Synthesis of the core bicyclic system of hyperforin and nemorosone

Different routes for the construction of biologically active diversely functionalized bicyclo[3.3.1]nonanes: an exploration of new perspectives for anticancer chemotherapeutics

Cancer is the second most high-morbidity disease throughout the world. From ancient days, natural products have been known to possess several biological activities, and research on natural products is one of the most enticing areas where scientists are engrossed in the extraction of valuable compounds from various plants to isolate many life-saving medicines, along with their other applications. It has been noticed that the bicyclo[3.3.1]nonane moiety is predominant in most biologically active natural products owing to its exceptional characteristics compared to others. Many derivatives of bicyclo[3.3.1]nonane are attractive to researchers for use in asymmetric catalysis or as potent anticancer entities along with their successful applications as ion receptors, metallocycles, and molecular tweezers. Therefore, this review article discusses several miscellaneous synthetic routes for the construction of bicyclo[3.3.1]nonanes and their heteroanalogues in association with the delineation of their anticancer activities with few selective compounds.

A review of nemorosone: Chemistry and biological properties

Nemorosone is a bicyclic polyprenylated acylphloroglucinol derivative originally isolated from Clusia spp. and it can be obtained through chemical synthesis employing different synthetic strategies. Since its discovery, it has attracted great attention both from a biological and chemical viewpoint. In the present article, we attempted to review various chemical and biological topics around nemorosone, with an emphasis on its antiproliferative activities. For this purpose, relevant data was collected from different scientific databases including Google Scholar, PubMed, Scopus and ISI Web of Knowledge. This natural compound has shown activity against several types of malignancies such as leukemia, human colorectal, pancreatic, and breast cancer because it modulates multiple molecular pathways. Nemorosone has both cytostatic and cytotoxic activity and it also seems to induce apoptosis and ferroptosis. Additionally, it has antimicrobial capabilities against Gram-positive bacteria and parasites belonging to genus Leishmania. Its promising antiproliferative pre-clinical effects deserve further attention for anticancer and anti-parasitic drug development and translation to the clinic.

The Biochemical and Genetic Basis for the Biosynthesis of Bioactive Compounds in Hypericum Perforatum L., One of the Largest Medicinal Crops in Europe

Hypericum perforatum L. commonly known as Saint John's Wort (SJW), is an important medicinal plant that has been used for more than 2000 years. Although H. perforatum produces several bioactive compounds, its importance is mainly linked to two molecules highly relevant for the pharmaceutical industry: the prenylated phloroglucinol hyperforin and the naphtodianthrone hypericin. The first functions as a natural antidepressant while the second is regarded as a powerful anticancer drug and as a useful compound for the treatment of Alzheimer's disease. While the antidepressant activity of SJW extracts motivate a multi-billion dollar industry around the world, the scientific interest centers around the biosynthetic pathways of hyperforin and hypericin and their medical applications. Here, we focus on what is known about these processes and evaluate the possibilities of combining state of the art omics, genome editing, and synthetic biology to unlock applications that would be of great value for the pharmaceutical and medical industries.

Stereoselective total synthesis of nemorosone

The highly stereoselective total synthesis of nemorosone via a new approach to the bicyclo[3.3.1]nonane-2,4,9-trione core which features intramolecular cyclopropanation of an α-diazo ketone, stereoselective alkylation at the C8 position, and regioselective ring-opening of cyclopropane is described. The total synthesis of nemorosone includes chemo- and stereoselective hydrogenation directed by the internal alkene.

The chemistry of the polycyclic polyprenylated acylphloroglucinols

With their fascinating biological profiles and stunningly complex molecular architectures, the polycyclic polyprenylated acylphloroglucinols (PPAPs) have long provided a fertile playing field for synthetic organic chemists. In particular, the recent advent of innovative synthetic methods and strategies together with C-C bond-forming reactions and asymmetric catalysis have revitalized this field tremendously. Consequently, PPAP targets which once seemed beyond reach have now been synthesized. This Review aims to highlight the recent achievements in the total synthesis of PPAPs, as well as notable methods developed for the construction of the bicyclo[3.3.1] core of these chemically and biologically intriguing molecules.

Total synthesis of plukenetione A

We describe an alkylative dearomatization/acid-mediated adamantane annulation sequence that allows facile access to type A polyprenylated acylphloroglucinol natural products including plukenetione A. Introduction of the 2-methyl-1-propenyl moiety was achieved via stereodivergent S(N)2 and S(N)1 cyclizations of allylic alcohol substrates.

Biosynthesis of biphenyls and benzophenones--evolution of benzoic acid-specific type III polyketide synthases in plants

Type III polyketide synthases (PKSs) generate a diverse array of secondary metabolites by varying the starter substrate, the number of condensation reactions, and the mechanism of ring closure. Among the starter substrates used, benzoyl-CoA is a rare starter molecule. Biphenyl synthase (BIS) and benzophenone synthase (BPS) catalyze the formation of identical linear tetraketide intermediates from benzoyl-CoA and three molecules of malonyl-CoA but use alternative intramolecular cyclization reactions to form 3,5-dihydroxybiphenyl and 2,4,6-trihydroxybenzophenone, respectively. In a phylogenetic tree, BIS and BPS group together closely, indicating that they arise from a relatively recent functional diversification of a common ancestral gene. The functionally diverse PKSs, which include BIS and BPS, and the ubiquitously distributed chalcone synthases (CHSs) form separate clusters, which originate from a gene duplication event prior to the speciation of the angiosperms. BIS is the key enzyme of biphenyl metabolism. Biphenyls and the related dibenzofurans are the phytoalexins of the Maloideae. This subfamily of the Rosaceae includes a number of economically important fruit trees, such as apple and pear. When incubated with ortho-hydroxybenzoyl (salicoyl)-CoA, BIS catalyzes a single decarboxylative condensation with malonyl-CoA to form 4-hydroxycoumarin. A well-known anticoagulant derivative of this enzymatic product is dicoumarol. Elicitor-treated cell cultures of Sorbus aucuparia also formed 4-hydroxycoumarin when fed with the N-acetylcysteamine thioester of salicylic acid (salicoyl-NAC). BPS is the key enzyme of benzophenone metabolism. Polyprenylated benzophenone derivatives with bridged polycyclic skeletons are widely distributed in the Clusiaceae (Guttiferae). Xanthones are regioselectively cyclized benzophenone derivatives. BPS was converted into a functional phenylpyrone synthase (PPS) by a single amino acid substitution in the initiation/elongation cavity. The functional behavior of this Thr135Leu mutant was rationalized by homology modeling. The intermediate triketide may be redirected into a smaller pocket in the active site cavity, resulting in phenylpyrone formation by lactonization.

Aza- and Carbo-[3 + 3] Annulations of Exo-Cyclic Vinylogous Amides and Urethanes. Synthesis of Tetrahydroindolizidines and An Unexpected Formation of Hexahydroquinolines

[3 + 3] Annulations of exo-cyclic vinylogous amides and urethanes with vinyl iminium salts are described here. We observed an intriguing dichotomy in their reaction pathways. For pyrrolidine- and azepane-based vinylogous amides or urethanes, aza-[3 + 3] annulation would dominate to give tetrahydroindolizidines, whereas, unexpectedly, for piperidine-based vinylogous amides or urethanes, carbo-[3 + 3] annulation was the pathway, leading to hexahydroquinolines. The origin for such a contrast is likely associated with a switch in the initial reaction pathway between C-1,2-addition and C-1,4-addition.

Progress towards the synthesis of Papuaforin A: Selective formation of α-bromoenones from silyl enol ethers

The selective one-pot conversion of enol silyl ethers into α-bromoenones allows a direct preparation of a tricyclic intermediate to papuaforin A.

Stereochemical investigation on the construction of poly-functionalized bicyclo[3.3.1]nonenones by successive Michael reactions of 2-cyclohexenones

A method for the practical construction of poly-functionalized bicyclo[3.3.1]nonenones by successive Michael reactions of cyclohexenones with acrylates using K2CO3 and TBAB (n-Bu4N+ Br-) was developed. The construction could be carried out in both stepwise and one-pot reactions with similar tendencies in regioselectivity. The alpha-regioselectivity in the intramolecular Michael reaction agreed with that stereoelectronically expected in intermolecular reactions based upon consideration of the HOMO orbital profile of the enolate I, the precursor to ring-closure, although the reaction site was trisubstituted and prone to steric hindrance in most of the examples presented. For the acetoxymethylacrylates substituted at either the alpha or gamma position, steric hindrance of the substituents (R2 and R3) served as a controlling factor to induce high regiocontrol. Facial selection in the protonation of enolate II, formed upon ring-closure, was also affected by these substituents. In both the intramolecular Michael reaction and the protonation of enolate II, the ammonium counter cation played an important role.

Hyperforin

Hyperforin is a polyprenylated acylphloroglucinol derivative from Hypericum perforatum (St. John's wort). It exhibits antidepressant activity by a novel mechanism of action, antibiotic activity against gram-positive bacteria, and antitumoral activity in vivo. However, it also produces drug-drug interactions by activation of the pregnan X receptor. No total synthesis has been described. Some natural and semisynthetic analogues are available to study structure-activity relationships. Enzymatically, the skeleton of hyperforin is formed by isobutyrophenone synthase from isobutyryl-CoA and three molecules of malonyl-CoA. The first prenylation step is catalyzed by a soluble and ion-dependent dimethylallyltransferase. Hyperforin mainly accumulates in pistils and fruits where it probably serves as defensive compound.

Tandem Diels−Alder Cycloadditions of 2-Pyrone-5-acrylates for the Efficient Synthesis of Novel Tetracyclolactones

Readily prepared from the regioselective Pd-catalyzed coupling reactions of 3,5-dibromo-2-pyrone, 3-bromo-2-pyrone-5-carboxylates undergo tandem uninterrupted sequential Diels-Alder cycloaddition reactions with allyl vinyl ethers in a highly regio- and stereoselective fashion to provide a series of novel tetracyclolactones in good yields.

Tandem or Sequential Coupling−IMDA Cycloaddition Approach to Highly Fused Polycarbocycles

The Diels-Alder cycloadduct made from 3,5-dibromo-2-pyrone and 2-bromo-styrene was successfully transformed stereoselectively into a series of novel benzotetracycles via a tandem or sequential Pd-catalyzed coupling-intramolecular Diels-Alder (IMDA) cycloaddition. The resulting polycarbocycles can be readily converted into a bicyclo[3.3.1]nonane system upon ozonolysis of the internal double bond.

A New Synthetic Approach to the Polycyclic Polyprenylated Acylphloroglucinols

[reaction: see text] The three-carbon alpha,alpha'-annulation of a sterically hindered cyclic beta-keto ester can be achieved by alkynylation with 3,3-diethoxypropyne, syn reduction of the alkyne with Co(2)(CO)(8) and Et(3)SiH, and an intramolecular aldol reaction. The method is potentially useful for the synthesis of nemorosone, hyperforin, and other polycyclic polyprenylated acylphloroglucinols.