Cembranoids, Pseudopteranoids, and Cubitanoids of Natural Occurrence

Py-GC–MS Investigation of Pyrolysis Behaviors and Decomposition Products of α- and β-2,7,11-cembratriene-4,6-diols

Py-GC–MS Investigation of Pyrolysis Behaviors and Decomposition Products of α- and β-2,7,11-cembratriene-4,6-diols May 1, 2022 Shen Huang, Chen Yang, Ning Ma, Lifeng Zhou, Chunxiao Jia, Tao Wei, Duobin Mao LCGC North America, May 2022, Volume 40, Issue 5 Pages: 223–228 To study the thermal stability of cembratriene, α- and β-2, 7, 11-cembratriene-4, 6-diols (α- and β-CBT) were isolated from tobacco leaves. Thermogravimetric (TG) and differential thermogravimetric (DTG) analyses were used to evaluate the cleavage differences between the two compounds. The TGA results showed the peak temperatures (Tp) were 263.3 °C and 254.1 °C with the largest weight loss rate; the significant weight losses were 90.96% and 99.45%. Pyrolysis gas chromatography–mass spectrometry (Py-GC–MS) was employed for the pyrolysis products at different temperatures (300, 600, and 900 °C) under either N2 or an O2:N2 (10%:90%) mixture. The results showed that the major pyrolysates from α- and β-CBT were simple hydrocarbons, such as toluene, 1, 4-pentadiene, and p-xylene, as well as several important flavor compounds, such as 2-methylfuran, benzaldehyde, and 4-methylbenzaldehyde. More pyrolysis products were obtained at higher temperatures, and almost all of the harmful aromatic ingredients were produced at 900 °C. Importantly, solanone, a significant flavor component, was only obtained from the pyrolysis of α-CBT under 10% O2 in N2 at both 600 and 900 °C. The number of the pyrolysates changed with the change in pyrolysis temperature and the presence of oxygen. The study of the thermal behavior and pyrolysis products of these terpenoids could possibly suggest flavor precursors that could be used to provide specific flavors.

Sacraoxides A-G, Bioactive Cembranoids from Gum Resin of Boswellia sacra

Seven undescribed cembranoids, sacraoxides A–G (1, 3–8) were isolated from the gum resin of Boswellia sacra. Their structures were elucidated by extensive physicochemical and spectroscopic analysis, as well as ECD calculation, modified Mosher’s method and X-ray diffraction crystallography. Compounds 6 and 7 exhibited inhibitory activities on nitric oxide (NO) production induced by lipopolysaccharide in RAW264.7 cells with IC₅₀ values of 24.9 ± 1.7 and 36.4 ± 2.9 μM.

A Review on Bioactivities of Tobacco Cembranoid Diterpenes

Cembranoids are carbocyclic diterpenes comprising four isoprene units and are natural products with a parent skeleton consisting of a 14-membered ring. They have gained wide interest in recent years and are a major hotspot in the research of natural product chemistry. Since 1962, various tobacco cembranoid diterpenes have been identified. This review systematically discusses and summarises the excellent antimicrobial, insecticidal, cytotoxic and neuroprotective activities of tobacco cembranoid diterpenes. These compounds show potential to be developed as botanical fungicides, cytotoxic drugs and drugs for the treatment of human immunodeficiency virus, Alzheimer's disease, Parkinson's disease, and other neurodegenerative diseases. However, there are relatively few studies on the structure⁻activity relationship (SAR) of tobacco cembranoid diterpenes. Therefore, future studies should focus on their structural modification, SAR and biogenic relationships.

A cembranoid from tobacco prevents the expression of nicotine-induced withdrawal behavior in planarian worms

Using an adaptation of published behavioral protocols, we determined that acute exposure to the cholinergic compounds nicotine and carbamylcholine decreased planarian motility in a concentration-dependent manner. A tobacco cembranoid (1S,2E,4R,6R,7E,11E)-cembra-2,7,11-triene-4,6-diol (4R-cembranoid), also decreased planarian motility. Experiments in the presence of 1 microM 4R-cembranoid did increase the IC50 for nicotine- but not carbamylcholine-induced decrease in planarian motility. When planarians were exposed for 24 h to either nicotine or carbamylcholine at concentrations near their respective IC50 values and then transferred to plain media, nicotine-exposed, but not carbamylcholine- or cembranoid-exposed worms displayed withdrawal-like distress behaviors. In experiments where planarians were pre-exposed to 100 microM nicotine for 24 h in the presence of 1 microM 4R-cembranoid, the withdrawal-like effects were significantly reduced. These results indicate that the 4R-cembranoid might have valuable applications for tobacco abuse research. This experimental approach using planarians is useful for the initial screening of compounds relevant to drug abuse and dependence.

Biocatalytic and semisynthetic studies of the anticancer tobacco cembranoids

Historically, tobacco use was primarily recreational and has been smoked in cigarettes, cigars and pipes, as well as smokeless forms of consumption, all of which are associated with adverse health effects. However, recent scientific investigations indicate that tobacco also contains several diverse secondary metabolites that may provide potential health benefits in the treatment of cancer and neurodegenerative diseases. Specifically, the leaf and flower of Nicotiana tabacum contain high amounts of the key flavor ingredient, cembranoids. Tobacco alpha- and beta-2,7,11-cembratriene-4,6-diols display potent anticancer activity. These compounds have also been found to inhibit phorbol ester-stimulated (32)P(i) incorporation into phospholipids, induction of Epstein-Barr virus early antigen and protein phosphorylation. This review focuses on the biocatalytic and semisynthetic studies of tobacco cembanoids and their anticancer activity.

Microbial Transformation of 5-Episinuleptolide

5-episinuleptolide (1) is an abundant norcembranolide diterpene isolated from several species of the soft coral genus Sinularia. Biocatalytic transformation studies of 1 using Streptomyces lavendulea ATCC 8664 resulted in the isolation and characterization of two new metabolites 2 and 3. Compound 2, 6alpha-hydroxy-5-episinuleptolide was produced via a stereoselective reduction of 1 and was further metabolized into compound 3 which has a 3,8-bicylized cembranoid skeleton. The structures and configurations of the metabolites were determined by spectroscopic and X-ray crystallographic analyses.

Differential inhibition of nicotine- and acetylcholine-evoked currents through alpha4beta2 neuronal nicotinic receptors by tobacco cembranoids in Xenopus oocytes

In tobacco, there are two types of compounds that interact with neuronal nicotinic acetylcholine receptors (nnAChRs) in the brain. The first is the addictive component of tobacco and an agonist of these receptors, nicotine. The second are cyclic diterpenoids called cembranoids that non-competitively inhibit many types of nnAChRs. Nictotinic receptors composed of alpha4beta2 subunits are the predominant type of nicotinic receptors in the brain. These alpha4beta2 receptors are up-regulated upon chronic exposure to nicotine and have been implicated in nicotine addiction. The present study was designed to determine whether the inhibitory effects of two cembranoids from tobacco [(1S, 2E, 4R, 6R, 7E, 11E)-2,7,11-cembratriene-4,6-diol (4R) and its diastereoisomer (1S, 2E, 4S, 6R, 7E, 11E)-2,7,11-cembratriene-4,6-diol (4S)] were comparable on acetylcholine (ACh) and nicotine-evoked currents through alpha4beta2 nnAChRs. alpha4beta2 nnAChRs from rat brain were expressed in Xenopus oocytes and studied using the two-electrode voltage-clamp technique. The dose-response curves for acetylcholine and nicotine were hyperbolic and bell-shaped, respectively. Although there was no difference in the potency between cembranoids 4R and 4S, both of these cembranoids more potently inhibited nicotine-induced currents than acetylcholine-induced currents. Furthermore, both cembranoids were more potent inhibitors of this receptor when they were preincubated for 1 min prior to application of agonist. The finding that cembranoids preferentially inhibit nicotine-induced currents over those elicited by the natural neurotransmitter acetylcholine may have important implications when developing strategies to prevent nicotine addiction and tobacco use.