Revision of the Structure of Hypatulone A by NMR, Computations, and Biosynthetic Considerations

Lignans and phenols with potential anti-inflammatory effect from the stems of Mallotus paxii Pamp

Phytochemical investigation of the stems of Mallotus paxii Pamp. led to the isolation and identification of four new compounds, including three neolignans (1-3) and one phenol (13), along with eight known neolignans (4-12) and one known phenol (14). Their structures were determined by spectroscopic methods, including NMR, MS and ECD analyses. Bioassay demonstrated that malloapelin A (4) exhibited a most potent anti-inflammatory activity to NO release with IC50 value of 21.32 μM. Furthermore, malloapelin A (4) markedly decreased the secretion of TNF-α, iNOS, and NF-κB and inhibited the expression of COX-2 and NF-κB/p65 in LPS-induced RAW264.7 cells in a dose-dependent manner.

Isolation of four new monoterpenes from Ailanthus altissima (mill.) Swingle and their enzyme inhibitory effects

A phytochemical study of the ethanol extract from Ailanthus altissima (Mill.) Swingle leaves resulted in the isolation of four new monoterpenoids (1-3, 5). The structures were elucidated using HRESIMS data, NMR spectroscopic data, quantum chemical calculations for NMR and ECD, and custom DP4+ probability analysis. Additionally, the absolute configuration of sugar was determined by acid hydrolysis. Compounds 1-4 are cyclogeraniane monocyclic monoterpenes, while compound 5 contains an acyclic mycrane monoterpenes skeleton. Anti-tyrosinase, anti-acetylcholinesterase, and anti-butyrylcholinesterase activities were tested. Compound 1 showed notable anti-acetylcholinesterase activity, and compound 3 exhibited significant inhibitory effects on anti-tyrosinase activity. Furthermore, the potential binding sites of compounds 1 and 3 were predicted by molecular docking.

Structure Revision of Type B Polycyclic Polyprenylated Acylphloroglucinols Fused to a Partly Reduced Furan Ring

Four previous papers reported the isolation and structural determination of 10 polycyclic polyprenylated acylphloroglucinols (PPAPs), uraliones F, G, K, and O, attenuatumiones E and F, and scabrumiones A-D, from Hypericum species. Their structures were identified as type B PPAPs that featured not only the characteristic acyl group at C-3 of the bicyclo[3.3.1]nonane core but also a partly reduced furan ring fused to the C-1-C-2-O-2 atoms of the core. However, the 1D and 2D NMR data of these compounds were more consistent with type A PPAPs that featured not only the acyl group at C-1 but also a partially reduced furan ring fused to the C-3-C-2-O-2 atoms of the core. Now we revise these 10 previously proposed structures to the corresponding type A PPAPs via NMR analysis. Additionally, we propose a rule that uses NMR data to determine whether a particular PPAP that is fused to a partly reduced furan ring at C-3-C-2-O-2 or C-1-C-2-O-2 is type A or type B, respectively. We also propose a rule to assign the relative configurations of corresponding type A PPAPs at C-18 and revise the configurations of sampsonione N, hypericumoxides A-C, and hyperscabin G.

Total synthesis and structural reassignment of garcinielliptone FC, a polycyclic polyprenylated acylphloroglucinol with diverse bioactivity

Garcinielliptone FC (GFC) was assigned to be a type A polycyclic polyprenylated acylphloroglucinol (PPAP) and was found to exhibit diverse biological activities. Now we revise the structure of GFC to xanthochymol, a type B PPAP, via NMR and total synthesis methods. The total syntheses of (±)-xanthochymol and (±)-cycloxanthochymol were accomplished in 12 and 13 steps, respectively.

Prenylated acylphloroglucinols from the fruits of Garcinia xanthochymus

Our continuous study of the dry fruits of Garcinia xanthochymus led to the isolation and structural characterization of four new prenylated acylphloroglucinols, xanthochymusones J-M (1-4), together with the known polycyclic polyprenylated acylphloroglucinols, garciniagifolone A (5) and garcinialiptone A (6). Their structures were elucidated by interpretation of NMR and MS spectroscopic data. Compound 1 bearing a similar core to that of hulupinic acid should be derived via oxidization and ring contraction of prenylated acylphloroglucinol. The inhibitory activities of all the compounds against three human hepatocellular carcinoma cell lines Huh-7, Hep 3B, and Hep G2 were evaluated, and compounds 4 and 5/6 exhibited moderate cytotoxic activities against Hep G2 cells with IC₅₀ values10.4 and 8.8 μM.

Polycyclic Polyprenylated Acylphloroglucinols Bearing a Lavandulyl-Derived Substituent from Garcinia xanthochymus Fruits

Many type B polycyclic polyprenylated acylphloroglucinols (PPAPs) bear a lavandulyl-derived substituent, and the configurational assignment of this side chain can be difficult and sometimes leads to erroneous conclusions. In this study, 21 PPAPs, including the new xanthochymusones A-I (1-9), have been isolated from the fruits of Garcinia xanthochymus and structurally characterized. The relative configuration of the C-30 stereocenter was assigned by a combination of chemical transformations, ¹H-¹H coupling constants, conformational analysis, and NOE experiments. The configurational assignment of compound 7 indicates that the relative configuration at C-30 of PPAPs is not always the same. The absolute configurations of the new compounds were assigned by ECD and X-ray diffraction data, as well as by biosynthetic considerations. Analysis of NMR data enabled the configurational revision of garcicowins C and D. All the isolated PPAPs were tested for antiproliferative activity against three human hepatocellular carcinoma cell lines, including Huh-7, Hep 3B, and HepG2. Compounds 5 and 6, 7-epi-isogarcinol (16), and coccinone C (17) exhibited moderate antiproliferative activity. Compounds 6 and 16 induced apoptosis and inhibited cell migration in Huh-7 cells, probably through downregulating the STAT3 signaling pathway. This study provides effective methods for configurational assignments of type B PPAPs.

Structural Revisions of Two Highly Aromatic Naphthoquinone-Derived Dimers Based on NMR Analysis, Computer-Assisted Structure Elucidation Methods, and Computations

Eleucanainones A and B are two structurally complex naphthoquinone-derived dimers whose structure identification is difficult. Large yellow fragments of the preliminary CASE (computer-assisted structure elucidation) analysis revealed that the original structures might be questionable. Structural revisions of the two compounds were proposed on the basis of NMR analysis, CASE methods, conformation analysis, and DFT (density functional theory) NMR calculations with a custom DP4+ analysis. In addition, a polyketide-folded biosynthetic pathway of the two revised structures was proposed.

Structural Revision of Hyperibrin B and Hyperscabrones H and I by Biosynthetic Considerations, NMR Analysis, and Chemical Synthesis

Previously, Gao et al. reported the isolation and structural determination of three natural products, hyperibrin B (HB), hyperscabrone H (HH), and hyperscabrone I (HI), from Hypericum scabrum. HB and HH had different NMR spectroscopic data, but they were assigned identical structures. Furthermore, these compounds should be derived from bicyclic polyprenylated acylphloroglucinols (BPAPs) via degradation, but the assigned structural features of the prenyl and prenylmethyl groups being cis and meta-substituted on the cyclohexanone core were not consistent with their biosynthetic origin. In this note, we revise the structures of HB, HH, and HI via NMR and MS spectroscopic analyses and biosynthetic considerations. We also complete a total synthesis of the revised structure of HB as well as its analogue, hyperibrin A, to further confirm the revision. The revised structures of HB, HH, and HI have not been reported.

Natural potential neuroinflammatory inhibitors from Stephania epigaea H.S. Lo

Stephania epigaea H. S. Lo is a folk medicine widely distributed in the south of China, especially in Yunnan and Guangxi province. An in vitro anti-neuroinflammatory study showed that total alkaloids of it can potently inhibit LPS-induced NO releasing of BV2 cells with an IC₅₀ value of 10.05 ± 2.03 μg/mL (minocycline as the positive drug, IC₅₀ 15.49 ± 2.14 μM). The phytochemical investigation of the total alkaloids afforded three new phenanthrene (1-3), two lactams (4a, 4b), and nine aporphine derivatives (5-13). The final structure of 1 was identified by computer-assisted structure elucidation (ACD/Structure Elucidator software and the ¹³C NMR calculation with GIAO method) due to many possibilities of the substituent pattern. All isolates were evaluated for their anti-neuroinflammatory effects, and as a result, 5, 8, 10, and 11 exhibited stronger inhibitory activities than the minocycline. The results suggested S. epigaea could provide potential therapeutic agents for neurodegenerative diseases.

Structural Revision of Garcinielliptin Oxide and Garcinielliptone E

Previously, Lin et al. reported the isolation and structural determination of two triterpenoids, garcinielliptin oxide (GO) and garcinielliptone E (GE). Their unusual structural features, which remained unparalleled in subsequent decades despite the intervening discovery of hundreds of other polycyclic polyprenylated acylphloroglucinols (PPAPs), caused us to question the originally assigned structures, so GO was reisolated from Garcinia subelliptica, and its NMR spectra were reacquired. In this Note, we revise the structures of GO and the related GE via NMR analysis, biosynthetic considerations, and chemical conversion. Garcinielliptone T, a new PPAP, was also isolated and characterized. GO exhibited weak inhibitory activity against acetylcholinesterase with an IC₅₀ value of 20.7 μM.

Hyperforones A–C, benzoyl-migrated [5.3.1]-type polycyclic polyprenylated acylphloroglucinols from Hypericum forrestii

Unprecedented benzoyl-migrated polycyclic polyprenylated acylphloroglucinols with a unique C-1 H-substituted bicyclo[5.3.1]hendecane framework, hyperforones A–C (1–3), were isolated from Hypericum forrestii.