New alkaloids from Stemona tuberosa and structural revision of tuberostemonols P and R

Three Stemona alkaloids named stemotuberines A-C (1-3) with unique C17N frameworks, presumably formed by elimination of the C-11-C-15 lactone ring of the stichoneurine skeleton, were isolated from the roots of Stemona tuberosa. Their structures were elucidated by spectroscopic analysis, X-ray diffraction, and computational methods. Compounds 2 and 3 showed inhibition (IC50 values of 37.1 and 23.2 μM, respectively) against LPS-induced nitric oxide production in RAW 264.7 cells. In addition, concern was expressed about the reported plant origin (S. sessilifolia) of the recently described alkaloids tuberostemonols O-R (4-7), which should be S. tuberosa. NMR calculations indicated structural misassignment of these compounds except for 6. Isolation of tuberostemonol P (5) from our material of S. tuberosa allowed for a close examination of the spectroscopic data leading to the revised structure 5a. Tuberostemonol R (7) was found to have identical 1H and 13C NMR data to the well-known alkaloid croomine, and therefore its structure including relative stereochemistry must be revised as 7a.

Nocaviogua A and B: two lipolanthines from root-nodule-associated Nocardia sp

Nocaviogua A (1) and B (2), two lipolanthines featuring a non-canonical avionin (Avi)-containing macrocycle and a long acyl chain, were identified from the mutualistic actinomycete Nocardia sp. XZ19_369, which was isolated from the nodules of sea buckthorn collected in Tibet. Their planar structures were elucidated via extensive analyses of 1D and 2D NMR, as well as HRMS data. The absolute configurations were fully elucidated by advanced Marfey's analysis and GIAO NMR calculations, representing the first time that the configurations of this family of lipolanthines have been determined. Nocaviogua A (1) exhibited weak cytotoxicity against human chronic uveal melanoma cells (UM92-1), non-small cell lung cancer (NCI-H2170), and breast cancer (MDA-MB-231). Our work provides valuable information on this burgeoning class of lipolanthines for further investigations.

The hypothesis of tautomeric equilibrium between epimers in ciquitins A and B

Recently, ciquitins A and B isolated from the powdered and defatted airdried aerial parts of Leucophyllum ambiguum were reported as a mixture of conformers in a solution at room temperature. Considering the existence of a hemiacetal hydroxyl fragment in the ciquitins A and B, they are more likely to exist in the form of epimer rather than the mixture of conformers. To confirm this hypothesis, the NMR calculations of two epimers at C-9 (1-a and 1-b) were performed and the results matched well with experimental NMR data of mixtures (1). Moreover, a brief discussion on the reason for this hypothesis was also presented.

Polyprenylated Acylphloroglucinols With Different Carbon Skeletons From the Fruits of Garcinia multiflora

Eleven new polycyclic polyprenylated acylphloroglucinols (PPAPs, 1-11) and three new monocyclic polyprenylated acylphloroglucinols (MPAPs, 12-14), together with ten known analogues were isolated from the fruits of Garcinia multiflora. These PPAPs belong to three types including the bicyclic polyprenylated acylphloroglucinols (BPAPs), the caged PPAPs, and the complicated PPAPs. Their structures and absolute configurations were determined through HRESIMS, NMR spectroscopy data, electronic circular dichroism (ECD) calculations, and gauge-independent atomic orbital (GIAO) NMR calculations with DP4+ analyses. Moreover, compounds 2 and 7 exhibited moderate cytotoxicity against three human cancer lines (MCF-7, T98, and HepG2) with IC50 values ranging from 9.81 ± 1.56 to 17.00 ± 2.75 μM.

Arteannoides U-Z: Six undescribed sesquiterpenoids with anti-inflammatory activities from the aerial parts of Artemisia annua (Qinghao)

Four previously unreported sesquiterpenoid diasteromers, arteannoides U-X (1-4), together with one new norsesquiterpenoid 5 (arteannoide Y) and one undescribed rearranged cadinene sesquiterpenoid 6 (arteannoide Z) were obtained from the dried aerial parts of Artemisia annua (Qinghao). Notably, arteannoides U-X (1-4) are four stereoisomers that possess the same molecules and the same planar connectivity, but differ from each other in configuration at a certain stereocenter. Their accurate structures were unambiguously identified and distinguished by extensive spectroscopic analyses, NMR calculations with DP4+ analysis, electronic circular dichroism (ECD) calculations and X-ray diffraction analyses. Compounds 1, 3, and 4 showed inhibitory activities against the production of inflammatory cytokines (PGE₂, NO, IL-6 and TNF-α) in lipopolysaccharide (LPS)-induced RAW 264.7 macrophages.

The identification of alkaloids from the stems of Picrasma quassioides via computer-assisted structure elucidation and quantum chemical calculations

Four new alkaloids (1-4) and one known alkaloid were isolated from the stems of Picrasma quassioides. The structures of these isolated compounds were elucidated by spectroscopic analyses, a combination of computer-assisted structure elucidation software (ACD/Structure Elucidator) and gauge-including atomic orbital (GIAO) calculation of 1 D NMR data. All compounds were evaluated for their cytotoxic activities against hepatocellular carcinoma HepG2 and Hep3B cells. However, they did not show obvious inhibitory activities.[Figure: see text].

Chlorinated bianthrones from the cyanolichen Nephroma laevigatum

While depsidones, depsides or dibenzofuran-like compounds dominate the chemical composition of lichens, the cyanolichen Nephroma laevigatum affords a diversity of quinoid pigments represented by chlorinated anthraquinones derived from emodin and new bianthrones resulting from the homo- or heterodimerization of monomers. Bianthrones were pointed out from the dichloromethane extract by MS/MS-based molecular networking, then isolated and characterized on the basis of extensive spectroscopic analyzes and GIAO NMR shift calculation followed by CP3 analyzes.

Stereo- and Enantioselective Addition of Organolithiums to 2-Oxazolinylazetidines as a Synthetic Route to 2-Acylazetidines

A new synthetic route to N-alkyl-2-acylazetidines was developed through a highly stereoselective addition of organolithiums to N-alkyl-2-oxazolinylazetidines followed by acidic hydrolysis of the resulting oxazolidine intermediates. This study revealed an unusual reactivity of the C=N bond of the oxazoline group when reacted with organolithiums in a non-polar solvent such as toluene. The observed reactivity has been explained considering the role of the nitrogen lone pair of the azetidine ring as well as of the oxazolinyl group in promoting a complexation of the organolithium, thus ending up with the addition to the C=N double bond. The high level of stereoselectivity in this addition is supported by DFT calculations and NMR investigations, and a model is proposed for the formation of the oxazolidine intermediates, that have been isolated and fully characterized. Upon acidic conditions, the oxazolidine moieties were readily converted into 2-acylazetidines. This synthetic approach has been applied for the preparation of highly enantioenriched 2-acylazetidines starting from chiral not racemic N-alkyl-2-oxazolinylazetidines.

The 125Te Chemical Shift of Diphenyl Ditelluride: Chasing Conformers over a Flat Energy Surface

The interest in diphenyl ditelluride (Ph₂Te₂) is related to its strict analogy to diphenyl diselenide (Ph₂Se₂), whose capacity to reduce organic peroxides is largely exploited in catalysis and green chemistry. Since the latter is also a promising candidate as an antioxidant drug and mimic of the ubiquitous enzyme glutathione peroxidase (GPx), the use of organotellurides in medicinal chemistry is gaining importance, despite the fact that tellurium has no recognized biological role and its toxicity must be cautiously pondered. Both Ph₂Se₂ and Ph₂Te₂ exhibit significant conformational freedom due to the softness of the inter-chalcogen and carbon–chalcogen bonds, preventing the existence of a unique structure in solution. Therefore, the accurate calculation of the NMR chemical shifts of these flexible molecules is not trivial. In this study, a detailed structural analysis of Ph₂Te₂ is carried out using a computational approach combining classical molecular dynamics and relativistic density functional theory methods. The goal is to establish how structural changes affect the electronic structure of diphenyl ditelluride, particularly the ¹²⁵Te chemical shift.

Structural elucidation of dioxa-cage compounds from tetrahydroisobenzofuran-1(3H)-one: analysis of NMR data and GIAO chemical shifts calculations

The polycyclic compounds, especially the dioxa-cages, have attracted considerable attention in recent years. In our work, a series of 9β-substituted 3-oxo-4,11-dioxatetracyclo[5.2.1.1^5,8 .0^2,6 ]undecane compounds were unexpectedly isolated during bromination, chlorination and epoxidation reactions of the 3-hydroxy-3a,4,7,7a-tetrahydro-4,7-methanoisobenzofuran-1(3H)-one. After careful analysis of the NMR data, the chemical shifts of the isolated and the expected products were predicted by theoretical calculations using density functional theory and gauge including atomic orbitals. The best correlation between calculated and experimental data was evaluated by comparing mean absolute errors and applying DP4 probability methodology. Results from both approaches indicated a correct structural elucidation. Copyright © 2016 John Wiley & Sons, Ltd.

Investigations on Synperiplanar and Antiperiplanar Isomers of Losartan: Theoretical and Experimental NMR Studies

Losartan inhibits the renin-angiotensin-aldosterone system by blocking the angiotensin II receptor. It is commonly used in cardiovascular diseases, such as hypertension. Several publications applied the ab initio and density functional theory methods to investigate the molecule of losartan. Only in one of them were the nuclear magnetic resonance spectra calculations carried out, and their results were correlated with the experimental values. The authors focused their attention on calculations of the anion form of losartan, taking into consideration both its synperiplanar and antiperiplanar configurations. Coefficients of determination and mean absolute deviation parameters were calculated for the experimental and calculated chemical shifts for every used basis set. They showed a noticeably stronger correlation for the anti-isomers than for the syn-isomers. Moreover, the solvation model increased the value of this parameter. The results of calculations confirmed that an anti-conformation of the analyte seems to be the preferred one, and such an orientation might be most potent within the receptor cavity, which is in agreement with the results of previous studies.