Naturally Occurring Norsteroids and Their Design and Pharmaceutical Application

The main focus of this review is to introduce readers to the fascinating class of lipid molecules known as norsteroids, exploring their distribution across various biotopes and their biological activities. The review provides an in-depth analysis of various modified steroids, including A, B, C, and D-norsteroids, each characterized by distinct structural alterations. These modifications, which range from the removal of specific methyl groups to changes in the steroid core, result in unique molecular architectures that significantly impact their biological activity and therapeutic potential. The discussion on A, B, C, and D-norsteroids sheds light on their unique configurations and how these structural modifications influence their pharmacological properties. The review also presents examples from natural sources that produce a diverse array of steroids with distinct structures, including the aforementioned A, B, C, and D-nor variants. These compounds are sourced from marine organisms like sponges, soft corals, and starfish, as well as terrestrial entities such as plants, fungi, and bacteria. The exploration of these steroids encompasses their biosynthesis, ecological significance, and potential medical applications, highlighting a crucial area of interest in pharmacology and natural product chemistry. The review emphasizes the importance of researching these steroids for drug development, particularly in addressing diseases where conventional medications are inadequate or for conditions lacking sufficient therapeutic options. Examples of norsteroid synthesis are provided to illustrate the practical applications of this research.

Ergosterols with rare peroxide, oxetane ring moiety, and a lactone ring from Aspergillus spectabilis and their immunosuppressive activities

Ten ergostane-type steroids, including seven undescribed ones named spectasteroids A-G, were obtained from Aspergillus spectabilis. Their structures and absolute configurations were determined based on HRESIMS, NMR, ECD calculations, and single-crystal X-ray diffraction analyses. Structurally, spectasteroid A was a unique example of aromatic ergostane-type steroid that featured a rare peroxide ring moiety; spectasteroid B contained a rare oxetane ring system formed between C-9 and C-14; and spectasteroid C was an unusual 3,4-seco-ergostane steroid with an extra lactone ring between C-3 and C-9. Spectasteroids F and G specifically showed inhibitory effects against concanavalin A-induced T lymphocyte proliferation and lipopolysaccharide-induced B lymphocyte proliferation, with IC50 values ranging from 2.33 to 4.22 μM. Spectasteroid F also showed excellent antimultidrug resistance activity, which remarkable enhanced the inhibitory activity of PTX on the colony formation of SW620/Ad300 cells.

Secoergostane- and ergostane-type steroids from Pleurotus cornucopiae var. citrinopileatus

In this study, we described the isolation of an 8,14-secoergostane-type, a 9,11-secoergostane-type, and three ergostane-type steroids from the fruiting bodies of Pleurotus cornucopiae var. citrinopileatus. The structure of (22Z)-3β,5α,11-trihydroxy-9,11-secoergosta-7,22-diene-6,9-dione, previously reported, have been revised to (22E). Their structures were established using NMR, UV, IR, and mass spectroscopic analyses. Three of the isolated compounds were found to exhibit inhibitory activity on the production of nitric oxide in lipopolysaccharide-stimulated RAW264.7 macrophages with IC₅₀ values of 21.3, 17.6, and 23.1 μM, respectively.

Steroids and dihydroisocoumarin glycosides from Xylaria sp. by the one strain many compounds strategy and their bioactivities

The fungus Xylaria sp. KYJ-15 was isolated from Illigera celebica. Based on the one strain many compounds (OSMAC) strategy, the strain was fermented on potato and rice solid media, respectively. As a result, two novel steroids, xylarsteroids A (1) and B (2), which are the first examples of C₂₈-steroid with an unusual β- and γ-lactone ring, respectively, along with two new dihydroisocoumarin glycosides, xylarglycosides A (3) and B (4), were identified. Their structures were elucidated by spectroscopic methods, X-ray diffraction and electronic circular dichroism (ECD) experiments. All isolated compounds were evaluated for cytotoxicity, DPPH radical scavenging activity, acetylcholinesterase inhibitory and antimicrobial effect. Compound 1 exhibited potent AChE inhibitory activity with an IC₅₀ value of 2.61 ± 0.05 μmol·L^-1. The β-lactone ring unit of 1 is critical for its AChE inhibitory activity. The finding was further confirmed through exploring the interaction of 1 with AChE by molecular docking. In addition, both compounds 1 and 2 exhibited obvious antibacterial activity against Bacillus subtilis with a minimum inhibitory concentration (MIC) of 2 μg·mL^-1. Compounds 3 and 4 exhibited antibacterial activities against Staphylococcus aureus with MICs of 4 and 2 μg·mL^-1, respectively, which also exhibited DPPH radical scavenging activity comparable to the positive control with IC₅₀ values of 9.2 ± 0.03 and 13.3 ± 0.01 μmol·L^-1, respectively.

Survey of natural products reported by Asian research groups in 2020

The new natural products reported in 2020 in peer-reviewed articles in journals with good reputations were reviewed and analyzed. The advances made by Asian research groups in the field of natural products chemistry in 2020 were summarized. Compounds with unique structural features and/or promising bioactivities originating from Asian natural sources were discussed based on their structural classification.

Carapanins A-C: new limonoids from andiroba (Carapa guianensis) fruit oil

Carapanins A-C (1-3) were isolated from the fruit oil of Carapa guianensis. Compounds 1 and 2 are limonoids with unique structures. Namely, compound 1 is an andirobin-type limonoid with a C-15/C-30 γ-lactone instead of the δ-lactone of the D-ring, and compound 2 is a mexicanolide-type limonoid with a C-16/C-30 δ-lactone ring. The absolute structures of 1 and 2 were determined using X-ray crystallography, whereas the structure of 3 was established mainly via NMR and mass spectroscopy. The inhibitory effects of 1-3 on nitric oxide production were evaluated, and it was revealed that 2 and 3 were potent nitric oxide inhibitors.