Ascorbigen A-NMR identification.

The connectivities of all atoms in ascorbigen A, an important metabolite, were determined unambiguously for the first time. The connectivity between carbon atoms was established by 2D INADEQUATE, and one-bond 13 C-13 C coupling constants were determined for all pairs of directly connected carbon atoms except for two strongly coupled carbon pairs. The 13 C-13 C coupling in one of the pairs was proved by a modification of standard INADEQUATE; however, the signals from the other pair were too weak to be observed. The connectivity within the two strongly coupled C-C pairs was confirmed by a combination of COSY and gHSQC; the latter experiment also identified all C-H bonds. The proton nuclear magnetic resonance (1 H NMR) spectra in dry dimethyl sulfoxide allowed identification and assignment of the signals due to NH and OH protons. The derived structure, 3-((1H-indol-3-yl)methyl)-3,3a,6-trihydroxytetrahydrofuro[3,2-b]furan-2(5H)-one, agrees with the structure suggested for ascorbigen A in 1966. The density functional theory (DFT) calculations showed that among 16 possible stereoisomers, only two complied with the almost zero value of the measured 3 J(H6-H6a). Of the two stereoisomers, 3S,3aS,6S,6aR and 3R,3aR,6R,6aS, the latter was excluded on synthetic grounds. The nuclear Overhauser effect measurements unveiled close proximity between H2' proton of the indole and the H6a proton of the tetrahydrofuro[3,2-b]furan part. Detailed structural interpretation of the measured NMR parameters by means of DFT NMR was hampered by rotational flexibility of the indole and tetrahydrofuro[3,2-b]furan parts and inadequacy of Polarizable Continuum Model (PCM) solvent model.

Synthesis, Analysis, Cholinesterase-Inhibiting Activity and Molecular Modelling Studies of 3-(Dialkylamino)-2-hydroxypropyl 4-[(Alkoxy-carbonyl)amino]benzoates and Their Quaternary Ammonium Salts.

Tertiary amines 3-(dialkylamino)-2-hydroxypropyl 4-[(alkoxycarbonyl)amino]benzoates and their quaternary ammonium salts were synthesized. The final step of synthesis of quaternary ammonium salts was carried out by microwave-assisted synthesis. Software-calculated data provided the background needed to compare fifteen new resulting compounds by their physicochemical properties. The acid dissociation constant (pKa) and lipophilicity index (log P) of tertiary amines were determined; while quaternary ammonium salts were characterized by software-calculated lipophilicity index and surface tension. Biological evaluation aimed at testing acetylcholinesterase and butyrylcholinesterase-inhibiting activity of synthesized compounds. A possible mechanism of action of these compounds was determined by molecular modelling study using combined techniques of docking; molecular dynamics simulations and quantum mechanics calculations.

Synthesis and Characterization of New 3-(4-Arylpiperazin-1-yl)-2-hydroxypropyl 4-Propoxybenzoates and Their Hydrochloride Salts.

Five new 3-(4-arylpiperazin-1-yl)-2-hydroxypropyl 4-propoxybenzoates were designed and synthesized as potential dual antihypertensive agents. The compounds were prepared as free bases and subsequently transformed to hydrochloride salts. The position of protonation of nitrogen atoms in the piperazine ring of hydrochloride salts was determined by means of (13)C-CP/MAS and (15)N-CP/MAS NMR and IR spectroscopy. Using these solid-state analytical techniques, it was found that both nitrogen atoms were protonated when excess hydrogen chloride was used for preparation of salts. On the other hand, when the equimolar amount of hydrogen chloride was used, piperazine nitrogen substituted by aryl was protonated.

Identification of key structural characteristics of Schisandra chinensis lignans involved in P-glycoprotein inhibition.

The aim of the present study was to determine the structural requirements for dibenzocyclooctadiene lignans essential for P-glycoprotein inhibition. Altogether 15 structurally related lignans isolated from Schisandra chinensis or prepared by modification of their backbone were investigated, including three pairs of enantiomers. P-Glycoprotein inhibition was quantified using a doxorubicin accumulation assay in human promyelotic leukemia HL60/MDR cells overexpressing P-glycoprotein. A preliminary quantitative structure-activity relationship analysis revealed three main structural features involved in P-glycoprotein inhibition: a 1,2,3-trimethoxy moiety, a 6-acyloxy group, and the absence of a 7-hydroxy group. The most effective inhibitors, (-)-gomisin N (1) and (+)-deoxyschizandrin [(+)-2], were selected for further evaluation of their effects. Both these lignans restored the cytotoxic effect of doxorubicin in HL60/MDR cells and when combined with a subtoxic concentration of this compound increased the proportion of G2/M cells significantly, which is a usual response to treatment with this anticancer drug.

1H-, 13C-, and 15N-NMR chemical shifts for selected glucosides and ribosides of aromatic cytokinins.

The (1)H and (13)C NMR resonances of 16 purine glucosides were assigned by a combination of one- and two-dimensional NMR experiments, including gs-COSY, gs-HSQC, and gs-HMBC, in order to characterize the effect of substituent and the position of glucose unit on the NMR chemical shifts. In addition, (15)N NMR chemical shifts for selected derivatives were investigated by using (1)H-(15)N chemical shift correlation techniques. To map the influence of sugar moiety on the directly bonded nitrogen atom, selected N(9)-glucosides and their ribose analogs were compared. Characteristic long-range (1)H-(15)N coupling constants, measured by using (1)H-(15)N gradient-selected single-quantum multiple bond correlation (GSQMBC), are also reported and discussed. All compounds investigated here belong to cytokinins, an important group of plant hormones.

Validated method for bioactive lignans in Schisandra chinensis in vitro cultures using a solid phase extraction and a monolithic column application.

A simple and rapid method for determination of six lignans found in plant cell cultures of Schisandra chinensis was developed and validated. The lignans were extracted from plant samples with methanol and the extracts were effectively cleaned by solid-phase extraction using Strata C18-E (Phenomenex) cartridges. Chromatographic separation was carried out on a Chromolith Performance RP-18e monolithic column (100 x 4.6 mm, Merck) using an isocratic mobile phase of acetonitrile and water in a 50:50 (v/v) ratio. The eluent was monitored at 220 nm. The baseline separation of schizandrin, gomisin A, deoxyschizandrin, gamma-schizandrin, gomisin N and wuweizisu C was achieved in a relatively short time period (20 min), which was made possible by the relatively high flow rate of the mobile phase (2 mL/min). The lower limit of quantitation was 0.1 mg/L for schizandrin and gomisin A, 0.3 mg/L for deoxyschizandrin, gamma-schizandrin, and gomisin N and 1 mg/L for wuweizisu C. The analysis of spiked samples containing six lignans provided absolute recoveries between 93 and 101% in all cases. The validated method was successfully applied to the determination of lignans in embryogenic plant cell cultures of Schisandra chinensis.

Mass spectrometry of 1,3- and 1,5-dicaffeoylquinic acids.

Samples of 1,3- (1) and 1,5-dicaffeoylquinic acid (2) and their hexaacetate derivatives were examined using positive and negative electrospray ionization mass spectrometry and tandem mass spectrometry. Differences in the various spectra allow the discrimination of each of the isomers. Specific losses in the spectra of 2 also permit the identification of the site of substitution of one of the caffeic acid moieties as being at the 5-position. The spectra of 3,5- (3) and 4,5-dicaffeoylquinic (4) acids and their hexaacetate derivatives were compared with those of 1 and 2 and their derivatives, and differences in ion abundances or the presence/absence of specific ions can be used to identify uniquely each of the compounds.