Structural Revision of Tinotufolins from Tinospora crispa Leaves Guided by Empirical Rules and DFT Calculations

Clerodane diterpenes are a class of secondary metabolites that can be classified into four types according to the configuration of the H3-19/H-10-H3-17/H3-20 fragment, i.e., trans-cis (TC), trans-trans (TT), cis-cis (CC), and cis-trans (CT). Tinotufolins A-C and E (1a-3a and 5a), isolated from the leaves of Tinospora crispa, were previously elucidated as CT-type clerodanes; however, our established 13C NMR-based empirical rules and density functional theory calculations suggested that these clerodanes belong to the CC type. Therefore, tinotufolins A-F (1-6) were reisolated from the leaves of T. crispa, along with an undescribed compound 7 and known compounds 8-11, and their structures were established by extensive spectroscopic analyses. The structures of tinotufolins A-C and E were revised to CC-type 1-3 and 5, and undescribed compound 7 was established as a CC-type clerodane. The present study demonstrates that empirical rules and calculations can efficiently identify and revise erroneous structures in clerodane diterpenes.

Enantioselective and collective total synthesis of pentacyclic 19-nor-clerodanes

We report herein the collective asymmetric total synthesis of seven pentacyclic 19-nor-clerodane diterpenoids, namely (+)-teucvin (+)-cracroson A, (+)-cracroson E, (+)-montanin A, (+)-teucvisin C, (+)-teucrin A, and (+)-2-hydroxyteuscorolide. An ytterbium-catalyzed asymmetric inverse-electron-demand Diels-Alder reaction of 4-methyl-2-pyrone with a chiral C5-substituted cyclohexa-1,3-dienol silyl ether is the key feature of the synthesis, which provides the common cis-decalin intermediate with five continuous stereocenters in excellent yield and stereoselectivity. From this diversifiable intermediate, the total synthesis of (+)-teucvin and (+)-2-hydroxyteuscorolide was realized in thirteen and eighteen steps, respectively. From (+)-teucvin, five other pentacyclic 19-nor-clerodanes were divergently and concisely generated through late-stage oxidation state adjustments.

Diterpene Sonderianin isolated from Croton blanchetianus exhibits acetylcholinesterase inhibitory action and anxiolytic effect in adult zebrafish (Danio rerio) by 5-HT system

Croton blanchetianus is known as 'marmeleiro preto', a very widespread shrub in Northeast Brazil. Terpenoids, steroids and phenolic compounds are among the reported secondary metabolites of the Croton genus that are a potential source of bioactive compounds. This study evaluated the anxiolytic potential of clerodine-type diterpene, sonderianin (CBWS) isolated from the stem bark of C. blanchetianus and its mechanism of action in adult zebrafish (Danio rerio) (ZFa). The anticonvulsant and anti-acetylcholinesterase effects have also been explored. ZFa (n = 6/group) were treated intraperitoneally (ip; 20 µL) with CBWS (4, 12 and 40 mg/kg) and vehicle (3% DMSO; 20 µL) and subjected to locomotor activity tests, as well as toxicity acute 96 h. CBWS was also administered for analysis in the light/dark test. The involvement of the serotonergic system (5-HT) was investigated using 5-HTR₁, 5-HTR_2A/2C and 5-HTR_3A/3B receptor antagonists. Anxiolytic doses were tested for pentylenetetrazol-induced seizure in ZFa. The inhibitory activity of the enzyme acetylcholinesterase (AChE) was measured. CBWS was not considered toxic and reduced locomotor activity. The results of the present study identified for the first time the interaction of the diterpene sonderianina in the CNS. This study provides evidence that CBWS has an anxiolytic effect mediated by serotonergic (5-HT) involvement and anti-acetylcholinesterase action. The 5-HTR₁ and 5-HTR_2A/2C receptors may be implicated in the low anticonvulsant effect in CBWS.Communicated by Ramaswamy H. Sarma.

The genus Paraconiothyrium: species concepts, biological functions, and secondary metabolites

The genus Paraconiothyrium has worldwide distribution with diverse host habitats and exhibits potential utilisation as biocontrol agent, bioreactor and antibiotic producer. In this review, we firstly comprehensively summarise the current taxonomic status of Paraconiothyrium species, including their category names, morphological features, habitats, and multigene phylogenetic relationships. Some Paraconiothyrium species possess vital biological functions and potential applications in medicine, agriculture, industry, and environmental protection. A total of 147 secondary metabolites have been reported so far from Paraconiothyrium, among which 95 are novel. This paper serves to provide an overview of their diverse structures with chemical classification and biological activities. To date, 27 species of Paraconiothyrium have been documented; however, only seven have been investigated for their secondary metabolites or biological functions. Our review is expected to draw more attention to this genus for providing a taxonomic reference, discovering extensive biological functions, and searching in-depth for new bioactive natural products.

Nitric oxide production inhibitory activity of clerodane diterpenes from Monoon membranifolium

A new clerodane diterpene, 2β-methoxyhardwickiic acid (1), and four known compounds (2-5) were isolated from the twigs of Monoon membranifolium. The structure of the new compound was determined by extensive spectroscopic methods and ESITOFMS data. The absolute configuration of 1 was established by a comparison of its ECD spectrum and specific rotation with those of related previously reported compounds. All compounds were evaluated for their nitric oxide (NO) production inhibitory activities in RAW264.7 macrophage cells. Compounds 3 and 5 inhibited NO production with IC₅₀ values of 16.1 and 28.9 μM, respectively, which were better than that of standard compound, indomethacin (IC₅₀ = 32.2 μM).