Heteronuclear Multiple Bond Correlation Research Articles

Characterization of elusive rhamnosyl dioxanium ions and their application in complex oligosaccharide synthesis

Attaining complete anomeric control is still one of the biggest challenges in carbohydrate chemistry. Glycosyl cations such as oxocarbenium and dioxanium ions are key intermediates of glycosylation reactions. Characterizing these highly-reactive intermediates and understanding their glycosylation mechanisms are essential to the stereoselective synthesis of complex carbohydrates. Although C-2 acyl neighbouring-group participation has been well-studied, the reactive intermediates in more remote participation remain elusive and are challenging to study. Herein, we report a workflow that is utilized to characterize rhamnosyl 1,3-bridged dioxanium ions derived from C-3 p-anisoyl esterified donors. First, we use a combination of quantum-chemical calculations and infrared ion spectroscopy to determine the structure of the cationic glycosylation intermediate in the gas-phase. In addition, we establish the structure and exchange kinetics of highly-reactive, low-abundance species in the solution-phase using chemical exchange saturation transfer, exchange spectroscopy, correlation spectroscopy, heteronuclear single-quantum correlation, and heteronuclear multiple-bond correlation nuclear magnetic resonance spectroscopy. Finally, we apply C-3 acyl neighbouring-group participation to the synthesis of complex bacterial oligosaccharides. This combined approach of finding answers to fundamental physical-chemical questions and their application in organic synthesis provides a robust basis for elucidating highly-reactive intermediates in glycosylation reactions.

Chaenomelin, a New Phenolic Glycoside, and Anti-Helicobacter pylori Phenolic Compounds from the Leaves of Salix chaenomeloides.

Salix chaenomeloides Kimura, commonly known as pussy willow, is a deciduous shrub and tree belonging to the Salicaceae family. The genus Salix spp. has been known as a healing herb for the treatment of fever, inflammation, and pain relief. The current study aimed to investigate the potential bioactive natural products from S. chaenomeloides leaves and evaluate their antibacterial activity against Helicobacter pylori. A phytochemical investigation of the ethanol (EtOH) extract of S. chaenomeloides leaves led to the isolation of 13 phenolic compounds (1-13) from the ethyl acetate (EtOAc) fraction, which showed antibacterial activity against H. pylori strain 51. The chemical structure of a new phenolic glycoside, chaenomelin (1), was established by a detailed analysis of 1D and 2D (1H-1H correlation spectroscopy (COSY), heteronuclear single-quantum coherence (HSQC), and heteronuclear multiple-bond correlation (HMBC)) nuclear magnetic resonance (NMR), high-resolution electrospray ionization mass spectroscopy (HR-ESIMS), and chemical reactions. The other known compounds were identified as 5-O-trans-p-coumaroyl quinic acid methyl ester (2), tremulacin (3), citrusin C (4), benzyl 3-O-β-d-glucopyranosyl-7-hydroxybenzoate (5), tremuloidin (6), 1-[O-β-d-glucopyranosyl(1→2)-β-d-glucopyranosyl]oxy-2-phenol (7), arbutin cinnamate (8), tremulacinol (9), catechol (10), 4-hydroxybenzaldehyde (11), kaempferol 3-rutinoside (12), and narcissin (13), based on the comparison of their NMR spectra with the reported data and liquid chromatography/mass spectrometry (LC/MS) analysis. The isolated compounds were evaluated for antibacterial activity against H. pylori strain 51. Among the isolates, 1-[O-β-d-glucopyranosyl(1→2)-β-d-glucopyranosyl]oxy-2-phenol (7) and arbutin cinnamate (8) exhibited antibacterial activity against H. pylori strain 51, with inhibitions of 31.4% and 33.9%, respectively, at a final concentration of 100 μM. These results were comparable to that of quercetin (38.4% inhibition), which served as a positive control. Generally, these findings highlight the potential of the active compounds 7 and 8 as antibacterial agents against H. pylori.

FLAVONOIDES E ÁCIDOS FENÓLICOS ISOLADOS DOS EXTRATOS METANÓLICOS DAS FOLHAS E GALHOS DE Macrolobium acaciifolium (FABACEAE)

FLAVONOIDS AND PHENOLIC ACIDS ISOLATED FROM Macrolobium acaciifolium (FABACEAE) LEAVES AND BRANCHES METHANOLIC EXTRACTS. The phytochemical study of Macrolobium acaciifolium extracts allowed the isolation and identification of 18 substances, 15 of which are reported for the first time in this species. From the methanolic extract of the leaves, the flavonoids luteolin-3’-O-α-L-rhamnoside (1), neoastilbin (2), astilbin (3), neoisoastilbin (4), isoastilbin (5), quercetin-3-O-α-L-rhamnoside (6), quercetin-3-O-rutinoside (7), kaempferol-3-O-rutinoside (8), quercetin-3-O-glicoside (9) and kaempferol-7-O-rutinoside (10) were isolated. From the methanolic extract of branches, the flavonoids chrysoeriol (13), apigenin (14), 7,4’-dihydroxyflavone (16), eriodictyol (17) and luteolin (18), in addition to the phenolic acids 3,4-dihydroxybenzoic acid (11), 3-methoxy,4-hydroxybenzoate (12) and methyl 3,4-dihydroxybenzoate (15) were isolated. The structural identification of the compounds was established by proton nuclear magnetic resonance (1H NMR), carbon-13 nuclear magnetic resonance (13C NMR), heteronuclear single quantum coherence (HSQC), heteronuclear multiple bond correlation (HMBC) and correlated spectroscopy (COSY) analyses. In this paper, we also discuss about the anisotropic effects on H-1’’, H-2’’, H-5’’ and H-6’’ rhamnose of isomers dihydroflavonoids.

A multiplex approach of MS, 1D-, and 2D-NMR metabolomics in plant ontogeny: A case study on Clusia minor L. organs (leaf, flower, fruit, and seed).

The genus Clusia L. is mostly recognised for the production of prenylated benzophenones and tocotrienol derivatives. The objective of this study was to map metabolome variation within Clusia minor organs at different developmental stages. In total 15 organs/stages (leaf, flower, fruit, and seed) were analysed by UPLC-MS and 1H- and heteronuclear multiple-bond correlation (HMBC)-NMR-based metabolomics. This work led to the assignment of 46 metabolites, belonging to organic acids(1), sugars(2) phenolic acids(1), flavonoids(3) prenylated xanthones(1) benzophenones(4) and tocotrienols(2). Multivariate data analyses explained the variability and classification of samples, highlighting chemical markers that discriminate each organ/stage. Leaves were found to be rich in 5-hydroxy-8-methyltocotrienol (8.5 μg/mg f.w.), while flowers were abundant in the polyprenylated benzophenone nemorosone with maximum level detected in the fully mature flower bud (43 μg/mg f.w.). Nemorosone and 5-hydroxy tocotrienoloic acid were isolated from FL6 for full structural characterisation. This is the first report of the NMR assignments of 5-hydroxy tocotrienoloic acid, and its maximum level was detected in the mature fruit at 50 μg/mg f.w. Seeds as typical storage organ were rich in sugars and omega-6 fatty acids. To the best of our knowledge, this is the first report on a comparative 1D-/2D-NMR approach to assess compositional differences in ontogeny studies compared with LC-MS exemplified by Clusia organs. Results derived from this study provide better understanding of the stages at which maximal production of natural compounds occur and elucidate in which developmental stages the enzymes responsible for the production of such metabolites are preferentially expressed.

Solvents Influence 1H NMR Chemical Shifts and Complete 1H and 13C NMR Spectral Assignments for Florfenicol

Florfenicol (FFC) is an important and widely used veterinary drug, and its structure has been characterized by nuclear magnetic resonance (NMR) spectroscopy. The study aimed to investigate the influences of solvent type, solvent concentration, and temperature on the chemical shifts of the 1H NMR of FFC. The results showed that different types of solvents significantly affected the chemical shifts, especially the chemical shifts of 2-H, 3-H, 5-H, and the active protons. When DMSO-d 6 is used as the solvent, there is no significant difference in the chemical shifts of FFC with a concentration ranging from 20 to 250 mmol/L; however, as the temperature increases, the chemical shifts of the active protons move to a higher field. Besides, the NMR spectroscopic data and structural analysis of FFC were refined by 1H, 13C, distortionless enhancement by polarization transfer-135 (DEPT-135), 1H–1H correlation spectroscopy (1H–1H COSY), phase-sensitive gradient heteronuclear singular quantum correlation (gHSQC), and heteronuclear multiple bond correlation (gHMBC) NMR spectroscopy using DMSO-d 6 as a solvent. The study will help with qualitative and quantitative analysis of FFC in the future.

Separation, identification, and structural characterization of sucrose ester isomers from tobacco.

Sucrose esters (SEs) are crucial tobacco smoke flavor precursors and play a significant role in tobacco's functionality. Due to their structural complexity, the separation and analysis of SEs in tobacco remain a major challenge, and massive structures of SEs have not yet been fully identified. In this study, the fractions enriched in SEs were obtained from oriental and flue-cured tobacco through a series of pretreatments, and two types of SEs (Types I and II) were distinguished by liquid chromatography-tandem mass spectrometry (LC-MSn ) analysis, with Type II SEs newly characterized in tobacco. Five groups of main SEs were further purified using preparative high-performance LC (HPLC) coupled to an evaporative light scattering detector, and their structures were characterized by nuclear magnetic resonance spectrometry techniques including 1 H, 13 C, correlation spectroscopy, heteronuclear single quantum correlation, and heteronuclear multiple bond correlation. By combining LC-MSn and nuclear magnetic resonance spectrometry, the structures of eight SE isomers were finally proposed, of which four were newly identified. These findings further enhance the understanding of the structural diversity of SEs in tobacco, serving as a valuable reference for future research on the elucidation, synthesis, and metabolism of SEs.

Evaluation of Cytotoxic and Antioxidant Effect of Guaianolid Sesquiterpenes fromFerula hindukushensis

AbstractFerulaspecies have been recognized as crucial medicinal plants that are known for producing a variety of sesquiterpenes, such as sesquiterpene lactones and sesquiterpene coumarins. However, guaianolide sesquiterpenes, which are sesquiterpene lactones that contain an alpha‐methylene‐gamma‐lactone moiety, are rare inFerulaspp.Ferula hindukushensis, an endemic species found in Afghanistan, Pakistan, and Iran, belongs to theFerulagenus. In this study, the normal column chromatography technique was employed to fractionate the dichloromethane extract ofF. hindukushensis. The structures of two guaianolide sesquiterpenes were identified using various nuclear magnetic resonance (NMR) spectra, such as13C NMR,1H NMR, and heteronuclear multiple bond correlation (HMBC), and were compared with the literature interpretation to confirm their structural characteristics. Moreover, the 3‐(4,5‐dimethylthiazol‐2‐yl)‐2,5‐diphenyl‐2H‐tetrazolium bromide (MTT) assay was employed to examine the cytotoxicity of guaianolide compounds on various cell lines, including MCF‐7, 3T3, HT‐29, MCF‐10, PC12, and A549. The antioxidant effects of these compounds were evaluated using ferric reducing antioxidant power (FRAP) and 2,2‐diphenyl‐1‐picrylhydrazyl (DPPH) assays. The findings indicated that the antioxidant activity of the compounds was lower than that of vitamin C at the same concentration. The cytotoxic effects of the compounds varied depending on the cell types. Nevertheless, except for HT‐29, a concentration lower than 125 μg/mL was found to be non‐toxic for all cell lines.

Synthesis of some new 2-(substituted-phenyl)imidazo[4,5-c] and [4,5-b]pyridine derivatives and their antimicrobial activities.

The synthesis of 5H-imidazo[4,5-c]pyridines analogues (1a - 1h) and 4H-imidazo[4,5-b]pyridines (3a - 3c) was achieved by reacting 3,4-diaminopyridine or 2,3-diaminopyridine with Na2S2O5 adduct of corresponding benzaldehydes (a1 - a8). Alkylation of compounds (1a - 1h) and (3a - 3c) using 4-chlorobenzyl and /or butyl bromide under basic conditions (K2CO3, DMF) predominantly resulted in the formation of N5 regioisomers (2a - 2l) and N4,3 regioisomers (4a - 4c1,2), respectively. The N5,4,3-regioisomeric structures were confirmed using 2D-NOESY (Nuclear Overhauser Effect Spectroscopy) and HMBC (Heteronuclear Multiple Bond Correlation) spectra. The antibacterial and antifungal activities of the synthesized compounds (2a - 2g, 4a - 5d) were evaluated in vitro against Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, Methicillin resistant S. aureus, Enterococcus faecalis and Candida albicans, Candida parapsilosis. Among the synthesized compounds, promising activities were observed with compounds 2g, 2h, 4a and 4b with lowest MIC values (4-8µg/mL). The compounds 2i, 2j, 2k, 2l showed moderate activity. Additionally, a computational approach (ADMETlab 2.0) was used to evaluate the drug likeness properties of the compounds.

Targeted and Logical Discovery of Piperazic Acid-Bearing Natural Products Based on Genomic and Spectroscopic Signatures.

A targeted and logical discovery method was devised for natural products containing piperazic acid (Piz), which is biosynthesized from ornithine by l-ornithine N-hydroxylase (KtzI) and N-N bond formation enzyme (KtzT). Genomic signature-based screening of a bacterial DNA library (2020 strains) using polymerase chain reaction (PCR) primers targeting ktzT identified 62 strains (3.1%). The PCR amplicons of KtzT-encoding genes were phylogenetically analyzed to classify the 23 clades into two monophyletic groups, I and II. Cultivating hit strains in media supplemented with 15NH4Cl and applying 1H-15N heteronuclear multiple bond correlation (HMBC) along with 1H-15N heteronuclear single quantum coherence (HSQC) and 1H-15N HSQC-total correlation spectroscopy (HSQC-TOCSY) NMR experiments detected the spectroscopic signatures of Piz and modified Piz. Chemical investigation of the hit strains prioritized by genomic and spectroscopic signatures led to the identification of a new azinothricin congener, polyoxyperuin B seco acid (1), previously reported chloptosin (2) in group I, depsidomycin D (3) incorporating two dehydropiperazic acids (Dpz), and lenziamides A and B (4 and 5), structurally novel 31-membered cyclic decapeptides in group II. By consolidating the phylogenetic and chemical analyses, clade-structure relationships were elucidated for 19 of the 23 clades. Lenziamide A (4) inhibited STAT3 activation and induced G2/M cell cycle arrest, apoptotic cell death, and tumor growth suppression in human colorectal cancer cells. Moreover, lenziamide A (4) resensitized 5-fluorouracil (5-FU) activity in both in vitro cell cultures and the in vivo 5-FU-resistant tumor xenograft mouse model. This work demonstrates that the genomic and spectroscopic signature-based searches provide an efficient and general strategy for new bioactive natural products containing specific structural motifs.

Sonochemical parallel synthesis of novel 1,2,3-triazoles utilizing gold-supported titania catalyst

BackgroundA lower carbon society can be achieved with innovative recycling and parallel organic and pharmaceutical synthesis practices that reduce the chemical industry's environmental footprint; this is crucial to fulfilling the principles of green chemistry and engineering. MethodRegioselective azide-alkyne cycloadditions were investigated using heterogeneous catalysts based on gold supported on titania (Au/TiO2) and ultrasonic irradiation. The catalysts were used in the base-free synthesis of 1,2,3-triazoles via azide-alkyne click reactions. The catalyzed azide-alkyne cycloaddition reaction protocol was completed in a short amount of time (5 min) with high product yields in parallel synthesis design Significant findingThe superior catalytic efficacy of Au/TiO2 catalysts for achieving the highest product yield emphasizes the ultimate sympathetic of the catalyst structure and role. The scanning electron microscope (SEM) was used to distinguish the synergetic effect of Au/TiO2 catalysts, and the ultrasound irradiation tool for fresh and spent catalysts. Furthermore, the Heteronuclear Multiple Bond Correlation (HMBC) 2D NMR technique was used as a valuable tool to unambiguously assign the obtained structures.

1H and 13C NMR spectral assignments for low-concentration bile acids in biological samples

Bile acids are the main body of enterohepatic circulation in vivo. They have essential functions such as emulsifying fat, bacteriostasis and regulating multiple metabolic pathways as signal molecules. However, the assignments of NMR signals for some low-concentration bile acids are still needed. This study combined 1D nuclear magnetic resonance (NMR) and 2D NMR techniques including 1H–1H correlation spectroscopy (COSY), 1H–1H total correlation spectroscopy (TOCSY), 1H J-resolved spectroscopy (J-Res), 1H–13C heteronuclear single quantum coherence spectroscopy (HSQC), and 1H–13C heteronuclear multiple bond correlation spectroscopy (HMBC) to assign the 1H and 13C signals of six bile acids in aqueous solution at physiological pH (∼7.4) and nine bile acids in methanol. These data are of importance to the NMR-based studies on lipid digestion, absorption, and metabolism.

(2R, 4S, 5S) 1-(4-(4-(((7-Chloroquinolin-4-yl)amino)methyl)-1H-1,2,3-triazol-1-yl)-5-(hydroxymethyl)tetrahydrofuran-2-yl)-5-methylpyrimidine-2,4(1H,3H)-dione

1,2,3-triazole pharmacophore is a widely recognized motif used for a variety of applications, including drug discovery, chemical biology, and materials science. We herein report the synthesis of a derivative of azidothymidine (AZT), which was combined with the 7-chloro quinoline scaffold through a 1,4-disubstituted 1,2,3-triazole. The chemical structure of the new molecule was fully characterized by Fourier transform infrared (FTIR) spectroscopy, proton nuclear magnetic resonance (1H-NMR), carbon-13 nuclear magnetic resonance (13C-NMR), heteronuclear single quantum coherence (HSQC), heteronuclear multiple bond correlation (HMBC) distortionless enhancement by polarization transfer (DEPT), correlation spectroscopy (1H-1H-COSY), ultraviolet (UV) spectroscopy, and high-resolution mass spectrometry (HRMS). Computational studies were used to predict the interaction of the synthesized compound with HIV reverse transcriptase, a target of relevance for developing new therapeutics against AIDS. The drug-likeness of the compound was also investigated by computing the physico-chemical properties that are important for the pharmacokinetic profile.

Identification of hexahydrocannabinol (HHC), dihydro-iso-tetrahydrocannabinol (dihydro-iso-THC) and hexahydrocannabiphorol (HHCP) in electronic cigarette cartridge products.

Since 2021, products claiming to contain hexahydrocannabinol (HHC) and hexahydrocannabiphorol (HHCP), which are tetrahydrocannabinol (THC) analogs, have been distributed via the Internet. Owing to the presence of three asymmetric carbons in their structure, HHC and HHCP have multiple stereoisomers. This study aimed to identify the actual stereoisomers of HHC and HHCP isolated from electronic cigarette cartridge products using nuclear magnetic resonance (NMR) spectroscopy. Gas chromatography-mass spectrometry (GC-MS) and liquid chromatography-photodiode array-mass spectrometry (LC-PDA-MS) were used for the analyses of two major peaks and one minor peak in product A and two major peaks in product B. These five compounds were isolated by silica gel column chromatography, and their structures were analyzed by 1H, 13C-NMR and various two-dimensional NMR techniques, i.e., H-H correlation spectroscopy, heteronuclear multiple quantum coherence, heteronuclear multiple-bond correlation, and nuclear Overhauser effect spectroscopy. Three compounds isolated from product A were identified as rel-(6aR,9R,10aR)-hexahydrocannabinol (11β-hexahydrocannabinol; 11β-HHC), rel-(6aR,9S,10aR)-hexahydrocannabinol (11α-hexahydrocannabinol, 11α-HHC), and a minor compound (2R,5S,6R)-dihydro-iso-tetrahydrocannabinol (dihydro-iso-THC). Meanwhile, the structural isomers of the major compound isolated from product B were identified as rel-(6aR, 9R, 10aR)-hexahydrocannabiphorol (11β-hexahydrocannabiphorol; 11β-HHCP) and rel-(6aR, 9S, 10aR)-hexahydrocannabiphorol (11α-hexahydrocannabiphorol; 11α-HHCP). The presence of both 11β-HHC and 11α-HHC in the HHC products analyzed in this study suggests that they were most likely synthesized via the reduction reaction of Δ8-THC or Δ9-THC. Dihydro-iso-THC was probably obtained as a byproduct of the synthesis of Δ8-THC or Δ9-THC from cannabidiol. Similarly, 11β-HHCP and 11α-HHCP in the HHCP product could stem from Δ9-tetrahydrocannabiphorol.

Methoxy 13C NMR Chemical Shift as a Molecular Descriptor in the Structural Analysis of Flavonoids and Other Phenolic Compounds

The interpretation of nuclear magnetic resonance (NMR) chemical shifts plays an increasingly important role in the structure elucidation of flavonoids. Despite the fact that the 3H signal of the methoxy (OMe) group appears as a singlet in the 1H NMR spectrum, its chemical shift is not reliably indicative of the OMe-substitution in the aromatic rings, unlike its 13C NMR chemical shift, which can be useful for the determination of the molecular structure of flavonoids. For example, the chemical shift of ortho-substitutions is at 56 ± 1 ppm for flavonoids having one OMe-substituent in either the ortho or orthó position and 61.5 ± 2 ppm for those having substituents in both ortho positions. The nuclear Overhauser effect spectroscopy ( δH-OMe→ ortho-aryl-H or adjacent substituent) and heteronuclear multiple-bond correlation ( δH-OMe→ ipso-aryl-C) data have been widely employed for the structure analysis of flavonoids and to identify the site of OMe-substitution. Thus, OMe chemical shifts can act as molecular descriptors. However, we have noticed that there are several examples that are not in accordance with this generalization, and a reinvestigation of such reported data seems to be relevant for reconsideration of assigned structures, and a few examples are cited herein.

Refinement and complete solution NMR analysis of the structure of a 6-branched 1,3-β-D-glucan (OL-2) isolate from Omphalialapidescens

OL-2 is a water-soluble β-glucan produced by Omphalia lapidescens. This versatile glucan has potential applications in various industries, including food, cosmetics, and pharmaceuticals. In addition, OL-2 is known for its promising applications as a biomaterial and drug, owing to its reported antitumor and antiseptic properties. Although the biological activities of β-glucans vary depending on their primary structure, holistic clarification of OL-2 via solution NMR spectroscopy to ascertain its complete and unambiguous structure has not yet been achieved. In this study, a chain of solution NMR techniques, such as correlation spectroscopy, total correlation spectroscopy (TOCSY), nuclear Overhauser effect and exchange spectroscopy, 13C-edited heteronuclear single quantum coherence (HSQC), HSQC-TOCSY, heteronuclear multiple bond correlation, and heteronuclear 2-bond correlation pulse sequences were used to unambiguously assign all 1H and 13C atoms in OL-2. Based on our investigation, OL-2 consists of a 1,3-β-glucan backbone chain decorated with a single 6-branched β-glucosyl side unit on every fourth residue.

The study of structure and effects of two new proanthocyanidins from Anogeissus pendula leaves on rumen enzyme activities.

Two novel proanthocyanidins, (2R, 3R)-(+)-Gallocatechin-(4β → 8)4-(2R, 3R)-(+)-gallocatechin (compound 1) and 3-O-galloyl-(2S, 3S)-(-)-epicatechin-(4α → 8)-[3-O-galloyl-(2S, 3S)-(-)-epicatechin (4α → 8)]2-(2S, 3S)-(-)-epicatechin (compound 2), were structurally characterized from leaves of Anogeissus pendula. The structures were determined by ultraviolet spectroscopy (UV), proton nuclear magnetic resonance (1H NMR), 13C NMR, and heteronuclear multiple bond correlation. Molinspiration and Osiris property explorer applications were used to predict bioactivity and drug score. Drug scores of 0.08 and 0.05 were predicted for compounds 1 and 2, respectively. Predicted bioactivity scores were high. Due to their molecular weight, chemical structure, and conformation, the newly discovered proanthocyanidins possess an inclination to interact with proteins. Based on this premise, both compounds were subjected to in vitro testing against ruminal enzymes. They exhibited significant inhibition activities (p < 0.01) with a range of half maximal effective concentration (EC50) of 14.80-17.88 mg/mL of glutamic oxaloacetic transaminase in both protozoa and bacteria fractions. The ruminal glutamic pyruvic transaminase activity was significantly inhibited (p < 0.01) from EC50 12.59-16.29 mg/mL, and R-cellulase inhibition was recorded with EC50 18.20-21.98 mg/mL by compounds 1 and 2, respectively. Protease activity decreased with increasing incubation time and concentration of both compounds. The novel proanthocyanidins have potential roles in improving feed conversion ratios and in drug development.

One-pot synthesis of liquid photocrosslinkable poly(l-lactide) with terminal triacrylate.

We synthesized a poly(l-lactide)-pentaerythritol triacrylate (PETA) polymer modified with acrylic trifunctional groups using a one-pot method based on ring-opening polymerization of l-lactide and PETA. We calculated the molecular weight and structure of PLA-PETA using gel permeation chromatography (GPC) and nuclear magnetic resonance (NMR) (1H, 13C, heteronuclear multiple bond correlation [HMBC]) spectroscopy. Photocrosslinking PLA-PETA using the Omnirad 1173 photoinitiator yielded a transparent sample with 91% crosslinkage. The crosslinked sample was analyzed using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and thermomechanical analysis (TMA) to determine its thermal properties and thermal expansion coefficient. In vitro cell toxicity tests showed an average cell viability >90%, indicating that the PLA-PETA polymer had good biocompatibility with cells after photocrosslinking.

Multiblock poly(ether-b-amide) copolymers comprised of PA1212 and PPO-PEO-PPO with specific moisture-responsive and antistatic properties

Functional multiblock poly(ether-b-amide) (PEBA) copolymers, comprised of PA1212 (polyamide 1212) as hard segments and Jeffamine ED-2003 as soft segments, were successfully prepared via two-step melt polycondensation without any amidation catalyst. Here, using diamino-terminated poly(propylene oxide)-poly(ethylene oxide)-poly(propylene oxide) (PPO-PEO-PPO), Jeffamine ED-2003, enhances the compatibility between polyamide oligomer and polyether, which is better than the traditional route using hydroxyl-terminated polyether. The chemical structure of multiblock PEBAs, as well as the microphase separated structure with crystalline phase of polyamide and polyether, were confirmed by heteronuclear multiple-bond correlation spectrum, heteronuclear multiple quantum correlation spectrum, Fourier transform infrared spectroscopy (FT-IR), differential scanning calorimetry and dynamic mechanical analysis. The hydrophilic PEBA copolymers showed water adsorption ranging from 87.3% to 17.1% depending on the polyether content, and specially showed moisture responsive behavior within seconds when exposed to moisture. The corresponding mechanism was studied using time-resolved attenuated total reflectance FT-IR spectroscopy in the molecular level and the water diffusion coefficient was estimated to be 1.07 × 10–8 cm2∙s–1. Two-dimensional correlation FT-IR spectra analysis was performed to confirm that the interaction between water and polyether phase was in preference to that between water and polyamide matrix, and water molecule only forms hydrogen bond with the polyether segment. Due to the incorporation of PEO segments, the PEBAs have the surface resistivity varying from 5.6 × 109 to 6.5× 1010 Ω, which makes PEBA potential candidate as permanent antistatic agent.

Chemical constituents from the stem barks of polyscias serrata balf

Plants of the genus Polyscias (the family Araliaceae) are represented as perennial shrubs and are commonly cultivated in southeastern Asia and the Pacific regions. Pharmacological studies revealed that Polyscias crude extracts and their isolated compounds exhibited a variety of biological activity, such as antibacterial, antifungal, cytotoxic, immuno-stimulant, wound healing and anti-asthmatic activities. For the first time, phytochemical study on the methanol (MeOH) extract of the stem barks of Vietnamese species Polyscias serrata Balf. (locally named Dinh lang rang) resulted in the isolation and NMR (Nuclear Magnetic Resonance)-determination of six compounds 1-6. They include one nucleobase uracil (1), two nucleosides uridine (2) and adenosine (3), one alkaloid indole-3-carboxylic acid (4), one mono-phenol glucoside koaburside (5), and one saponin randianin (6). The chemical structures of these phytochemicals were elucidated by physicochemical, the 1D-NMR [1H, 13C-NMR, and DEPT (Distortionless Enhancement by Polarization Transfer)], the 2D-NMR [HSQC (heteronuclear single quantum coherence), HMBC (Heteronuclear Multiple Bond Correlation), and COSY (correlation spectroscopy)] spectral, and ESI-MS (Electron Spray Ionization-Mass Spectrum) data. This is the first time that compounds 2-6 have been obtained from the genus Polyscias. In agreement with various reports, the nitrogenous compounds and triterpene saponins can be seen as characteristic metabolites of genus Polyscia

Complete Structure Assignment of Azathioprine as a Proton-Deficient Nucleic Acid Analogue Using 1H-13C Long-Range Heteronuclear Single Quantum Multiple Bond Correlation.

In this Note, the successful structural assignment of a proton-deficient nucleic acid analogue using the 1H-13C long-range heteronuclear single quantum multiple bond correlation (LR-HSQMBC) technique is described. LR-HSQMBC is a 2D NMR technique for the sensitive detection of weak C-H spin couplings. The immunosuppressant drug, azathioprine, served as the target compound. The LR-HSQMBC measurements revealed the existence of covalent bonds between the purine and imidazole rings based on observations of 5JCH and 6JCH with good sensitivity.