Steroidal Alkaloids with a Potent Analgesic Effect Based on N-type Calcium Channel Inhibition

C-H Functionalization-Enabled 11-Step Semisynthesis of (-)-Veragranine A and Characterization of Synthetic Analogs in Osteoarthritis-related Pain Treatment

We report an efficient semisynthesis of the cholestane steroidal alkaloid (-)-veragranine A with a 6/6/6/5/6/6 hexacyclic ring system, eight stereocenters, and a unique C12-C23 linkage. Our synthesis features a Schönecker-Baran C-H oxidation at C12, a Suzuki-Miyaura cross-coupling to form the C12-C23 bond, and a hydrogen atom transfer (HAT)-initiated Minisci C-H cyclization to forge the C20-C22 bond with desired stereochemistry at C20. These enabling transformations significantly enhanced the overall synthetic efficiency and delivered (-)-veragranine A in 11 steps and over 200 mg from cheap and readily available dehydroepiandrosterone. In addition, this approach allowed flexible syntheses of novel synthetic analogs for biological evaluations in sensory neurons in vitro and in an in vivo model of arthritic pain, from which two novel lead compounds were identified for further development.

Steroidal Alkaloids from the Roots of Veratrum mengtzeanum Loes. with Their Anti-Inflammatory Activities

The phytochemical investigation of Veratrum mengtzeanum Loes. roots resulted in the isolation and characterization of two novel, namely Mengtzeanines A (1), Mengtzeanines B (2), and eight known steroidal alkaloids (3-10). Their structural properties were assessed though extensive spectroscopic techniques. All constituents 1-10 were analyzed for suppression of NO formation in LPS-induced RAW264.7 macrophages. Among them, constituent 6 (Verazine) showed inhibition against LPS-induced NO production (IC50 = 20.41 μM). Additionally, compound 6 could inhibit the secretion of IL1β, IL6, and TNFα, and downregulate the productions of iNOS and COX2 in LPS-induced RAW264.7 macrophages. Further experiments revealed that 6 exhibited a potent anti-inflammatory level in LPS-stimulated RAW264.7 macrophages via inhibiting NF-κB, and triggering of Keap1/Nrf2/HO-1 axis, implying that compound 6 may be a promising candidate for treating inflammatory disorders.

Steroidal alkaloids from the roots of Veratrum stenophyllum

Three new steroidal alkaloids, veratrasines A - C (1-3), along with ten known analogues (4-13) were isolated from the roots of Veratrum stenophyllum. Their structures were elucidated by NMR and HRESIMS data and comparison with the reported data in the literatures. A plausible biosynthetic pathway for 1 and 2 were proposed. Compounds 1, 3, and 8 showed moderate cytotoxic activity against MHCC97H and H1299 cell lines.

Steroidal alkaloid with unprecedented triheterocyclic architecture

Veratrazine A (1), a steroidal alkaloid with a unique 6/5/5 triheterocyclic scaffold as the side chain, was isolated from Veratrum stenophyllum, and its structure was established via spectroscopic analyses and X-ray diffraction. A plausible biosynthetic pathway for 1 is proposed. Bioassy exhibits moderate anti-inflammatory activities in vitro and in vivo.

Aspersterols A-D, Ergostane-Type Sterols with an Unusual Unsaturated Side Chain from the Deep-Sea-Derived Fungus Aspergillus unguis

Four previously undescribed ergostane-type sterols, aspersterols A-D (1-4), were isolated from a deep-sea-derived fungus, Aspergillus unguis IV17-109. The structures of the new compounds were determined by extensive analyses of their spectroscopic data, pyridine-induced deshielding effect, Mosher's method, and electronic circular dichroism calculations. The key feature of these sterols is the presence of a rare unsaturated side chain with conjugated double bonds at Δ¹⁷ and Δ²². The absolute configuration of C-24 in the side chain was determined by hydrogenation and comparing ¹³C NMR chemical shifts of the hydrogenated products with literature values. In addition, aspersterol A (1) is the second representative of anthrasteroids with a hydroxy group at the C-2 position. Compound 1 showed cytotoxicity against six cancer cell lines, with GI₅₀ values of 3.4 ± 0.3 to 4.5 ± 0.7 μM, while 2-4 showed anti-inflammatory activity, with IC₅₀ values ranging from 11.6 ± 1.6 to 19.5 ± 1.2 μM.

Synthesis of 5α,6-Dihydroveragranines A and B

The 5α,6-dihydro congeners of veragranines A and B, two steroidal alkaloids with an unprecedented hexacyclic skeleton and potent analgesic effects, were synthesized from hecogenin acetate within six steps. This work enables quick access to the hexacyclic skeleton and is amendable to prepare other D-ring-modified congeners.

New steroidal alkaloids with anti-inflammatory and analgesic effects from Veratrum grandiflorum

ETHNOPHARMACOLOGICAL RELEVANCE

"Li-Lu", the roots and rhizomes of Veratrum grandiflorum (Melianthiaceae), has been historically used as a traditional folk medicine for the treatment of wrist pain, fractures, sores, and inflammation in Yunnan Province, China. However, the anti-inflammatory and analgesic studies of this plant have seldom reported.

AIM OF THE STUDY

To evaluate the anti-inflammatory and analgesic properties related to the traditional usage of V. grandiflorum both in vitro and in vivo, and further explore the accurate bioactive compounds from the medicinal plant.

MATERIALS AND METHODS

Phytochemical investigation was carried out by chromatographic methods and their structures were established based on extensive spectra and comparison with corresponding data in the reported literatures. Anti-inflammatory activities were assessed by the suppression of lipopolysaccharide-activated inflammatory mediators in RAW 264.7 macrophage cells in vitro. Furthermore, anti-inflammatory and analgesic effects were evaluated based on carrageenan-induced paw edema and acetic acid-stimulated writhing in mice.

RESULTS

The methanol extract (ME) of V. grandiflorum significantly alleviated the paw edema caused by carrageenan and the writhing numbers induced by acetic acid. Subsequent phytochemical investigation led to isolated of 21 steroidal alkaloids, including seven new compounds, veragranines C-I (1-7). Anti-inflammatory test indicated that steroidal alkaloids could decrease the expression of cyclooxygenase-2 (COX-2), interleukin-1β (IL-1β), and tumor necrosis factor α (TNF-α) in lipopolysaccharide (LPS)-stimulated RAW 264.7 macrophage cells at a concentration of 5.0 μg/ml in vitro, comparable to DXM. Moreover, five new steroidal alkaloids (2, 4, 5, 6, and 7) and two major steroidal alkaloids (9 and 13) significantly decreased the numbers of writhing in mice at the doses of 0.5 and/or 1.0 mg/kg (p < 0.01/0.05), roughly comparable to Dolantin™ at 10.0 mg/kg.

CONCLUSIONS

The investigation supported the traditional use of V. grandiflorum and provided new steroidal alkaloids as potent analgesic agents.

Chemistry and bioactivities of natural steroidal alkaloids

Steroidal alkaloids possess the basic steroidal skeleton with a nitrogen atom in rings or side chains incorporated as an integral part of the molecule. They have demonstrated a wide range of biological activities, and some of them have even been developed as therapeutic drugs, such as abiraterone acetate (Zytiga^®), a blockbuster drug, which has been used for the treatment of prostate cancer. Structurally diverse natural steroidal alkaloids present a wide spectrum of biological activities, which are attractive for natural product chemistry and medicinal chemistry communities. This review comprehensively covers the structural classification, isolation and various biological activities of 697 natural steroidal alkaloids discovered from 1926 to October 2021, with 363 references being cited.

Identification of Veratrum Species in Pimacao Based on ITS2 Sequences and Steroidal Alkaloids by a Pseudo-Targeted Metabolomics Method

Pimacao is a traditional Chinese folk medicine and is the main component of the famous Chinese herbal remedy "Yunnan Baiyao" for its significant analgesic activity in the treatment of wounds. Due to increases in consumption, its wild population is now difficult to find, and adulterant from the same genus has occurred. However, this is challenging to distinguish the species of Veratrum in Pimacao using dried roots and rhizomes or medicinal powder. ITS2 sequences and steroidal alkaloids by the non-targeted and pseudo-targeted metabolomics methods were taken advantage of establishing an effective identification method. Based on the ITS2 sequence, metabolite profiling of steroidal alkaloids and morphological characteristics, the classification of two distinct subspecies in V. mengzeanum has been reinforced. In addition, the new subspecies V. mengzeanum subsp. phuwae was collected in China for the first time. The ITS2 sequence could be used in the identification of V. taliense, V. mengtzeanum, V. stenophyllum, and V. nigrum, but is insufficient for intraspecific identification. Simultaneously, 147 variables were labeled by non-targeted analysis accomplished utilizing an ultra-high-performance liquid chromatography electrospray ionization orbitrap tandem mass spectrometry (UPLC-ESI-QE-Orbitrap-MS) system consisting of an Orbitrap QE HF-X. Followed by a pseudo-targeted analysis method developed for the Qtrap 6500-plus mass spectrometry system coupled with an ESI source, 29 labeled steroidal alkaloids detected by the MRM mode could distinguish between four species. Notably, 25 labeled steroidal alkaloids could distinguish between three closely related species. These have the potential to be used as markers for identification. Furthermore, there were several variables with statistical differences between two subspecies of V. mengtzeanum and populations of V. taliense, V. mengtzeanum, and V. stenophyllum.

Hot off the Press

A personal selection of 32 recent papers is presented, covering various aspects of current developments in bioorganic chemistry and novel natural products, such as daphnepapytone A from Daphne papyracea.