NOE Difference Research Articles

Seco-Sesquiterpenes and acorane-type sesquiterpenes with antiviral activity from the twigs and leaves of Illicium henryi Diels

Chemical investigation of an alcohol extract from the twigs and leaves of Illicium henryi Diels resulted in the isolation of two new acorane-related seco-sesquiterpenes (1 and 3), two new acorane-related seco-norsesquiterpenes (2 and 4), one new 2-epi-cedrane sesquiterpene (5), eight new acorane-type sesquiterpenes (6–13), and a known major constituent of acorenone B (14). Their structures were established by interpreting extensive spectroscopic data, including HRESIMS, NMR (1H and 13C NMR, 1H-1H COSY, HSQC, and HMBC), and NOE difference spectra analysis. The absolute configurations of 1, 2, 4–7, 9, 10, and 14 were determined by X-ray crystallography, while chemical transformation methods were performed with compound 14 as the starting material to elegantly solve the absolute configuration issue of compounds 8 and 11–13. Notably, 1 and 2 are seco-sesquiterpenes that are related to acorane and possess an unusual ketal-linked hemiacetal in a 6,8-dioxabicyclo[3.2.1]octan-7-ol scaffold ring system. Plausible biosynthetic pathways for compounds 1–14, which were derived from the acorane skeleton, were proposed. All the isolated compounds (1–14) were evaluated for their antiviral and cytotoxic activities.

Secondary metabolites of the leaves of Tricalysia atherura N. Hallé (Rubiaceae) and their potential antiplasmodial activity

One monoterpene indole alkaloid, atheruramine (1) bearing an ether bridge linking, one hydrobenzoin derivative, tricalydioloside (2) and two ursane-type triterpenes, atherurosides (A and B) (3 and 4) were isolated from the leaves of Tricalysia atherura, together with eight known compounds. The structures of these new compounds were elucidated on the basis of the results of spectroscopic analysis, and the relative configurations of compounds 1–3 were established by NOE difference. Four of the metabolites were screened in vitro against both chloroquine (CQ)-sensitive (3D7) and -resistant (Dd2) strains of Plasmodium falciparum; they were found to exhibit moderate activity against chloroquine-resistant (Dd2) (IC50 64.99–92.29 μg/mL). Meanwhile, crude extract possesses high antiplasmodial activity against both 3D7 and Dd2 strains of P. falciparum (IC50 4.39–7.54 μg/mL) and high selectivity indices values (SI > 10) and was found to be safe.

The structure and spectroscopic characterization of coordination compounds with -phenyl-N-methylnitrone in solution and in solid state

New coordination compounds of a-phenyl-N-methylnitrone with Cu2+, Mn2+, Ni2+, and UO22+ were synthesized. Complexes were studied by means of IR, NMR and UV-Vis spectroscopies. The crystal and molecular structure of uranyl complex with a-phenyl-N-methylnitrone was determined by X-ray diffraction study. The monodentate nitrone ligands are coordinated to the metal ion via oxygen atom. The coordination polyhedron of uranium is a distorted hexagonal bipyramide. It was shown that there is dynamic process in the acetone solution in the temperature range of 203–297 K. The ligand exists as a trans-isomer for both present forms of organic ligand by the NOE difference. Dimeric copper(II) benzoate was obtained via recrystallization of the copper complex with a-phenyl-N-methylnitrone from methanol solution. According to X-ray diffraction analysis, the environment of each of the copper atoms is octahedral. The coordination sphere is formed by six oxygen atoms. Three anions of benzoic acid are coordinated bidentate-bridged through oxygen atoms of the carboxyl group, while one molecule of benzoic acid is coordinated monodentatically through the carboxyl oxygen atom.

Configurational E/Z and photo-induced cis-trans isomerism in the Pd(II) complex of asymmetrical N,N-methyl-ethyl-N′-benzoylthiourea

The palladium complex prepared from an asymmetrically di-substituted N,N-methyl-ethyl-N′-benzoylthiourea ligand exists in chloroform as a pure mixture of the configurational isomers cis-ZZ-[Pd(L-κS,O)2], cis-EE-[Pd(L-κS,O)2] and cis-ZE-[Pd(L-κS,O)2]. These have been have been characterized by 1H, 13C, HMBC and 1D NOE difference NMR spectroscopy in organic solvents. The single-crystal X-ray diffraction structures of crystals of the cis-EE-[Pd(L-κS,O)2] isomer isolated from either acetonitrile or dichloromethane solutions in the dark, confirmed its molecular structure. In acetonitrile, the analytically pure mixture of the cis-ZZ/ZE/EE-[Pd(L-κS,O)2] complexes undergo reversible photo-induced cis → trans isomerization when irradiated with polychromatic light to form all the configurational isomers trans-ZZ/ZE/EE-[Pd(L-κS,O)2]. In the absence of light, the latter trans-complexes slowly revert back to trans-ZZ/ZE/EE-[Pd(L-κS,O)2] in the dark in both acetonitrile and chloroform-d solutions, as monitored by RP-HPLC and 1H NMR spectroscopy as a function of time at 25 °C. Estimates of the relative rate of the trans → cis reversion reaction in the dark, is 2.8 × 10−2 min−1 in acetonitrile, compared to that in chloroform-d of ca 0.38 × 10−2 min−1.

15N CEST data and traditional model-free analysis capture fast internal dynamics of DJ-1

Previous studies have shown that relaxation parameters and fast protein dynamics can be quickly elucidated from 15N-CEST experiments [1]. Longitudinal R1 and transverse R2 values were reliably derived from fitting of CEST profiles. Herein we show that 15N-CEST experiments and traditional modelfree analysis provide the internal dynamics of three states of human protein DJ-1 at physiological temperature. The chemical exchange profiles show the absence of a minor state conformation and, in conjunction with 1H-15N NOEs, show increased mobility. R1 and R2 values remained relatively unchanged at the three naturally occurring oxidation states of DJ-1, but exhibit striking NOE differences. The NOE data was, therefore, essential in determining the internal motions of the DJ-1 proteins. To the authors' knowledge, we present the first study that combines 15N CEST data with traditional model-free analyses in the study of a biological system and affirm that more ‘lean’ model-free approaches should be used cautiously.

Gardenifolins A-H, Scalemic Neolignans from Gardenia ternifolia: Chiral Resolution, Configurational Assignment, and Cytotoxic Activities against the HeLa Cancer Cell Line.

From the tropical plant Gardenia ternifolia Schumach. and Thonn. (Rubiaceae), eight stereoisomeric 2,3-dihydrobenzo[b]furan neolignans, named gardenifolins A-H (1a-d and 2a-d), were isolated and fully structurally characterized. Reversed-phase chromatography of a stem bark extract afforded two peaks, viz. mixtures I and II, each one consisting of two diastereomers and their respective enantiomers. They were resolved and stereochemically analyzed by HPLC on a chiral phase coupled to electronic circular dichroism (ECD) spectroscopy, giving single ECD spectra of all eight stereoisomers. The double-bond geometries (E or Z) of the gardenifolins A-H and their relative configurations (cis or trans) at the stereogenic centers C-7 and C-8 in the dihydrofuran ring system were assigned by 1D and 2D NMR methods, in particular, using NOE difference experiments, whereas the absolute configurations of the isolated enantiomers were established by ECD spectroscopy by applying the reversed helicity rule. The individual pure gardenifolin isomers A-H showed the most different cytotoxic effects against the human cancer HeLa cell line, with 1d and 2a displaying the highest activities, with IC50 values of 21.0 and 32.5 μM, respectively. Morphological experiments indicated that gardenifolin D (1d) induces apoptosis of HeLa cells at 25 μM.

Choerosponins A and B, Two New Cytotoxic Bridged-Ring Ketones and the Determination of Their Absolute Configurations.

Bioactivity-directed fractionation of antitumor compounds from the stem barks of Choerospondias axillaries (Roxb.) Burtt et Hill (Anacardiaceae) afforded two new cytotoxic bridged-ring ketones, choerosponins A (1) and B (2), and their structures were elucidated by spectroscopic methods; their stereochemistry was determined by NOE difference experiments, CD spectra and the modified Mosher’s method. Compound 1 has a rare dioxatricyclo skeleton. Flow cytometry and SRB methods were employed to evaluate the antitumor activity of the two compounds against tsFT210, HCT-15, HeLa, A2780 and MCF-7 cell lines, and both of them showed strong cytotoxicity. MTT and paper disc methods were also used to evaluate their anti-hypoxia and antibacterial activities, and both of them showed no apparent activities.

Rubrolides as model for the development of new lactones and their aza analogs as potential photosynthesis inhibitors.

Natural phytotoxins and their synthetic analogs are a potential source of new bioactive compounds for agriculture. Analogs of rubrolides, a class of γ-alkylidene-γ-lactones isolated from different ascidians, have been shown to interfere with the photosynthetic electron-transport chain, yet their activity needs to be improved. With this aim, ten 5-aryl-6-benzyl-4-bromopyridazin-3(2H)-ones were prepared in yields ranging from 44 to 88% by reaction of their correspondent γ-alkylidene-γ-lactones with NH2 NH2 . The structures of these rubrolide analogs were determined by (1) H- and (13) C-NMR, 2D-NMR (COSY and HETCOR), NOE difference, and MS techniques. These compounds were evaluated for their abilities of interfering with the light-driven reduction of ferricyanide by isolated spinach chloroplasts. Lactones with electron-withdrawing substituents in the para-position of the benzylidene ring were the most effective inhibitors. Characterization of the activity of 11b/11b' suggested a mechanism based on the interaction with the plastoquinone binding site of photosystem II. Addition of several compounds to the culture medium of a cyanobacterial model strain was found to inhibit algal growth. However, the relative effectiveness was not consistent with their activity in vitro, suggesting the occurrence of multiple targets and/or detoxyfication mechanisms. Indeed, the compounds showed differential effects on the heterotrophic growth of some crop species, Cucumis sativus and Sorghum bicolor. Pyridazin-3(2H)-ones 12e, 12i, and 12j, which have been found poorly active against the photosynthetic electron transport, were the most effective in inhibiting the growth of some weeds, Ipomoea grandifolia and Brachiaria decumbens, under greenhouse conditions.

Molecular structure of bridged peri-aroylnaphthalene compound having cyclohexane-cis-1,2-dioxy hinge moiety in solution

The bridged peri -aroylnaphthalene compound having cyclohexane- cis- 1,2-dioxy hinge moiety connecting two benzoyl groups was successfully synthesized through the nucleophilic aromatic substitution of 1,8-bis(4-fluorobenzoyl)-2,7-dimethoxynaphthalene and cyclohexane- cis­- 1,2-diol. The compound consists of two ingredients in solution. The ingredients were successfully separated by repeated preparative thin layer chromatographical treatments to give stable solids. By the aid of 1 H NMR spectroscopic time course tracing, the ingredients have proved to undergo mutual transformations between them to yield an equilibrium mixture of constant fraction values by standing the individual solution within several weeks, revealing that the ingredients are conformational isomers to each other. Spatial organizations of the isomers of the bridged compound in solution have been elucidated by difference NOE measurement showing rough geometry of the isomers as two “extended” forms.

Inhibition of Enterococcus faecalis biofilm formation by highly active lactones and lactams analogues of rubrolides

Seven β-aryl substituted γ-alkylidene-γ-lactones analogues of rubrolides were synthesized from mucobromic acid and converted through a lactamization with isobutylamine into their corresponding γ-hydroxy-γ-lactams (76–85%). These lactams were converted into (Z)- and (E)-γ-alkylidene-γ-lactams (23–45%). All compounds were fully characterized by IR, NMR (1H and 13C), COSY and HETCOR bidimensional experiments, and NOE difference spectroscopy experiments when necessary. Evaluation of these three different classes of compounds against Enterococcus faecalis biofilm formation showed that all classes are active and the highest biofilm inhibition activity was caused by lactam 13f (IC50 = 0.76 μg/mL). Moreover, in almost all cases at least one of the lactams is more active than its correspondent γ-alkylidene-γ-lactone. The use of rubrolides as a lead structure has proven successful for the identification of new compounds displaying novel antibacterial activities, namely biofilm inhibition, which have the potential for the development of antimicrobial drugs targeted to inhibition of the initial stages of bacterial infections, rather than bacterial viability. Such drugs are less prompt to induce bacterial resistance, being therefore a more cost-effective investment for pharmaceutical research.

Synthesis, characterization, and antifungal activity of novel (Z)-N-(2-cyano-3-phenylprop-2-en-1-yl)-alkyl/aryl-sulfonamides derived from a Morita–Baylis–Hillman adduct

A series of allyl sulfonamides prepared from the reaction of the Morita–Baylis–Hillman adduct 2-[hydroxy(phenyl)methyl]acrylonitrile with primary sulfonamides (RSO2NH2), where R=C6H5 (1), 4-FC6H4 (2), 4-ClC6H4 (3), 4-BrC6H4 (4), 4-NO2C6H4 (5), CH3 (6), CH3CH2 (7), CH3(CH2)3 (8), and CH3(CH2)7 (9), were characterized by IR, 1H and 13C NMR spectroscopies, mass spectrometry and elemental analyses. BLYP/6-31G* calculations suggested stereoselective reactions, resulting in the exclusive formation of the thermodynamically more stable Z-products. The Z-configuration of the products was confirmed by NOE difference spectroscopy and single crystal X-ray diffraction measurements. The allyl sulfonamides were active against Colletotrichum gloeosporioides, an important agent of anthracnose in plants.

Reversal of Stereoselectivity in Lithiation of Ferrocenyl‐imidazolones: Epimeric Substrates lead to Planar Chiral Enantiomers

AbstractDiastereoselective induction of planar chirality in ferrocenes often employs chiral sulfur‐, carbon‐ or phosphorus‐based directing groups. The origin of stereoselectivity in these reactions may be classified as (a) cyclopentadiene (Cp) ring‐controlled or (b) base‐controlled. These two categories are represented by auxiliaries that typically have stereogenic centers α or γ to the ferrocene core, respectively. In this study, it is shown that (−)‐2‐ferrocenyl‐1S‐triethylsilyloxy‐7aS‐hexahydropyrrolo[1,2‐c]imidazol‐3‐one, the anti‐epimer of the previously reported syn‐(1R,7aS) substrate, induces lithiation of the pro‐Rp rather than the pro‐Sp Cp hydrogen in >95:5 dr, leading to enantiomers of the syn‐derived planar chiral imidazolones upon electrophile quench and elimination. This outcome provides a practical way to prepare planar chiral enantiomers in this series without having to synthesize a more expensive D‐proline‐derived starting material, since both the syn and anti starting materials are available from a common L‐proline‐derived intermediate. The origin of stereoselectivity in lithiation of the syn and anti epimers, which have β,γ‐stereogenic centers, appears to be driven primarily by the conformational bias exerted by the β‐silyloxy moiety in each chiral auxiliary, which positions the urea carbonyl within the proximity of one of the two prochiral ortho Cp hydrogens. As such, stereoselectivity is likely Cp ring‐controlled for both compounds despite their lack of α‐ferrocenyl stereogenic centers. This conclusion is supported by the insensitivity of lithiation selectivity to the bulkiness of the base, comparisons of enantiomers, deuteration experiments, nOe difference studies, and computational modeling of the ground states and lithiation transition states for both substrates.

Antiprotozoal Isoflavan Quinones from Abrus precatorius ssp. africanus

A library of 206 extracts from selected South African plants was screened in vitro against a panel of protozoan parasites, Plasmodium falciparum, Trypanosoma brucei rhodesiense, and Leishmania donovani. A CH2Cl2/MeOH (1 : 1) extract of Abrus precatorius L. ssp. africanus strongly inhibited P. falciparum (98 %), T. b. rhodesiense (100 %), and L. donovani (76 %) when tested at a concentration of 10.0 µg/mL. The active constituents were tracked by HPLC-based activity profiling and isolated by preparative and semipreparative RP-HPLC chromatography. Structures were established by HR-ESIMS, and 1D and 2D NMR (1H, 13C, COSY, HMBC, HSQC, and NOE difference spectroscopy). Five compounds were obtained and identified as two isoflavan hydroquinones, abruquinone H (1) and abruquinone G (2), and three isoflavan quinones, abruquinone I (3), abruquinone B (4), and 7,8,3''5'-tetramethoxyisoflavan-1',4'-quinone (5). Compounds 1 and 3 were new natural products. The absolute configuration of compounds was determined by comparison of electronic circular dichroism spectra with calculated ECD data. Compounds 3 and 4 showed strong activity against T. b. rhodesiense (IC50 values of 0.30 and 0.16 µM, respectively) and good selectivity (selectivity indices of 73.7 and 50.5, respectively).

Determination of the binding epitope of RGD-peptidomimetics to αvβ3 and αIIbβ3 integrin-rich intact cells by NMR and computational studies

NMR experiments (transferred NOE and Saturation Transfer Difference) were used to shed light on the binding epitope of RGD peptidomimetics 1-3 with integrins αvβ3 and α(IIb)β3, expressed on the membrane of ECV304 bladder cancer cells and human platelets, respectively. The NMR results were supported by docking calculations of 1-3 in the active sites of αvβ3 and α(IIb)β3 integrin receptors and were compared to the results of competitive αvβ3 receptor binding assays and competitive ECV304 cell adhesion experiments. While cis RGD ligand 1 interacts mainly with the α integrin subunit through its basic guanidine group, trans RGD ligands 2 and 3 are able to interact with both the α and β integrin subunits via an electrostatic clamp.

Bisabololoxide derivatives from Artemisia persica, and determination of their absolute configurations by ECD

Five antiplasmodial bisabololoxide sesquiterpene diesters were isolated from an EtOAc extract of the aerial parts of Artemisia persica following an HPLC-time-based activity profiling of the extract. Structure elucidation was achieved by 1D and 2D NMR experiments. Relative configurations of cyclohexenone/cyclohexene and tetrahydropyran moieties of 1–5 were established on the basis of 3JH–H coupling constants and NOE difference spectra. Stereochemical correlation of the two rings, and assignment of absolute configuration of 1–5 were achieved by comparison of experimental ECD spectra with simulated ECD data for possible stereoisomers, by using time dependent density function theory (TDDFT). Bisaboloids 1–4 exhibited in vitro antimalarial activity against Plasmodium falciparum, with IC50 values ranging from 2.8 to 20.1μM, and selectivity indices (SI) in L-6 cells of 3.7–11.9.

NMR Spectroscopic Analysis Reveals Extensive Binding Interactions of Complex Xyloglucan Oligosaccharides with the Cellvibrio japonicus Glycoside Hydrolase Family 31 α‐Xylosidase

The study of the interaction of glycoside hydrolases with their substrates is fundamental to diverse applications in medicine, food and feed production, and biomass-resource utilization. Recent molecular modeling of the α-xylosidase CjXyl31A from the soil saprophyte Cellvibrio japonicus, together with protein crystallography and enzyme-kinetic analysis, has suggested that an appended PA14 protein domain, unique among glycoside hydrolase family 31 members, may confer specificity for large oligosaccharide fragments of the ubiquitous plant polysaccharide xyloglucan (J. Larsbrink, A. Izumi, F.M. Ibatullin, A. Nakhai, H.J. Gilbert, G.J. Davies, H. Brumer, Biochem. J. 2011, 436, 567-580). In the present study, a combination of NMR spectroscopic techniques, including saturation transfer difference (STD) and transfer NOE (TR-NOE) spectroscopy, was used to reveal extensive interactions between CjXyl31A active-site variants and xyloglucan hexa- and heptasaccharides. The data specifically indicate that the enzyme recognizes the entire cello-tetraosyl backbone of the substrate and product in positive enzyme subsites and makes further significant interactions with internal pendant α-(1→6)-linked xylosyl units. As such, the present analysis provides an important rationalization of previous kinetic data on CjXyl31A and unique insight into the role of the PA14 domain, which was not otherwise obtainable by protein crystallography.

Antiprotozoal isoflavan quinones from Abrus precatorius

A library of 309 extracts from selected South African plants was screened in vitro against a panel of protozoan parasites. A CH2Cl2/MeOH (1:1) extract of the whole plant of Abrus precatorius L. ssp. africanus Verdc. (Fabaceae) inhibited Plasmodium falciparum (97.8%), Trypanosoma brucei rhodesiense (100%), and Leishmania donovani (75.5%) when tested at 4.8 mg/mL. Active constituents in two different batches of plant material were tracked by HPLC-based activity profiling, and isolated by normal phase flash chromatography and RP-HPLC. Structures and relative configuration of compounds were established by NMR (1H, 13C, COSY, HMBC, HSQC, NOE difference). The absolute configuration was determined by comparison of electronic circular dichroism (ECD) spectra with calculated ECD data. Ten compounds (Fig. 1) were obtained and identified as isoflavan quinones and hydroquinones, among them five new natural products. Abruquinone I (1) and abruquinone B (8) showed strong in vitro activity against T. brucei rhodesiense (IC50s of 0.30µM ± 0.1 and 0.16µM ± 0.1, respectively). Selectivity indices (SI) as calculated from cytotoxicity data in L-6 cells were 78.3 and 61.3. These SI qualify 1 and 8 as good candidates for assessment of in vivo activity. In contrast, compound 2 was not selective, even though very active (IC50 0.88µM ± 0.1; SI 4.5) [1]. Given that 1 and 8 possess a tenfold higher SI than cynaropicrin, the only plant derived compound with demonstrated in vivo activity against T. b. rhodesiense [2], 1 and 8 are of considerable interest.

Bisabololoxide derivatives from Artemisia persica, and determination of their absolute configurations by ECD

Five new antiplasmodial bisabololoxide sesquiterpene diesters were isolated from an EtOAc extract of the aerial parts of Artemisia persica following an HPLC-time-based activity profiling of the extract. Structure elucidation was achieved by 1D and 2D NMR experiments. Relative configurations of cyclohexenone/cyclohexene and tetrahydropyran moieties of 1–5 were established on the basis of 3 J H-H coupling constants and NOE difference spectra. Stereochemical correlation of the two rings, and assignment of absolute configuration of 1–5 were achieved by comparison of experimental ECD spectra with simulated ECD data for possible stereoisomers, by using time dependent density function theory (TDDFT). Bisaboloids 1-4 exhibited in vitro antimalarial activity against Plasmodium falciparum, with IC50 values ranging from 2.8 to 20.1µM, and selectivity indices (SI) in L-6 cells of 3.7 to 11.9.

Synthesis of new β-amidodehydroaminobutyric acid derivatives and of new tyrosine derivatives using copper catalyzed C–N and C–O coupling reactions

Several β-amidodehydroaminobutyric acid derivatives were prepared from N,C-diprotected β-bromodehydroaminobutyric acids and amides by a copper catalyzed C-N coupling reaction. The best reaction conditions include the use of a catalytic amount of CuI, N,N'-dimethylethylenediamine as ligand and K(2)CO(3) as base in toluene at 110 °C. The stereochemistry of the products was determined using NOE difference experiments and the results obtained are in agreement with an E-stereochemistry. Thus, the stereochemistry is maintained in the case of the E-isomers of β-bromodehydroaminobutyric acid derivatives, but when the Z-isomers were used as substrates the reaction proceeds with inversion of configuration. The use of β-bromodehydrodipeptides as substrates was also tested. It was found that the reaction outcome depend on the stereochemistry of the β-bromodehydrodipeptide and on the nature of the first amino acid residue. The products isolated were the β-amidodehydrodipeptide derivatives and/or the corresponding dihydropyrazines. The same catalytic system (CuI/N,N'-dimethylethylene diamine) was used in the C-O coupling reactions between a tyrosine derivative and aryl bromides. The new O-aryltyrosine derivatives were isolated in moderate to good yields. The photophysical properties of two of these compounds were studied in four solvents of different polarity. The results show that these compounds after deprotection can be used as fluorescence markers.

A simple and straightforward method for determination of oxime group configuration in ethanone oximes by differential NOE experiments

Differential NOE experiments in DMSO- d 6 with pre-saturation of the N–OH protons of the oxime are described for the simple and straightforward determination of the configuration of ethanone oximes. A characteristic relative NOE of about 1% has been observed for the methyl group of E-isomers, while the Z-isomers gave an undetectable response together with an NOE interaction to the α- or β-hydrogens on the other substituent attached to oxime carbon atom.