Synthesis and biological activity of S-oxo-[(methylthio)-methyl]cysteinols

A convenient route was developed to synthesize S-oxo-[(methylthio)-methyl]cysteinols on a large scale from cheap l-serine as the starting material. The structures of diastereoisomers were determined by NMR, CD spectra, and X-ray diffraction analysis. All four diastereoisomers were examined for their ability to inhibit certain bacteria from growing.     

Spontaneous generation of chirality and chiroptical spectra of N-nitroso-2,4-diaryl-3-azabicyclo[3.3.1]nonanes

The crystal structures of several bicyclic N-nitrosamines indicate that they crystallize in the chiral (Sohncke) space group P2₁2₁2₁ as conglomerates. This allows the resolution of these compounds by manual picking of the enantiomorphous crystals. The optical activity of the single crystals was confirmed by their CD spectra taken in KBr disks. The absolute configurations of the title nitrosamines were assigned by crystallographic measurements and by a comparison of their CD spectra with those of a reference compound resolved by classical methods. The observed Cotton effect signs, corresponding to the n–π¹ transition, were correlated with the helicity of the inherently chiral nitrosamine chromophore.     

Glabralides A – C,three novel meroterpenoids from Sarcandra glabra

Glabralides A–C (1–3), three novel meroterpenoids including two unprecedented skeletons were isolated from the whole plants of Sarcandra glabra. Glabralide A (1) represented a unique skeleton of the chalcone-coupled monoterpenoid, bearing a bicyclo [2.2.2] octene core unit with five chiral centers. The structures were established by spectroscopic methods, including 2D NMR experiments, and the absolute configurations were determined using circular dichroic (CD) spectra. The plausible biogenetic pathway for 1 suggested that α-phellandrene was conjugated with chalcone by Diels-Alder cyclization, and for 3 implied that α-phellandrene and o-hydroxy phenylacetate cyclized by an uncommon radical addition and cationic cyclization.     

Absolute stereostructure of Andirolides A-G from the flower of Carapa guianensis (Meliaceae)

A new gedunin, three new mexicanolides and three new phragmalin-type limonoids named Andirolides A (1), B (2), C (3), D (4), E (5), F (6), and G (7) were isolated from oil of the flower of Carapa guianensis Aublet (Meliaceae). Their absolute stereostructures were determined by 2D NMR and CD spectra, and single-crystal X-ray analysis, and all compounds were confirmed to have the C-17βH configuration. Considering the similarity in CD spectra between Andirolide G (7) and the xyloccensins reported by Wu, we concluded that the structures of xyloccensins should be revised so as to have the absolute configuration of 17R.     

Fluevirines A–D,four new securinega-type alkaloids from Flueggea virosa

Four new securinega-type alkaloids, fluevirines A–D (1–4), along with ten known ones, were isolated from the twigs and leaves of Flueggea virosa. The structures of the new ones were elucidated by means of spectroscopic methods, and their absolute configurations were assigned by CD spectra. Among them, fluevirine A (1) was a novel C,C-linked dimeric indolizidine alkaloid and showed weak antimicrobial activity against Staphylococcus aureus.     

New macrocyclic sesterterpenoids from a scale insect (ceroplastes ceriferus)

Six new macrocyclic sesterterpenoids 1–6 were isolated from the secretion of a scale insect, Ceroplastes ceriferus Anderson, and their structures determined. Chemical correlation has also been accomplished. Stereochemistry was elucidated by comparison of the CD spectra of the ozonolysis product of 1-acetate and a corresponding synthetic substance of known absolute configuration.     

Syntheses and characterization of copper(II) complexes with Schiff-base ligands derived from ethylenediamine,diphenylethylenediamine and nitro,bromo and methoxy salicylaldehyde

Copper(II) quelates with Schiff bases derived from ethylenediamine, 1R,2R-(+)- or 1S,2S-(−)-1,2-diphenylethylenediamine and 5-X-salicylaldehyde (X=OCH₃, H, Br, NO₂) have been synthesized and characterized by elemental analysis and IR and UV-visible spectroscopies. The ORD and CD spectra of the chiral ligands and their related complexes have also been measured. The absorption and CD spectra of the metal complexes in the visible region are consistent with near square planar coordination geometries. Trends in absorption spectra over the series of complexes can be correlated with electronic effects of the substituents at position 5 of the salicylaldehyde. The sign patterns of the CD spectra in both UV and visible regions suggest the prevalence of δ and λ conformations for the chelate ring in the complexes of Schiff bases derived, respectively, from R,R- and S,S-diamines. Specific features of the CD spectra of the metal complexes are discussed in terms of the exciton chirality method.     

Pheromone synthesis. Part 264: Synthesis of the core 3-oxabicyclo[3.3.0]octane structures of gomadalactones A,B and C,the components of the contact sex pheromone of the white-spotted longicorn beetle,Anoplophora malasiaca

The core bicyclic cyclopentanelactone structures of gomadalactones A, B and C with α-hydroxyketone system were synthesized from (R)-pulegone, employing deconjugation of an α,β-unsaturated lactone as the key step. Comparison of the CD spectra of the synthetic compounds with those of the natural products confirmed the absolute configuration of the natural pheromone components as proposed in 2007. X-ray crystallographic analysis of the model compound of gomadalactone B core structure was carried out.     

Vernodalidimers A and B, novel orthoester elemanolide dimers from seeds of Vernonia anthelmintica

Two novel elemanolide dimers, vernodalidimers A (1) and B (2), possessing a rare tricyclic ortho ester moiety, were isolated from the seeds of Vernonia anthelmintica. Their structures were elucidated by 1D and 2D NMR data and CD spectra. Vernodalidimers A (1) and B (2) exhibited potent cell growth inhibitory activity against HL-60 cells (IC₅₀ 0.72 and 0.47 μM, respectively).     

Synthesis and chiral discrimination of cyclic aromatic amides and the determination of their absolute configuration by TD-DFT calculations

Novel chiral cyclic molecules composed of aromatic triamides were constructed in modest yield from 4-N-(4′-methoxybenzyl)amino-3-decyloxybenzoic acid using dichlorotriphenylphosphorane, because of the preorganized component of the tertiary benzanilide moieties. A racemic mixture of two diastereomers, syn and anti conformers of cyclic aromatic triamides, was resolved into enantiomers by HPLC using a preparative chiral column. The absolute configuration of each enantiomer in both diastereomers was determined by comparison of the time-dependent density functional theory (TD-DFT) calculated circular dichroic (CD) spectra with the experimentally derived CD spectra recorded on each sample.     

Pestalustaines A and B,unprecedented sesquiterpene and coumarin derivatives from endophytic fungus Pestalotiopsis adusta

Pestalustaines A (1) and B (2), one unique sesquiterpene possessing an unusual 5/6/7-fused tricyclic ring system and one unprecedented coumarin derivative bearing 6/6/5/5-fused tetracyclic ring system, were isolated from the plant-derived Pestalotiopsis adusta. Their structures with absolute configurations were established by extensive NMR analysis, X-ray crystallography, and CD spectra associated with TD-DFT calculation. Hypothetical biosynthetic pathways for compounds 1 and 2 are proposed. Compounds 1 and 2 showed weak to moderate cytotoxic activities against three human tumor cell lines HeLa, HCT116, and A549, whose IC₅₀ values were ranged from 21.01 to 55.43?μM.     

Bieremoligularolide and eremoligularin, two novel sesquiterpenoids from Ligularia muliensis

From the roots of Ligularia muliensis, a novel bieremophilanolide and a new eremophilanolide have been isolated and their structures were elucidated by spectroscopic techniques, including HRMS, IR, UV, 1D-NMR, 2D-NMR, and CD spectra.     

In-situ interaction of nano-PbS with gelatin

Water-soluble gelatin–PbS bionanocomposites(BNCs)were synthesized via a facile one-pot chemical reaction method at pH7.40.The samples were characterized by transmission electron microscopy(TEM),X-ray diffraction(XRD),UV-vis absorption spectra(UV-vis),Fourier transform infrared spectra(FT-IR)and circular dichroism(CD).FT-IR data were used to envisage the binding of PbS particles with oxygen atoms of carbonyl groups of gelatin molecule.The possible integration mechanism between gelatin and PbS was discussed in detail.The effect of Pb2+and PbS on the conformations of gelatin has also been analyzed by means of UV-vis,CD and FT-IR spectra,resulting in less-helix content and more open structures(-sheet,β-turn,or expanded).A new formula to calculate the association constant was proposed according to the relationship between the absorbance of gelatin–PbS BNCs and the free concentration of PbS,and apparent association constants K(298/303/308 K:3.11/2.00/1.60×106mol/L)at three different temperatures were calculated based on this formula.Thermodynamic parameters such asΔGθ,ΔHθ andΔSθ were also determined.The results of the thermodynamic investigations indicated that the reaction was spontaneous(ΔGθ<0),and enthalpy-driven(ΔHθ<0).     

Stereoselective synthesis of (3S,4R)-3,4-dimethyl-(S)-glutamine and the absolute stereochemistry of the natural product from papuamides and callipeltin

(3S,4R)-3,4-Dimethyl-(S)-glutamine, a common component of cyclodepsipeptides, papuamide A and callipeltin A, was stereoselectively prepared from (S)-pyroglutamic acid. The stereostructure of natural dimethylglutamine was unambiguously confirmed to be (2S,3S,4R) by comparison of the CD and NMR spectra of the synthetic 3,4-dimethylpyroglutamic acid with the hydrolysate of callipeltin A.     

MD‐based CD calculations for the assignment of the absolute axial configuration of the naphthylisoquinoline alkaloid dioncophylline A

The circular dichroism (CD) of the biaryl alkaloid dioncophylline A ( 2 ) was investigated by CD calculations; the structures were generated by molecular dynamics (MD) simulations using the force field CVFF. From these structures the CD spectra were calculated with the semiempirical method CNDO/2S. Summing up the single CD spectra yielded the final spectrum. In contrast to our earlier method based on the Boltzmann weighting, the MD‐assisted approach permitted to assign the flexible biaryl axis of dioncophylline A ( 2 ), which is found to be P. © 2001 John Wiley & Sons, Inc. J Comput Chem 22: 1273–1278, 2001     

Microwave spectrum,structure, dipole moment and internal rotation of ethyl fluorosilane

Microwave spectra of the trans and gauche isomers of ethyl fluorosilane and their eleven isotopically substituted species have been measured. The r_s structures of the two isomers were determined from the observed moments of inertia. The molecular structures found for the two isomers in the present study are compared with those of analogous molecules. Dipole moments of the two isomers were determined by Stark-effect measurements and are also compared with those of analogous molecules. The energy difference between the trans and gauche isomers was obtained from the relative intensity measurements of the spectra and the barrier to internal rotation of the methyl group for the gauche isomer was obtained from the A—E splittings of the spectra in the first excited methyl torsional state. The V₃ value was 2775 ± 25 cal mol^?1.     

Sorbifuranones A-C, sorbicillinoid metabolites from Penicillium strains isolated from Mediterranean sponges

Three novel natural products, sorbifuranones A-C (4-6), were isolated from a Penicillium chrysogenum fungus isolated from the marine sponge Ircinia fasciculata. Sorbifuranones B (5) and C (6) and 2′,3′-dihydrosorbicillin, a putative precursor to sorbifuranone B, were also found in the culture of another Penicillium strain, which was isolated from the sponge Tethya aurantium. Their constitutions were elucidated mainly by 2D NMR. NOE correlations in combination with quantum chemical calculations and comparison of experimental and calculated electronic circular dichroism (CD) spectra permitted assignment of the absolute configuration of sorbifuranone C. The structures hint at a two-step cleavage-cyclization sequence of sorbifuranone A (4) leading to the spiro compound sorbifuranone C, while sorbifuranone B is likely to be the respective cleavage product of a putative 2′,3′-dihydrosorbifuranone A, which cannot cyclize further.     

Globostelletins J–S,isomalabaricanes with unusual cyclopentane sidechains from the marine sponge Rhabdastrella globostellata

Nine new isomalabaricane-type triterpenoids namely globostelletins J–R (1–9) were isolated from the marine sponge Rhabdastrella globostellata. Their structures were established on the basis of extensive spectroscopic data analysis including IR, MS, 1D and 2D NMR, and CD spectra. Globostelletins J–R are characterized by the presence of an unusual cyclopentane unit linked at different positions of sidechains. These unprecedented structures enriched a number of new skeletons in isomalabaricane family. The biogenetic relationship of the isolated compounds is postulated. All compounds were tested for the inhibitory activities against human tumor-related protein kinases.     

Six new monoterpenoid indole alkaloids from the aerial part of Gelsemium elegans

Six new monoterpenoid indole alkaloids along with four known analogues were isolated from the aerial part of Gelsemium elegans. Their structures with absolute configurations were elucidated by NMR, HRESIMS, X-ray diffraction, CD spectra, and molecular modeling calculation. Among them, gelselenidine (1) is a new gelsedine-type alkaloid with a 2,3-epoxybutane unit. Gelseziridine (2) is the first example of monoterpenoid indole alkaloids with an oxaziridine residue. Compounds 6 and 7 are a pair of N₄ epimers of humantenine N₄-oxide. A plausible biogenetic pathway for compounds 1-4 was also proposed.     

Circular dichroism spectra of trans-chalcone epoxides

The electronic absorption and CD spectra of (−)-trans-chalcone epoxide and its derivatives with methyl and alkoxy substituents at the ortho-positions of the aromatic rings have been measured. The spectra have been assigned with help of the energies, oscillatory strengths, and rotatory strengths of the singlet transitions obtained from DFT calculations. The features of the CD spectra, indicative of the absolute configuration, are the carbonyl n–π¹ band and two further strong bands assigned to the overlapping signals of π–π¹ and n_epoxy–π¹ excitations.