Eucalyptals A-C with a new skeleton isolated from Eucalyptus globulus

Eucalyptals A-C (1-3) with a new skeleton of 3,5-diformyl-isopentyl phloroglucinol-coupled cadinane were isolated from the fruits of Eucalyptus globulus. Their structures were elucidated by spectroscopic analysis, and that of 1 was confirmed by single-crystal X-ray diffraction. The biosynthetic pathway of 1-3 was also postulated. Compounds 1-3 exhibited selective cytotoxicity against the HL-60 cell line.     

Automatic assignment of absolute configuration from 1D NMR data

[reaction: see text] Opposite enantiomers exhibit different NMR properties in the presence of an external common chiral element, and a chiral molecule exhibits different NMR properties in the presence of external enantiomeric chiral elements. Automatic prediction of such differences, and comparison with experimental values, leads to the assignment of the absolute configuration. Here two cases are reported, one using a dataset of 80 chiral secondary alcohols esterified with (R)-MTPA and the corresponding (1)H NMR chemical shifts and the other with 94 (13)C NMR chemical shifts of chiral secondary alcohols in two enantiomeric chiral solvents. For the first application, counterpropagation neural networks were trained to predict the sign of the difference between chemical shifts of opposite stereoisomers. The neural networks were trained to process the chirality code of the alcohol as the input, and to give the NMR property as the output. In the second application, similar neural networks were employed, but the property to predict was the difference of chemical shifts in the two enantiomeric solvents. For independent test sets of 20 objects, 100% correct predictions were obtained in both applications concerning the sign of the chemical shifts differences. Additionally, with the second dataset, the difference of chemical shifts in the two enantiomeric solvents was quantitatively predicted, yielding r(2) 0.936 for the test set between the predicted and experimental values.     

Antimicrobial activity of globulol isolated from the fruits of Eucalyptus globulus Labill

An antimicrobial sesquiterpene was separated by bioassay-guided isolation from the petroleum ether fraction of the ethanol crude extract of Eucalyptus globulus Labill (Myrtaceae) fruits, and was identified as globulol by physicochemical properties and spectroscopic analysis. Mycelial growth method revealed that the median effective inhibitory concentration (IC50) values of globulol on Alternaria solani, Fusarium oxysporum f.sp. niverum, F. graminearum, Rhizoctonia solani and Venturia pirina were 47.1 microg mL(-1), 114.3 microg mL(-1), 53.4 microg mL(-1), 56.9 microg mL(-1), 32.1 microg mL(-1) and 21.8 microg mL(-1), respectively. MTT-colorimetric assay revealed that IC50 values of globulol on Xanthomonas vesicatoria and Bacillus subtilis were 158.0 microg mL(-1) and 737.2 microg mL(-1), respectively. The results indicated that globulol could be a main antimicrobial compound in the ethanol crude extract of E. globulus fruits.     

A new pair of enantiomeric lignans from the fruits of Morinda citrifolia and their absolute configuration

A new pair of sesamin-type lignan enantiomers (±)-morifolia A (1a/1b) together with eight known analogues (2–9) were isolated from the fruits of Morinda citrifolia. Their structures were established by spectroscopic data and the absolute configurations of 1a/1b were determined by ECD calculation. All compounds were examined for their inhibitory effects on the nitric oxide (NO) production induced by lipopolysaccharide (LPS) in RAW 264.7 macrophages, and compounds 1a, 1b, 2–4 and 7–9 exhibited pronounced inhibition with IC₅₀ values in the range of 1.97–8.01 (μM, being more active than the positive control, quercetin (IC₅₀ = 15.32 (M).     

Chiral HPLC separation and absolute configuration assignment of a series of new triazole compounds

A series of novel chiral triazole compounds were synthesized. They were separated into enantiomers by liquid chromatography on an amylose tris(3,5-dimethylphenylcarbamate) (ADMPC) chiral stationary phase (CSP). The absolute configuration of each enantiomer of the investigated compounds was established by combined use of chemical correlation, chiral HPLC and circular dichroism (CD) spectra analysis methods. The influence of the mobile-phase modifiers and the structure of chiral triazole compounds on the chiral separation and retention were investigated. Reversal of the elution order of some enantiomeric pairs upon using different mobile-phase modifier was observed. The temperature effect on the chiral separation and the thermodynamic properties including enthalpy and entropy change of binding to the ADMPC-CSP were also investigated.     

Three challenges toward the assignment of absolute configuration of gymnocin-B

The absolute configuration of gymnocin-B has been determined to be (S)-10 and (S)-37. Three challenges toward the configurational assignment of this largest of the polyether marine toxin include (i) introduction of p-(meso-triphenylporphyrin)-cinnamate group (TPPcinnamate) on sterically hindered 10-, 37-hydroxyls under mild conditions, (ii) conformational analysis in the presence of TPPcinnamates at C-10 and C-37 positions on the flexible seven-membered rings embodied in a large polyether ladder-like scaffold structure, and (iii) determination of the chirality at C-10 and C-37 on the basis of porphyrin/porphyrin circular dichroism exciton-coupled interaction over a large distance. The experimentally obtained positive exciton couplet by CD and FDCD of the bis-TPPcin derivative of gymnocin-B is in good agreement with that of theoretically calculated CD of the MMFF optimized structures, by employing DeVoe's coupled oscillator approach, thus establishing the full absolute configuration of gymnocin-B.     

Synthesis of eupomatilone-6 and assignment of its absolute configuration

[Reaction: see text]. The Zn-mediated Barbier reaction of the biarylaldehyde 8 with crotyl bromide followed by hydroboration and oxidation provided the gamma-butyrolactones 4 and 5. The stereoselective installation of methyl group at C-3 by using LiHMDS and MeI completed the synthesis of racemic eupomatilone-6 (2) and its diastereomer 3. The spectroscopic data of 2 was in full agreement with reported spectra of natural product, thus confirming the revised relative configuration of eupomatilone-6. Similarly, an optically active (3R,4R,5S)-isomer of eupomatilone-6 (23) was prepared in which the aldol reaction with thiazolidinethione as a chiral auxiliary was employed as a key step. On the basis of the spectroscopic data and optical rotation values of 23, the absolute configuration of eupomatilone-6 was proposed.     

The assignment of absolute configuration of cyanohydrins by NMR

Derivatization of aldehyde cyanohydrins as (R)- and (S)-MPA esters and comparison of the corresponding 1H- and 13C-NMR spectra allows the assignment of their absolute configuration.     

On the assignment of the absolute configuration at the isolated methyl branch in miyakosyne A,cytotoxic linear acetylene,from the deep-sea marine sponge Petrosia sp.

Absolute configuration of miyakosyne A at its isolated branched methyl stereogenic center has been studied by chemical degradation in combination with esterification with the Ohrui's acid. Comparison of the ¹H NMR data of the relevant diesters for the degradation product and the synthetic standards indicated the 14R-configuration.     

Resolution of racemic carbonucleosides and assignment of the absolute configuration by NMR

Resolution of racemic cis-6-chloro-9-[2-(hydroxymethyl)cyclopentyl]-9H-purine 1 was performed using HPLC with a semipreparative column of β-cyclodextrin using 85:15 water/acetonitrile as eluent. The absolute configurations of the enantiomers were determined by NMR studies of their (R)- and (S)-methoxyphenylacetates.     

Eucaglobulin, A New Complex of Gallotannin and Monoterpene from Eucalyptus globulus

EucalyPtusgl0bulusLabill.(Myrtaceae)isakindofmedicinalplantwidelydistributedintheYunnanpr0vinceofChina.ItSleaves,rootSandffoitShavebeenusedastraditionalremediesforthetreatmentofinfluenza,dysentery,enteritis,rheumatalgiaandbleeding.BesidesvolatileterpenoidconstituentSintheessential0iloftheleavesandfruits,theoccurrenceofanumber0fphloroglucinol-sesquiterpene-or-m0n0terpene-c0upledcomPoundsnamedmacrocarpals'andeugl0bals'intheleavesandbudshasbeenrepofted.Inordertostudythechendcalandbioactivecon…     

Some new protocols for the assignment of absolute configuration by NMR spectroscopy using chiral solvating agents and CDAs

The utility of enantiopure BINOL (1,10-Bi-2-naphthol), in a ternary ion-pair complex, which is obtained using a carboxylic acid and an organic base, as a versatile chiral solvating agent (CSA) has been demonstrated for chiral analysis and the absolute configuration assignment of hydroxy acids. Another protocol where the utility of NOBIN as a CSA has been developed for discrimination and absolute configuration assignment of acids, hydroxy acids and their derivatives with a distinct strategy where a third ingredient, p-toluenesulfonic acid (p-TsOH) serves as a linker. In addition some three component chiral derivatization protocols have been introduced, such as the use of 2-formylphenylboronic acid and enantiopure mandelic acid or a primary amine for the determination of the configuration of primary amines and hydroxy acids, respectively. A simple, rapid and highly efficient three component chiral derivatizing protocol has also been discussed which was developed for assigning the absolute configuration of chiral α-hydroxy acids and their derivatives, which involves the coupling of 2-formylphenylboronic acid with (R)-[1,1-binaphthalene]-2,2-diamine, and (S)-[1,1-binaphthalene]-2,2-diamine separately. In a few examples, the DFT based theoretical calculations have been carried out to determine the geometry optimized structures of the complexes.     

First synthesis and absolute configuration of decaturin D

The first synthesis of (+)-decaturin D (1), an antiinsectant diterpenoid isolated from Penicillium thiersii, was accomplished by employing our original spiro-cyclization reaction as the key step. The absolute configuration of the naturally occurring 1 was determined.     

Perisomalien A,a new cytotoxic scalarane sesterterpene from the fruits of Periploca somaliensis

Abstract

The CHCl₃ fraction of MeOH extract of Periploca somaliensis (family Asclepiadaceae) fruits afforded a new scalarane sesterterpene, namely perisomalien A (1), along with lupeol acetate (2), β-amyrin (3), cycloart-23Z-ene-3β,25-diol (4), and β-sitosterol-3-O-β-D-glucopyranoside (5). Their chemical structures were established by various spectroscopic analyses, in addition to comparison with the formerly reported data. Moreover, the cytotoxic activity of these metabolites was assessed towards MCF-7, HepG2, and HCT-116 tumour cell lines using sulforhodamine B (SRB) assay. Compound 4 showed the most potent cytotoxic profile with IC₅₀ 9.0?µM towards MCF-7, compared to doxorubicin (IC₅₀ 0.18?µM). Also, 1 and 4 possessed the most potent effect towards HepG2 with IC₅₀s 26.7 and 25.9?μM, respectively. In addition, all tested compounds showed cytotoxic effects with IC₅₀ values ranging from 19.9 to 39.3?µM against HCT-116.     

Diverse prieurianin-type limonoid derivatives from the fruits of Aphanamixis grandifolia and their absolute configuration determination

Twenty-five new highly oxygenated prieurianin-type limonoids, zaphaprinins A–Y (1–25), were isolated from the fruits of Aphanamixis grandifolia. Their structures were elucidated by extensive spectroscopic analyses. Absolute configurations for the key structures like 1 were assigned by a comprehensive method, such as comparing the calculated electronic circular dichroism (ECD) with the experimental one, single-crystal X-ray and Mosher ester method were also involved for other compounds' study. The solid data from X-ray diffraction allowed revision of the stereochemistry of the C₁–C₁₄ tetrahydropyran ring-type limonoid. The insecticidal activities of all the limonoids were evaluated.     

A convenient method for the assignment of the absolute configuration to cyclic amines

We have assigned the absolute configuration to trans-2,5-dimethylpyrrolidine and trans-2,6-dimethyl-piperidine through radical chlorination in ω-1 position of optically active amines, 2 and 5, of known absolute configuration, followed by cyclization. CD curves of 1f and 4g derivatives indicate that the reaction is stereospecific. The absolute configuration of trans-2,5-dimethyl-Δ³-pyrròline has also been determined.