Reassigning the stereochemistry of bioactive cepharanthine using calculated versus experimental chiroptical spectroscopies

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. In this work, we demonstrated, for the first time, its power to fully elucidate the 2-dimensional and 3-dimensional structures of two epimers in an epimeric mixture of 6-hydroxyhippeastidine. DFT calculation of chemical shifts was first performed to assist the assignment of planar structures. Furthermore, relative and absolute configurations were established by three different ways of computer-assisted structure elucidation (CASE) coupled with ORD/ECD/VCD spectroscopies. In addition, the significant added value of OR/ORD computations to relative and absolute configuration determination was also revealed. Remarkably, the differentiation of two enantiomeric scaffolds (crinine and haemanthamine) was accomplished via OR/ORD calculations with cross-validation by ECD and VCD.

Vibrational Circular Dichroism Absolute Configuration of Natural Products From 2015 to 2019

Although demonstrated in 1975, vibrational circular dichroism (VCD) finally started to popularize during this century as a reliable tool to determine the absolute configuration (AC) of organic molecules. This research field continues to be a very dynamic one, in particular for the study of natural products which are a unlimited source of chiral molecules. It therefore turns of interest to summarize the accomplishments published in recent years and to comment on some eventual difficulties that emerged in rare cases to complete the AC determination task. Therefore the aim of this review is to update VCD results for the AC assignment of natural products published from 2015 to 2019, a period in which VCD was reported in some 126 publications involving almost 300 molecules. They are organized according the type of studied metabolite allowing an easily search. The molecules correspond to 28 monoterpenes concerning 17 papers, to 42 sesquiterpenes in 14 papers, to 51 diterpenes in 19 publications, to 5 other terpenoids in three papers, to 48 aromatic molecules in 15 reports, to 20 polyketides in 10 publications, to 27 miscellaneous formulas also in 10 papers, and to 76 nitrogen containing compounds, which include alkaloids and their synthetic analogs, in 38 articles. The landscape of reviewed molecules is quite wide as it goes from simple monoterpenes, like borneol or camphor, to very relevant biological molecules like the alkaloid cocaine or tadalafil samples to distinguish genuine and counterfeit Cialis®. In addition, 5 natural products and a simple derivative published outside the reviewed period, were used to illustrate some aspects of density functional theory calculations.

New protein tyrosine phosphatase inhibitors from fungus Aspergillus gorakhpurensis F07ZB1707

Twelve new compounds, aspergorakhins A-L (1-12) coupled with one known xanthone leptosphaerin D (13), were isolated from the extract of soil-derived fungus Aspergillus gorakhpurensis F07ZB1707. Their structures were elucidated by spectroscopic data analysis including UV, IR, NMR, and HRESIMS. The absolute configurations of 5 and 8-11 were identified using ECD and OR calculations. All compounds were tested by enzyme inhibitory activity assay in vitro. Aspergorakhin A (1) showed selective activities against PTP1B and SHP1 over TCPTP with IC₅₀ values 0.57, 1.19, and 22.97 μM, respectively. Compounds 1 and 2 exhibited modest cytotoxicity against tumor cell lines A549, HeLa, Bel-7402, and SMMC-7721 with IC₅₀ values in the range of 6.75-83.4 μM.

Analgesic bisbenzylisoquinoline alkaloids from the rhizoma of Menispermum dauricum DC

Fifteen new bisbenzylisoquinoline alkaloids (1-15) were isolated from the rhizome of Menispermum dauricum DC. Compounds 1-9 were new N-oxides of dauricine-type alkaloids. Compounds 10-14 were rare tail-to-tail quaternary alkaloids. Their structures were characterized by comprehensive analysis of spectroscopic data, and absolute configurations were established from electronic circular dichroism (ECD) data and ECD calculations. Compounds were assayed on analgesic-related G-protein coupled receptors (GPCRs) including dopamine D1 and D2 receptors, opioid Mu receptor and muscarinic M3 receptor. Compound 1 showed high affinity and selective antagonistic activity on the M3 receptor with an IC₅₀ value of 2.2 ± 0.5 μM; compound 15 exhibited the highest antagonistic affinity among the evaluated compounds on Mu (IC₅₀ = 1.1 ± 0.6 μM) and it also acted as a D1 receptor antagonist (IC₅₀ = 8.8 ± 2.9 μM). These findings expanded the existing library of bisbenzylisoquinoline alkaloids and provided new structures for the related future drug design and synthesis.

Vibrational optical activity for structural characterization of natural products

This review presents the recent progress towards elucidating the structures of chiral natural products and applications using vibrational optical activity (VOA) spectroscopy.

Cepharanthine: An update of its mode of action, pharmacological properties and medical applications

BACKGROUND

Cepharanthine (CEP) is a drug used in Japan since the 1950s to treat a number of acute and chronic diseases, including treatment of leukopenia, snake bites, xerostomia and alopecia. It is the only approved drug for Human use in the large class of bisbenzylisoquinoline alkaloids. This natural product, mainly isolated from the plant Stephania cephalantha Hayata, exhibits multiple pharmacological properties including anti-oxidative, anti-inflammatory, immuno-regulatory, anti-cancer, anti-viral and anti-parasitic properties.

PURPOSE

The mechanism of action of CEP is multifactorial. The drug exerts membrane effects (modulation of efflux pumps, membrane rigidification) as well as different intracellular and nuclear effects. CEP interferes with several metabolic axes, primarily with the AMP-activated protein kinase (AMPK) and NFκB signaling pathways. In particular, the anti-inflammatory effects of CEP rely on AMPK activation and NFκB inhibition.

CONCLUSION

In this review, the historical discovery and development of CEP are retraced, and the key mediators involved in its mode of action are presented. The past, present, and future of CEP are recapitulated. This review also suggests new opportunities to extend the clinical applications of this well-tolerated old Japanese drug.