Hybridaphniphyllines A and B, Daphniphyllum alkaloid and iridoid hybrids suggestive of Diels-Alder cycloaddition in Daphniphyllum longeracemosum

Phukettosides A-E, mono- and bis-iridoid glycosides, from the leaves of Morinda umbellata L

Four undescribed bis-iridoid glycosides, named phukettosides A-D, and one iridoid glycoside, referred to as phukettoside E, were isolated and fully characterized from the leaves of Morinda umbellata L. Phytochemical analysis also revealed the presence of eight known compounds. The structures were determined through extensive analysis of 1D and 2D-NMR spectroscopic and HRMS spectral data, and the absolute configurations of the isolates were deduced through ECD calculations. Biogenetic pathways for the bis-iridoid glycosides, phukettosides A-C, through intermolecular Diels-Alder type reactions, were proposed. The isolated compounds, with the exception of phukettosides B and D, were evaluated against a panel of cancer cell lines (MOLT-3, HuCCA-1, A549, HeLa, HepG2, and MDA-MB-231) and a non-cancerous cell line (MRC-5) for their cytotoxicity. None of the isolates had significant cytotoxic effects on the tested cell lines.

ECD exciton chirality method today: a modern tool for determining absolute configurations

The application of the exciton chirality method (ECM) to interpret electronic circular dichroism (ECD) spectra is a well‐established and still popular approach to assign the absolute configuration (AC) of natural products, chiral organic compounds, and organometallic species. The method applies to compounds containing at least two chromophores with electric dipole allowed transitions (e.g., π–π* transitions). The exciton chirality rule correlates the sign of an exciton couplet (two ECD bands with opposite sign and similar intensity) with the overall molecular stereochemistry, including the AC. A correct application of the ECM requires three main prerequisites: (a) the knowledge of the molecular conformation, (b) the knowledge of the directions of the electric transition moments (TDMs), and (c) the assumption that the exciton coupling mechanism must be the major source of the observed ECD signals. All these prerequisites can be easily verified by means of quantum‐mechanical (QM) calculations. In the present review, we shortly introduce the general principles that underpin the use of the ECM for configurational assignments and survey its applications, both classic ones and some reported in the recent literature. Based on these examples, we will stress the advantages of the ECM but also the key requisites for its correct application. Additionally, we will discuss the dependence of the couplet sign on geometrical parameters (angles α,β,γ between TDMs), which can be helpful for discerning the sign of exciton chirality in ambiguous situations. Finally, we will present a molecular orbital (MO) description of the exciton coupling phenomenon.

The chemistry of Daphniphyllum alkaloids

The triterpenoids Daphniphyllum alkaloids share the unique fused hexacyclic ring framework are isolated from the genus Daphniphyllum. These natural products possess comprehensive biological activities and exhibit excellent potential medicinal appliment. This review covers the reported isolation studies and biological activities of Daphniphyllum alkaloids spanning the period from 1966 to the beginning of 2020, In the meantime, the total synthesis of Daphniphyllum alkaloids will be emphatically summarized for supplement over this review series.

Concise Construction of the ACDE Ring System of Calyciphylline A Type Alkaloids by a [5+2] Cycloaddition

A concise route for construction of the ACDE ring skeleton in calyciphylline A type alkaloids was developed using an intramolecular [5+2] cycloaddition reaction of an oxidopyrylium species bearing a tetrasubstituted olefin. Key to the success of this reaction was the combination of acid and base, which accelerated the construction of this skeleton containing a spiro ring and vicinal quaternary carbon centers. The resultant tricyclic ADE ring compound was converted to an ACDE ring model through C-H oxidation and an aza-Wittig reaction.

Polysubstituted Isoflavonoids from Spatholobus suberectus, Flemingia macrophylla, and Cudrania cochinchinensis

Four hitherto unknown polysubstituted isoflavonoids, including three isoflavans: 7,4'-dihydroxy-8,2',3'-trimethoxyisoflavan (1), 7,2',4'-trihydroxy-8,3'-dimethoxyisoflavan (2), and 7,2',4'-trihydroxy-5-methoxyisoflavan (3), and one prenylated isoflavone cudraisoflavone M (4) were isolated from the ethanol extracts of Spatholobus suberectus (for 1 and 2), Flemingia macrophylla (for 3), and Cudrania cochinchinensis (for 4), respectively. Their structures were established on the basis of extensive spectroscopic analysis. Compounds 1 and 4 exhibited weak cytotoxic activity against five human cancer cell lines (HL-60, A-549, SMMC-7721, MCF-7, and SW-480).

Recent Progress in the Chemistry of Daphniphyllum Alkaloids †

Daphniphyllum is an evergreen species known since 1826. After initial systematic investigations, more than 320 members of this family have been isolated, which comprise complex and fascinating structures. Unique azapolycyclic architectures containing one or more quaternary stereocenters render these alkaloids synthetically challenging. This review covers efforts toward the synthesis of Daphniphyllum alkaloids spanning the period from 2005 to the beginning of 2016, including reported biological activities as well as the isolation of new members of this genus.

Prenylated Coumarins from Heracleum stenopterum, Peucedanum praeruptorum, Clausena lansium, and Murraya paniculata

Four hitherto unknown prenylated coumarins, namely 6″-O-β-D-apiofuranosylapterin (1), 4'-O-isobutyroylpeguangxienin (2), 6-(3-methyl-2-oxobutyroyl)-7-methoxycoumarin (3), and 6-hydroxycoumurrayin (4), were isolated from the ethanol extract of Heracleum stenopterum, Peucedanum praeruptorum, Clausena lansium, and Murraya paniculata, respectively. Their chemical structures were established on the basis of extensive spectroscopic analysis. Compound 2 exhibited in vitro cytotoxic activity against five human cancer cell lines (HL-60, A-549, SMMC-7721, MCF-7, and SW-480) with IC₅₀ values ranging from 15.9 to 23.2 μM.