri-benzyl derivative 26 or compound 27 , depending on the reaction conditions. Treating 17 with 2-naphthol produced the spiranic compounds 29 – 31 . The reaction of 17 with bis(trimethylsilyl)uracil produced the mononucleoside 28 , which preserves the fluorine atom in the more substituted carbon.

A Theoretical and Experimental Study of the Interaction of C6F6 with Electron Donors

The NMR effects produced on the nitrogen absolute shieldings in a series of electron donors when they interact with hexafluorobenzene, C6F6, have been theoretically studied. The complexes have been optimized at the B3LYP/6-311++G** level and the NMR shieldings have been calculated using the GIAO method. The results obtained have allowed devising an experiment (C6F6···NCCH3 complex) that is compatible with the theoretical calculations.

1H NMR Study of the Conformation of Metallapentacycles N—C—C—O—M [M = Rh(III) and Ir(III)] Resulting in a Karplus‐Type Relationship for Vicinal H–C(sp3)–N(sp13)–H Coupling Constants

The complete analysis of the 1H NMR spectra of [(C5Me5)Ir(glycinate)Cl] and [(C5Me5)Ir(N‐methyl‐ glycinate)Cl] provide information for the conformational analysis of the five‐membered N—C—C—O—Ir ring. A Karplus relationship has been established for these metallacycles [3J(H,H) = 8.9 cos2 ϕ‐1.0 cos ϕ+0.8].

Synthesis of potentially-bioactive lactosyl-oligofructosides by a novel bi-enzymatic system using bacterial fructansucrases

Efficient enzymatic synthesis of lactosyl-oligofructosides (LFOS) with a degree of polymerization from 4 to 8 was achieved in the presence of sucrose:lactosucrose and sucrose:lactose mixtures by transfructosylation reaction. The main synthesized LFOS which consist of β-2,1-linked fructose to lactosucrose: β-d-galactopyranosyl-(1→4)-α-d-glucopyranosyl-[(1→2)-β-d-fructofuranosyl]n-(1→2)-β-d-fructofuranoside (where n refers to the number of transferred fructose moieties) was structurally characterized by nuclear magnetic resonance (NMR). The maximum formation of LFOS was 81% (in weight with respect to the initial amount of lactosucrose) and was obtained after 24h of transfructosylation reaction based on sucrose:lactosucrose (250gL-1 each) catalyzed by an inulosucrase from Lactobacillus gasseri DSM 20604 (IS). The production of LFOS in the presence of sucrose:lactose mixtures required a previous high-yield lactosucrose synthesis step catalyzed by using a levansucrase from Bacillus subtilis CECT 39 (LS) before the inulosucrase-catalyzed reaction. This novel one-pot bi-enzymatic system led to the synthesis of about 22% LFOS in weight, with respect to the initial amount of lactose (250gL-1). The results revealed a high specificity for the substrate involved in the inulosucrase-catalyzed reaction given that, although lactosucrose (O-β-d-galactopyranosyl-(1→4)-O-α-d-glucopyranosyl-(1→2)-β-d-fructofuranoside) acted as a strong acceptor of β-2,1-linked fructose, lactose (β-d-galactopyranosyl-(1→4)-α-d-glucose) was found to be an extremely weak acceptor.

Rotational isomerism in 6-β-D-glucopyranosides of methyl-1,2,6-thiadiazin-3(2H)-one 1,1-dioxides

Glucopyranosides of methyl-1,2,6-thiadiazin-3(2H)-one 1,1-dioxides have been synthesized and their rotational isomerism studied. Two of them exist, in solution, as mixtures of syn : anti rotamers, at room temperature. In the case of the diglucoside, the barriers to rotation about both glycosidic bonds have been calculated by dynamic 13C NMR.

Stereochemical and Steric Control of Photophysical and Chiroptical Properties in Bichromophoric Systems

Stereochemical and steric control of the relative spatial arrangement of the chromophoric units in multichromophoric systems offers an interesting strategy for raising unusual and appealing light-induced emission states. To explore and exploit this strategy, a series of conformationally restricted boron-dipyrromethene (BODIPY) dimers were designed by using tartaric acid as a symmetrical connector between the boron atoms of the dyes. The variety of stereoisomeric forms available for this bis(hydroxy acid) allows the relative spatial orientation of the chromophoric units in the dimer to be modified, which thus opens the door to modulation of the photophysical and chiroptical properties of the new bichromophoric systems. Chromophore alkylation introduces an additional level of control through distance-dependent steric interactions between the BODIPY units in the dimer, which also modulates their relative spatial disposition and properties.

FAILED ATTEMPT TO INDUCE CHIRALITY USING A MAGNETIC FIELD: THE CASE OF CHIRAL HELICITY OF TRIS-(2-METHYLBENZIMIDAZOL-1-YL)METHANE

Recently, Breitmaier and coworkers described enantioselective reactions in a static magnetic field (1). They use, as a model, the transformation of carbonyl compounds (aldehydes and ketones) into carbinols using Grignard reagents and complex metal hydrides. We decided to test this method in a quite different reaction. For this purpose, we selected the synthesis of tris-(2-methylbenzimidazol-l-yl)methane 3 from 2methylbenzimidazole (2MeBz) 1 and chloroform 2 under PTC conditions (2).

Synthesis, X-ray structure, and nuclear magnetic resonance (1H and 13C) studies of ruthenium(II) complexes containing pyrazolyl ligands

The synthesis and n.m.r. spectra (1H and 13C) are reported for 24 p-cymeneruthenium complexes belonging to one of the following families: [Ru(MeC6H4Pri-p)(acac)X](3)–(9), [Ru(MeC6H4Pri-p)(acac)L]BF4(10)–(17), [Ru(MeC6H4Pri-p)ClL2]BF4(19)–(22), and [Ru(MeC6H4Pri-p)L3][BF4]2(23), [Ru(MeC6H4Pri-p)XL2]BF4(24), and [Ru(MeC6H4Pri-p)X2L](25), where X = Br, I, N3, pz, mpz, dmpz, or idz, and L = pyridine, PPh3, CNBut, P(OMe)3, Hpz (pyrazole), Hmpz (3-methylpyrazole), Hdmpz (3,5-dimethylpyrazole), and Hidz (indazole) for complexes (3)–(17), and only azoles (pyrazoles and indazole) for the remaining ones. Crystals of [Ru(MeC6H4Pri-p)(pz)(Hpz)2]BF4 are monoclinic, space group P21/c, with a= 9.882 6(2), b= 13.966 3(3), c= 31.690 2(15)A, β= 94.650(3)°, and Z= 8. The structure was determined by X-ray diffraction and refined to R= 0.045 (R′= 0.036). There are two crystallographic units, each having an intramolecular hydrogen bond between a pyrazole and a pyrazolate ring, and another between the other pyrazole ligand and the BF4 anion. The n.m.r. data (δ and J) of the azole complexes were carefully determined and are thoroughly discussed.