13C-NMR Spectral Data of Alkaloids Isolated from Psychotria Species (Rubiaceae)

Alkaloids and Lignans from the Aerial Parts of Rauvolfia tetraphylla Inhibit NO Production in LPS-activated RAW 264.7 Cells

Three previously undescribed compounds named rauvolphyllas A-C (1-3), along with thirteen known compounds, 18β-hydroxy-3-epi-α-yohimbine (4), yohimbine (5), α-yohimbine (6), 17-epi-α-yohimbine (7), (E)-vallesiachotamine (8), (Z)-vallesiachotamine (9), 16S-E-isositsirikine (10), Nb -methylisoajimaline (11), Nb -methylajimaline (12), ajimaline (13), (+)-lyoniresinol 3α-O-β-D-glucopyranoside (14), (+)-isolarisiresinol 3α-O-β-D-glucopyranoside (15), and (-)-lyoniresinol 3α-O-β-D-glucopyranoside (16) were isolated from the aerial parts of Rauvolfia tetraphylla L. Their chemical structures were elucidated based on the extensive spectroscopic interpretation of HR-ESI-MS, 1D and 2D NMR spectra. The absolute configurations of 2 and 3 were determined by experimental ECD spectra. Compounds 5, 6, 7, and 11-13 exhibited nitric oxide production inhibition activity in LPS-activated RAW 264.7 cells with the IC50 values of 79.10, 44.34, 51.28, 33.54, 37.67, and 28.56 μM, respectively, compared to that of the positive control, dexamethasone, which showed IC50 value of 13.66 μM. The other isolates were inactive with IC50 values over 100 μM.

Stereodivergent Complexity-to-Diversity Strategy en Route to the Synthesis of Nature-Inspired Skeleta

The complexity-to-diversity (CtD) strategy has become one of the most powerful tools used to transform complex natural products into diverse skeleta. However, the reactions utilized in this process are often limited by their compatibility with existing functional groups, which in turn restricts access to the desired skeletal diversity. In the course of employing a CtD strategy en route to the synthesis of natural product-inspired compounds, our group has developed several stereodivergent strategies employing indoloquinolizine natural product analogues as starting materials. These transformations led to the rapid and diastereoselective synthesis of diverse classes of natural product-like architectures, including camptothecin-inspired analogues, azecane medium-sized ring systems, arborescidine-inspired systems, etc. This manifestation required a drastic modification of the synthetic design that ultimately led to modular and diastereoselective access to a diverse collection of various classes of biologically significant natural product analogues. The reported strategies provide a unique platform that will be broadly applicable to other late-stage natural product transformation approaches.

A methanol extract and N,N-dimethyltryptamine from Psychotria viridis Ruiz & Pav. inhibit Zika virus infection in vitro

Zika virus (ZIKV) is a public health problem due to its association with serious fetal and neurological complications and the lack of antiviral agents and licensed vaccines against this virus. Surveillance studies have alerted about the potential occurrence of a new South American epidemic episode due to the recent circulation of an African ZIKV strain detected in Brazil. Therefore, it is essential to discover antiviral agents, including natural substances, that are capable of neutralizing the action of ZIKV. Several Psychotria species have antimicrobial and anti-inflammatory properties. Thus, a methanol extract and dimethyltryptamine from Psychotria viridis were evaluated for their ability to inhibit ZIKV infection in vitro by measuring the effective concentration that protects 50% of cells and investigating their possible mechanisms of action. The tested samples showed antiviral activity against ZIKV. The extract showed virucidal activity, affecting viral and non-cellular elements, inactivating the virus before infection or when it becomes extracellular after the second cycle of infection. It was also observed that both extract and dimethyltryptamine could inhibit the virus at intracellular stages of the viral cycle. In addition to dimethyltryptamine, it is believed that other compounds also contribute to the promising virucidal effect observed for the methanol extract. To our knowledge, this is the first report of the activity of a methanolic extract and dimethyltryptamine from Psychotria viridis against cellular ZIKV infection. These two samples, extracted from natural sources, are potential candidates for use as antiviral drugs to inhibit ZIKV infections.

Stereoselective Late-Stage Transformations of Indolo[2,3-a]quinolizines Skeleta to Nature-Inspired Scaffolds

The indolo[2,3-a]quinolizines, canthines, and arborescidines natural products exhibit a wide range of bioactivities including anticancer, antiviral, antibacterial, and anti-inflammatory, among others. Therefore, the development of modular and efficient strategies to access the core scaffolds of these classes of natural products is a remarkable achievement. The Complexity-to-Diversity (CtD) strategy has become a powerful tool that transforms natural products into skeletal and stereochemical diversity. However, many of the reactions that could be utilized in this process are limited by the type of functional groups present in the starting material, which restrict transformations into a variety of products to achieve the desired diversity. In the course of employing a (CtD) strategy en route to the synthesis of nature-inspired compounds, unexpected stereoelectronic-driven rearrangement reactions have been discovered. These reactions provided a rapid access to indolo[2,3-a]quinolizines-, canthines-, and arborescidines-inspired alkaloids in a modular and diastereoselective manner. The disclosed strategies will be widely applicable to other late-stage natural product transformation programs and drug discovery initiatives.

Optimization of Hyperglycemic Induction in Zebrafish and Evaluation of Its Blood Glucose Level and Metabolite Fingerprint Treated with Psychotria malayana Jack Leaf Extract

A standard protocol to develop type 1 diabetes in zebrafish is still uncertain due to unpredictable factors. In this study, an optimized protocol was developed and used to evaluate the anti-diabetic activity of Psychotria malayana leaf. The aims of this study were to develop a type 1 diabetic adult zebrafish model and to evaluate the anti-diabetic activity of the plant extract on the developed model. The ability of streptozotocin and alloxan at a different dose to elevate the blood glucose levels in zebrafish was evaluated. While the anti-diabetic activity of P. malayana aqueous extract was evaluated through analysis of blood glucose and LC-MS analysis fingerprinting. The results indicated that a single intraperitoneal injection of 300 mg/kg alloxan was the optimal dose to elevate the fasting blood glucose in zebrafish. Furthermore, the plant extract at 1, 2, and 3 g/kg significantly reduced blood glucose levels in the diabetic zebrafish. In addition, LC-MS-based fingerprinting indicated that 3 g/kg plant extract more effective than other doses. Phytosterols, sugar alcohols, sugar acid, free fatty acids, cyclitols, phenolics, and alkaloid were detected in the extract using GC-MS. In conclusion, P. malayana leaf aqueous extract showed anti-diabetic activity on the developed type 1 diabetic zebrafish model.

Antimycobacterial and Nitric Oxide Production Inhibitory Activities of Triterpenes and Alkaloids from Psychotria nuda (Cham. & Schltdl.) Wawra

A phytochemical study of leaves and twigs of Psychotria nuda resulted in 19 compounds, including five indole alkaloids, N,N,N-trimethyltryptamine, lyaloside, strictosamide, strictosidine, and 5α-carboxystrictosidine; two flavonolignans, cinchonain Ia and cinchonain Ib; an iridoid, roseoside; a sugar, lawsofructose; a coumarin, scopoletin; a diterpene, phytol; three triterpenes, pomolic acid, spinosic acid, and rotungenic acid; and five steroids, sitosterol, stigmasterol, campesterol, β-sitosterol-3-O-β-d-glucoside, and β-stigmasterol-3-O-β-d-glucoside. Some compounds were evaluated for their in vitro activity against Mycobacterium tuberculosis and their ability to inhibit NO production by macrophages stimulated by lipopolysaccharide (LPS). The compounds pomolic acid, spinosic acid, strictosidine, and 5α-carboxystrictosidine displayed antimycobacterial activity with minimum inhibitory concentrations ranging from 7.1 to 19.2 µg/mL. These compounds showed promising inhibitory activity against NO production (IC₅₀ 3.22 to 25.5 μg/mL). 5α-carboxystrictosidine did not show cytotoxicity against macrophages RAW264.7 up to a concentration of 100 µg/mL. With the exception of strictosamide, this is the first report of the occurrence of these substances in P. nuda.