Stereodivergent Strategy in Structural Determination: Asymmetric Total Synthesis of Garcinol, Cambogin, and Related Analogues

Asymmetric aza-Henry reaction toward trifluoromethyl β-nitroamines and biological investigation of their adamantane-type derivatives

Amino acid-derived quaternary ammonium salts were successfully applied in the asymmetric aza-Henry reaction of nitromethane to N-Boc trifluoromethyl ketimines. α-Trifluoromethyl β-nitroamines were synthesized in good to excellent yields with moderate to good enantioselectivities. This reaction is distinguished by its mild conditions, low catalyst loading (1 mol%), and catalytic base. It also proceeded on a gram scale without loss of enantioselectivity. The products were transformed to a series of adamantane-type compounds containing chiral trifluoromethylamine fragments. The potent anticancer activities of these compounds against liver cancer HepG2 and melanoma B16F10 were evaluated. Six promising compounds with notable efficacy have potential for further development.

Caged xanthone derivatives to promote mitochondria-mediated apoptosis in breast cancer cells

Caged xanthones represent a class of natural secondary metabolites exhibiting significant potential as antitumor agents. These compounds are characterized by their distinct cage-like structures, which offer novel and compelling frameworks for drug design. Nonetheless, there exists a dearth of research focused on the structural modification of these compounds, particularly in relation to their cage-like architectures. This study aims to address this gap by introducing an innovative synthetic method for constructing a novel caged structure that incorporates a widely employed maleimide group. Drawing upon the well-established synthetic approach for dihydroxanthones previously developed within our research group, we successfully synthesized 13 new caged xanthones using the Diels-Alder reaction. Subsequently, we evaluated their anti-proliferative activity against HepG2, A549, and MDA-MB-231 cell lines. The results revealed that compound 10i exhibited IC50 values of 15.86 µM ± 1.29, 19.27 µM ± 1.58, and 12.96 µM ± 0.09 against these cell lines, respectively. Further investigations into the mechanism of action of 10i demonstrated its ability to induce G2/M cell cycle arrest and initiate mitochondria-mediated apoptosis in breast cancer cells.

Sequential Dieckmann cyclization enables the total synthesis of 7-epi-clusianone and 18-hydroxy-7-epi-clusianone

A unified approach for the construction of the bicyclo[3.3.1]nonane-2,4,9-trione core of polycyclic polyprenylated acylphloroglucinols (PPAPs) was reported. This approach involves a sequential process of two distinct Dieckmann condensation reactions from the linear precursor. Using this method, the divergent total synthesis of the natural products 7-epi-clusianone and 18-hydroxy-7-epi-clusianone and the formal synthesis of sampsonione P were achieved. Additionally, other key steps to realize this strategy include RuCl3-catalyzed oxidative olefin cleavage and Pd-catalyzed Tsuji-Trost decarboxylative allylation. The synthesis indicated that bicyclo[3.3.1]nonane-2,4,9-triones could also be constructed via 6-membered intermediates.

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.

Garcinol and its analogues: Synthesis, cytotoxic activity and mechanistic investigation

Garcinol is a polyisoprenylated benzophenone isolated from Garcinia. It has been reported to have a variety of intriguing biological effects, including anticancer, anti-inflammatory, and antioxidant capabilities. The purpose of this research is to thoroughly evaluate garcinol and a series of its analogues in terms of synthesis, structural diversity, biosynthesis, and potential for preventing carcinoma cell proliferation. Garcinopicrobenzophenone and eugeniaphenone, which contain a unique cyclobutyl unit at C-5, were initially synthesized using the procedures utilized in the synthesis of garcinol. All the natural analogs of garcinol were produced at completion of the synthesis, and their structures and absolute configurations were clarified. Based on the synthesis, a possible biogenetic synthesis pathway towards cambogin, 13,14-didehydroxyisogarcinol via O-cyclization, and garcinopicrobenzophenone or eugeniaphenone via C-cyclization was proposed. The cytotoxicity of polyisoprenylated benzophenones produced in our group was tested, and the structure-activity relationship was summarized. The mechanism by which garcinol, cambogin, and 21' induce apoptosis was studied. Cambogin and 21' were shown to have a greater capacity to cause apoptosis in pancreatic cancer BXPC3 cells, and the suppression of BXPC3 cells by 21' might be attributed to the target of STAT3 signaling. Garcinol could cause pyroptosis and apoptosis in pancreatic cancer cells at the same time, which was the first time that garcinol was identified as a possible chemotherapeutic agent that could significantly promote pyroptosis in cancer cells.

Guttiferones: An insight into occurrence, biosynthesis, and their broad spectrum of pharmacological activities

Guttiferones belong to the polyisoprenylated benzophenone, a class of compounds, a very restricted group of natural plant products, especially in the Clusiaceae family. They are commonly found in bark, stem, leaves, and fruits of plants of the genus Garcinia and Symphonia. Guttiferones have the following classifications according to their chemical structure: A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S, and T. All of them have received growing attention due to its multiple biological activities. This review provides a first comprehensive approach to plant sources, phytochemical profile, specific pharmacological effects, and mechanisms of guttiferones already described. Studies indicate a broad spectrum of pharmacological activities, such as: anti-inflammatory, immunomodulatory, antioxidant, antitumor, antiparasitic, antiviral, and antimicrobial. Despite the low toxicity of these compounds in healthy cells, there is a lack of studies in the literature related to toxicity in general. Given their beneficial effects, guttiferones are expected to be great potential drug candidates for treating cancer and infectious and transmissible diseases. However, further studies are needed to elucidate their toxicity, specific molecular mechanisms and targets, and to perform more in-depth pharmacokinetic studies. This review highlights chemical properties, biological characteristics, and mechanisms of action so far, offering a broad view of the subject and perspectives for the future of guttiferones in therapeutics.

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.

Polyprenylated Benzophenones and Tocotrienol Derivatives from the Edible Fruits of Garcinia oblongifolia Champ. ex Benth. and Their Cytotoxicity Activity

The fruits of Garcinia oblongifolia Champ. ex Benth. were famous as an edible fruit in tropical regions of China. Because of its unique taste and great nutritional value, the ripe fresh fruits of G. oblongifolia could be eaten directly or used as raw materials for natural beverages and food supplements. In this work, six new polyprenylated benzophenones (1-6) and one new dimeric tocotrienol derivative (7), together with 18 known ones (8-25), were isolated from the fruits of G. oblongifolia. Compounds 1-4 were peculiar polycyclic polyprenylated acylphloroglucinols (PPAPs) featuring the rare carbon skeleton of a bicyclo[3.4.1]decane-1,3-diketone. Moreover, all isolates (1-25) were evaluated for their cytotoxicity activities against nasopharyngeal carcinoma (NPC) cell lines (CNE1 and CNE2). Among these isolates, compound 6 exhibited the strongest cytotoxicity activity on CNE1 and CNE2 cells with the IC₅₀ values of 7.8 ± 0.2 and 9.1 ± 0.3 μM, respectively. Further mechanistic investigation demonstrated that 6 could induce mitophagy to promote Caspase-9/GSDME-mediated pyroptosis through triggering ROS in NPC cells.

Recent advances in the synthesis of natural products containing the phloroglucinol motif

Covering: June 2009 to 2021Natural products containing a phloroglucinol motif include simple and oligomeric phloroglucinols, polycyclic polyprenylated acylphloroglucinols, phloroglucinol-terpenes, xanthones, flavonoids, and coumarins. These compounds represent a major class of secondary metabolites which exhibit a wide range of biological activities such as antimicrobial, anti-inflammatory, antioxidant and hypoglycaemic properties. A number of these compounds have been authorized for therapeutic use or are currently being studied in clinical trials. Their structural diversity and utility in both traditional and conventional medicine have made them popular synthetic targets over the years. In this review, we compile and summarise the recent synthetic approaches to the natural products bearing a phloroglucinol motif. Focus has been given on ingenious strategies to functionalize the phloroglucinol moiety at multiple positions. The isolation and bioactivities of the compounds are also provided.

Polyprenylated Acylphloroglucinols With Different Carbon Skeletons From the Fruits of Garcinia multiflora

Eleven new polycyclic polyprenylated acylphloroglucinols (PPAPs, 1-11) and three new monocyclic polyprenylated acylphloroglucinols (MPAPs, 12-14), together with ten known analogues were isolated from the fruits of Garcinia multiflora. These PPAPs belong to three types including the bicyclic polyprenylated acylphloroglucinols (BPAPs), the caged PPAPs, and the complicated PPAPs. Their structures and absolute configurations were determined through HRESIMS, NMR spectroscopy data, electronic circular dichroism (ECD) calculations, and gauge-independent atomic orbital (GIAO) NMR calculations with DP4+ analyses. Moreover, compounds 2 and 7 exhibited moderate cytotoxicity against three human cancer lines (MCF-7, T98, and HepG2) with IC50 values ranging from 9.81 ± 1.56 to 17.00 ± 2.75 μM.

Enantioselective Total Synthesis of (+)-Garsubellin A

Garsubellin A is a meroterpene capable of enhancing the enzyme choline acetyltransferase whose decreased level is believed to play a central role in the symptoms of Alzheimer's disease. Due to the potentially useful biological activity together with the novel bridged and fused cyclic molecular architecture, garsubellin A has garnered substantial synthetic interest, but its absolute stereostructure has been undetermined. We report here the first enantioselective total synthesis of (+)-garsubellin A. Our synthesis relies on stereoselective fashioning of a cyclohexanone framework and double conjugate addition of 1,2-ethanedithiol that promotes aldol cyclization to build the bicyclic [3.3.1] skeleton. The twelve-step, protecting group-free synthetic route has enabled the syntheses of both the natural (-)-garsubellin A and its unnatural (+)-antipode for biological evaluations.