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Metabolic profiling of natural products is used to map correlated concentration variances of known and unknown secondary metabolites in extracts. NMR-spectroscopy is in this respect regarded as a convenient and reproducible technique with the ability to detect a wide range of small organic compounds. Two-dimensional J-resolved NMR-spectra are used in this context to resolve overlapping signals by separating the effect of J-coupling from the effect of chemical shifts. Often one-dimensional projections of these data are used as input for standard multivariate statistical methods, and only the intensity variances along the chemical shift axis are taken into account. Here, we describe the use of parallel factor analysis (PARAFAC) as a tool to preprocess a set of two-dimensional J-resolved spectra with the aim of keeping the J-coupling information intact. PARAFAC is a mathematical decomposition method that fits three-way experimental data to a model whose parameters in this case reflect concentrations and individual component spectra along the chemical shift axis and corresponding profiles along the J-coupling axis. A set of saffron samples, directly extracted with methanol-d(4), were used as a model system to evaluate the feasibility and merits of the method. To successfully use PARAFAC, the two-dimensional spectra (n = 96) had to be aligned and processed in narrow windows (0.04 ppm wide) along the chemical shift axis. Selection of windows and number of components for each PARAFAC-model was done automatically by evaluating amount of explained variance and core consistency values. Score plots showing the distribution of objects in relation to each other, and loading plots in the form of two-dimensional pseudospectra with the same appearance as the original J-resolved spectra but with positive and negative contributions are presented. Loadings are interpreted not only in terms of signals with different chemical shifts but also the associated J-coupling profiles.

An array of analogues of the wasp toxin philanthotoxin-433, in which the asymmetric polyamine moiety was exchanged for spermine and the headgroup replaced with a variety of structurally diverse moieties, was prepared using parallel solid-phase synthesis approaches. In three analogues, the spermine moiety was extended with an amino acid tail, six compounds contained an N-acylated cyclohexylalanine, and four analogues were based on a novel diamino acid design with systematically changed spacer length between N-cyclohexylcarbonyl and N-phenylacetyl substituents. The analogues were studied using two-electrode voltage-clamp electrophysiology employing Xenopus laevis oocytes expressing GluA1(i) AMPA or GluN1/2A NMDA receptors. Several of the analogues showed significantly increased inhibition of the GluN1/2A NMDA receptor. Thus, an analogue containing N-(1-naphtyl)acetyl group showed an IC(50) value of 47 nM. For the diamino acid-based analogues, the optimal spacer length between two N-acyl groups was determined, resulting in an analogue with an IC(50) value of 106 nM.

Introduction – Rhodiola rosea is a broadly used medicinal plant with largely unexplored natural variability in secondary metabolite levels. Objective – The aim of this work was to develop a non-target procedure for 1H NMR spectroscopic fingerprinting of rhizome extracts for pattern recognition analysis and identification of secondary metabolites responsible for differences in sample composition. To achieve this, plants from three different geographic areas (Swiss Alps, Finland, and Altai region in Siberia) were investigated. Results – A sample preparation procedure was developed in order to remove polymeric polyphenols as the 1H NMR analysis of low-molecular-weight metabolites was hampered by the presence of tannins. Principal component analysis disclosed tight clustering of samples according to population. PCA models based on the aromatic region of the spectra showed that the first two components reflected changes in the content of salidroside and rosavin, respectively, the rosavin content being negatively correlated to that of rhodiocyanoside A and minor aromatics. Score plots and non-parametric variance tests demonstrated population-dependent changes according to harvest time. Data consistency was assessed using score plots and box-and-whisker graphs. In addition, a procedure for presenting loadings of PCA models based on bucketed data as high-resolution plots, which are reminiscent of real 1H NMR spectra and help to identify latent biomarkers, is presented. Conclusion – This study demonstrated the usefulness of the established procedure for multivariate non-target 1H NMR metabolic profiling of Rhodiola rosea. Copyright © 2010 John Wiley & Sons, Ltd.

1H NMR metabolic profiles of urine from sheep exposed to prenatal nutritional restriction (n = 19) and a control group with normal prenatal nutritional requirements (n = 19), followed by either conventional (n = 10 + 10) or high carbohydrate high fat postnatal diet (n = 9 + 9), were studied. Urine was sampled from 2, 6, 19 and 24-month-old animals receiving differential dietary treatments during the first 6 months and the same normal diet later. Principal component analysis of 1H NMR spectra (n = 164) showed a V-shaped metabolic trajectory as a function of age and diet, starting with urines with a high amount of glucose, indicative of monogastric-like metabolism, and exhibiting concomitant increase of metabolites related to rumen microflora (mainly glycine conjugates of benzoic and phenylacetic acid) as the ruminal metabolism developed. Urines from young (2-month-old) animals exposed to prenatal undernutrition followed by normal postnatal diet showed metabolic patters that are ahead in time on the metabolic trajectory relative to the prenatal control group. No long-term effects of fetal undernutrition, alone or in combination with postnatal hypernutrition were observed.

An efficient and versatile solid-phase route for the preparation of aryl-alkyl ethers is described. Regioselective ring opening of a resin-bound chiral aziridine with phenolic nucleophiles constitutes the key feature of the present protocol that allows incorporation of fluorescent moieties and subsequent on-resin protecting group interconversion. Initial experiments demonstrated that a competing oligomerization may occur by concomitant attacks of transient nosylamide anions on neighboring aziridines, resulting in formation of dimeric and trimeric byproduct. Expectedly, the significance of this alternative reaction pathway was strongly dependent on resin loading, and a low loading (

The aim of this study was to explore feasibility of 1H NMR metabolic fingerprinting for discrimination of authenticity of saffron using principal component analysis (PCA) modeling. Authentic reference Iranian saffron (n = 31) and commercial samples (n = 32) were used. Cross-validated PCA models based on 1H NMR spectra of solutions prepared by direct extraction of grinded saffron with methanol-d4 distinguished reference Iranian saffron samples from commercial samples that formed several distinct clusters, some of which represent falsified samples as confirmed by microscopic analysis. The production sites and drying conditions of the authentic reference Iranian samples were not reflected in the current dataset. Picrocrocin and glycosyl esters of crocetin emerged as the most important 1H NMR markers of authentic saffron by using statistical correlation spectroscopy. In conclusion, 1H NMR spectra of saffron extracts combined with pattern recognition by PCA provide immediate means of unsupervised classification of saffron samples.

Brain activation provokes nonoxidative carbohydrate consumption and during exercise it is dominated by the cerebral uptake of lactate resulting in that up to approximately 1 mmol/ 100 g of glucose equivalents cannot be accounted for by cerebral oxygen uptake. The fate of this 'extra' carbohydrate uptake is unknown, but it may be that brain metabolism is balanced by a yet-unidentified substance(s). This study used a nuclear magnetic resonance-based metabolomics approach to plasma samples obtained from the brachial artery and the right internal jugular vein in 16 healthy young males to identify carbon species going to and from the brain. We observed a carbohydrate accumulation of 255+/-37 micromol/100 g glucose equivalents at exhaustion not accounted for by the oxygen uptake. Although the cumulated uptake was lower than earlier observed, the results show that glucose and lactate are responsible for the majority of the carbon exchange across the brain. Even during intense exercise associated with the largest nonoxidative carbohydrate consumption, the brain did not show significant release of any other metabolite. We conclude that during exercise, the surplus carbohydrate uptake by the brain cannot be accounted for by changes in the NMR-derived plasma metabolome across the brain.

The aim of this study was to investigate structures and acetylcholinesterase inhibitory activities of lycopodane-type alkaloids isolated from an Icelandic collection of Lycopodium annotinum ssp. alpestre. Ten alkaloids were isolated, including annotinine, annotine, lycodoline, lycoposerramine M, anhydrolycodoline, gnidioidine, lycofoline, lannotinidine D, and acrifoline, as well as a previously unknown N-oxide of annotine. 1H and 13C NMR data of several of the alkaloids were provided for the first time. Solvent-dependent equilibrium constants between ketone and hemiketal form of acrifoline were determined. Conformation of acrifoline was characterized using NOESY spectroscopy and molecular modelling. The isolated alkaloids were evaluated for their in vitro inhibitory activity against acetylcholinesterase and butyrylcholinesterase. Ligand docking studies based on mutated 3D structure of Torpedo californica acetylcholinesterase provided rationale for low inhibitory activity of the isolated alkaloids as compared to huperzine A or B, which are potent acetylcholinesterase inhibitors belonging to the lycodine class. Based on the modelling studies the lycopodane-type alkaloids seem to fit well into the active site gorge of the enzyme but the position of their functional groups is not compatible with establishing strong hydrogen bonding interactions with the amino acid residues that line the binding site. The docking studies indicate possibilities of additional functionalization of the lycopodane skeleton to render potentially more active analogues.

The reaction between the high-dose drug substance 5-aminosalicylic acid (5-ASA) and the excipient citric acid during storage of an experimental enema preparation has been studied and three isobaric reaction products, i.e., an ester and an amide with non-symmetrically substituted citric acid moieties and a symmetrical amide, were identified by combined use of HPLC–SPE–NMR and HPLC–MS. After storage for 1 week at 70 °C, approximately 5% of the 5-ASA present in the formulation was transformed into these impurities. Storage of the enema for 32 months at room temperature led to loss of approximately 10% of the original amount of 5-ASA, with the ester as the main reaction product.

In order to clarify the interaction of gossypol with proteins, the pure diastereoisomeric Schiff bases from L-tryptophan methyl ester and both gossypol enantiomers were prepared. Their c.d. and n.m.r. spectra demonstrate that the interaction between gossypol and tryptophan, previously reported to involve a weakly associated complex, consists in Schiff base formation. Recent studies on enzyme inhibition by gossypol are discussed; it is suggested that nonspecific covalent binding of gossypol to proteins may be responsible for a significant proportion of the in vitro effects of gossypol.

article i nfo Article history: Novel peptidomimetic backbone designs with stability towards proteases are of interest for several pharmaceutical applications including intracellular delivery. The present study concerns the cellular uptake and membrane-destabilising effects of various cationic chimeras comprised of alternating N-alkylated β- alanine and α-amino acid residues. For comparison, homomeric peptides displaying octacationic functionalities as well as the Tat47-57 sequence were included as reference compounds. Cellular uptake studies with fluorescently labelled compounds showed that guanidinylated chimeras were taken up four times more efficiently than Tat47-57. After internalisation, the chimeras were localised primarily in vesicular compartments and diffusively in the cytoplasm. In murine NIH3T3 fibroblasts, the chimeras showed immediate plasma membrane permeabilising properties, which proved highly dependent on the chimera chain length, and were remarkably different from the effects induced by Tat47-57. Finally, biophysical studies on model membranes showed that the chimeras in general increase the permeability of fluid phase and gel phase phosphatidylcholine (PC) vesicles without affecting membrane acyl chain packing, which suggests that they restrict lateral diffusion of the membrane lipids by interaction with phospholipid head groups. The α- peptide/β-peptoid chimeras described herein exhibit promising cellular uptake properties, and thus represent proteolytically stable alternatives to currently known cell-penetrating peptides.

The Letter describes an improved, rapid and mild strategy for the loading of primary alcohols onto a polystyrene trityl resin via a highly reactive trityl bromide linker. This protocol facilitates an efficient resin loading even of acid-sensitive or heat-labile alcohols, which otherwise require expensive or non-commercial resin types. Secondary alcohols were only attached in moderate to low yields, while attempts to load a tertiary alcohol expectedly failed. Importantly, selective attachment of diols via a primary alcohol group in the presence of more hindered alcohol groups proved possible. The effects of activation time and reagent excess as well as alcohol structure were investigated. This improved method provides a convenient access to O-linked resin-bound N -Fmoc-protected amino alcohols that may be employed in SPS of peptides with C-terminal alcohol functionalities. In the case of a sensitive alcohol containing an activated aziridine functionality, the use of the trityl bromide linker proved superior to a recently described silver triflate-assisted trityl chloride resin-based procedure.

Recently, a novel type of antimicrobial and proteolytically stable peptidomimetic oligomers having an α-peptide-β-peptoid chimeric backbone was reported. The present paper describes efficient protocols for the preparation of a wide range ofdimeric building blocks, displaying different types of side-chains, for use in solid-phase synthesis (SPS) of libraries of this type of oligomers. The β-peptoid monomers were obtained by microwave-assisted aza-Michael additions to acrylic esters. Subsequent solution-phase peptide coupling with suitably protected α-amino acids afforded dimeric intermediates. Even sluggish peptide couplings, involving sterically hindered N-alkyl-β-alanines or amino acids with bulky side-chains, gave high yields on multigram-scale when using microwave (MW) irradiation. Protecting group and side-chain manipulations were performed as one-pot solution-phase procedures to afford ten different building blocks in good to excellent yields. Finally, the efficiency of SPS oligomerization of a representative dimer was demonstrated by preparing 10- to 16-residue homomers and by the assembly of four different building blocks to give a diversely functionalized octamer.

The hyphenated technique HPLC–SPE–NMR is proving to be a useful analytical tool for structure elucidation of mixture components, particularly for mass-limited samples where traditional isolation procedures are either time consuming or challenging. In this work, we investigated SPE trapping performance of 25 model natural products within a format corresponding to that of HPLC–SPE–NMR hyphenation. Six different silica-based bonded phases and two polymeric phases were evaluated. The trapping efficiency of polystyrene/divinylbenzene polymers was generally superior compared to silica bonded phases, which showed variable results and performed well only with hydrophobic analytes. Acetonitrile concentration in the loading solvent was critical for trapping on polymeric phase (Resin GP), as small changes of the organic solvent concentration (±3%) could alter the trapping efficiency significantly. Flow rate changes of the loading solvent within 0.8–5.0 mL/min did not affect trapping kinetics. Simulation of multiple trapping showed excellent performance of this approach for hydrophobic analytes, and moderate gain for more polar analytes that do not trap quantitatively in a single trapping step. Determination of 50% breakthrough levels by frontal chromatography analysis showed feasibility of accumulation of analyte amounts corresponding to about 0.5 μmol (10 mm × 2 mm i.d. Resin GP cartridge).

The hyphenated technique, high-performance liquid chromatography-solid-phase extraction-nuclear magnetic resonance spectroscopy (HPLC-SPE-NMR), has been applied for rapid identification of novel natural products in crude extracts of Hubertia ambavilla and Hubertia tomentosa. The technique allowed full or partial identification of all major extract constituents and demonstrated the presence of unusual quinic acid derivatives containing the (1-hydroxy-4-oxocyclohexa-2,5-dienyl)acetyl residue that exhibit strongly coupled ABXY patterns, the parameters of which were obtained by spin simulations. Using homo- and heteronuclear 2D NMR data acquired in the HPLC-SPE-NMR mode, complete structure determination of three new natural products, i.e., 3,5-di-O-caffeoyl-4-O-[(1-hydroxy-4-oxocyclohexa-2,5-dienyl)acetyl]quinic acid (1), its 2-hydroxy derivative (2), and 3,5-di-O-caffeoyl-4-O-[(4-hydroxyphenyl)acetyl]quinic acid (3), was performed. Finally, targeted isolation of 1 was achieved by SPE fractionation and preparative HPLC, followed by evaluation of its antioxidant and antimicrobial activity. In contrast to chlorogenic acid and 3,5-di-O-caffeoylquinic acid, which act as antioxidants, compound 1 proved at the same conditions to possess prooxidant activity in an assay evaluating the oxidation of human low-density lipoprotein induced by Cu(2+).

Four prenylated acetophenones 2,6-dihydroxy-4-geranyloxyacetophenone (1), 4-geranyloxy-2,6,β-trihydroxyacetophenone (2), 2,6-dihydroxy-4-geranyloxy-3-prenylacetophenone (3), and 4-geranyloxy-3-prenyl-2,6,β-trihydroxyacetophenone (4) have for the first time been isolated from Melicope obscura (1 and 2) and Melicope obtusifolia ssp. obtusifolia var. arborea (3 and 4). The distribution of prenylated acetophenones in Rutaceae is reviewed and the results, including the new records, indicate that prenylated acetophenones are valuable as chemotaxonomic markers for the subfamily Rutoideae, tribe Xanthoxyleae sensu Engler.

N-alkyl-beta-alanine oligomers (beta-peptoids) with alpha-chiral side chains [(R)- or (S)-1-(phenylethyl)amino groups] were synthesized and analyzed by CD spectroscopy. These chiral beta-peptoid homomers exhibited chain-length-dependent and solvent-dependent ellipticity, strongly indicating the presence of a secondary structure in solution. The CD behaviour was only slightly temperature-dependent upon heating, as also previously observed for stable alpha-peptoid helices containing the same type of side chains. Thus, the data presented here comprise the first evidence for a chain length-dependent secondary folding of compounds with this novel peptidomimetic backbone design. In addition, applicability of a novel hyphenated technique, HPLC-SPE-NMR/MS, for analysis of crude SPPS reaction products was demonstrated.

Aziridines are versatile and powerful building blocks in organic synthesis due to their high reactivity as well as stereo- and regioselectivity of their ring-opening reactions with nucleophiles. Thus, aziridines possess potential as building blocks in the preparation of combinatorial libraries for biological high-throughput screening. Although the development of strategies for parallel synthesis and solid-phase chemistry utilizing aziridines is still in its infancy, the diverse applications described so far emphasize their utility. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

We describe the synthesis and characterization of the first generation of oligomers consisting of alternating repeats of α-amino acids and chiral N-alkyl-β-alanine (β-peptoid) residues. These chimeras are stable toward proteolysis, non-hemolytic, and possess antibacterial activity comparable to well-known antimicrobial agents. Moreover, the chimeras exhibit length-dependent, concentration-dependent, solvent-dependent, and ion-strength-dependent ellipticity, indicating the presence of a secondary structure in solution. Thus, α-peptide/β-peptoid oligomers represent a promising novel peptidomimetic backbone construct for biologically active ligands.

Polyamine toxins isolated from the venoms of spiders and wasps and their synthetic analogues are uncompetitive antagonists of ligand-gated ionotropic receptors in the central- and peripheral nervous systems, and have proved valuable as tools for the investigation of receptor structure and function. In the present letter we describe the efficient solid-phase synthesis (SPS) of novel hybrid toxins using a BAL resin. This strategy enables the bidirectional construction of toxin molecules and has a potential in SPS of chemically diverse libraries of toxin analogues for structure–activity relationship (SAR) studies.

Biotransformation of deoxypodophyllotoxin to epipodophyllotoxin by three major human hepatic enzymes, CYP1A2, CYP2C9 and CYP3A4, heterologously expressed in E coli DH5 alpha, was investigated. It was shown that CYP3A4 catalysed the hydroxylation of deoxypodophyllotoxin into epipodophyllotoxin in yields up to 90%. The structure of the metabolite was determined using HPLC-MS and HPLC-SPE-NMR. techniques. There was no detectable production of epipodophyllotoxin or podophyllotoxin by CYP1A2 and CYP2C9 enzymes. The CYP3A4 enzyme shows a distinctly different reactivity to deoxypodophyllotoxin compared to the semi-synthetic derivatives etoposide and teniposide, which are degraded by 3-O-demethylation. These findings demonstrate a novel system for the production of 2,7'-cyclolignans, starting from the easily accessible deoxypodophyllotoxin. (c) 2006 Elsevier B.V. All rights reserved.

The HPLC-SPE-NMR technique, supported by HPLC-MS measurements, was used to determine structures of major as well as some minor constituents of ethanol and petroleum ether extracts of Harpagophytum procumbens (Devil's claw) roots. This method was also shown to be applicable for rapid and precise on-line identification of secondary metabolites present in commercial herbal products of H. procumbens. A total of 15 compounds (1-14 and 17) were identified from the ethanol and petroleum ether extracts, including a novel Diels-Alder dimer 14. Optimization of the HPLC-SPE-NMR experiments included quantitative (1)H NMR measurements, determination of trapping and elution efficiency, effect of multiple trapping of analytes, use of various deuterated solvents for SPE cartridge elution, and effect of post-column dilution ratio of eluent with water. Linear accumulation of apolar and relatively polar analytes was demonstrated for at least 8-10 repeated trappings, resulting in greatly improved signal-to-noise ratios in NMR spectra and reduced acquisition times. Thus, the HPLC-SPE-NMR technique provides an efficient means of identification of multiple components of crude extracts. By allowing on-line generation of high-quality 2D NMR data without traditional purification of extract components, the HPLC-SPE-NMR methodology represents a paradigm shift in natural products research with respect to structure elucidation.

Commercial herbal preparations are typically very complex mixtures and the relationship between content of various constituents and pharmacological action of the formulation is usually unclear. Such formulations are nevertheless standardized using a single marker constituent or a group of closely related constituents, which provides no information about other abundant constituents present in the extract. In this study, principal component analysis of 600 MHz H-1-NMR spectra of extracts of commercial formulations of St. John's wort (Hypericum perforatum), acquired in methanol-d(4) and DMSO-d(6), was shown to be able to discriminate between various preparations according to their global composition, including differentiation between various batches from the same supplier, while no clustering into classes of tablets and capsules was observed. This suggests that the plant extract variability rather than the manufacturing process accounts for the data clustering. Major variations in the content of flavonoids, recently linked to the antidepressant activity of St. John's wort extracts, were detected. Use of two NMR solvents provided complementary data sets, allowing assessment of various aspects of sample composition from separate PCA models. Both integrated (about 200 variables) and full-resolution NMR data (about 30000 variables) have been used. The latter approach, applied for the first time in analysis of a herbal preparation, provided via loading plots more precise information about constituents responsible for data clustering, and may be generally preferable for PCA analysis of NMR data of plant extracts and herbal medicines.

HPLC-SPE-NMR experiments with crude extracts of Harpagophytum procumbens allowed the rapid identification of novel, unstable chinane-type tricyclic diterpenes (1 and 2), along with numerous other constituents. Dramatic sensitivity gains achieved with this novel hyphenated technique establish a new paradigm in natural products research: rapid and rigorous structure determination of multiple extract components, including minor components, without preparative-scale isolation.

A novel hyphenated technique, HPLC-SPE-NMR, was used for accelerated identification of isoflavonoids from the roots of Smirnowia iranica. The extract constituents eluted from a HPLC column were automatically trapped on solid-phase extraction (SPE) cartridges, and NMR spectra were acquired with concentrated solutions after solvent change. The structures of 10 new isoflavonoids (1, 4, 5, 7-10, 12, 13, 16) and of seven previously described constituents (2, 3, 6, 11, 14, 15, 17) were elucidated from NMR spectra acquired in the HPLC-SPE-NMR mode. Multiple peak trapping on the same SPE cartridge increased analyte amounts and provided access to 2D NMR data. It was demonstrated that linear accumulation of material is possible in up to seven repeated trapping steps. The use of HPLC-SPE-NMR speeded up dereplication of the S. iranica extract considerably by providing detailed information about the constituents of a complex, essentially crude extract prior to their preparative-scale isolation or extract pre-fractionation, and the information obtained could be used to direct preparative isolation work. In connection with structure elucidation of isoflavonoids containing O-methylated 1,2,3-benzenetriol moieties as the B-ring, O-methylation-induced changes of chemical shifts of aromatic hydrogens were found to depend on the conformation of the resulting methoxy group, i.e., on the number of its ortho substituents. The recognized regularities will be useful in structure determination of partially O-methylated polyphenols based on 1D (1)H NMR spectra obtainable from HPLC-SPE-NMR experiments, diminishing dependence on 2D NMR data and (13)C NMR chemical shifts.

1. Subject and source Vincetoxicum pumilum Decne. [syn. Alexitoxicon pumilum (Decne.) Pobed., Antitoxicum pumilum (Decne.) Pobed., Cynanchum pumilum (Decne.) Bornm.] (ApocynaceaeeAsclepiadoideae) is a perennial herb endemic to Central Asia (Jalili and Jamzad, 1999). The plant (roots and aerial parts) was collected in Deh-Ghaibi near Mashhad, Iran. A voucher specimen (accession number 35007) was deposited in herbarium FUMH (Ferdowsi University Mashhad Herbarium).

This review describes the principles and performance of a novel and highly promising hyphenated technique, HPLC-SPE-NMR, which is based on post-column analyte trapping by solid-phase extraction. The analytes are subsequently eluted from the SPE cartridges using deuterated solvents. This indirect HPLC-NMR hyphenation offers numerous advantages compared to direct HPLC-NMR methods. Multiple trapping leads to a dramatic increase of analyte amounts available for NMR, enabling acquisition of high-quality 2D NMR data within a short time. Other new developments, including combination of solenoidal coil capillary flow-probes with microflow HPLC, are also discussed. Fast extract dereplication using these techniques enables focusing of isolation efforts on truly novel and promising natural products, based on precise structural data obtained with crude extracts or fractions.

Aliphatic and aromatic amino functionalities are present in a wide variety of natural products and drugs, as well as in synthetic small molecular probes with therapeutic and/or diagnostic potential in drug discovery. As solid-phase synthesis and combinatorial chemistry have emerged as important tools for generation of compound libraries, development of broad-scope and efficient chemistry for the introduction of various functional groups into resin-anchored substrates is highly important. Herein, we present a review of the literature concerning formation of the amino functionality on solid phase.

A protocol for parallel solid-phase synthesis of ω-amino acid-elongated philanthotoxins was developed for exploration of structure-activity relationships for unnatural wasp toxin analogues. Several methods for on-resin activation of N-trityl-linked ω-amino acids were investigated, and the influence of chain length upon activation as pentafluorophenyl (Pfp) esters was examined. Comparison of Pfp-ester activation with phosphonium- and aminium/ uronium-promoted coupling without pre-activation of the resin-bound carboxylic acids showed that only benzotriazol-1-yloxytris(pyrrolidino)phosphonium hexafluorophosphate (PyBOP) exhibited a comparable efficiency. The present Pfp ester protocol gave high yields and purities of the resulting philanthotoxin analogues; however, in the case of γ-aminobutyric acid (GABA), use of PyBOP was required in order to avoid lactamization to 2-pyrrolidone.

The Fukuyama–Mitsunobu amination strategy has emerged as an efficient means of N-alkylation of peptides and sulfonamides, as well as a method for synthesis of polyamines on solid phase. Here, an array of reagent combinations for solid-phase alkylation with secondary alcohols was examined in various solvents. The classical reagents DEAD–PPh 3 as well as DEAD–PEt 3 proved applicable for a single alkylation step. Sharply dropping yields in successive alkylation steps were identified as the most serious limitation of the use of Fukuyama–Mitsunobu reaction in SPS of polyamines using primary and in particular secondary alcohols.

Extract of Naravelia zeylanica (Ranunculaceae) yielded three simple benzamides, 3,4-methylenedioxybenzamide, 4-methoxybenzamide and 4-hydroxy-3-methoxybenzamide. These simple C6C1 metabolites have been encountered as natural products for the first time. The compounds were identified by direct comparison of their spectral (1H- and 13C-NMR) and chromatographic (GCMS) data with those of authentic samples. Authentic 4-hydroxy-3-methoxybenzamide was synthesized in one step by treatment of 4-hydroxy-3-methoxybenzonitrile with sodium perborate. Authentic 3,4-methylenedioxybenzamide was synthesized from the corresponding acid.

[reaction: see text] A mild resin-immobilization strategy employing a readily prepared trityl bromide resin for anchoring building blocks via a phenol group has been developed. With N(alpha)-Fmoc-Tyr-OPfp as a starter building block, it was possible to prepare asymmetrically substituted hybrids of spider- and wasp-type polyamine toxins using solid-phase peptide synthesis conditions.

A new natural product, named selagoline, and two known alkaloids, huperzine A and serratidine, were isolated from Huperzia selago (Lycopodiaceae) collected in Iceland. Their structures were determined using 600 and 800MHz one- and two-dimensional NMR methods supported by Fourier-transform mass spectrometry. Possible role of selagoline as a precursor of 5,15-oxidolycopodane, a component of the classical alkaloids L28 and L31, is discussed.

[reaction: see text] An expedient solid-phase synthetic approach to secondary and tertiary amines was developed. The protocol employs conversion of resin-bound amino alcohols to the corresponding iodides, followed by iodide displacement with primary or secondary amines or with unprotected amino alcohols. This two-step procedure, affording products in good to excellent yields, is suitable for solid-phase synthesis of polyamines.

A library of nine aromadendrane-type sesquiterpenes (1-9), including eight new natural products (1-5 and 7-9), was isolated from Landolphia dulcis var. barteri along with a previously described cadinane derivative (10) and a new muurolane derivative (11). The structures of all compounds were established by means of NMR methods including COSY, NOESY, HSQC, and HMBC experiments, supported by HRMS and optical rotation data. Virtual characterization of the aromadendrane library (1-9) was performed using chemoinformatics tools. 3D molecular fields were calculated with the GRID program using low-energy structures obtained with the MMFF force field. VolSurf descriptors were calculated from the GRID maps and subsequently analyzed by multivariate statistics. The analysis disclosed the presence of a common motif for possible interactions of the aromadendranes with a putative target receptor. At the same time, a considerable chemical diversity within the library was disclosed, despite a close biosynthetic relationship of its members. The results can be interpreted in terms of evolutionary optimization of structures of secondary metabolites for interaction with macromolecular targets and are of interest in terms of assessment of potential "drug-likeness" of natural products.

Three new naphthylisoquinoline alkaloids, the 7,3'-coupled ancistrotanzanine C (6), the 5,1'-coupled O-methylancistrocladinine (7), and the likewise 5,1'-coupled O,N-dimethylancistrocladine (8, previously known only as a partial-synthetic compound), have been isolated from the highland liana Ancistrocladus tanzaniensis, along with the two known 7,3'-coupled naphthylisoquinoline alkaloids ancistrocladidine (4) and ancistrotectorine (5). All of the compounds are S-configured at C-3 and bear an oxygen at C-6, and thus belong to the so-called Ancistrocladaceae type, similar to 1-3 previously isolated from this newly discovered plant species. The structural elucidation was achieved by chemical, spectroscopic, and chiroptical methods. The biological activities of the alkaloids against the pathogens causing malaria tropica, leishmaniasis, Chagas' disease, and African sleeping sickness were evaluated.

Six labdanes (1-6) and four isopimaranes (7-10), including three new natural products (7, 9, and 10), were isolated from Platycladus orientalis, and their structures determined using 1D and 2D NMR methods, ion-cyclotron resonance HRMS, and optical rotation data. Relative configurations of all chiral centers in the isopimaranes were determined using NOESY experiments at 600 and 800 MHz. Specific optical rotation data were used to correlate absolute configurations. Compounds 1-9 and aframodial (11) were tested for their in vitro antiplasmodial activity and for their ability to induce changes of erythrocyte shape in order to obtain data about possible correlation between the two effects. All compounds tested exhibited weak (IC(50) > 25 microM) in vitro antiplasmodial effects against Plasmodium falciparum strain 3D7. At the same time, the compounds caused echinocytic or stomatocytic changes of the erythrocyte membrane curvature, indicative of their incorporation into the lipid bilayer, in the concentration region where the antiplasmodial activity was observed. The antiplasmodial effect of these compounds thus appears to be an indirect effect on the erythrocyte host cell. Weak or moderate antiplasmodial activity observed with many other apolar natural products, in particular those with amphiphilic structures, is also likely to be an indirect effect.

The natural triterpene betulinic acid and its analogues (betulinic aldehyde, lupeol, betulin, methyl betulinate and betulinic acid amide) caused concentration-dependent alterations of erythrocyte membrane shape towards stomatocytes or echinocytes according to their hydrogen bonding properties. Thus, the analogues with a functional group having a capacity of donating a hydrogen bond (COOH, CH2OH, CONH2) caused formation of echinocytes, whereas those lacking this ability (CH3, CHO, COOCH3) induced formation of stomatocytes. Both kinds of erythrocyte alterations were prohibitive with respect to Plasmodium falciparum invasion and growth; all compounds were inhibitory with IC50 values in the range 7–28 μM, and the growth inhibition correlated well with the extent of membrane curvature changes assessed by transmission electron microscopy. Erythrocytes pre-loaded with betulinic acid or its analogues and extensively washed in order to remove excess of the chemicals could not serve as hosts for P. falciparum parasites. Betulinic acid and congeners can be responsible for in vitro antiplasmodial activity of plant extracts, as shown for Zataria multiflora Boiss. (Labiatae) and Zizyphus vulgaris Lam. (Rhamnaceae). The activity is evidently due to the incorporation of the compounds into the lipid bilayer of erythrocytes, and may be caused by modifications of cholesterol-rich membrane rafts, recently shown to play an important role in parasite vacuolization. The established link between erythrocyte membrane modifications and antiplasmodial activity may provide a novel target for potential antimalarial drugs.

In continuation of our investigations of the genus Plantago L. (Plantaginaceae), sixteen species were investigated with respect to water-soluble glycosides. The iridoids auroside, strictoloside and globularicisin, as well as poliumoside, 3-[(4-β-D-glucopyranosyloxy)phenyl]propionic acid and 2-[4-(β-D-glucopyranosyloxy)phenyl]acetic acid were isolated from Plantago for the first time. The latter compound has not previously been isolated as a natural product. Sorbitol was the main carbohydrate in all the species investigated. The distribution of iridoids correlates well with the morphological classification of Rahn and also with a recently published molecular phylogenetic study of nuclear ribosomal and plastid DNA sequences. A new chemotaxonomic finding is an abundance of iridoid glucosides present in one of the two groups within subgenus Coronopus section Coronopus, while the other group lacks iridoids, supporting a subdivision of this section. Moreover, in subgenus Albicans, 10-benzoylcatalpol is a characteristic constituent of section Gnaphaloides, while the corresponding cinnamoyl ester globularin occurs in section Lanceifolia. In biosynthetic experiments, labelled epideoxyloganic acid and deoxygeniposidic acid were incorporated into aucubin and geniposidic acid in Plantago ovata, consistent with earlier findings, but no incorporation into asperuloside was observed. The evolution of biosynthetic pathways in Plantago is discussed.

Philanthotoxin-433 (PhTX-433) is a polyamine wasp toxin that antagonizes certain ionotropic receptors noncompetitively. Four analogues of PhTX-433, C-methylated in the polyamine chain, were synthesized from (RS)-1,3-butanediol, two diamine building blocks, and an activated/protected tyrosine derivative. Use of a phosphane reagent more bulky than trimethylphosphane gave a high intramolecular selectivity between primary and secondary hydroxy groups in the Fukuyama−Mitsunobu reaction. Thus, trimethylphosphane proved to be the only phosphane reagent that enabled alkylation of 2-nitrobenzenesulfonamides with a wide range of secondary alcohols, whereas tributylphosphane was selective for primary alcohol groups. This selectivity was utilized to obtain orthogonally protected, asymmetric, branched tetraamines, employed for solution-phase synthesis of philanthotoxin analogues. The branched philanthotoxin analogues thus obtained were tested in an electrophysiological assay using rat brain ionotropic glutamate receptors expressed in Xenopus laevis oocytes. Their potencies proved to be similar to the corresponding nonbranched analogues. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

The first phytochemical investigation of the recently discovered East African liana Ancistrocladus tanzaniensis is described, resulting in the isolation and structural elucidation of two new naphthylisoquinoline alkaloids, ancistrotanzanines A (5) and B (6), and the known compound ancistrotectoriline A (7). Ancistrotazanine A (5) represents a hitherto unprecedented 5,3'-coupling type between the naphthalene and isoquinoline portions, while 6 and 7 are 5,8'-coupled. The structures of the compounds were determined by spectroscopic, chemical, and chiroptical methods. Compounds 5 and 6 showed good activities against the pathogens of leishmaniasis and Chagas' disease, Leishmania donovani and Trypanosoma cruzi, while 5-7 displayed moderately potent antiplasmodial activities against Plasmodium falciparum parasites.

Leaves of Melicope borbonica (Bory) T.G. Hartley (syn. Euodia borbonica var. borbonica (Bory) Engl.) were collected in July 1998 at Plaine d’Affouches, Reunion Island. Leaves of Melicope obscura (Cordem.) T.G. Hartley (syn. Euodia obscura Cordem.) were collected in February 2000 at Plaine de Palmiste, Reunion Island. Voucher specimens (DFHAA3 and DFHAA4) were deposited in Herbarium C (Botanical Museum, University of Copenhagen, Copenhagen, Denmark).

Voltage-dependent, non-competitive inhibition by philanthotoxin-343 (PhTX-343) analogues, with reduced charge or length, of nicotinic acetylcholine receptors (nAChR) of TE671 cells and ionotropic glutamate receptors (N-methyl-D-aspartate receptors (NMDAR) and alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (AMPAR)) expressed in Xenopus oocytes from rat brain RNA was investigated. At nAChR, analogues with single amine-to-methylene or amine-to-ether substitutions had similar potencies to PhTX-343 (IC(50)=16.6 microM at -100 mV) whereas PhTX-(12), in which both secondary amino groups of PhTX-343 were replaced by methylenes, was more potent than PhTX-343 (IC(50)=0.93 microM at -100 mV). Truncated analogues of PhTX-343 were less potent. Inhibition by all analogues was voltage-dependent. PhTX-343 (IC(50)=2.01 microM at -80 mV) was the most potent inhibitor of NMDAR. At AMPAR, most analogues were equipotent with PhTX-343 (IC(50)=0.46 microM at -80 mV), apart from PhTX-83, which was more potent (IC(50)=0.032 microM at -80 mV), and PhTX-(12) and 4,9-dioxa-PhTX-(12), which were less potent (IC(50)s>300 microM at -80 mV). These studies show that PhTX-(12) is a selective nAChR inhibitor and PhTX-83 is a selective AMPAR antagonist.

Three novel triterpenes, (11R,20R)-11,20-dihydroxy-24-dammaren-3-one (1), (17S,20R,24R)-17,25-dihydroxy-20,24-epoxy-14(18)-malabaricen-3-one (2), and (17R,20S,24R)-17,25-dihydroxy-20,24-epoxy-14(18)-malabaricen-3-one (3), were isolated from leaves of Caloncoba echinata. The structures were established using mainly 800 MHz NOESY and HMBC connectivities. The absolute stereochemistry of C-11 in 1 and that of C-17 in 2 were established by the Mosher method. The stereochemistry of the side chains of the malabaricanes is compatible with their biosynthesis by a cascade opening of diepoxides. The isolated triterpenes inhibited growth of Plasmodium falciparum parasites in vitro apparently via incorporation into erythrocyte membrane, as suggested by transformation of erythrocytes into stomatocytes at a concentration level at which the growth inhibition was observed.

Two known phenanthroindolizidine alkaloids, (-)-(R)-13aalpha-antofine (1) and (-)-(R)-13aalpha-6-O-desmethylantofine (2), and two new natural products, (-)-(R)-13aalpha-secoantofine (3) and (-)-(R)-13aalpha-6-O-desmethylsecoantofine (4), were isolated from Cynanchum vincetoxicum. The structures of all compounds were established by means of NMR methods including COSY, NOESY, HSQC, and HMBC experiments, supported by HRMS and optical rotation data. Cytotoxic activity of the isolated alkaloids, and of three other alkaloids previously isolated from Tylophora tanakae, (-)-(R)-13aalpha-tylophorine (5), (-)-(R)-13aalpha-7-O-desmethyltylophorine (6), and (+)-(S)-13abeta-isotylocrebrine (7), was assessed in vitro using a drug-sensitive KB-3-1 and a multidrug-resistant KB-V1 cancer cell line. Structure-activity relationships in this series of alkaloids are discussed. The IC(50) values of some of the alkaloids are in the low nanomolar range, being thus comparable to the activity of clinically used cytotoxic drugs. Previously reported adverse side effects of these alkaloids could possibly be overcome by modern tissue-specific drug targeting techniques.

Nineteen species of Passiflora (Passifloraceae) were examined for the presence of cyanogenic glycosides. Passibiflorin, a bisglycoside containing the 6-deoxy-β- d -gulopyranosyl residue, was isolated from P. apetala , P. biflora , P. cuneata , P. indecora , P. murucuja and P. perfoliata . In some cases this glycoside co-occurs with simple β- d -glucopyranosides: tetraphyllin A, deidaclin, tetraphyllin B, volkenin, epivolkenin and taraktophyllin. P. citrina contains passicapsin, a rare glycoside with the 2,6-dideoxy-β- d - xylo -hexopyranosyl moiety, while P. herbertiana contains tetraphyllin A, deidaclin, epivolkenin and taraktophyllin, P. discophora tetraphyllin B and volkenin, and P. × violacea tetraphyllin B sulfate. The remaining species were noncyanogenic. The glycosides were identified by 1 H and 13 C NMR spectroscopy following isolation by reversed-phase preparative HPLC. From P. guatemalensis , a new glucoside named passiguatemalin was isolated and identified as a 1-(β- d -glucopyranosyloxy)-2,3-dihydroxycyclopentane-1-carbonitrile. An isomeric glycoside was prepared by catalytic hydrogenation of gynocardin. α-Hydroxyamides corresponding to the cyanogenic glycosides were isolated from several Passiflora species. These α-hydroxyamides, presumably formed during processing of the plant material, behave as cyanogenic compounds when treated with commercial Helix pomatia crude enzyme preparation. Thus, the enzyme preparation appears to contain an amide dehydratase, which converts α-hydroxyamides to cyanohydrins that liberate cyanide; this finding is of interest in connection with analysis of plant tissues and extracts using Helix pomatia enzymes.

Philanthotoxin?433 (PhTX?433) is a known potent inhibitor of ionotropic glutamate receptors, and analogues have been synthesised to identify more potent and selective antagonists. Herein we report the synthesis of four PhTXs with a cyclopropane moiety introduced into their polyamine chain, and their inhibition of an ??amino?3?hydroxy?5?methyl?4?isoxazolepropionic acid (AMPA) receptor subtype by using two?electrode voltage?clamp assays on Xenopus oocytes expressing the GluA1flop subunit. All analogues were found to be more potent than PhTX?343, with trans?cyclopropyl?PhTX?343 being the most potent (?28?fold) and cis?cyclopropyl?PhTX?343 least potent (?4?fold). Both cis? and trans?cyclopropyl?PhTX?444 had intermediate potency (both ?12?fold). Molecular modelling indicates that a cyclopropane moiety confers a favourable steric constraint to the polyamine part, but this is compromised by a cis conformation due to enhanced intramolecular folding. Elongated PhTX?444 analogues alleviate this to some extent, but optimal positioning of the amines is not permitted.