Biomedical subjects

V Brecht

Publications and source records attributed to V Brecht.

4 recordsLinked to original sources

PubMed2001

Parameters influencing the determination of liposome lamellarity by 31P-NMR.

The lamellarity of liposomes influences to a great extent the encapsulation efficiency, the efflux rate of liposomally encapsulated material, and the fate of a drug after cellular uptake. 31P-NMR in combination with the use of chemical shift reagents has been described for the determination of lamellarity of liposomes and this study was performed to evaluate the applicability of 31P-NMR analysis as published in the past. To date, very few details about the required conditions throughout the measurements are known. In this study the influence of various parameters on the measurement, such as different buffers with changing ion concentrations, varying pH and different shift reagents at increasing concentrations was investigated. Results were discussed by using cryo-electronmicroscopy as a reference method. The data of this study show that 31P-NMR might not result in the correct determination of liposome lamellarity, depending on the experimental settings and the shape of the liposomes.

Indicators and Reagents↗

PubMed2001

Germacranolides from Mikania guaco.

Fourteen novel sesquiterpene lactones of the germacranolide type have been isolated from the aerial parts of Mikania guaco: six costunolide, two melampolide and six germacra-4-trans,10(14),11(13)-trien-12.6alpha-olide derivatives. Except for one compound all the others possess a carbonyl function at C-9. Eight were obtained in the form of four isomer pairs which were difficult to separate. Structure elucidation was based on mass and ID and 2D NMR measurements. Low energy conformations were obtained by quantum mechanical calculations. Pyrrolizidine alkaloids could not be detected.

Asteraceae↗

PubMed2000

Phytochemical investigation of Aglaia rubiginosa.

The phytochemical investigation of a methanolic leaf extract of Aglaia rubiginosa furnished 15 isoprenoid constituents, eight of which represented new natural entities. Two androstane derivatives (1 and 2), previously synthesized, and also obtained by microbiological transformations; an extraordinary 17-octanor-cycloartane-ring-A-seco acid (3); four cycloartane-type triterpenes (4-7); and three unusual cholesterol derivatives (8-10) were isolated, along with two known dammaranes (11 and 12), a stigmastandiol (13), and beta-sitosterol and its beta-D-glucoside. Spectroscopic structure elucidation of the new natural products (1-3, 6, 7, 8-10) is described.

Asia, Southeastern↗

PubMed2000

Phytochemical investigation of Aglaia andamanica.

Four new compounds, the limonoid 24-epi-melianodiol (8), the tirucallane aglaiodiol (9), and the two cyclopentatetrahydrobenzopyran derivatives pyramidaglain A (11) and B (12) were isolated from the leaves of Aglaia andamanica Hiern (Meliaceae), together with the eleven known constituents beta-sitosterol, beta-sitosterol glucoside, cycloart-23E-ene-3 beta,25-diol (1), three flavonoids 5-hydroxy-3,4',7-trimethoxyflavone (2), retusin (3) and pachypodol (4), the tirucallane 24-epi-piscidinol A (5), the lignan yangambin (6), the limonoid melianodiol (7), the bisamide pyramidatine (10) and the amino acid N-methyl-trans-4-hydroxy-L-proline (13). All structures were established by means of detailed spectroscopic analysis.

Molecular Structure↗