Journal of Natural Products 最新文献

Dibenzopyrrocoline alkaloids, found in lauraceous and hernandiaceous plants, have been studied since the 1950s. The absolute configuration of these alkaloids, including cryptaustoline, has been a topic of debate due to conflicting studies. Having in our laboratory some authentic samples of dibenzopyrrocoline-type Cryptocarya alkaloids, we decided to reinvestigate their absolute configuration using modern spectroscopic techniques along with TDDFT calculations. The NMR reinvestigation of the authentic sample of cryptowolinol led us to revise its relative configuration using ML-J-DP4 and DP4+ analyses. Moreover, the absolute configuration of all dibenzopyrrocoline alkaloids reported to date benefitted from a complete re-evaluation based on a comparison with TDDFT-SR and TDDFT-ECD predictions leading to a unified absolute configuration. At last, this patrimonial reinvestigation unveiled a historical sample corresponding to a heretofore unpublished dibenzopyrrocoline alkaloid, which we named isocryptaustoline. The reisolation of this molecule from the total alkaloid extract of Cryptocarya oubatchensis makes it a genuine natural product.

The 1,3-oxazin-6-one-containing spinoxazines A and B (2 and 3, respectively) have been isolated from the marine-derived Streptomyces spinoverrucosus strain SNB-048 and, by another group, from the Solar Saltern-derived Streptomyces sp. KMF-004. Two distinct pathways have been proposed for the conversion of the co-occurring pyrrolizidine alkaloid bohemamine D (1) into compound 3. Here, we report that the readily prepared compound 10, which embodies the 2-hydroxy-1,2-dihydro-3H-pyrrol-3-one core of bohemamine D (1) and is the bis-O-methyl ether of the alkaloid discoipyrrole C, is converted into 1,3-oxazin-6-one 11 on heating at elevated temperatures in air. The mechanism of this conversion was studied using density functional theory and the biosynthetic implications of it are discussed. The photochemical reaction of compound 10 in the presence of oxygen is also detailed and, again, the possible biosynthetic implications of the resulting conversion are considered.

Natural hydroxycinnamic acid amides (HCAAs) and riparins offer significant health benefits. However, their extraction from natural sources is difficult, and traditional synthetic methods remain wasteful, raising the need for more efficient alternatives. In this work, a two-step chemo-enzymatic flow method for the efficient esterification and amidation of phenolic acids was developed and successfully applied to the synthesis of riparin derivatives and HCAAs. The flow Fischer esterification was optimized using vanillic acid as a model starting material and SiliaBond Tosic Acid (SCX-3) as an immobilized acid catalyst, achieving a quantitative yield in a short residence time. The following amidation step, catalyzed by immobilized Candida antarctica lipase B, was optimized in toluene, leading to the desired amides. The synthesized compounds were evaluated for their radical scavenging, antibacterial, and antileishmanial properties. Overall, this work disclosed a novel approach for the efficient synthesis of riparin derivatives and HCAAs with interesting biological properties.

Sealgamide (1), a new antitrypanosomal lipopeptide, was isolated from a marine Okeania sp. cyanobacterium. Elucidation of its structure was challenging due to signal overlap caused by conspicuous rotamers but was ultimately achieved through partial hydrolysis and subsequent spectroscopic analyses. Sealgamide (1) exhibited moderate antitrypanosomal activity against Trypanosoma brucei rhodesiense (IC₅₀ 2.9 μM) while showing no antimalarial activity (IC₅₀ > 25 μM) or cytotoxicity (IC₅₀ > 30 μM). Furthermore, we discovered that an artificial C-terminal methyl ester analogue (2) exhibited notably enhanced antiparasitic activity.

An azaphilone, 6,7-iso-felinone A (2), was isolated from Diaporthales sp. KT3922 along with the known felinone A (1). While compound 2 exhibited weak Cotton effects, its naphthoate derivative (2a) displayed pronounced Cotton effects, enabling the determination of its absolute configuration through electronic circular dichroism (ECD) spectral analysis. Interestingly, the spectroscopically derived relative structure of compound 2 proved identical to previously reported hypoillexidiol (3) and xylariphilone (4). However, substantial differences in ¹H nuclear magnetic resonance data among these compounds warranted structural reinvestigation of the entire series, including the structurally related fungal metabolites, fusaraisochromenone (5) and aspergillusone C (6). Comparative analysis revealed identical relative configurations of compounds 1, 3, 4, and 5. Furthermore, compounds 1 and 3 were determined to have an identical absolute configuration, whereas the absolute configuration of compound 4 remained inconclusive due to a significant mismatch in its ECD spectral profile compared to compound 1. Compound 5 was identified as the enantiomer of compounds 1 and 3. Additionally, we discussed the stereochemistry of the 6,7-cis-diol isomer, aspergillusone C (6).

Seven new sesquiterpene hydroquinone/quinone (SQ) meroterpenoids, cinerols L-R (1-7), along with four known analogues (8-11), were identified from a marine sponge, Dysidea cinerea, collected from the shore of the Xisha Islands in the South China Sea. The structures of 1-7 were established by the analysis of NMR, high-resolution MS, and comparison of the experimental and calculated electronic circular dichroism (ECD) spectra. Cinerol L (1) is particularly noteworthy, as it features a 5H-pyrrolo[1,2a]-benzimidazole moiety modified by an ethyl sulfonate, while cinerols N (3) and O (4) possess a unique acetyl-substituted hydroquinone moiety. Cinerols L-R (1-7) were evaluated for their inhibitory activity against inflammatory cytokines, tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), and prostaglandin E2 (PGE₂) with IC₅₀ values of 5-20 μM in lipopolysaccharide (LPS)-induced RAW 264.7 mouse macrophages. Furthermore, the potent inhibitory activity on inflammatory cytokines of 4 prompted us to evaluate its effect on the nuclear factor-κB (NF-κB)/mitogen-activated protein kinase (MAPK) signaling pathway, a critical pathway that contributes to the inflammatory responses. Cinerol O (4) was unveiled to inhibit cyclooxygenase-2 (COX-2) expression and the production of inflammatory cytokines via suppressing the expression of NF-κB and MAPKs in LPS-induced RAW 264.7 macrophages.

Twelve new isocoumarins, spegazmarins A-L (1-12), including nine novel dimeric derivatives (1-9), three monomeric derivatives (10-12), as well as eight known ones (13-20), were isolated from the endophytic fungus Spegazzinia sp. MDCW-573. Their structures were elucidated by analysis of NMR, X-ray crystallography, and ECD data. Notably, the dimeric isocoumarins (1-9) possess a unique linkage, where the phenyl of one monomer is connected to the lactone of another. The methods for determining the configurations of both the monomeric and dimeric isocoumarins within this class were proposed, leading to the correction of the configurations of two previously reported isocoumarins. The isolated compounds inhibited Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa, with MIC values of 1 to 64 μg/mL. Compounds 5, 6, and 12 significantly promoted the growth of zebrafish intersegmental vessels at concentrations of 10, 20, and 40 μM, respectively.

Recent analyses of genome data indicate that members of the cyanobacterial order Pleurocapsales show tremendous potential for natural product discovery. However, only a few compounds have been reported from this order. Here, we report the isolation of hyellamide (1), a glycosylated N-acyl tyrosine-derived eneamide, from the pleurocapsalean cyanobacterium Hyella patelloides LEGE 07179. The putative biosynthetic gene cluster for 1 was identified in the genome of the producing organism and a biosynthetic proposal is presented. This work sheds light on the chemistry of the Pleurocapsales and expands the chemical repertoire of cyanobacterial natural products to include N-acyl tyrosine-derived molecules.

Menominin A (1) and B (2), two cyclodepsipeptides containing a 3,8-dihydroxy-2-methyltetradecanoic acid residue, were isolated from the freshwater sponge-associated cyanobacterium, Nostoc sp. UIC 10607, using bioactivity-guided and spectroscopic approaches. The planar structures of 1 and 2 were established using HRESIMS and one- and two-dimensional NMR experiments. Comparative genomic analysis revealed unique differences in the putative menominin biosynthetic gene cluster compared to that of the closely related cyanobacterial cyclic lipodepsipeptide, hapalosin, assisting in structure elucidation and highlighting the structural diversity of this class of compounds. Configuration assignments were determined using a combination of J-based configuration analysis, chiral HPLC, modified Mosher's ester analysis, and DFT calculations. Menominin A and B demonstrate antiproliferative bioactivity against the high-grade serous ovarian cancer cell line OVCAR3 (IC₅₀ = 3.1 (1) and 2.4 μM (2)). Menominin A and B are the first reported secondary metabolites from a freshwater sponge-associated cyanobacterium, underscoring the potential of freshwater sponges as a microbial culture source in natural product discovery.

LaeA is a putative nuclear methyltransferase protein that epigenetically influences secondary metabolite production in fungi. LaeA has drawn attention as one of the promising approaches to activate fungal chemical production, and the laeA gene has been introduced into some fungal strains with the aim of producing secondary metabolic changes mainly based on the evaluation of mycotoxicity. However, these studies were applied for limited fungal species, and its utility and versatility for broad fungal species remained unclear. In this study, 47 strains were selected composed of three different genera, Pochonia spp., Gamszarea kalimantanensis, and Lecanicillium spp., which have never been modified with the laeA gene. We obtained a total of 125 mutants with laeA genes for our fungal strain library. The chemical productivity and the biological activity of the library were analyzed, and two natural products, radicicol (1) and sch210972 (2), were isolated in more than 10-fold the yield of the parent strains.