Isopimarane diterpenoids from Lycopus europaeus

Pimarane diterpenoids: sources, structures and biological activities

The pimarane diterpenoids, a widespread class of secondary metabolites, have been found in several dozens of plant species from various families and in organisms from other taxonomic groups. According to the different chiral centres, pimarane diterpenes can be divided into four types, including pimarane, isopimarane, ent-pimarane, and ent-isopimarane. Meanwhile, these compounds possessed many pharmacological activities, such as cytotoxic, anti-inflammatory, and antibacterial activities. Due to their notable structure and biological activities these substances have attracted interest in recent years. A comprehensive account of the structural diversity (368 structures, 117 references) and biological activities of pimarane diterpenes discovered from 2000 until 2023 is given in this review.

Lipskynoids A-G, New Acyclic Diterpenes from the Flowers of Carpesium lipskyi

Seven new acyclic diterpenes, namely lipskynoids A-G (1-7), were isolated from the flowers of Carpesium lipskyi, a traditional Tibetan herbal medicine with anti-inflammatory and antipyretic-analgesic effects. These new compounds were elucidated by analysis of extensive spectroscopic data including ESI-MS, 1D, 2D NMR, and DP4+ analyses. Biological assays showed that 1-7 display significant inhibitory effects against the NO production in LPS-induced RAW264.7 cells with its IC50 values from 9.9 to 18.47 μM, however, no cytotoxicity effect was observed of these isolates against the growth of HePG2, PC3, DU145, and A549 cells.

Antibiotic Potentiators Against Multidrug-Resistant Bacteria: Discovery, Development, and Clinical Relevance

Antimicrobial resistance in clinically important microbes has emerged as an unmet challenge in global health. Extensively drug-resistant bacterial pathogens have cropped up lately defying the action of even the last resort of antibiotics. This has led to a huge burden in the health sectors and increased morbidity and mortality rate across the world. The dwindling antibiotic discovery pipeline and rampant usage of antibiotics has set the alarming bells necessitating immediate actions to combat this looming threat. Various alternatives to discovery of new antibiotics are gaining attention such as reversing the antibiotic resistance and hence reviving the arsenal of antibiotics in hand. Antibiotic resistance reversal is mainly targeted against the antibiotic resistance mechanisms, which potentiates the effective action of the antibiotic. Such compounds are referred to as resistance breakers or antibiotic adjuvants/potentiators that work in conjunction with antibiotics. Many studies have been conducted for the identification of compounds, which decrease the permeability barrier, expression of efflux pumps and the resistance encoding enzymes. Compounds targeting the stability, inheritance and dissemination of the mobile genetic elements linked with the resistance genes are also potential candidates to curb antibiotic resistance. In pursuit of such compounds various natural sources and synthetic compounds have been harnessed. The activities of a considerable number of compounds seem promising and are currently at various phases of clinical trials. This review recapitulates all the studies pertaining to the use of antibiotic potentiators for the reversal of antibiotic resistance and what the future beholds for their usage in clinical settings.

Virtual Screening for Reactive Natural Products and Their Probable Artifacts of Solvolysis and Oxidation

Chemically unstable natural products are prone to show their reactivity in the procedures of extraction, purification, or identification and turn into contaminants as so-called "artifacts". However, identification of artifacts requires considerable investments in technical equipment, time, and human resources. For revealing these reactive natural products and their artifacts by computational approaches, we set up a virtual screening system to seek cases in a biochemical database. The screening system is based on deep learning models of predicting the two main classifications of conversion reactions from natural products to artifacts, namely solvolysis and oxidation. A set of result data was reviewed for checking validity of the screening system, and we screened out a batch of reactive natural products and their probable artifacts. This work provides some insights into the formations of natural product artifacts, and the result data may act as warnings regarding the improper handling of biological matrixes in multicomponent extraction.

Sesquiterpenes and diterpenes with cytotoxic activities from the aerial parts of Carpesium humile

Carpesium humile Winkl is an endemic Chinese species and no previous phytochemical studies have been reported for this species. Two new germacranolides (1 and 2) and a new phytane diterpene (5), together with five known compounds (two sesquiterpenoids and three diterpenoids), were isolated from the aerial parts of C. humile. Their structures were elucidated on the basis of extensive spectroscopic analysis. The conformations and absolute configurations of 1 and 2 were established by combinative analysis of NMR, CD exciton chirality, and X-ray crystallography data. Four germacranolides (1-4) showed strong cytotoxic activities, with broad spectrum activities against six human cancer (HepG2, HeLa, HL60, SGC7901, Lewis, and MDA231) cell lines in vitro using MTT assay, with IC₅₀ values from 3.09 to 7.71 μg/mL. Diterpenes (5, 6, and 8) also displayed good cytotoxic activities for selected cancer cell lines, with IC₅₀ values in the range 5.46-8.08 μg/mL.

Lycopus europaeus: phenolic fingerprint, antioxidant activity and antimicrobial effect on clinical Staphylococcus aureus strains

Lycopus europaeus L. leaves water extract (LEL) was subjected to phytochemical analysis, and evaluated for its antibacterial and antioxidant effects. Antibacterial activity testing was performed on Staphylococcus aureus clinical strains from catheter-related and skin infections by broth microdilution test. LEL showed bactericidal activity at concentrations from 2500 to 5000 μg/mL against all, including methicillin resistant and polyresistant nosocomial, strains. Antioxidant activity was examined using DPPH and ABTS (11.3 and 9.8 μg/mL, respectively) and by ferric reducing ability of the plasma method (891 μmol AAE/g dry extract). Phytochemical analysis of LEL was performed by LC-DAD-MS/MS. Ten phenolic compounds were identified; two minor compounds (glucopyranosyl rosmarinic acid and sagerinig acid) have not been described in Lycopus yet. The major compounds, considered to be responsible for biological activities detected in the study, were determined as rosmarinic acid (76 mg/g) and luteolin-7-O-glucuronide (23 mg/g). L. europaeus arises from our study as a promising source of antibacterial agent for topical usage.

Structural Elucidation of Pimarane and Isopimarane Diterpenoids: The 13C NMR Contribution

13C NMR spectroscopy is actually one of the first tools used for the structural elucidation of natural and synthetic compounds and it is also used in biosynthetic studies. The aim of this review is to present the 13C NMR assignments of a large number of pimarane diterpenoids, describing the most significant effects caused by different substitution patterns and different stereochemistry at their chiral centers.

Antimicrobial Activities of Some Plants from the Eastern Anatolia Region of Turkey

Crude extracts obtained from the roots and aerial parts of Rumex crispus.L. and Acinos rotundifolius.Pers. and the whole plants of Ajuga chamaepitys. L. and of Lycopus europaeus. L. were evaluated for in vitro. antimicrobial activity against five Gram-positive bacteria including Staphylococcus aureus., Micrococcus luteus, Mycobacterium smegmatis, Bacillus subtilis, Bacillus subtilis. var. niger., and three Gram-negative bacteria including Aeromonas hydrophila, Klebsiella pneumoniae, Pseudomonas aeruginosa., and the yeast Candida albicans.. The inhibition zone diameter was determined for each extract using the agar well diffusion method at a concentration of 12.5 mg/ml. The acetone extracts of the roots of R. crispus. and A. rotundifolius. demonstrated significant inhibitory effects against most microorganisms under test.

Diterpenoids from Tetraclinis articulata that inhibit various human leukocyte functions

Ten new compounds, eight of them pimarane derivatives (1-8), together with a menthane dimer (9) and a totarane diterpenoid (10), were isolated from the leaves and wood of Tetraclinis articulata. The structures of 1-10 were established by using spectroscopic techniques, including 2D NMR spectra. Pimaranes 1-5 were found to possess an unusual cis interannular union of the B and C rings, which, from a biogenetic perspective, could be derived from the hydration of a carbocation at C-8. Compounds 4-6 and a mixture of 7 and 11 modulated different human leukocyte functions at a concentration of 10 microM, mainly the degranulation process measured as myeloperoxidase release and, to a lesser extent, the superoxide production measured by chemiluminescence.

Bacterial resistance modifying agents from Lycopus europaeus

As part of an ongoing project to identify plant natural products which modulate bacterial multidrug resistance (MDR), bioassay-guided isolation of an extract of Lycopus europaeus yielded two new isopimarane diterpenes, namely methyl-1alpha-acetoxy-7alpha 14alpha-dihydroxy-8,15-isopimaradien-18-oate (1) and methyl-1alpha,14alpha-diacetoxy-7alpha-hydroxy-8,15-isopimaradien-18-oate (2). The structures were established by spectroscopic methods. These compounds and several known diterpenes were tested for in vitro antibacterial and resistance modifying activity against strains of Staphylococcus aureus possessing the Tet(K), Msr(A), and Nor(A) multidrug resistance efflux mechanisms. At 512 microg/ml none of the compounds displayed any antibacterial activity but individually in combination with tetracycline and erythromycin, a two-fold potentiation of the activities of these antibiotics was observed against two strains of S. aureus that were highly resistant to these agents due to the presence of the multidrug efflux mechanisms Tet(K) (tetracycline resistance) and Msr(A) (macrolide resistance).