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We synthesized the naturally occurring carbasugar ampelomin A and its epimer from a common starting material. The enantiomerically pure starting material was obtained by base-catalyzed asymmetric Diels-Alder reaction of 3-hydroxy-2-pyrone and chiral acrylate. The total yield of ampelomin A was 14% in seven synthetic steps. The key step of the synthesis of ampelomin A was inversion of the stereochemistry at the C-6 position, which was achieved by stereoselective catalytic hydrogenation of the corresponding methylidene group. Further synthesis of the epimer was straightforward, because all stereogenic centers had already been introduced on the starting material; the total yield was 44% in four synthetic steps. Both the final products were obtained in pure form without contamination with undesired isomers. The reported (1)H NMR chemical shift of the C-7 methyl protons and the H-5axial coupling pattern of natural ampelomin A were inconsistent with those of our synthetic product. After careful comparison of the spectra and examination of the stable conformation obtained through MM2 calculations, we present revised NMR data for ampelomin A.

A new aaptamine-related alkaloid, 1,3-dioxolo [4,5- d] benzo [ de]-1,6-naphthyridine (methylenedioxyaaptamine, 1), was isolated from the organic extracts of the Bornean marine sponge Aaptos aaptos, together with a known aaptamine derivative, 8,9,9-trimethoxy-9 H-benzo [ de]-1,6-naphthyridine (2). The structure of compound 1 was elucidated by interpretation of its spectroscopic data. Two compounds were tested for their cytotoxic potentials against adult T-cell leukemia (ATL) cells, and compound 1 showed moderate cytotoxic potential.

The base-catalyzed Diels-Alder (DA) reaction is a unique cycloaddition, which comprises the combination of electron deficient dienophiles and dienes having acidic functional groups that are activated by bases. It is quite opposite to the well-known Lewis acid-catalyzed DA reactions that include electron rich dienes and dienophiles that are activated by Lewis acids or Bronsted acids. In our continuous effort to develop the base-catalyzed DA, we have found that three different classes of compounds, 3-hydroxy-2-pyrone, 3-hydroxy-2-pyridone, and α-tropolone can be used as dienes suitable for the DA reaction. All the base-catalyzed DA reactions we have developed are accelerated by mild amine bases and give the corresponding products in quantitative to moderate yields. As well as acid-catalyzed DA reactions, chiral base catalysts and/or chiral dienophiles provide the enantioselective DA reactions. Because the resulting DA adducts that have various functional groups and rigid bicyclic ring systems, are attractive building blocks for natural products, particularly for cyclohexene oxides and carbasugars, some synthetic applications to give biologically active compounds using the DA adducts are described.

Investigation of the root bark extract of Entandrophragma angolense led to identification of two gedunin-type limonoids 5-hydroxy-7-deacetoxy-7-oxogedunin ( 1 ) and 5,6-dehydro-7-deacetoxy-7-oxogedunin ( 2 ), and three methyl angolensate derivatives, 6-deacetoxydomesticulide D ( 3 ), 6-deacetoxydomesticulide D 21-methylether ( 4 ), and entangosin ( 5 ), together with known compounds, methyl angolensate ( 6 ), 6-acetoxymethyl angolensate ( 7 ) and secomahoganin ( 8 ). Their structures were established by extensive NMR experiments in conjunction with mass spectrometry. Entangosin is a rare example of a limonoid derivative having a fully O -substituted furan moiety.

A Diels–Alder reaction of α-tropolone and electron-deficient dienophiles prompted by Et3N or silica gel was performed. Reaction with the highly reactive dienophile, N-methylmaleimide, proceeded smoothly in the presence of Et3N or silica gel to yield adducts as a mixture of endo and exo isomers. Both catalysts accelerated endo/exo isomerization of the product, and detailed examination of the reaction using hinokitiol and N-methylmaleimide revealed that isomerization proceeds via an intramolecular path without retro Diels–Alder reaction. Successful cycloaddition reactions were established with six other dienophiles: acrylonitrile, methyl acrylate, ethyl vinyl ketone, dimethyl fumalate, dimethyl malate, and dimethyl acetylenedicarboxylate, and the corresponding adducts were obtained in good to moderate yields.

A new manoalide-related sesterterpene, (4E,6E)-dehydro-25-O-methylmanoalide (1), was isolated from the organic extracts of the Bornean marine sponge Luffariella variabilis, together with the known compound (4E,6E)-dehydromanoalide (2). The structure of compound 1 was elucidated by interpretation of its spectroscopic data.

Six phragmalin limonoids, named tabulalin and tabulalides A-E, were isolated from the root bark of Chukrasia tabularis (Meliaceae). Their structures were determined by spectroscopic methods, and their antifeedant properties evaluated.

Investigation of the fruits of Khaya senegalensis resulted in the isolation of three new mexicanolide limonoids containing a rare conjugated diene lactone system named seneganolide A (1), 2-hydroxyseneganolide A (2) and 2-acetoxyseneganolide A (3). Two known limonoids, 3-deacetyl-7-deacetoxy-7-oxokhivorin (4) and methyl 6-hydroxyangolensate (5), were also found. The structures of the new compounds were elucidated on the basis of spectral methods. The antifungal activity of compounds 1, 3 and 5 was tested against the fungus Botrytis cinerea.

An efficient asymmetric total synthesis of naturally occurring cyclohexeneoxides, (+)-epiepoformin and (−)-phyllostine has been achieved using the chiral building block available from the base-catalyzed Diels–Alder reaction of 3-hydroxy-2-pyrone. Since (−)-theobroxide was derived from the same precursor of (+)-epiepoformin, the formal total synthesis of (−)-theobroxide has also been achieved.

Three novel ring D opened limonoids corresponding to the phragmalin 8,9,14-orthoacetate with the addition of methyl 2,30-orthoacetate or a propionate, swietenialides A, B, and C and two ring-D opened phragmalin-type 1,8,9-orthoacetates, swietenialides D and E, were isolated together with one known mexicanolide, 2-hydroxyswietenin, from the ether extract of the stem bark of Swietenia mahogani JACQ. (Meliaceae). The structure of these unique compounds was elucidated by spectroscopic means.

A highly stereoselective base-catalyzed asymmetric Diels–Alder reaction of 3-hydroxy-2-pyrone and simple aryl vinyl sulfoxide is reported. Furthermore, the synthetic utility of the resulting produc...

The asymmetric synthesis of eutipoxide B, a metabolite of the phytopathogenic fungus Eutypa lata , is described. Quick and efficient synthesis of each enantiomer was achieved through base-catalyzed asymmetric Diels–Alder reactions with 3-hydroxy-2-pyrone and chiral acrylates.

Three new rearranged phragmalin-type limonoids, named khayanolides A, B and C, were isolated as insect antifeedant together with four known rings B,D-seco compounds, seneganolide, methyl angolensate and its 6-hydroxy and 6-acetoxy derivatives from the ether extract of the stem bark of Khaya senegalensis. The structure of new compounds was elucidated by spectroscopic means and the absolute structure of khayanolide A was established by X-ray analysis and CD study. The antifeedant activity of the isolated compounds was also reported.

A simple one-step preparation method to prepare gold nanoparticles (AuNPs) using 4-acylamidobenzenethiol derivatives as reductive stabilizers has been developed. The stabilizers were easily prepare...

Khayanolides A and B, two new rearranged phragmalin limonoids, were isolated as insect antifeedants together with two known rings B,D-seco compounds, methyl angolensate and its 6-hydroxy derivative from the ether extract of the stem bark of Khaya senegalensis. The structure of the new compounds was elucidated by spectroscopic means and the absolute structure of khayanolide A was established by X-ray analysis and CD study. The antifeedant activity is also reported.

An asymmetric synthesis of the key intermediate of RPR 107880, a substance P antagonist, using a base-catalyzed Diels–Alder reaction of 3-hydroxy-2-pyrone and N -benzylmaleimide is described.

Four limonoids were isolated from Melia toosendan together with two known limonoids, nimbolinin B and its 1-deacetyl derivative. Among the new limonoids included one skeletal spiro-, one ring- C-seco nimbolinin-type, and two trichilinin-type apo-euphol-triterpenoids derivatives. Their structures were determined on the basis of spectroscopic data.

Two new degraded limonoids, azedararide and 12alpha-acetoxy fraxinellone, were isolated together with two known degraded limonoids, fraxinellone and fraxinellonone, as ichthyotoxic substances from the root bark of Melia azedarach. Their structures were elucidated by spectroscopic and chemical means.

In the presence of a cinchona alkaloid as a catalyst, the Diels-Alder reaction of 3-hydroxy-2-pyrone with chiral N -acryloyl oxazolidinone afforded a bicyclolactone adduct with high diastereoselectivities (up to 95%de) in almost quantitative yield.

Four new tricarbocyclic diterpenes 2–5 containing the bicyclic [4.3.1] ring system found in floridicin (1), and an additional four dicarbocylic terpenes 6–9 containing the same bicyclic moiety, have been isolated from the soft coral, Xenia florida. Their structures were elecidated by spectroscopic means.

The first synthesis of (±)-fraxinellonone and its short step conversion into (±)-fraxinellone and (±)-isofraxinellone is described. The synthesized compounds exhibited moderate insect-antifeeding activity against Spodoptera exigua H. (Boisduval) and ichthyotoxicity against killifish.

Ten new ichthyotoxic cembranoids: sartol A (1), 4-O-methylsartol A (2), sartones A (3), B (4), C (5), D (6), 4-O-methylsartone B (7), epoxysartone A (8), 6β-hydroxysarcotol acetate (9), and 4-O-methylsarcotol (10) have been isolated from the soft coral, Sarcophyton sp. The ichthyotoxicity tests were performed for 1, 3—7, and 10, including the reduction product and the acetate of 1.

Seven new xenia diterpenoids including seco-type variants have been isolated from a soft coral, Xenia sp., and their structures elucidated on the basis of spectroscopy.

Seven new diterpenoids with an opened A-ring containing an aliphatic acid, called azamilides A—G (1—7), have been isolated from an acetone extract of Xenia sp. and their structures elucidated on the basis of spectroscopic analysis.

Three new ring C-seco-limonoids, nimbolidins C-E, were isolated from the root bark of Melia toosendan along with two known seco-limonoids, nimbolidin B and salannin. These compounds have properties as insect feeding inhibitors. Their structures were elucidated by spectroscopic means.

Two new insect antifeeding limonoids, trichilins K and L, were isolated from the stem bark of Melia toosendan along with five known limonoids, trichilins H, I and J, azedarachin A and 12-O-acetyl-azedarachin B. Their structures were elucidated by spectroscopic means and their antifeeding properties were examined with the larvae of Spodoptera eridania.

The structures of nine new xenia diterpenoids, xeniatine A (1), xeniatine A epoxide (2), isoxeniatines A (3) and B (4), and xeniaethers A (5) and B (6), together with three methoxyacetals 7–9, from a soft coral Xenia species have been elucidated.

Three new limonoid antifeedants, meliacarpinins 1–3, were isolated along with fourteen known limonoids from the root bark of Chinese Melia azedarach. Linn (Meliaceae). Their structures and antifeedant activity were elucidated.

The structures and absolute structures of three new 13-membered carbocyclic cembranoids, sarcotol (1), sarcotol acetate (2), and sarcotal acetate (3) from a soft coral, Sarcophyton sp. have been determined by spectroscopic and single crystal X-ray analyses, and chemical conversion. Ichthyotoxity tests were performed for 1, 2, 3, and their reduction products.

Three novel bis(indole) alkaloids with an unprecedented skeleton have been isolated from a stony coral, Tubastraea sp. These indoles could biogenetically be derived from two molecules of aplysinopsin via a Diels–Alder reaction.

Through bioassay-guided isolation, five compounds with growth inhibitory activity on S1T, an adult T-cell leukemia (ATL) cell line, were isolated from the crude methanol extract of the aerial parts of Hyptis verticillata.

A highly stereoselective base-catalyzed asymmetric Diels–Alder reaction of 3-hydroxy-2-pyrone and simple aryl vinyl sulfoxide is reported. Furthermore, the synthetic utility of the resulting produc...

Three azedarachins, insect antifeedant limonoids, have been isolated from the root bark of Chinese Melia azedarach Linn (Meliaceae), along with six trichilins. Their structures show a 14,15-epoxide and a 19/29 acyl acetal bridge system, as elucidated by spectroscopic studies. They are antifeedants active against the larvae of Spodoptera exigua Hubner (Boisduval).

Three new rings B/D opened limonoids, two rearranged phragmalin limonoids named khayanolides D and E (1 and 2), and one limonoid glucoside named khayanoside (3) were isolated as insect antifeedants from the stem bark of Egyptian Khaya senegalensis. The structures of these compounds were established by spectroscopic methods, including 2D NMR and CD.

A new azadirachtin related antifeedant, 1-deoxy-3-tigloyl-11-methoxymeliacarpinin, was isolated from the root bark of Chinese Melia azedarach L. It inhibited completely the feeding of the larvae of S. exigua (Boisduval) at the concentration of 3 μg/cm2 by the leaf disk method.

Seven new labdane-type glucosides with antibacterial activity have been isolated from Viburnum suspensum. Their structures were elucidated by spect

Asymmetric total synthesis of (+)-epiepoformin was achieved in short steps using the base-catalyzed asymmetric Diels–Alder (DA) reaction of 3-hydroxy-2-pyrone with chiral acrylate. Since the synthesis produced Ogasawara's intermediate, it is also presented as a formal synthesis of (−)-theobroxide.

Seven new isomalabaricane derivatives, rhabdastins A-G (1-7), and a new monocyclic triterpene glycoside, rhabdastoside A (8), have been isolated from the methanol extract of the sponge Rhabdastrella globostellata, collected at Amami-oshima, Japan. Three of them were isolated as their corresponding methyl esters, rhabdastins A-D (1-3). Their structures were determined on the basis of spectroscopic and X-ray diffraction analyses. The isolated compounds were evaluated for their cytotoxicity against the proliferation of promyelocytic leukemia HL-60 cells. Compounds 4, 5, 7, and 11, possessing a cyclopentane side chain, exhibited weak activity, with IC(50) values of 21, 29, 44, and 11 μM, respectively, while compounds 1, 2, and 3, with a 2-substituted-propanoate side chain, were inactive at 100 μM. In addition, the mechanism of cytotoxicity of compounds 4 and 5 was investigated.

A new azadirachtin related antifeedant, 1-deoxy-3-tigloyl-11-methoxymeliacarpinin, was isolated from the root bark of Chinese Melia azedarach L. It inhibited completely the feeding of the larvae of S. exigua (Boisduval) at the concentration of 3 μg/cm2 by the leaf disk method.

Floridicin 1, a diterpene containing a [4.3.1] bicyclic ring system, has been isolated from the soft coral Xenia florida, and represents a new class of tricarbocyclic diterpenes.

Two glucosides of lindenane sesquiterpenes have been first isolated along with three known lindenane sesquiterpenes from Chloranthus glaber Makino and the structures were elucidated by spectroscopi...