Optical Rotation Values Research Articles

Photophysical Properties of Chiral Tetraphenylethylene Derivatives with the Fixed Propeller-Like Conformation

The recent synthesized helical tetraphenylethylene (TPE) exhibits broad application prospects such as display, catalysis, and medical imaging. A full understanding of the intricate relation between structure and property is rather important to structural design and performance improvement. Here, we employed density functional theory (DFT) and time-dependent DFT to calculate their ground- and excited-state structures, electron transition properties, optical rotation (OR), and second-order nonlinear optical (NLO) properties. For compound 1, the simulated UV–vis/CD spectra and calculated OR value are in reasonable agreement with the experimental ones, allowing us to reliably assign the electron transition and determine the absolute configuration. Intriguingly, TPE derivatives are excellent candidates for the second-order NLO materials in view of the large first hyperpolarizability values and intrinsic asymmetric structures. The intramolecular charge transfer cooperativity for this kind of compound was achiev...

Towards Acacia seyal protocol in Sudan: Preliminary study pertinent to colour identification and physiochemical properties

Despite the significant contribution of A. seyal to the exports portfolio of Sudan, farmers have slightly poor knowledge regarding post-harvest cultural practices in terms of proper methods of gum drying, storage conditions and gum stacking which might significantly be resulted in colour deterioration and inferior quality. Nevertheless, the current preliminary investigation is intended to study colour identification and physiochemical properties of A. seyal gums from samples obtained viafour exporting companies in Sudan and produced in three different geographical areas namely Buram, Hejleij and Deain.Each sample was graded visually into three colours: light, pale and dark and based on further chemical analysis to the colour within the samples and across the production areas significant variation was obtained as the colour is ranging from 16.73 to 44.53 within the different graded samples and across the production areas. The results show that each sample is graded into three different colour scale refereed to light, pale and dark.The physiochemical properties within the tested samples and across the production areas showed no significant differences between all parameters including moisture content, ash content and pH. The specific optical rotation varies from + 40 to + 60 within the samples and across the different production areas. However, both minimum and maximum values of specific optical rotation were obtained from Hejleij production area and representing light and dark colour, respectively.

Bioactive halogenated dihydroisocoumarins produced by the endophytic fungus Lachnum palmae isolated from Przewalskia tangutica

Guided by the UPLC-ESIMS profile, seven previously undescribed halogenated dihydroisocoumarins, palmaerones A-G, along with eleven known dihydroisocoumarins, were isolated from Lachnum palmae, an endophytic fungus from Przewalskia tangutica by exposure to a histone deacetylase inhibitor SAHA. Structures of the isolates were elucidated by analysis of their NMR, MS and optical rotation values. The antimicrobial, anti-inflammatory and cytotoxic activities of palmaerones A-G were evaluated. Palmaerones A-G showed antimicrobial activities against the strains (C. neoformans, Penicillium sp., C. albicans, B. subtilis and S. aureus), and palmaerone E exhibited potential antimicrobial activities against all the test strains with the MIC value in the range of 10–55 μg/mL. Palmaerones A and E exhibited moderate inhibitory effects on NO production in LPS-induced RAW 264.7 cells, with the IC50 values of 26.3 and 38.7 μM, respectively and no obvious toxicities were observed at 50 μM. Palmaerone E showed weak cytotoxicity against HepG2 with the IC50 value of 42.8 μM. This work provides an effective strategy for expanding natural product resource.

Chiroptical properties of 2,2'-bioxirane.

The two enantiomers of 2,2'-bioxirane were synthesized, and their chiroptical properties were thoroughly investigated in various solvents by polarimetry, vibrational circular dichroism (VCD), and Raman optical activity (ROA). Density functional theory (DFT) calculations at the B3LYP/aug-cc-pVTZ level revealed the presence of three conformers (G+ , G- , and cis) with Gibbs populations of 51, 44, and 5% for the isolated molecule, respectively. The population ratios of the two main conformers were modified for solvents exhibiting higher dielectric constants (G- form decreases whereas G+ form increases). The behavior of the specific optical rotation values with the different solvents was correctly reproduced by time-dependent DFT calculations using the polarizable continuum model (PCM), except for the benzene for which explicit solvent model should be necessary. Finally, VCD and ROA spectra were perfectly reproduced by the DFT/PCM calculations for the Boltzmann-averaged G+ and G- conformers.

Anti-inflammatory activity of caffeic acid derivatives isolated from the roots of Salvia miltiorrhiza Bunge.

Ten caffeic acid derivatives (1-10) were isolated from the roots of Salvia miltiorrhiza by using various chromatographic methods and their chemical structures were spectroscopically elucidated. The absolute configurations of chiral centers were determined by comparison with reported coupling constants, optical rotation values, and CD techniques. Anti-inflammatory activities were evaluated using nitric oxide (NO), inducible nitric oxide synthase (iNOS), cyclooxygenase (COX)-2 inhibition assays, and by determining the expression of heme oxygenase (HO)-1. Two new caffeic acid derivatives, 8-epiblechnic acid 9-methyl ester (4) and 8-epiblechnic acid 9'-methyl ester (5), and eight known derivatives, caffeic acid methyl ester (1), shimobashiric acid B (2), rosmarinic acid methyl ester (3), salvianolic acid C (6), methyl salvianolate C (7), lithospermic acid monomethyl ester (8), lithospermic acid dimethyl ester (9), and dimethyl lithospermate B (10), were isolated from the ethyl acetate fraction of S. miltiorrhiza. All caffeic acid derivatives were evaluated for their inhibitory effect on NO production. Compounds 2 and 3 inhibited NO production with IC50 values of 1.4 and 0.6μM, respectively. These compounds also strongly inhibited the production of iNOS and COX-2. In addition, compound 3 induced the expression HO-1 in a concentration-dependent manner at 0.1, 0.3, and 1.0μM.

Diverse Secondary Metabolites from the Marine-Derived Fungus Dichotomomyces cejpii F31-1.

By adding l-tryptophan and l-phenylalanine to GPY medium, twenty-eight compounds, including amides, polyketides, a sesquiterpenoid, a diterpenoid, a meroterpenoid, diketopiperazines, β-carbolines, fumiquinazolines, and indole alkaloids, were discovered from the marine-derived fungus Dichotomomyces cejpii F31-1, demonstrating the tremendous biosynthetic potential of this fungal strain. Among these compounds, four amides dichotomocejs A–D (1–4), one polyketide dichocetide A (5), and two diketopiperazines dichocerazines A–B (15 and 16) are new. The structures of these new compounds were determined by interpreting detailed spectroscopic data as well as calculating optical rotation values and ECD spectra. Obviously, Dichotomomyces cejpii can effectively use an amino acid-directed strategy to enhance the production of nitrogen-containing compounds. Dichotomocej A (1) displayed moderate cytotoxicity against the human rhabdomyosarcoma cell line RD with an IC50 value of 39.1 µM, and pityriacitrin (22) showed moderate cytotoxicity against the human colon carcinoma cell line HCT116 with an IC50 value of 35.1 µM.

Specific optical rotation is a versatile tool for the identification of critical micelle concentration and micellar growth of tartaric acid-based diastereomeric amphiphiles.

Four novel tartaric acid-based diastereomeric chiral amphiphiles, two being enantiomers of the other two, have been synthesized and investigated using chiroptical spectroscopic methods, along with tensiometry and dynamic light scattering experiments. We found that an inflection point in specific optical rotation (SOR) values at ~0.32mM corresponds to the critical micelle concentration (CMC). The increase in magnitude of SOR values beyond CMC corresponds to the growth of aggregates. For enantiomers, oppositely signed SOR values were observed, ruling out the possibility for the presence of aggregation size mediated artefacts. SOR values did not exhibit concentration dependence for a chiral tartaric acid based non-aggregating analogue further establishing the absence of artefacts or anomalous interaction of tartaric acid based head group with solvent. Electronic circular dichroism spectra showed no significant changes in band positions or intensities with concentration. Due to the requirement for higher concentrations (~200mM) needed to obtain vibrational circular dichroism spectra, these measurements are not found to be useful for studying concentration dependent properties of chiral amphiphiles.

Two Furanosesterterpenoids from the Sponge Luffariella variabilis.

Two new sesterterpenoids, 1 and 2, were isolated from the sponge Luffariella variabilis. Their planar structures were characterized with spectroscopic analyses. The sole chiral center of compound 1 was elucidated as 12R by comparing observed and calculated optical rotation values. The configurations of compound 2 were determined by NMR and electronic circular dichroism (ECD) studies. Furthermore, compound 2 showed cytotoxicity at IC50 1.0 µM against NBT-T2 cells.

Photocontrol over Molecular Shape: Synthesis and Photochemical Evaluation of Glycoazobenzene Macrocycles.

Reversible shape switching due to external stimuli is an attractive property for the control of molecular features. Hence, we aimed at macrocycles to investigate photoswitching of molecular shape. We prepared the first carbohydrate-based macrocycles comprising a photoresponsive azobenzene hinge. These macrocycles were readily obtained by cyclization of isothiocyanate-armed bis-azobenzene glycosides with piperazine. The unprotected macrocycles exhibit favorable photochromic properties in water and DMSO. Notably, the efficient trans→cis isomerization results in a remarkable shape transformation of the molecule. Additionally, the structure is characterized by restricted conformational freedom of the backbone, resulting in a single main conformer in each geometrical state (trans or cis). Measurement of optical rotation values and circular dichroism spectra revealed a tremendous change in chirality upon photoisomerization, with a strong helical induction in the cis state. These findings highlight the applicability of the new macrocycles as chiroptical molecular switches.

Cytotoxic Anomoian B and Aplyzanzine B, New Bromotyrosine Alkaloids from Indonesian Sponges.

Two new bromotyrosine derivatives, anomoian B (1) and aplyzanzine B (2), were isolated, respectively, from the organic extracts of a Verongida sponge belonging to the Hexadella genus and from a two-sponge association (Jaspis sp. and Bubaris sp.), both collected off the coast of Indonesia. The planar structure of 1 and 2 was determined by 1D and 2D NMR experiments and by high-resolution mass spectrometry, while their absolute stereochemistry was assigned by comparison with optical rotation values of known bromotyrosines and by chemical degradation. Both compounds showed moderate antiproliferative activity against a panel of different cancer cell lines. Their cytotoxic activity is facilitated through the induction of apoptosis, which is mediated neither by the generation of reactive oxygen species nor by the inhibition of histone deacetylases in these cell lines.

Phytochemical study of Illicium angustisepalum and its biological activities

Sixteen compounds, including two new natural products (1 and 2), were obtained from the twigs of Illicium angustisepalum. The structures were elucidated based on NMR, MS, IR data and optical rotation values. Compounds 4, 5, 6 and 8 displayed moderate antibacterial activities against clinical isolates; compounds 4, 5, 8, 9 and 15 protected neural cells against oxidative stress; and compounds 10 and 14 exhibited anti-acetylcholinesterase activity.

Three new polyketides from the marine sponge-derived fungus Trichoderma sp. SCSIO41004

Three new polyketides named trichbenzoisochromen A (1), 5,7-dihydroxy-3-methyl -2-(2-oxopropyl)naphthalene-1,4-dione (2) and 7-acetyl-1,3,6-trihydroxyanthracene-9,10- dione (3) together with six known compounds (4–9) were isolated from a sponge-derived fungus Trichoderma sp. SCSIO41004. The structures of three new polyketides (1–3) were determined by the extensive spectroscopic analysis, including 1D, 2D NMR and HRESIMS data. The absolute configuration of compound 1 was confirmed by the specific optical rotation value and CD spectra analyses. Compound 4 exhibited significant inhibitory activity against EV71 with the IC50 value of 25.7 μM.

New comonomers in malic acid polyesters

Here, we report the synthesis of polyesters of l-malic acid, β-cyclodextrin, and two other comonomers, resorcinol and salicylic acid that, involved in the polyester chain by direct polycondensation, could improve the antibacterial activity. The copolymers were characterized by thermal analysis, infrared spectroscopy as well as by specific optical rotation values. The thermogravimetric and differential scanning calorimetry (TG–DSC) measurement results showed the influence of the comonomers on the thermal stability of the copolymers, which was higher when ZnO was present in the reaction mixture. The FTIR spectra confirmed the presence of the comonomers in the polyesters and the influence of the ZnO on the products. The specific optical rotation values showed similar tendency, and the results were in accordance with those got by TG–DSC and FTIR techniques. In short, the zinc oxide helped not only in ester formation but improved the polyester stability. Results allowed elaboration of reproducible polyester synthesis with tailor-made characteristic.

Identification of Cyclic Depsipeptides and Their Dedicated Synthetase from Hapsidospora irregularis.

Seven cyclic depsipeptides were isolated from Hapsidospora irregularis and structurally characterized as the calcium channel blocker leualacin and six new analogues based on the NMR and HRESIMS data. These new compounds were named leualacins B-G. The absolute configurations of the amino acids and 2-hydroxyisocaproic acids were determined by recording the optical rotation values. Biological studies showed that calcium influx elicited by leualacin F in primary human lobar bronchial epithelial cells involves the TRPA1 channel. Through genome sequencing and targeted gene disruption, a noniterative nonribosomal peptide synthetase was found to be involved in the biosynthesis of leualacin. A comparison of the structures of leualacin and its analogues indicated that the A2 and A4 domains of the leualacin synthetase are substrate specific, while A1, A3, and A5 can accept alternative precursors to yield new molecules.

New compounds from a hydrothermal vent crab-associated fungus Aspergillus versicolor XZ-4.

Three new quinazoline derivatives (1-3), one new oxepin-containing natural product (4) and four new cyclopenin derivatives (5-7 and 9) have been isolated from an EtOAc extract of the Taiwan Kueishantao hydrothermal vent crab-associated fungus Aspergillus versicolor XZ-4. Their planar structures were established by HRMS, 1D and 2D NMR spectroscopic data analyses. The absolute configurations for compounds 1 and 4 were determined by chiral phase HPLC analysis of their hydrolysis products. The absolute configurations of 2, 3 and 7 were defined mainly by comparison of the quantum chemical TDDFT calculated and the experimental ECD spectra, and the absolute configuration of 5 was deduced from comparison of the optical rotation values reported in the literature. The presence of two atropisomers of 5 was established by NOE analyses. The Ile & Val units in compounds 1-3 allowed the assignment of a new quinazoline skeleton and it's the first time the configuration of isoleucine in the quinazoline skeleton was defined. A series of 7-methoxy cyclopenin derivatives were reported for the first time in this study. The bioevaluation of compounds 5, 7, 8 and 9 revealed inhibitory activities against E. coli at MIC values around 32 μg mL-1.

Reversed-Phase UHPLC Enantiomeric Separation of Rasagiline Salts Using a Chiralpak® AGP Column.

We report the first rapid ultra-high performance liquid chromatographic (UHPLC) enantiomeric reversed-phase separation of rasagiline mesylate and its tartrate salts using a Chiralpak® AGP column (50 mm × 2.1 mm, 5 μm) as a stationary phase. This method was developed as an alternative to the usage of previously reported normal-phase chiral LC columns for isomer separation. Our method is based on an isocratic approach using a mixture of ammonium acetate and isopropyl alcohol (90:10, v/v) as the mobile phase (0.6 mL/min flow rate). The detection limit (at a detection wavelength of 210 nm) and quantification limit for the rasagiline enantiomers were 0.06 and 0.2 μg/mL, respectively. This method is compatible with the UHPLC-MS technique. The successful separation of rasagiline and its enantiomer was confirmed by determining the corresponding specific optical rotation values. Our method will be applicable for detecting rasagiline enantiomers during the control of manufacturing processes, and for use in rapid analysis for quality control in pharmaceutical industry to obtain optically pure pharmaceutical substances. This method was validated in terms of its precision, limit of detection, limit of quantification, linearity, accuracy, robustness, ruggedness, specificity, forced degradation, and solution stability, according to International Council on Harmonization Validation Guidelines Q2 (R1).

Unusual Chiroptical Properties of the Cryptophane-222 Skeleton.

Enantiopure cryptophane-222 derivative (1) devoid of substituents was obtained via high-performance liquid chromatography (HPLC) using chiral stationary phases. The chiroptical properties of 1 were determined from polarimetry, electronic circular dichroism (ECD), synchrotron radiation circular dichroism (SRCD), vibrational circular dichroism (VCD), and Raman optical activity (ROA) experiments and were compared to those of the cryptophane-A (2) derivative. Unusual polarimetric results were obtained for 1 in CHCl3 solvent as the sign of the optical rotation (OR) values changes in the nonresonance region above 365 nm, whereas no change was observed in the CH2Cl2 solvent. ECD spectra in the 1La and 1Lb regions were very similar for the two solutions and could not explain these unusual polarimetric properties. In contrast, SRCD spectra in the 1Bb region revealed spectral differences for the two solutions, which have been associated with conformational changes of the three linkers by time-dependent density functional theory (TDDFT) calculations. DFT calculations of the OR support that conformational changes may explain the polarimetric results obtained for the two solvents. Finally, TDDFT calculations of the ECD as well as DFT calculations of the VCD and ROA allowed the attribution of the (-)589-PP absolute configuration for 1 in solution, as determined from the X-ray structures of 1.

Enantiomeric Lignans and Neolignans from Phyllanthus glaucus: Enantioseparation and Their Absolute Configurations.

Eight pairs of enantiomeric neolignans, norlignans, and sesquineolignans (1a/1b–8a/8b), together with five known neolignans (9a/9b and 10–12), have been isolated from 70% acetone extract of the whole plants of Phyllanthus glaucus Wall. (Euphorbiaceae). The racemic or partial racemic mixtures were successfully separated by chiral HPLC using different types of chiral columns with various mobile phases. Their structures were elucidated on the basis of extensive spectroscopic data. The absolute configurations of 2a/2b were determined by computational analysis of their electronic circular dichroism (ECD) spectrum, and the absolute configurations of other isolates were ascertained by comparing their experimental ECD spectra and optical rotation values with those of structure-relevant compounds reported in literatures. Compounds 4a/4b featured unique sesquineolignan skeletons with a novel 7-4′-epoxy-8′-8′′/7′-2′′ scaffold, consisting of an aryltetrahydronaphthalene and a dihydrobenzofuran moiety. The planar structures of compounds 2, 3, 7, and 8 were documented previously; however, their absolute configurations were established for the first time in this study. The antioxidant activities of 1a/1b–8a/8b were evaluated using DPPH free radical scavenging assay, and the results demonstrated that compounds 1b and 3b showed potent DPPH radical scavenging activities with IC50 values of 5.987 ± 1.212 and 9.641 ± 0.865 μg/mL, respectively.

Enantiomerically Pure [2.2]Paracyclophane-4-thiol: A Planar Chiral Sulfur-Based Building Block Readily Available by Resolution with an Amino Acid Chiral Auxiliary.

Acyl chloride of N-phthaloyl-(S)-isoleucine is an efficient chiral auxiliary for the resolution of (±)-[2.2]paracyclophane-4-thiol. A preparative protocol, based on the conversion into diastereoisomeric thiolesters and separation by two fractional crystallizations and column chromatography, was developed. Deprotection with LiAlH4 allowed isolation of the individual thiol enantiomers in good yield (∼40%) and high enantiomeric purity (ee >93%). The absolute configurations were determined by comparison of the optical rotation value of the products with literature data and were confirmed by X-ray crystallography.

New streptophenazines from marine Streptomyces sp. 182SMLY

Six phenazines including three new ones were isolated from the culture of a marine actinomycete Streptomyces sp. 182SMLY. Based on the analyses of NMR, HRESIMS, optical rotation value, and CD data, the structures of these isolated compounds were determined as new phenazines of (-)-streptophenazines M–O and known phenazines of 1-carbomethoxyphenazine and (-)-streptophenazines A and B. (-)-Streptophenazine B showed activity in suppressing the growth of methicillin-resistant Staphylococcus aureus with MIC value of 4.2 μg/mL.