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At least 217 records · Page 12Linked to original sources
PubMed2002

Application of the anomeric samarium route for the convergent synthesis of the C-linked trisaccharide alpha-D-Man-(1-->3)-[alpha-D-Man-(1-->6)]-D-Man and the disaccharides alpha-D-Man-(1-->3)-D-Man and alpha-D-Man-(1-->6)-D-Man.

Studies are reported on the assembly of the branched C-trisaccharide, alpha-D-Man-(1-->3)-[alpha-D-Man-(1-->6)]-D-Man, representing the core region of the asparagine-linked oligosaccharides. The key step in this synthesis uses a SmI(2)-mediated coupling of two mannosylpyridyl sulfones to a C3,C6-diformyl branched monosaccharide unit, thereby assembling all three sugar units in one reaction and with complete stereocontrol at the two anomeric carbon centers. Subsequent tin hydride-based deoxygenation followed by a deprotection step produces the target C-trimer. In contrast to many of the other C-glycosylation methods, this approach employes intact carbohydrate units as C-glycosyl donors and acceptors, which in many instances parallels the well-studied O-glycosylation reactions. The synthesis of the C-disaccharides alpha-D-Man-(1-->3)-D-Man and alpha-D-Man-(1-->6)-D-Man is also described, they being necessary for the following conformational studies of all three carbohydrate analogues both in solution and bound to several mannose-binding proteins.

Carbohydrate Conformation↗
PubMed2004

Trifluoroacetyl-activated nitrogen-nitrogen bond cleavage of hydrazines by samarium(II) iodide.

[reaction: see text] Trifluoroacetyl derivatives of hydrazines undergo clean and efficient reductive cleavage of the N-N bond with SmI(2) in the presence of MeOH. After N-trifluoroacetylation, acyl-, aryl-, and alkyl-substituted hydrazines are reductively cleaved by this method to afford trifluoroacetamides in yields ranging from 70 to 96%. These conditions accommodate alkene functionality, avoid racemization, and furnish chiral amines bearing a readily removable TFA protecting group.

Hydrazines↗
PubMed2005

Samarium diiodide promoted generation and asymmetric hydroxyalkylation of N,O-diprotected (3S)-3-pyrrolidinol 2-carbanions.

The N,O-diprotected chiral nonracemic 2-pyridyl 3-pyrrolidinol-2-yl sulfide 5a undergoes efficient SmI(2) mediated reduction to give the N,O-diprotected 3-pyrrolidinol 2-carbanion intermediate D, which reacted under Barbier-type conditions with ketones and aldehydes to afford the protected N-alpha-hydroxyalkyl-3-pyrrolidines 10b-h with excellent diastereoselectivity at the newly formed chiral center in the pyrrolidine ring. Application of the present method led to the formal asymmetric syntheses of (2R,3S)-2-hydroxymethyl-3-pyrrolidinol (2) and (2S,3S)-3-hydroxyproline (12). [reaction: see text]

Anions↗
PubMed1991

Co-fluorescence of europium and samarium in time-resolved fluorimetric immunoassays.

In the presence of an excess of Y3+, the fluorescence intensities of Eu3+ and Sm3+, chelated with benzoyltrifluoroacetone (BTA) or thenoyltrifluoroacetone (TTA) in an aqueous solution containing 1,10-phenanthroline, were increased by factors ranging from 209- to 811-fold. This co-fluorescence phenomenon was used in a highly sensitive time-resolved fluorimetric detection of the lanthanides, Eu3+ and Sm3+. The detection limits of Eu3+ in the BTA- and TTA-based solutions were 4 and 15 fmol dm-3, respectively. The detection limits of Sm3+ were 0.11 and 0.12 pmol dm-3, respectively. The co-fluorescence enhancement systems were also applied in the double-label time-resolved fluorimetric immunoassay of luteinizing hormone and follicle stimulating hormone using specific antibodies labelled either with Eu3+ or Sm3+. The co-fluorescence enhancement solution was superior as compared with the commercial 'direct' fluorescence enhancement solution based on the acidic solution of beta-naphthoyltrifluoroacetone, trioctylphosphine oxide and Triton X-100, in respect to the signal level obtained and the sensitivity. It is suited to time-resolved fluorimetric immunoassays in which particularly high detection sensitivities are required, and it can also be used in double-label assays employing Eu3+ and Sm3+ chelate labels.

Europium↗
PubMed1987

Samarium-145: a new brachytherapy source.

A new radiation source has been produced for brachytherapy, with radiation energies slightly above those of 125I, and a T1/2 of 340 d. This source, 145Sm, is produced by neutron irradiation of 144Sm (96.5% enriched). Decay is by electron capture with 140 K x-rays per 100 disintegrations in the energy region between 38-45 keV, plus 13 gamma-rays at 61 keV. These sources are encapsulated in Ti tubes, approximately 0.8 mm X 4.5 mm, and have been developed for temporary implantation in brain and ocular tumours. The 38-61 keV photons should make such sources easy to shield, while providing a dose distribution from source arrays somewhat more homogeneous than that from 125I. In addition, the 340 d half life of 145Sm permits its use for times significantly longer than that of 60 d 125I. While the 145Sm sources have been designed primarily for implantation in a brain tumour, they should be useful for almost any conventional brachytherapy application.

Brachytherapy↗
PubMed2000

Reductive dimerization of alkylidenemalonates using samarium(II) diiodide and 1H-NMR behavior of the dimers, 2,3-diaryl-1,1,4,4-butanetetracarboxylates.

Alkylidenemalonates were readily dimerized in the presence of SmI2 to give 2,3-disubstituted 1,1,4,4-butanetetracarboxylates as mixtures of meso and racemic isomers in moderate to good yields. The structure of the less polar isomer of tetraethyl 2,3-diphenyl-1,1,4,4-butanetetracarboxylate was determined by X-ray crystallographic analysis to be the meso form. Characteristic 1H-NMR behavior of the meso and racemic isomers is also discussed.

Butanes↗
PubMed2005

Accumulation and distribution of samarium-153 in rat brain after intraperitoneal injection.

It is well known that rare earth elements (REEs) have come into extensive use in a number of fields. As a result, REEs are becoming closely related to human's daily life. However, until now, the distributions of REEs in the brain are not yet very clear. In this study, Sprague-Dawley male rats were intraperitoneally injected with 0.25 mL of (153)SmCl(3) solution (containing 10 microg Sm). The brains were perfused with saline to minimize the blood influence. The radioactivities of (153)Sm in the five brain regions (hypothalamus, cerebellum, hippocampus, corpus striatum, and cerebral cortex) were counted. The results suggested that Sm did enter into the brain. Although only about 0.0003% of the given dose was accumulated in the brain, Sm seemed to be remain in the brain for a long time. The highest amounts and lowest concentrations of (153)Sm were found in the cerebral cortex, and the highest concentrations of (153)Sm were found in the hypothalamus.

Animals↗