Hexahydroazulene-2(1H)-one Sesquiterpenoids with Bridged Cyclobutane, Oxetane, and Tetrahydrofuran Rings from the Stems of Daphne papyracea with α-Glycosidase Inhibitory Activity

Survey of natural products reported by Asian research groups in 2022

The new natural products reported in 2022 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 2022 were summarized. Compounds with unique structural features and/or promising bioactivities originating from Asian natural sources were discussed based on their structural classification.

2,4-Di-tert-butylphenol and 7-hydroxy-3-(2-methylpropyl)-2,3,6,7,8,8a-hexahydropyrrolo[1,2-a]pyrazine-1,4-dione: two natural products from Serratia marcescens Ha1 and their herbicidal activities

BACKGROUND

Weeds are one of the critical factors that negatively affect crop yield and quality. Microbial herbicides are a research hotspot for novel herbicides owing to their environmental safety and lack of weed resistance. In the current study, the active ingredients of Serratia marcescens Ha1, a new microbial herbicide, were investigated for their effectiveness against agricultural weeds using bioassay-guided fractionation.

RESULTS

The results revealed that petroleum ether and ethyl acetate extracts of S. marcescens Ha1 had high herbicidal activity. Forty-nine compounds were identified from the petroleum ether extract, including 2,4-di-tert-butylphenol (DB; C14 H22 O, 38.82%), ethyl 14-methyl-hexadecanoate, 1-nonadecene, and [1,1'-biphenyl]-2,3'-diol, 3,4',5,6'-tetrakis. Of these, DB showed significant inhibitory effects on root and shoot growth in Amaranthus retroflexus, with half-maximal inhibitory concentration (IC50 ) values of 389.17 and 832.44 mg L-1 , respectively. In addition, 7-hydroxy-3-(2-methylpropyl)-2,3,6,7,8,8a-hexahydropyrrolo[1,2-a]pyrazine-1,4-dione (HPD) was identified as the major active ingredient in the ethyl acetate extract of S. marcescens Ha1 using bioassay-guided fractionation, with IC50 values of 439.86 and 476.95 mg L-1 against A. retroflexus shoot and root growth, respectively. Scanning electron microscopy indicated that DB and HPD exert destructive effects on A. retroflexus root, and the damage is gradually aggravated with increasing treatment time and concentration.

CONCLUSION

The S. marcescens Ha1 extract and its active compounds DB and HPD exhibit significant herbicidal activity, which could be utilized further for the development of microbial herbicides. © 2023 Society of Chemical Industry.

Structurally diverse rearranged sesquiterpenoids, including a pair of rare tautomers, from the aerial parts of Daphne penicillata

Eight structurally diverse rearranged sesquiterpenoids, including seven undescribed sesquiterpenoids (1a/1b and 3-8) were obtained from the aerial parts of Daphne penicillata. 1a/1b, 3, 5 and 6 possess rare rearranged guaiane skeletons and 4 represents the first example of rearranged carotene sesquiterpenoids. Their structures and absolute configurations were determined by extensive spectroscopic analyses, NMR and ECD calculations. Interestingly, 1a and 1b were a pair of magical interconverting epimers that may interconvert by retro-aldol condensation. The mechanism of interconversion has been demonstrated indirectly by 9-OH derivatization of 1a/1b and a hypothetical biogenetic pathway was proposed. All compounds were evaluated for anti-inflammatory and cytotoxic activities. Among them, 1a/1b and 2 exhibited potential inhibitory activities on the production of NO against LPS-induced BV2 microglial cells.

Chemical Diversity and α-Glucosidase Inhibitory Activity in Needles Essential Oils of Four Pinus Species from Northwestern Himalaya, India

This work describes the study of the chemical profiling and α-glucosidase inhibitory activity of essential oils (EOs) from four Pinus species (P. wallichiana, P. patula, P. roxburghii and P. gerardiana). The identification and quantification of EOs metabolites were performed by GC/MS, GC-FID and ¹³ C-NMR. The needles of P. wallichiana and P. gerardiana presented the highest oil yields (0.35 % and 0.36 %, respectively). Twenty-four constituents were characterized in among samples exhibiting 93.8-97.7 % of the total EOs. The components and yields of the targeted samples were varied according to the species. Major components of the oils were α-pinene (20.5-34.1 %), β-pinene (1.4-53.0 %), δ-3-carene (0.2-47.0 %), limonene (1.7-13.4 %), β-phellandrene (0.2-23.4 %), β-myrcene (1.8-7.2 %) and α-terpinolene (0.6-7.9 %). The extracted EOs showed strong α-glucosidase inhibitory activity, which was close to the positive control, acarbose. This study showed that the EOs of Pinus species may be used as natural antidiabetic.

Targeted isolation of diterpenoids and sesquiterpenoids from Daphne gemmata E. Pritz. ex Diels using molecular networking together with network annotation propagation and MS2LDA

Investigation of the whole plant of Daphne gemmata E. Pritz. ex Diels (Thymelaeaceae) using molecular networking coupled to Network Annotation Propagation (NAP) and unsupervised substructure annotation (MS2LDA) led to the discovery of five tigliane diterpenoids, 14 guaiane sesquiterpenoids, one rhamnofolane diterpenoid and three carotene sesquiterpenoids. The structures of the eight undescribed compounds, daphnorbol A and daphnegemmatoids A-G, were characterized by detailed spectroscopic analyses, NMR and ECD calculations, application of Snatzke's method and single-crystal X-ray diffraction analysis. All isolated compounds were evaluated for their cytotoxic activities against HepG2, A549, and MCF-7 cells by MTT assay. Daphnorbol A exhibited significant cytotoxic activity against HepG2 and A549 cells with IC50 values of 4.06 μM and 6.35 μM, respectively. Prostratin showed potent cytotoxic activity against HepG2 and A549 cells with IC50 values of 6.06 μM and 5.45 μM, respectively. Further Hoechst 33,258 and AO-EB staining assays indicated that daphnorbol A and prostratin could induce apoptosis in HepG2 and A549 cells.

Detection of Corporate Environmental Information Disclosure Falsification Based on Support Vector Machine

Environmental information disclosure (EID) is an important embodiment of corporate social responsibility. With the awakening of public awareness of environmental protection and the increasing pressure of environmental preservation, enterprises tend to strategically manipulate environmental information for the pursuit of profit, which will consequently lead to environmental information disclosure falsification (EIDF) and disruption of both the market regulatory order and the development of green economy. In this article, support vector machine (SVM) technique is applied to construct the detection model of corporate EIDF. Based on the theory of “public pressure,” the detection indicators will be improved from three aspects: public pressure, corporate governance, and financial indicators. The training set and test set are constructed by combining the manually collected cases of environmental administrative penalties from 2015 to 2019 with the indicator information of nonfinancial listed enterprises in China's A-share market, and the SVM detection performance is compared with the logistic regression of the benchmark model. To solve the problem of category imbalance, we have introduced the Borderline-SMOTE oversampling technique. Based on the detection results of SVM and Borderline-SMOTE, we find that the Borderline-SMOTE-SVM model has the best detection performance, surpassing the SVM and logistic regression models. These conclusions have constructive policy implications for regulatory agencies, investors, the third-party service sector, enterprises, and government policy-making to achieve high-quality corporate EID.

Synthesis of Sulfur-Containing Analogues of Hedychenone, a Labdane Diterpenoid from Hedychium spicatum

The labdane diterpene hedychenone, isolated from Hedychium spicatum, is an example of a furan-containing natural product. Herein, a new and efficient method for the synthesis of 19 new thio analogues of hedychenone is reported. The present methodology exhibits a broad substrate scope with good to excellent yields without metal or base under mild reaction conditions. The natural compound 1 and four semisynthetic derivatives (3a, 3b, 3i, and 3j) exhibited strong α-glucosidase inhibition activity with IC₅₀ values of 15.93 ± 0.29, 9.70 ± 0.33, 11.82 ± 0.06, 12.23 ± 0.33, and 12.15 ± 0.14 μg/mL, respectively. In addition, compound 3e (6.0 ± 0.04 mm; zone of inhibition) displayed antibacterial activity against Staphylococcus aureus. This study increases the chemical diversity of bioactive hedychenone derivatives and provides a direction for the development of antidiabetic agents.

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.

Characteristic guaiane sesquiterpenes from Daphne penicillata and ECD/NMR-based assignment of C-1 configuration

40 compounds including the first C17 homo-guaiane sesquiterpene (1) were isolated from Daphne penicillata and an efficient method using ECD/NMR strategy to access the C-1 configuration of characteristic guaiane sesquiterpenes has been developed.