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

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.

Biomimetic synthesis of the non-canonical PPAP natural products yezo'otogirin C and hypermogin D, and studies towards the synthesis of norascyronone A

Oxidative degradation and rearrangement of polycyclic polyprenylated acylphloroglucinols (PPAPs) has created diverse families of unique natural products that are attractive targets for biomimetic synthesis. Herein, we report a racemic synthesis of hyperibrin A and its oxidative radical cyclization to give yezo'otogirin C, followed by epoxidation and House-Meinwald rearrangement to give hypermogin D. We also investigated the biomimetic synthesis of norascyronone A via a similar radical cyclization pathway, with unexpected results that give insight into its biosynthesis.