Total synthesis of cladocorans A and B: a structural revision

The Kornblum DeLaMare rearrangement in natural product synthesis: 25 years of innovation

Covering: 1998 up to the end of 2023Since its initial disclosure in 1951, the Kornblum DeLaMare rearrangement has proved an important synthetic transformation and has been widely adopted as a biomimetic step in natural product synthesis. Utilising the base catalysed decomposition of alkyl peroxides to yield a ketone and alcohol has found use in many syntheses as well as a key strategic step, including the unmasking of furans, as a biomimetic synthetic tool, and the use of the rearrangement to install oxygen enantioselectively. Since ca. 1998, its impact as a synthetic transformation has grown significantly, especially given the frequency of use in natural product syntheses, therefore this 25 year time period will be the focus of the review.

Halimanes and cancer: ent-halimic acid as a starting material for the synthesis of antitumor drugs

The development of new anti-cancer agents is an urgent necessity nowadays, as it is one of the major causes of mortality worldwide. Many drugs currently used are derived from natural products. Halimanes are a class of bicyclic diterpenoids present in various plants and microorganisms. Many of them exhibit biological activities such as antitumor, antimicrobial, or anti-inflammatory. Among them, ent-halimic acid is an easily accessible compound, in large quantities, from the ethyl acetate extract of the plant Halimium viscosum, and it has been used as a starting material in a number of bioactive molecules. In this work, we review all the natural halimanes with antitumor and related activities until date as well as the synthesis of antitumor compounds using ent-halimic acid as a starting material.

Terpenoids from the Sponge Sarcotragus sp. Collected in the South China Sea

Sarcotragusolides A-D (1-4), four new butenolide sesterterpenes featuring a rare methyl-transferred 6/6/6-tricyclic fused ring system with a butyrolactone moiety, and echinohalimane B (8), an unprecedented monocyclic diterpenoid featuring a 2,7-ring-opened halimane-type skeleton, were isolated from the sponge Sarcotragus sp. A γ-hydroxybutenolide sesterterpene derivative (5), a new scalarane sesterterpene (7), a new subersin-type diterpenoid (10), and two known terpenoids were also isolated and identified. The discovery of sarcotragusolides C and D (3 and 4) with an unprecedented inversion of configuration implied a distinct biosynthetic pathway. The structures of these compounds were elucidated based on their spectroscopic data, single-crystal X-ray diffraction, chemical derivatization, and quantum chemical calculations. Compounds 1a, 1b, and 2 presented modest cytotoxic activities against several human cancer cell lines.

The Methylene-Cycloalkylacetate (MCA) Scaffold in Terpenyl Compounds with Potential Pharmacological Activities

Recently, the methylene-cycloakylacetate (MCA) scaffold has been reported as a potential pharmacophore for neurite outgrowth activity. In this work, natural diterpenes that embed MCA fragments are reviewed, as they are major components of Halimium viscosum: ent-halimic acid, the prototype for these bioactive compounds. Herein, structures, sources, and activities for the natural diterpenes, as well as their synthetic derivatives of interest, are reviewed.

Two-step synthesis of chiral fused tricyclic scaffolds from phenols via desymmetrization on nickel

Tricyclic furan derivatives with multiple chiral centers are ubiquitous in natural products. Construction of such tricyclic scaffolds in a stereocontrolled, step-economic, and atom-economic manner is a key challenge. Here we show a nickel-catalyzed highly enantioselective synthesis of hydronaphtho[1,8-bc]furans with five contiguous chiral centers via desymmetrization of alkynyl-cyclohexadienone by oxidative cyclization and following formal [4 + 2] cycloaddition processes. Alkynyl-cyclohexadienone was synthesized in one step from easily accessible phenols. This reaction represents excellent chemo-selectivity, regio-selectivity, diastereo-selectivity, and enantio-selectivity (single diastereomer, up to 99% ee). An extraordinary regioselectivity in the formal [4 + 2] cycloaddition step with enones revealed the diverse reactivity of the nickelacycle intermediate. Desymmetrization of alkynyl-cyclohexadienones via oxidative cyclization on nickel was supported by the isolation of a nickelacycle from a stoichiometric reaction. Enantioenriched tricyclic products contain various functional groups such as C=O and C=C. The synthetic utility of these products was demonstrated by derivatization of these functional groups.

Tricyclic furanic compounds with multiple chiral centers are found in a variety of natural products. Here, the authors show a highly enantioselective nickel-catalyzed procedure to access tricyclic oxygen-containing scaffolds with five contiguous chiral centers.

Unusual cyclic terpenoids with terminal pendant prenyl moieties: from occurrence to synthesis

The paper reviews the known examples of cyclic terpenoids produced from open chain polyenic precursors by an "unusual" biosynthetic pathway, involving selective electrophilic attack on an internal double bond followed by cyclization. The resulting compounds possess cyclic backbones with pendant terminal prenyl groups. Synthetic approaches applied for the synthesis of such specifically functionalized compounds are also discussed, as well as biological activity of reported representatives.

Bicyclic C21 terpenoids from the marine sponge Clathria compressa

Three new bicyclic C(21) terpenoids, clathric acid (1) and two N-acyl taurine derivatives, clathrimides A (2) and B (3), were isolated from the marine sponge Clathria compressa. The structures of these compounds were elucidated by interpretation of spectroscopic data. Clathric acid showed mild antibacterial activity against several Gram-positive bacteria.

The binding mode of cladocoran A to the human group IIA phospholipase A(2)

The molecular basis for human group IIA phospholipase A(2) inactivation by the marine natural product cladocoran A (CLD A) has been studied in order to elucidate its relevant anti-inflammatory properties. Indeed, secretory phospholipases A(2) are well-known to be implicated in the pathogenesis of inflammation, such as rheumatoid arthritis, septic shock, psoriasis and asthma, thus the understanding of their inactivation mechanism could be useful for the development of new chemical classes of selective inhibitors. Our results, collected by a combination of biochemical approaches, advanced mass spectrometry and molecular modeling, suggest a competitive inhibition mechanism guided by a noncovalent molecular recognition event, and disclose the key role of the CLD A γ-hydroxybutenolide ring in the chelation of the catalytic calcium ion inside the enzyme active site. Moreover, CLD A is able to react selectively with Ser82, although this covalent event seems to play a secondary role in terms of enzyme inhibition.

Total synthesis of 10-isocyano-4-cadinene and its stereoisomers and evaluations of antifouling activities

The first enantioselective total synthesis of 10-isocyano-4-cadinene, a marine sesquiterpene isolated from nudibranchs of the family Phyllidiidae, and determination of its absolute stereochemistry were achieved. 10-Isocyano-4-cadinene is expected to be a novel nontoxic antifouling agent. In the synthesis, intermolecular Diels-Alder reaction and samarium diiodide induced Barbier-type cyclization were employed as key steps. The absolute configuration of 10-isocyano-4-cadinene was determined as (1S,6S,7R,10S) by comparison of the optical rotations between natural and synthetic samples. In addition, the authors successfully synthesized 10-epi- and di-1,6-epi-10-isocyano-4-cadinene through the same synthetic pathway. Antifouling activities against Balanus amphitrite with the cadinenes were also evaluated.

Inhibitors of protein tyrosine phosphatases: next-generation drugs?

The protein tyrosine phosphatases (PTPs) constitute a family of closely related key regulatory enzymes that dephosphorylate phosphotyrosine residues in their protein substrates. Malfunctions in PTP activity are linked to various diseases, ranging from cancer to neurological disorders and diabetes. Consequently, PTPs have emerged as promising targets for therapeutic intervention in recent years. In this review, general aspects of PTPs and the development of small-molecule inhibitors of PTPs by both academic research groups and pharmaceutical companies are discussed. Different strategies have been successfully applied to identify potent and selective inhibitors. These studies constitute the basis for the future development of PTP inhibitors as drugs.

PLA2 Inhibitory Activity of Marine Sesterterpenoids Cladocorans, Their Diastereomers and Analogues

Inhibition of secretory phospholipase A(2) (sPLA(2)) by cladocorans A and B and their diastereomers almost equaled that of manoalide.

Marine natural products

This review covers the literature published in 2003 for marine natural products, with 619 citations (413 for the period January to December 2003) referring to compounds isolated from marine microorganisms and phytoplankton, green algae, brown algae, red algae, sponges, coelenterates, bryozoans, molluscs, tunicates and echinoderms. The emphasis is on new compounds (656 for 2003), together with their relevant biological activities, source organisms and country or origin. Biosynthetic studies or syntheses that lead to the revision of structures or stereochemistries have been included (78), including any first total syntheses of a marine natural product.

Marine natural products: synthetic aspects

An overview of marine natural products synthesis during 2003 is provided. The emphasis on total syntheses of molecules of contemporary interest, new total syntheses, and syntheses that have resulted in structure conformation or stereochemical assignments.

Synthesis of bioactive sesterterpenolides from ent-halimic acid. 15-epi-ent-Cladocoran A and B

The bioactive sesterterpenoid gamma-hydroxybutenolides 15,18-bisepi-ent-Cladocoran A and B, 1 and 2, and 15-epi-ent-Cladocoran A and B, 57 and 55, were synthesized from ent-halimic acid. The synthesized sesterterpenolids 2, 55, 57, and 59 inhibited cellular proliferation (IC(50) congruent with 2 micro M) of a number of human leukaemic and solid tumor cell lines.