Synthetic Studies of Javaberine A Based on Intramolecular Hydroamination of Alkenes.

A total synthesis of javaberine A was achieved through a lithium amide-mediated intramolecular hydroamination of an N-allyl aminoalkene. The desired hydroamination was accomplished using an excess of i-PrNH with a substoichiometric amount of n-BuLi. Using an excess of both n-BuLi and i-PrNH led to tandem cyclization, however, resulting in the construction of a tricyclic structure through the formation of one C-N and two C-C bonds in a single operation.

Synthesis and biological evaluation of histone deacetylase and DNA topoisomerase II-Targeted inhibitors.

HDAC inhibitors enable histones to maintain a high degree of acetylation. The resulting looser state of chromatin DNA may increase the accessibility of DNA drug targets and consequently improve the efficiency of anticancer drugs targeting DNA, such as Topo II inhibitors. A novel class of nucleoside-SAHA derivatives has been designed and synthesized based on the synergistic antitumor effects of topoisomerase II and histone deacetylase inhibitors.

Design, synthesis, and evaluation of DNA topoisomerase II-targeted nucleosides.

We developed novel nucleoside-based topoisomerase II selective inhibitors and showed that small structural units, such as catechols, are essential for DNA topoisomerase II inhibitory activity. Moreover, nucleoside analogues containing TBS and 1,3-dithian moieties had potent and selective DNA topoisomerase II inhibitory activities. In further experiments, compound 25b having a beta configuration of the thymine moiety showed relatively strong growth inhibitory activity against cancer cell lines, and was more potent against all cancer cell lines than compound 26b, which carries a thymine moiety in the alpha configuration.

Exploration of Dimethylzinc-Mediated Radical Reactions.

In this account, our studies on radical reactions that are promoted by dimethylzinc and air are described. Advantages of this reagent and differences from conventional radical initiators, such as triethylborane, are discussed.

Total synthesis of (+)-trans-dihydronarciclasine utilizing asymmetric conjugate addition.

A highly efficient short-step construction of the common phenanthridine skeleton of pancratistatin-class alkaloids was accomplished in enantiomerically pure form using chiral ligand-controlled asymmetric conjugate addition. The utility of the intermediate was demonstrated by the total synthesis of (+)-trans-dihydronarciclasine with mild oxidation from an amine to an amide as a key step.

General entry to asymmetric one-pot [N + 2 + n] cyclization for the synthesis of three- to seven-membered azacycloalkanes.

Enantio- and diastereoselective one-pot synthesis of three- to seven-membered cis-azaheterocycles was achieved using a triggered asymmetric conjugate addition reaction of lithium amide with an enoate, followed by alkylation of the resulting lithium enolate with α,ω-dihaloalkane and N-alkylation. Isomerization of cis-azaheterocycles with a base yielded the trans-product, constituting a one-pot synthesis of cis-azacycles and a two-step synthesis of trans-azacycles. The four-step asymmetric synthesis of nemonapride highlights the general utility of the method.

Radical one-pot α,β-dual and β-mono-oxymethylation of alkylidenemalonate.

Dimethylzinc-mediated radical conjugate addition reaction of dimethyl alkylidenemalonates with iodomethyl pivalate gave a high yield of the α,β-dual oxymethylation product in one pot under air and the β-pivaloyloxymethylation product under argon.

High performance of N-alkoxycarbonyl-imines in triethylborane-mediated tin-free radical addition.

Triethylborane-mediated tin-free radical alkylation of N-alkoxycarbonyl-imines, such as N-Boc-, N-Cbz-, and N-Teoc-imines, proceeded smoothly at a low temperature (-78 to -20 °C) to give the corresponding adducts in high yield. Although the formation of isocyanate was the major unfavorable reaction at room temperature, a one-pot conversion of N-Boc-imine to N-ethoxycarbonyl-adduct was possible through the corresponding isocyanate generated in situ. The higher performance of N-alkoxycarbonyl-imine than those of N-Ts- and N-PMP-imines is rationalized by a moderate electron-withdrawing character of an alkoxycarbonyl group that makes both addition of alkyl radical and trapping of the resulting aminyl radical by triethylborane efficiently fast.

Chiral N-heterocyclic carbene-copper(I)-catalyzed asymmetric allylic arylation of aliphatic allylic bromides: steric and electronic effects on γ-selectivity.

Chiral N-heterocyclic carbene ligands were electronically and sterically tuned to improve γ-selectivity in copper(I)-catalyzed asymmetric allylic arylation of aliphatic allylic bromides with several aryl Grignard reagents. High γ-selectivity was realized when either the aryl group of the Grignard reagent or the aryl group on the N-substituent of the carbene ligand was electron-deficient or when either the carbene ligand or allylic bromide was bulky. The results indicated that electron deficiency and steric hindrance of the initially formed σ-allyl copper intermediate enhance the rate of the reductive elimination to give γ-products as major isomers.

Stereoselective formal synthesis of (+)-allokainic acid via thiol-mediated acyl radical cyclization.

Stereoselective formal synthesis of (+)-allokainic acid was accomplished starting from L-glutamate by using a thiol-mediated acyl radical cyclization as a key step. The cyclization of a formylalkenoate proceeded in a highly diastereoselective manner to give trans-4,5-disubstituted pyrrolidin-3-one without the production of the cis-isomer. The pyrrolidinone was then converted into the established synthetic intermediate of (+)-allokainic acid via the iron-catalyzed coupling reaction with an isopropenyl Grignard reagent.

Stereoselective radical addition of an acetal to sterically tuned enantiomerically pure N-sulfinyl imines.

Enantiomerically enriched sulfonamides were synthesized by the radical addition of an acetal to enantiomerically pure N-sulfinyl imines using dimethylzinc-air and boron trifluoride diethyl etherate. Higher levels of stereocontrol were observed by using a mesitylenesulfinyl group. Furthermore, an amine and an amino alcohol with high enantiomeric purity were obtainable from the sulfonamide product.

Is biliary bile acid a good predictor for acute cellular rejection in living donor liver transplantation?

Background: In liver transplantation, acute cellular rejection (ACR) is still a major complication that can lead to mortality. Bile secretion has been considered as a marker of early graft function.

Methods: The study included 41 adults who received living donor liver transplantation (LDLT) at Kyoto University Hospital between April 2007 and February 2008.

Steric tuning of the amidomonophosphane-rhodium(I) catalyst in asymmetric addition of arylboroxines to N-phosphinoyl aldimines.

Highly enantioselective rhodium-catalyzed addition of arylboroxines to N-phosphinoylaldimines was realized by the steric tuning of a diphenylphosphorus moiety to a di(o-tolyl)phosphorus moiety of a chiral amidomonophosphane. The presence of MS 4 A in a 5:1 solvent mixture of dioxane-propanol was essential to afford the corresponding diarylmethylamines in high yield.

Chiral amidophosphane-rhodium(i)-catalyzed asymmetric conjugate arylation of acyclic enones with arylboronic acids.

A catalytic asymmetric conjugate arylation of acyclic alpha,beta-unsaturated ketones with arylboronic acids was catalyzed by 3 mol% of chiral amidomonophosphane 1-rhodium(I) in the presence of potassium hydroxide in a mixture of 1,4-dioxane and water at 70 degrees C to afford 1,4-conjugate arylated acyclic ketones with high enantiomeric excess in high chemical yield. Thirteen examples of the reaction demonstrate the general applicability of the catalytic system.

Asymmetric construction of binaphthyl by the chiral diether-mediated conjugate addition of naphthyllithium to naphthalenecarboxylic acid 2,6-di-t-butyl-4-methoxyphenyl ester.

Two ways for the synthesis of binaphthyl were examined based on a chiral ligand-mediated asymmetric conjugate addition of 1-naphthyllithium to naththalene-2-carboxylic acid 2,6-di-t-butyl-4-methoxyphenyl esters. The one pot method by conjugate addition-elimination gave a relatively higher enantioselectivity than the two step synthesis based on addition and subsequent oxidative aromatization.

Enantioselective conjugate addition of a lithium ester enolate catalyzed by chiral lithium amides: a possible intermediate characterized.

Two 1:1 noncovalent mixed aggregates between a lithium enolate and two diastereomeric lithium amides have been identified spectroscopically in THF. The NMR data, as well as DFT theoretical calculations, shine some light on a puzzling reversal of induction, observed when switching from one diastereomer of the amide to the other in the enantioselective Michael addition of the lithium enolate to an unsaturated ester.

Asymmetric construction of three contiguous stereogenic centers by conjugate addition-alkylation of lithium ester enolate.

A chiral ligand- and lithium amide-assisted asymmetric conjugate addition of lithium enolate of propionate to cyclopentenecarboxylate gave the corresponding lithium enolate, whose allylation gave the key intermediate of the marine alkaloid halichlorine as a single diastereomer with moderate enantioselectivity.

Total synthesis of (-)-lycorine and (-)-2-epi-lycorine by asymmetric conjugate addition cascade.

Total syntheses of (-)-lycorine and (-)-2-epi-lycorine were accomplished using chiral ligand-controlled asymmetric cascade conjugate addition methodology, which enables the formation of two C-C bonds and three stereogenic centers in one pot to give synthetically useful chiral cyclohexane derivatives.

Asymmetric construction of quaternary carbon centers by sequential conjugate addition of lithium amide and in situ alkylation: utility in the synthesis of (-)-aspidospermidine.

Chiral diether ligand-controlled asymmetric conjugate addition of a lithium amide to cyclopentenecarboxylate and subsequent in situ alkylation gave a chiral cyclopentane derivative bearing a quaternary carbon with high enantio- and diastereoselectivity. The cyclopentane derivative was converted successfully to (-)-aspidospermidine.

Dimethylzinc-initiated radical reactions.

Developments in modern organic synthesis owe much to the field of radical chemistry. Mild reaction conditions, high selectivity, good functional group tolerance and high product yield are features that have made reactions involving radical species indispensable tools for synthetic chemists. In part, the discovery of new radical initiators has led to the efficiency that now characterizes most radical reactions.

Copper-catalyzed asymmetric allylic substitution with aryl and ethyl Grignard reagents.

Phenyl- and ethyl-magnesium bromides undergo regioselective asymmetric allylic substitution with high enantioselectivity under the catalysis of chiral amidophosphane-copper(I) complexes.

Chemoselective conjugate addition of dimethylzinc-mediated ether and acetal radicals to alkylidenemalonates and asymmetric reactions.

Cyclic and acyclic ether or acetal radicals were generated directly from ethers or acetals by the action of dimethylzinc-air, and their subsequent conjugate addition reaction with alkylidenemalonates afforded the corresponding conjugate adducts in reasonably high yields. The reaction with benzylidenemalonates bearing formyl and imino groups gave chemoselectively the conjugate addition products. The asymmetric reaction of bis(8-phenylmenthyl) benzylidenemalonate proceeded diastereoselectively to provide the adduct with 93:7 dr.

Tin-free radical addition of acyloxymethyl to imines.

Acyloxymethyl radicals were generated from the corresponding iodomethyl esters and successfully underwent addition to the CN bond of N-Ts, N-PMP, and N-Dpp imines by the action of dimethylzinc or triethylborane. Ethyl acetate, toluene, and benzene as well as dichloromethane were suitable solvents. The utility of acyloxymethyl radicals as a hydroxymethyl anion equivalent was highlighted by the facile hydrolysis of the acyloxy moiety of the adducts to give the corresponding amino alcohol derivatives in good to high yield.