Biomedical subjects
Publications and source records attributed to C Steinbeck.
Three new isoflavonoids, griffonianone A (1), B (2) and C (4) were isolated from the root bark of Millettia griffoniana, along with the known maximaisoflavone G (5) and 7-hydroxy-6-methoxy-3',4'-methylenedioxyisoflavone (6). Their structures were assigned on the basis of spectroscopic data and chemical transformations.
The last two or three years have seen exciting developments in the field of computer-assisted structure elucidation (CASE) with a number of programs becoming commercially or freely available. This was the conditio sine qua non for CASE to be widely applied in the daily work of bench chemists and spectroscopists. A number of promising applications have been published in the area of structure generators, deterministic and stochastic CASE tools and property predictions, including the automatic distinction between natural products and artificial compounds, as well as the determination of 3-D structure from a connection table based on IR spectroscopy. Advancements in coupling techniques between chromatographic and spectroscopic methods demonstrate progress towards a fully automated structure elucidation or identification process starting at the earliest steps of obtaining crude extracts.
Reported here is the solution structure of the aminoacyl-DNA duplex (W-TGCGCAC)(2). This duplex forms a continuously pi-stacked helix consisting of both nucleobases and amino acid side chains. According to NMR and UV analyses, the duplex melts in a cooperative transition and with 1.3-1.8% greater hyperchromicity than the control duplex (TGCGCAC)(2). A van't Hoff analysis of UV melting points at different concentrations shows that the two tryptophan residues contribute 4.8 kcal/mol to the DeltaH degrees of complex formation at 10 mM salt concentration and less than 1 kcal/mol at 150 mM salt. The entropic cost for duplex association in the presence of the amino acid residues is 13 cal/molK greater than that for the control at 10 mM salt concentration, and 3 cal/molK lower than that of the control at 0.15 ionic strength. The conformation of W-TGCGCAC in duplex form, determined via restrained torsion angle molecular dynamics, shows an undisturbed B-form DNA duplex with dangling 3'-termini. The tryptophanyl residue at the 5'-terminus packs tightly against T2 and the proximal part of adenine, without engaging in hydrogen bonding. While not providing strong enthalpic net stabilization of the duplex, the tryptophan "cap" on the duplex does seem to reduce the fraying at the termini, indicating a subtle balance of entropic and enthalpic factors contributing to the molecular dynamics. The structure also shows that, at least in the present sequence context, stacking on the terminal base pair is more favorable than intercalation, probably because the enthalpic cost associated with breaking up the stacking between DNA base pairs cannot be paid for by favorable pi-stacking interactions with the indole ring of tryptophan. These results are of importance for understanding stacking interactions in protein-DNA complexes, particularly those in enzyme-substrate complexes involving exposed nucleobases.
BACKGROUND: Selection experiments involving chemical libraries are routinely used in the pharmaceutical industry for finding and optimizing lead compounds. In principle, almost any process involving a binding event or a reaction could be probed systematically with chemical libraries prepared by combinatorial synthesis. Traditionally, however, the vast majority of library members cannot be monitored during the selection, making a systematic correlation of structure and activity difficult. To interpret selection experiments on the level of all library components, monitoring technologies are required that give a unique and quantitative spectroscopic signal for every compound in a mixture. RESULTS: Quantitative matrix-assisted laser desorption mass spectrometry of libraries of porphyrins and peptide-DNA hybrids consisting of 2-35 compounds is described. Porphyrin libraries were subjected to in vitro selections for liposome incorporation and binding to a protein pocket. It was shown that mesohydroxyphenyl substituted porphyrins, known high activity photosensitizers of tumors, are preferentially incorporated in liposome membranes. A mixture of peptide-DNA hybrids was assayed for the nuclease stability of its components. CONCLUSIONS: Small libraries of non-isobaric compounds can be exhaustively or near-exhaustively monitored by mass spectrometry. Monitored selection experiments can yield detailed structure-activity maps in a single experiment, speeding up drug discovery and the probing of biochemically relevant recognition events. It is proposed that monitored assays for target binding, membrane partitioning, and biostability could be run in parallel, to select drug candidates combining several favorable properties in 'multidimensional' selection experiments.
A so far unknown 4-methyl-7-hydroxyphthalideglycoside has been isolated from the methanol extract of the bark of Quillaja saponaria molina. Its structure has been established from NMR experiments as 7-O(-)[beta-glucopyranosyl-(1-->6)-beta-arabinopyranosyl]-7-hydrox y-4-methy l -1[3H]-isobenzofuranone. Two known compounds, 3,4,5-trimethoxyphenyl-beta-D-glucopyranoside and lyoniresinol-3 alpha-O-beta-D-glycopyranoside were also identified.
We studied the effects of slow-release gallopamil two-times 100 mg on exercise-induced ST-segment depression, as well as on the incidence of spontaneous myocardial ischemia detected by long-term ECG monitoring for 48 h in patients with coronary artery disease and stable angina pectoris. Three out of nine patients included in this study had to be excluded (because of frequent ventricular extrasystoles, paroxysmal atrial fibrillation, and development of instable angina pectoris). In all of the remaining six patients, the substance led to a doubling of working capacity (watts X min) evaluated by bicycle ergometry, paralleled by an increase of exercise duration until the occurrence of ST-segment depression greater than or equal to 0.1 mV. The number of spontaneous episodes of myocardial ischemia during long-term ECG recording, ranging 1-13 during control, decreased in all patients, paralleled by a decrease of the mean duration of ischemic episodes. On the other hand, no significant negative chronotropic effect was observed. Therefore, these preliminary results of this open-study protocol confirm the antischemic effects of slow-release gallopamil given 100 mg two times daily; on the other hand these promising results need to be confirmed in a doubleblind, placebo-controlled trial.
Two-dimensional-electrophoretic analysis has been applied to non-neoplastic mammary epithelium from eight healthy women, tumor tissue from eight "diploid" mammary adenocarcinomas, and tumor tissue from eight "aneuploid" mammary adenocarcinomas. Compared with non-neoplastic mammary epithelium, a slight numerical net non-neoplastic mammary epithelium, a slight numerical net increase of the protein spots was detected in "diploid" tumors and a marked increase in "aneuploid" tumors. Two prominent spots were present in all 16 malignant tissues examined and absent in all eight non-neoplastic tissues (silver staining method). The results suggest that a difference in the composition of cellular proteins exists both between non-neoplastic mammary cells and malignant tumor cells, and between "diploid" and "aneuploid" tumors.
The program package SENECA for Computer-Assisted Structure Elucidation (CASE) of organic molecules is described. SENECA is written completely in the programming language Java and divided into a server, a client, and a gatekeeper part. While the client allows for input of spectroscopic information, the server part performs the actual structure elucidation by stochastically walking through constitution space while optimizing the molecule toward agreement with given spectral properties. The convergence is guided by simulated annealing. The gatekeeper administers a list of server processes, which can be retrieved by the client. The package is completely platform-independent and its server part can be distributed over the Internet or an intranet using a heterogeneous network of almost any number and type of computers, thus allowing for parallel CASE computations on ordinary networks, present in almost any institution.