Bioactive abietenolide diterpenes from Suregada procera.

The phytochemical investigation of the leaves and the roots of Suregada procera afforded the new ent-abietane diterpenoid sureproceriolide A (1) along with the known secondary metabolites 8,14β:11,12α-diepoxy-13(15)-abietane-16,12-olid (2), jolkinolide A (3), jolkinolide E (4), ent-pimara-8(14),15-dien-19-oic acid (5), sitosterol (6), oleana-9(11):12-dien-3β-ol (7), and oleic acid (8). Their structures were elucidated by NMR spectroscopic and mass spectrometric analyses, and the structure of jolkinolide A (3) was confirmed by single-crystal X-ray diffraction analysis. Sureproceriolide A (1) showed modest activity against the Gram-positive bacterium Staphylococcus lugdunensis (MIC = 31.

Antimicrobial Dihydroflavonols and Isoflavans Isolated from the Root Bark of .

Three new dihydroflavonols, gloverinols A-C (-), a new flavon-3-ol, gloverinol D (), two new isoflavans, gloveriflavan A () and B (), and seven known compounds were isolated from the root bark of . The structures of the isolates were elucidated by using NMR, ECD, and HRESIMS data analyses. Among the isolated compounds, gloverinol B (), gloveriflavan B (), and 1-(2,4-dihydroxyphenyl)-3-hydroxy-3-(4-hydroxyphenyl)-1-propanone () were the most active against , with MIC values of 9.

Antiviral Rotenoids and Isoflavones Isolated from ssp. .

Three new (-) and six known rotenoids (-), along with three known isoflavones (-), were isolated from the leaves of ssp. . A new glycosylated isoflavone (), four known isoflavones (-), and one known chalcone () were isolated from the root wood extract of the same plant.

Absolute configuration assignment of highly fluorinated carboxylic acids via VCD and MRR spectroscopy.

Chiral analysis has become a crucial step in studying the stereospecific synthesis of Active Pharmaceutical Ingredients (APIs). Both Vibrational Circular Dichroism (VCD) and Molecular Rotational Resonance (MRR) spectroscopy are capable of determining absolute configurations (ACs) via comparison of experimental and calculated data. In this regard, each technique has its own caveats.

Impact of conformation and intramolecular interactions on vibrational circular dichroism spectra identified with machine learning.

Vibrational Circular Dichroism (VCD) spectra often differ strongly from one conformer to another, even within the same absolute configuration of a molecule. Simulated molecular VCD spectra typically require expensive quantum chemical calculations for all conformers to generate a Boltzmann averaged total spectrum. This paper reports whether machine learning (ML) can partly replace these quantum chemical calculations by capturing the intricate connection between a conformer geometry and its VCD spectrum.

Correction: Monaco et al. Chiral Phase Transfer Catalysis in the Asymmetric Synthesis of a 3,3-Disubstituted Isoindolinone and Determination of Its Absolute Configuration by VCD Spectroscopy. 2020, , 2272.

In this note, we report a correction to the published article, , , 2272 [...

Pushing the boundaries of VCD spectroscopy in natural product chemistry.

Vibrational circular dichroism (VCD) is one of the most powerful techniques to assess the stereochemistry of chiral molecules in solution state. The need for quantum chemical calculations to interpret experimental data, however, has precluded its widespread use by non-experts. Herein, we propose the search and validation of IR and VCD spectral markers to circumvent the requirement of DFT calculations allowing for absolute configuration assignments even in complex mixtures.

Anti-SARS-CoV-2 Activity and Cytotoxicity of Amaryllidaceae Alkaloids from .

The Amaryllidaceae species are well-known as a rich source of bioactive compounds in nature. Although has been studied for decades, its polar components were rarely explored. The current phytochemical investigation of Amaryllidaceae alkaloids from led to the identification of three previously undescribed compounds: -demethyl-norlycoramine (), (-)-2--pseudolycorine () and (+)-2--pseudolycorine (), together with eight known compounds: 6α-hydroxyhippeastidine (), 6β-hydroxyhippeastidine (), lycorine (), 2--lycorine (), zephyranthine (), ungeremine (), pancratistatin () and 9--demethyl-7--methyllycorenine ().

The effect of pH and nitrite on the haem pocket of GLB-33, a globin-coupled neuronal transmembrane receptor of Caenorhabditis elegans.

Out of the 34 globins in Caenorhabditis elegans, GLB-33 is a putative globin-coupled transmembrane receptor with a yet unknown function. The globin domain (GD) contains a particularly hydrophobic haem pocket, that rapidly oxidizes to a low-spin hydroxide-ligated haem state at physiological pH. Moreover, the GD has one of the fastest nitrite reductase activity ever reported for globins.

The Halogen Bond in Weakly Bonded Complexes and the Consequences for Aromaticity and Spin-Orbit Coupling.

The halogen bond complexes CF3X⋯Y and C2F3X⋯Y, with Y = furan, thiophene, selenophene and X = Cl, Br, I, have been studied by using DFT and CCSD(T) in order to understand which factors govern the interaction between the halogen atom X and the aromatic ring. We found that PBE0-dDsC/QZ4P gives an adequate description of the interaction energies in these complexes, compared to CCSD(T) and experimental results. The interaction between the halogen atom X and the π-bonds in perpendicular orientation is stronger than the interaction with the in-plane lone pairs of the heteroatom of the aromatic cycle.

Interaction of nitrite with ferric protoglobin from - an interesting model for spectroscopic studies of the haem-ligand interaction.

Protoglobin from (Pgb) is a dimeric globin belonging to the same lineage of the globin superfamily as globin-coupled sensors. A putative role in the scavenging of reactive nitrogen and oxygen species has been suggested as a possible adaptation mechanism of the host organism to different gaseous environments in the course of evolution. A combination of optical absorption, electronic circular dichroism (ECD), resonance Raman (rRaman), and electron paramagnetic resonance (EPR) reveal the unusual reaction of ferric Pgb with nitrite.

Epimeric Mixture Analysis and Absolute Configuration Determination Using an Integrated Spectroscopic and Computational Approach-A Case Study of Two Epimers of 6-Hydroxyhippeastidine.

Structural elucidation has always been challenging, and misassignment remains a stringent issue in the field of natural products. The growing interest in discovering unknown, complex natural structures accompanies the increasing awareness concerning misassignments in the community. The combination of various spectroscopic methods with molecular modeling has gained popularity in recent years.

Improving the IR spectra alignment algorithm with spectra deconvolution and combination with Raman or VCD spectroscopy.

The relative stereochemistry of organic molecules can be determined by comparing theoretical and experimental infrared (IR) spectra of all isomers and assessing the best match. For this purpose, we have recently developed the IR spectra alignment (IRSA) algorithm for automated optimal alignment. IRSA provides a set of quantitative metrics to identify the candidate structure that agrees best with the experimental spectrum.

Vibrational Optical Activity Study of Four Antibiotic (Lipo)glycopeptides: Vancomycin, Oritavancin, Dalbavancin, and Teicoplanin.

The antibiotic glycopeptide class, of which vancomycin is the original compound, has received due attention over the past few decades in search of antibiotics to overcome resistances developed by bacteria. Crucial for the understanding and further development of glycopeptides that possess desired antibacterial effects is the determination of their conformational behavior, as this sheds light on the mechanism of action of the compound. Among others, vibrational optical activity (VOA) techniques (vibrational circular dichroism and Raman optical activity) can be deployed for this, but the question remains to what extent these spectroscopic techniques can provide information concerning the molecular class under investigation.

GLB-3: A resilient, cysteine-rich, membrane-tethered globin expressed in the reproductive and nervous system of Caenorhabditis elegans.

The popular genetic model organism Caenorhabditis elegans (C. elegans) encodes 34 globins, whereby the few that are well-characterized show divergent properties besides the typical oxygen carrier function. Here, we present a biophysical characterization and expression analysis of C.

Discovery, isolation, heterologous expression and mode-of-action studies of the antibiotic polyketide tatiomicin from Amycolatopsis sp. DEM30355.

A genomic and bioactivity informed analysis of the metabolome of the extremophile Amycolatopsis sp. DEM30355 has allowed for the discovery and isolation of the polyketide antibiotic tatiomicin. Identification of the biosynthetic gene cluster was confirmed by heterologous expression in Streptomyces coelicolor M1152.

Insights in the vibrational optical activity spectra of the antibiotic vancomycin in DMSO.

Vibrational circular dichroism (VCD) and Raman optical activity (ROA) are two spectroscopic techniques that are sensitive towards the conformational behaviour of molecules, and are often complementary herein. In this work we pursue the determination of the conformational ensemble of the antibiotic glycopeptide vancomycin in DMSO through comparison of experimental and computational spectra, both for VCD and ROA. ROA is found to be highly suitable for the task, identifying an ensemble that strongly resembles the NMR conformation.

Paving the way to conformationally unravel complex glycopeptide antibiotics by means of Raman optical activity.

It is crucial for fundamental physical chemistry techniques to find their application in tackling real-world challenges. Hitherto, Raman optical activity (ROA) spectroscopy is one of the examples where a promising future within the pharmaceutical sector is foreseen, but has not yet been established. Namely, the technique is believed to be able to contribute in investigating the conformational behaviour of drug candidates.

A Combined Experimental/Quantum-Chemical Study of Tetrel, Pnictogen, and Chalcogen Bonds of Linear Triatomic Molecules.

Linear triatomic molecules (CO, NO, and OCS) are scrutinized for their propensity to form perpendicular tetrel (CO and OCS) or pnictogen (NO) bonds with Lewis bases (dimethyl ether and trimethyl amine) as compared with their tendency to form end-on chalcogen bonds. Comparison of the IR spectra of the complexes with the corresponding monomers in cryogenic solutions in liquid argon enables to determine the stoichiometry and the nature of the complexes. In the present cases, perpendicular tetrel and pnictogen 1:1 complexes are identified mainly on the basis of the lifting of the degenerate ν 2 bending mode with the appearance of both a blue and a red shift.

Tackling Stereochemistry in Drug Molecules with Vibrational Optical Activity.

Chirality plays a crucial role in drug discovery and development. As a result, a significant number of commercially available drugs are structurally dissymmetric and enantiomerically pure. The determination of the exact 3D structure of drug candidates is, consequently, of paramount importance for the pharmaceutical industry in different stages of the discovery pipeline.

Exploring machine learning methods for absolute configuration determination with vibrational circular dichroism.

The added value of supervised Machine Learning (ML) methods to determine the Absolute Configuration (AC) of compounds from their Vibrational Circular Dichroism (VCD) spectra was explored. Among all ML methods considered, Random Forest (RF) and Feedforward Neural Network (FNN) yield the best performance for identification of the AC. At its best, FNN allows near-perfect AC determination, with accuracy of prediction up to 0.

Antiplasmodial Oleanane Triterpenoids from Root Bark.

Phytochemical investigation of the -BuOH extract of the roots of Sc. Elliot (Combretaceae) led to the isolation and identification of 10 oleanane triterpenoids (-), among which six new compounds, i.e.

Synthesis, Structure and Photophysical Properties of a New Class of Inherently Chiral Boron(III) Chelates-The tert-Leucine Complexes.

A new family of boron(III) chelates is introduced whereby molecular chirality, confirmed by circular dichroism, is imported during synthesis such that isolation of the diastereoisomers does not require separation procedures. The photophysical properties of two members of the family have been examined: the N,O,O-salicylaldehyde-based derivative shows pronounced intramolecular charge-transfer character in fluid solution and is weakly fluorescent, with a large Stokes shift. The corresponding 2-methylamino-benzaldehyde-derived N,N,O-chelate absorbs and fluoresces in the visible region with a much smaller Stokes shift.

CFA-18: a homochiral metal-organic framework (MOF) constructed from rigid enantiopure bistriazolate linker molecules.

In this work, we introduce the first enantiopure bistriazolate-based metal-organic framework, CFA-18 (Coordination Framework Augsburg-18), built from the R-enantiomer of 7,7,7',7'-tetramethyl-6,6',7,7'-tetrahydro-3H,3'H-5,5'-spirobi[indeno[5,6-d]-[1,2,3]triazole] (H2-spirta). The enantiopurity and absolute configuration of the new linker were confirmed by several chiroselective methods. Reacting H2-spirta in hot N,N-dimethylformamide (DMF) with manganese(ii) chloride gave CFA-18 as colorless crystals.

A combined Raman optical activity and vibrational circular dichroism study on artemisinin-type products.

Artemisinin and two of its derivatives, dihydroartemisinin and artesunate, which are front line drugs against malaria, were investigated using Raman optical activity (ROA) and vibrational circular dichroism (VCD) experiments, both supported by density functional theory (DFT) level calculations. The experimental techniques combined with DFT calculations could show that dihydroartemisinin was present as an epimeric mixture in solution. In addition, an approximation of the epimeric ratio could be extracted which was in agreement with the ratio obtained by 1H-NMR spectroscopy.