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In a previous study, we found that the thiophene carboxamide solamin analog, which is a mono-tetrahydrofuran annonaceous acetogenin, showed potent antitumor activity through the inhibition of mitochondrial complex I. In this study, we synthesized analogs with short alkyl chains instead of the n-dodecyl group in the tail part. We evaluated their growth inhibitory activities against human cancer cell lines. We found that the alkyl chain in the tail part plays an essential role in their activity.

Acyclic asymmetric quaternary stereocenters, which are composed of four carbon-carbon bonds, were finely constructed by utilizing a face-selective alkylation of enolate intermediates derived from an asymmetric Michael addition reaction of a chiral lithium amide with trisubstituted (E)-α,β-unsaturated esters. The present face-selective alkylation was able to employ diverse alkyl halides as an electrophile to afford various Michael adducts having an all-carbon quaternary stereocenter. With regard to the deprotection of the chiral auxiliary, N-iodosuccinimide used in our previous study did not work in the present cases; however, we found that pyridine iodine monochloride in the presence of H2O was effective to remove the bornyl group and the benzyl group on the amino group to provide the β-amino ester derivative.

The details of the total syntheses of C2'-fluorinated analogs of solamin, an antitumor annonaceous acetogenin, are described. Fluorine was enantioselectively introduced at the C2'-position by organocatalytic α-fluorination of the aldehyde according to a previously reported method. C2'-fluorinated solamin and its C2'-diastereomer were synthesized by the Sonogashira coupling of a tetrahydrofuran fragment and fluorine-containing γ-lactone fragments.

A facile and convenient synthesis of trisubstituted (E)-α,β-unsaturated esters was developed by improving our previously established method. The new method circumvented the separation of the intermediates, which have an activating group of the hydroxyl group in β-hydroxy esters, furnishing α,β-unsaturated esters in shorter steps than the previous method: an acetylation of β-hydroxy group and subsequent E1cB reaction proceeded in tandem. In addition, the new method can not only employ a diastereomeric mixture of the substrate for the E1cB reaction, it has a wide substrate scope as well, which would enable the synthesis of various trisubstituted (E)-α,β-unsaturated esters.

We synthesize optically active (R)-terbutaline 2, which is an anti-asthmatic drug, through recyclable catalytic asymmetric transfer hydrogenation (RCATH). Various chloroketones 4 were prepared and RCATH was performed on them. The products exhibit moderate to high enantioselectivity. In particular, the hydrogenation of acyl substituted substrates 4c yields chiral secondary alcohols 5c in good yield and enantioselectivity. Furthermore, (R)-terbutaline 2 can be synthesized in one step from the resulting secondary alcohol 5 without racemization.

Using dimethylsulfoxonium methylide as the methylene transfer reagent, 2a,8b-dihydrobenzo[b]cyclobute[d]pyran-3-ones were converted into 2,2'-biphenol derivatives as major products and dihydrodibenzofurans as minor products. The reaction mechanism was extrapolated from a deuteration experiment with CD2=S(O)(CD3)2.

A series of benzo[b]furan derivatives having a five-membered heterocyclic substituent at the 2-position were prepared from 2-(1-chloro-2-formylvinyl)benzo[b]furans (2) and 2-(4-alkylcarbamoylbuta-1,3-dienyl)benzo[b]furans. These 2-heterocyclic benzo[b]furans were evaluated for their cysteinyl leukotriene receptor (cysLT1, cysLT2) inhibitory activity. Several compounds showed moderate inhibition of calcium mobilization in HEK 293T-cysLT2 or CHO-cysLT1 cells.

Eleven 3-substituted isocoumarins and a benzylidenephthalide were synthesized through thermal cyclization reaction of delta- and gamma-ketoamides, respectively. Subsequent deprotection of the hydroxyl groups of the resulting isocoumarin and benzylidenephthalide compounds afforded thunberginols A, B, and F, respectively, which originated from the processed leaves of Hydrangea macrophylla SERINGE var. thunbergii MAKINO. The synthesized isocoumarins and thunberginols were evaluated for their anti-allergic activity, in which thunberginol B exhibited the highest inhibitory potency on the degranulation of RBL-2H3 cells induced by antigen. Structure-activity relationship studies were carried out to determine the necessary substituents on the 3-phenylisocoumarin skeleton for inhibitory activity.

In the presence of samarium diiodide, 2-aryl and 2-heteroaryl cyclopropane-1, 1-dicarboxylic esters were readily dimerized to give 3, 4-disubstituted 1, 1, 6, 6-hexanetetracarboxylic esters as diastereomeric mixtures in moderate to good yields. The diastereomeric mixtures were separated by preparative HPLC and stereo-chemistries of the isolated meso and racemic compounds were determined on the basis of HPLC analysis on chiral stationary phases. Between the 1H-NMR spectra of the separated diastereomers, the characteristic differences in the chemical shifts of the C2-H (C5-H) signals were observed and explained based on the MOPAC calculation.

Trimethylsilylaion of 1, 2, 3-triazole regioselectively proceeded to give 2-trimethylsilyl-2H-1, 2, 3-triazole, which was treated with primary alkyl halides in the presence of tetrabutylammonium fluoride to give 1-alkyl-1H-1, 2, 3-triazoles as a sole product. 1-Methyl-5-substituted 1H-1, 2, 3-triazoles were prepared by alkylation of 5-lithio-1-methyl-1H-1, 2, 3-triazole, and 1-methyl-4-substituted 1H-1, 2, 3-triazoles were obtained by alkylaiton of 4-lithio-1-methyl-5-phenylthio-1H-1, 2, 3-triazole followed by reductive desulfurization.

Nortopsentins A-D, antifungal 1, 4-bisindolylimidazole marine alkaloids isolated from a sponge, were synthesized through palladium-catalyzed cross-coupling of 3-indolylboronic and 6-bromo-3-indolylboronic acids with halogenoimidazoles as the key reaction.

Cyclic ketone O-trimethylsilylcyanohydrins (2) were prepared and converted to various compounds : α-hydroxyketones (3), dehydroxylated ketones (4), α, β-unsaturated ketones (9), tricyclic ketones (10), 1-ethoxycarbonyl-4-phenyl-1, 2, 4a, 5, 6, 7, 8, 8a-octahydro-2-naphthalenone (13), 1-phenylperhydroisocoumarin (18) and 1, 2, 3, 4, 4a, 10, 11, 11a-octahydro-5H-benzo[a, d]cyclohepten-10-one (20).

The cyclopropane ring in 2-substituted 1, 1-cyclopropanedicarboxylates was regioselectively opened by using samarium(II) diiodide (SmI2) in a hexamethylphosphoric triamide (HMPA)-tetrahydrofuran (THF) (1 : 10) system under mild and neutral conditions to give (2-substituted ethyl)malonates in moderate to good yields. The cyclopropane ring in 2-substituted cyclopropanecarboxylates or 2-substituted 3-(trimethylsilyl)cyclopropanecarboxylates was similarly cleaved regioselectively by using SmI2 in a HMPA-THF (1 : 1) system to give 4-arylbutyrates or 4-aryl-3-(trimethylsilyl)butyrates in 16-89% yields. The reaction mechanism of these ring-opening reactions is discussed.

Synthesis of 3-alkylamino-1, 4-naphthoquinone-2-carboxylic acid (2) was attempted. Although 3-(1-piperidinyl)-1, 4-naphthoquinone-2-carboxylic acid (2a) was not obtained, probably because of its instability, the esters (18a, b)of 2a could be prepared. 2-Alkylamino-3-hydroxymethyl-1, 4-naphthoquinones (9a-g) were photochemically cyclized to the 1, 4, 5, 10-tetrahydro-5, 10-2H-naphth[2, 3-d][1, 3]oxazines (19a-g), containing a novel heterocyclic ring system in moderate yields. Anti-bacterial activity of the prepared compounds was weak or insignificant.

The 4-position of the 1-methyl-1H-imidazole ring was lithiated by treatment of the corresponding 4-bromo derivatives with tert-butyllithium. This procedure was applied to synthesis of the left-hand part of pyronaamidine (1), which is a biologically interesting marine alkaloid.

1, 2, 6-Trimethyltetracyclo[5.3.1.0 ]undecan-9-one (4) was prepared from 1, 5-dimethylbicyclo[3.3.0]octan-3-one (6) in fourteen steps. Its cyclopropane ring opening reaction was examined under various conditions. In all runs, 11-substituted 1, 2, 6-trimethyltricyclo[5.3.1.02, 6]undecan-9-ones 20 were obtained as major products along with 7-substituted 1, 2, 8-trimethyltricyclo[6.3.0.0 ]undecan-4-ones 21 and two other products 22 and 23.

Improved synthetic routes to (±)-pentalenene (1) and (±)-9-epipentalenene (6) were developed. Intramolecular alkylation of a tricyclic halo ester (7), obtained from 3, by treatment with lithium hexamethyldisilazide in tetrahydrofuran gave 14 and 15 in a ratio of 74 : 26. Compound 14 was successfully converted into the key intermediate (16) for (±)-1. On the other hand, catalytic hydrogenation of 8 afforded 20, a key intermediate for (±)-6, along with 16 (20 : 16=86 : 14).

2-Methylamino-3-(1-piperidinylmethyl)-1, 4-naphthoquinone (7) was prepared via several steps from 2-methyl-1, 4-naphthoquinone (vitamin K3, 3). The quinone (7) was photochemically oxidized to 2-methylamino-3-(1-piperidinylcarbonyl)-1, 4-naphthoquinone (8) and/or 2-alkoxycarbonyl-3-methylamino-1, 4-naphthoquinone (9), depending on the solvent used.

The cyclopropane ring opening reaction of 7, 7-dimethyl-3-oxotricyclo[3.3.0.02, 8]octane-5-acetic acid (5) was examined. A regioselective C(1)-C(2) bond cleavege of 5 proceeded smoothly under acidic conditions to give a bicyclo-[3.2.1]octan-3-one derivative 7 in good yield, as a result of neighboring-group participation of the carboxyl group. The lactone 7 was then successfully transformed into the 1, 4-diketone 9, a useful intermediate for total synthesis of (±)-descarboxyquadrone (4).

(±)-Pentalenene, the least oxidized triquinane sesquiterpene, was totally synthesized starting from 4, 4-dimethyl-2-cyclopenten-1-one via a regioselective C2-C8 bond opening of the tricyclo[3.3.0.02, 8]octan-3-one intermediate.

7, 7-Dimethyl-5-(2-propenyl)tricyclo[3.3.0.02, 8]octan-3-one (4) was prepared from 4, 4-di-methyl-2-cyclopentenone in several steps. The Birch reduction of 4 resulted in exclusive formation of a bicyclo[3.3.0]octanone (14)through C2-C8 bond clevage, while its substitutional reactions yielded bicyclo[3.2.1]octanones (15) through C1-C2 bond cleavage as major products.

This article deals with a formal total synthesis of (±)-quadrone (1), an antitumor sesquiterpene. The cyclopentenone (3) was trans-formed into cyclopropane derivative (2), a regioselective reductive ring opening of which and trapping of the enolate intermediate (16) by a C-1 unit afforded the diquinaneacetate (17). By a two-step sequence 17 was converted into methyl (1R*, 5R*, 6R*)-6-(2-hydroxyethyl)-7, 7-dimethyl-2-methylene-3-oxobicyclo [3. 3. 0] octane-1-acetate (19), which had already been proved to be an intermediate for (±)-1.

A total synthesis of (±)-descarboxyquadrone (5) starting from a bicyclo[3.2.1]octane (7;X=OH) is described. By a several-step sequence, the starting material was converted to a tricyclic compound (18), which was transformed to the target molecule, (±)-descarboxyquadrone (5), via a methoxymethylation.

A total synthesis of (±)-pentalenene (3), one of the least-oxidized triquinane sesquiterpenes, is described. By a several-step sequence, 4, 4-dimethyl-2-cyclopentenone (5) was derived to a tricyclooctanone (4), which was subjected to a reductive C2-C8 bond opening reaction to give 15. The triquinane derivative (20), obtained from 15, was transformed to (±)-pentalenene (3) and (±)-epi-pentalenene (21) in a 1.8 : 1 ratio.On the other hand, hydroboration-oxidation of 4 followed by tosylation gave easily separable products, 23 and 24, which were transformed to 20A and 20B, precuesors for (±)-3 and (±)-21, respectively.

The cyclopropane ring opening reaction of several tricyclo[3.3.0.02, 8]octan-3-ones (8a-c) was examined. Under acid-catalyzed substitutional conditions, compounds 8a and 8b gave predominantly the bicyclo[3.2.1]octan-3-one derivatives (9a, b), while compound 8c afforded exclusively the bicyclo[3.3.0]octan-3-one (10c). A candidate precursor for the synthesis of quadrone, 13, was also successfully prepared.