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Semi-preparative isolation and characterization of a principal oxidative degradation product in galantamine hydrobromide by LC-ESI-MSn and 2D-NMR

Thomas S., Paul S. K., Agarwal A., Mathela C. S.

Acta Chromatographica

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2014

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Vol. 26, no. 3

429--438

EN

Galantamine hydrobromide was subjected to oxidative stress degradation using hydrogen peroxide and analyzed as per the chromatographic conditions described in European Pharmacopoeia. The drug showed considerable degradation at ambient temperature resulting in the formation of two degradation products at relative retention times (RRTs) 0.63 and 2.52. The minor degradant at RRT 0.63 was identified as galantamine N-oxide. The principal degradant formed at RRT 2.52 was found to be unknown and has not been reported previously. The unknown impurity was identified by liquid chromatography-tandem mass spectrometry (LC-MS/MS) followed by isolation using semi-preparative high-performance liquid chromatography (HPLC). The isolated impurity was characterized using one-dimensional, two-dimensional nuclear magnetic resonance spectroscopy (1D and 2D NMR) and elemental analysis (EA). The principal degradant was found to be formed due to the generation of bromine and subsequent attack on the aromatic ring via in situ reaction between hydrogen bromide and hydrogen peroxide. The unknown impurity was characterized as (4aS,6R,8aS)-5,6,9,10,11,12-hexahydro-1-bromo-3-methoxy-11-methyl-4aH-[1]benzofuro [3a,3,2-ef] [2] benzazepin-6-ol.

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Quercetin and Kaempferol Glycosides from Ficaria verna Flowers and Tgheir Structure Studied by 2D NMR Spectroscopy

Tomczyk M., J. Gudej J.

Polish Journal of Chemistry

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2002

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Vol. 76 / nr 11

1601-1605

EN

From the flowers of Ficaria verna Huds. (Ranunculaceae), two flavonol triglycosides were isolated and their structures were elucidated by spectroscopic analysis (UV, NMR, MS) as 3-O-[_-L-rhamnopyranosyl-(1_6)-_-D-glucopyranosyl]-7-O-(_-D-glucopyranosyl) - quercetin (1) and 3-O-[_-L-rhamnopyranosyl-(1_6)-_-D-glucopyranosyl]-7- O-(_-D-glucopyranosyl) - kaempferol (2). In addition, the structure of 1 was determined using homo- and heteronuclear 2D NMR techniques.

3

Cyclic Analogue of Human Heat Shock Protein 70(29-42) Fragment. Synthesis, Conformational Studies and Evaluation of Its Immunogenicity

Karawajczyk B., Wirkus-Romanowska I., Wysocki J., Rolka K., Maćkiewicz Z., Głośnicka R., Kupryszewski G.

Polish Journal of Chemistry

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2001

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Vol. 75, nr 2

265-273

EN

The cyclic hexadecapeptide containing human heat shock protein 70(29-42) fragment cyclized by the disulfide bridge between two L-cysteine residues introduced at the N- and C-termini was synthesized by the solid phase method. It was established that the cyclic analogue, contrary to its linear counterpart, had much lower ability to generate immune response in rabbits. Conformational studies of cyclic peptide performed using 1D and 2D 1H-NMR spectroscopy in conjunction with theoretical conformational analysis revealed that the cyclization constrained the 3D structure of this peptide, reflected by the observed rate of cis/trans isomerization of Arg9-Thr10 peptide bond and the presence of Gly7-Asn8 peptide bond in cis geometry.We, therefore, postulate that the conformational flexibility in the case of Human Heat Shock Protein fragments is a key element for their immunogenicity.

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Cyclic Analogues of Proline-Rich Protein Fragments : part III. Synthesis of New Analogues, Conformational Studies and Evaluation of Immunotropic Activity

Wirkus-Romanowska I., Rodziewicz-Motowidło S., Miecznikowska H., Rolka K., Janusz M., Szymaniec S., Zabłocka A., Fortuna W.

Polish Journal of Chemistry

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2000

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Vol. 74, nr 8

1129-1141

EN

The immunotropic activity of peptides studied evaluated in the murine system indicated that they are as active as the linear precursor in the resistance to hydrocortisone, but did not show activity in the human system. As reported previously, similar immunotropic profiles were observed in the case of two cyclic analogues. Superposition of most representative conformations of all four peptides in the fragment mentioned above (RMSD of A carbons is0.86 A) leads to the conclusion that this hexapeptide segment might be considered as bioactive.

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Structure Elucidation of Saponins and Related Natural Products by NMR Spectroscopy

Duddeck H.

Polish Journal of Chemistry

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1999

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vol. 73 nr 1

163-171

EN

For a number of examples strategies are developed and explained how structures of complex natural products, such as triterpene glycosides and related compouns, can be efficiently elucidated by application of modern one- and two-dimensional NMR techniques.

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Cyclic Analogues of Proline-Rich Protein Fragments : Part II : Conformational Studies Using NMR Spectroscopy and Theoretical Conformational Analysis

Rodziewicz S., Wirkus-Romanowska I., Ciurak M., Miecznikowska H., Kupryszewski G., Czaplewski C., Liwo A., Rolka K.

Polish Journal of Chemistry

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1999

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Vol. 73, nr 10

1697-1710

EN

These peptides were designed based on the immunoregulatory activity of linear peptides obtained after chymotrypsin digestion of PRP. Despite the fact that the structures of both analogues cannot be interpreted in terms of a single conformation, the superposition of the most populated conformations of the cyclic peptides studied revealed a similar geometry for the Tyr-Val-pro-Leu-Phe-Pro fragment (RMSD=1.6 A) in both peptides and therefore might be considered to be responsible for the biological activity.