Sesquiterpene Esters from Salvia roborowskii

Two new sesquiterpene esters,3β,6β,8α-triacetyl-4β,5α-epoxy-1-oxogermacr10(14)-ene(1)and 3β,6β,8α-triacetyl-4β,5α-epoxygermacr-1(10)-ene(2) were isolated from the whole plant of Salvia roborowskii Maxim.Their structures were elucidated by means of spectral data(2DNMR and HRMS).     

Synthesis of β-Stannyl Esters

A synthesis of β-stannyl esters from ester enolates and iodomethyl (tri-n-butyl) stannane (3) is described.     

12-Deoxyphorbol Esters from Euphorbia Fischeriana

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ω-Iodoalkyl(methyl)malonate Esters

Abstract

ω-Iodoalkyl(methyl)malonate esters have potential utility in the bioconjugate chemistry of steroids. A representative set of these esters with a variety of protecting groups and alkyl groups has been prepared. The compounds offer a range of elution values on silica, as well as several convenient deprotection options.

ω-Bromoalkyl(methyl)malonate esters are precursors of chalcogenobarbiturates, which, in radiolabeled form, may be useful as brain imaging agents.[1] Grigsby, R.A., Irgolic, K.J. and Knapp, F.F. 1983. Synthesis and spectral properties of diethyl organylchalcogenoalkyl(alkyl)malonates and 5-alkyl-5-(organylchalcogenoalkyl)barbiturates. J. Organomet. Chem., 259: 171–181.  [Google Scholar] Recently, we have become interested in the analogous ω-iodoalkyl(methyl)malonate esters because of their possible utility in the bioconjugate chemistry of steroids. It is known that steroids can be conjugated to platinum through a malonate moiety.[2] Gandolfi, O., Apfelbaum, H.C., Migron, Y. and Blum, J. 1989. Syntheses of cis-dichlorodiammineplatinum analogs having steroidal hormones bound to the metal atom via malonato bridges. Inorg. Chim. Acta, 161: 113–123.  [Google Scholar] Such platinated steroids are significant because of their potential as tissue-selective antitumor agents.     

Two New Triterpene Esters from Daphniphyllum oldhami

Two new triterpene esters,2-O-eaffeoylalphitolic acid(1)and methyl 2-O-eaffeoyl-alphitolate(2),together with two known triterpenes were isolated from the shrub Daphniphyllum oldnami.The structures of new compounds were elucidated on the basis of detailed spectroscopic analysis and compared with related compound.     

Two New Oplopanol Esters from Ligularia narynensis

Mainly species of Ligularia have long been used for treatment of fever, inflammation, detoxication, invigorating the circulation of blood and smoothing pain1. So far the opl- opane derivatives were not found in the genus Ligularia. Here we report the stru…     

Stereoselective Aldol Reaction of α-Phenylseleno Esters

Abstract

The TiCl₄-catalyzed reaction of a-phenylseleno esters with aldehydes in the presence of Ph₃P or Ph₃P=O gives aldol products with high syn selectivity.     

Solvolysis of 1-Chloro-1-Alkenyl Phenyl Sulfides. Synthesis of α-Bromo Phenyl Thiocarboxylic Esters, α-Bromo Alkyl Carboxylic Esters and α-Phenylthio Methyl Carboxylic Esters

1-chloro-1-alkenyl phenyl sulfides treated with bromine followed by hydrolysis or methanolysis give α-bromo phenyl thiocarboxylic esters and α-phenyl-thio methyl carboxylic esters. Direct oxidative solvolysis with bromine and alcohol give α-bromo alkyl carboxylic esters.     

Base Promoted Rearrangement of Carbonate Esters Derived from Aldehyde Cyanohydrins: Application to the Synthesis of α-Keto Esters

Acylation of the cyanohydrin derivative (2) of representative aldehydes with ethyl chloroformate, followed by treatment of the corresponding mixed carbonate esters (3) with lithium hexamethyldisilazide, afforded the cyanohydrin derivative (4) of α-keto esters. Cleavage of the latter (4) with 2,6-lutidine in the presence of silver nitrate led to the procurement of α-keto esters in >50% overall yield.     

Synthesis of Optically Active trans-2-Aminocyclopropanecarboxylic Esters

The research on optical alicyclic β-amino acids has recently attracted increasingly attention due to their significant pharmacological properties endowed by rigid frameworks, stable conformation1. Numerous biologically active peptides, β-lactams and some other natural products2 contain optical alicyclic β-amino acids. Cyclopropyl-modified alanines have been proved to be useful intermediates in medicine synthesis because of their rigid framework and reactive functional groups (amino and carb…     

A General Synthesis of α-Substituted Acrylic Esters

During a study of synthetic approaches to various naturally-occurring sesquiterpenes lactones, we developed a new synthesis of the α-methylene-γ-butyrolactone group.¹ This new sequence suggested that it might be applicable to the general synthesis of α-methylenecarbonyl compounds.² This report describes the application to a general synthesis of α-substituted acrylic esters.     

Hydrolysis of Dipeptide Heptyl Esters with Newlase F

Peptides conjugates, such as lipo-, glyco-, phospho- and nucleopeptides1, are of great importance in the research of signal transmission2, protein phosphorylation/ dephosphorylation, antibody, and so on. However, the synthesis of these compounds is severely complicated by their pronounced acid and base lability as well as their multifunctionality. Under basic or acidic conditions, (-elimination reactions, anomerization, hydrolysis or rupture of these compounds may occur. The traditional peptid…     

Diastereoselective α-Alkylation of β-Amino Esters: Preparation of Novel α-Substituted β-Amino Esters from α-Amino Acids

b-Amino acids and their derivatives have attracted considerable attention in recent years due to their occurrence in biologically active natural products, such as dolastatins 11, cyclohexylnorstatine 22 and taxol 33. bAmino acids also find application in the synthesis of blactams4, piperidines5, indolizidines6. Moreover, the peptides consisting of bamino acids, the so called bpeptides, have been extensively studied recently7. Consequently, considerable efforts have been directed to the synt…     

Synthesis of α-Arylated Esters from Aryl Halides

The preparation of α-arylalkanoic acid esters has received significant attention, not only due to these compounds are important industrial materials, but also some of them are nonsteroidal anti-inflammatory drugs (NSAID)1. Arylation of β-dicarbonyl carb…     

Isothiourea-Catalyzed Acylative Kinetic Resolution of Tertiary α-Hydroxy Esters

A highly enantioselective isothiourea-catalyzed acylative kinetic resolution (KR) of acyclic tertiary alcohols has been developed. Selectivity factors of up to 200 were achieved for the KR of tertiary alcohols bearing an adjacent ester substituent, with both reaction conversion and enantioselectivity found to be sensitive to the steric and electronic environment at the stereogenic tertiary carbinol centre. For more sterically congested alcohols, the use of a recently-developed isoselenourea catalyst was optimal, with equivalent enantioselectivity but higher conversion achieved in comparison to the isothiourea HyperBTM. Diastereomeric acylation transition state models are proposed to rationalize the origins of enantiodiscrimination in this process. This KR procedure was also translated to a continuous-flow process using a polymer-supported variant of the catalyst.     

Reactions of Phosphorodiamidous Acid Esters with α-Halocarbonyl Compounds

Reactions of ethyl and tert-butyl phosphorodiamidites with chloroacetone, bromoacetone, and -chloroethyl acetate were studied. The reaction pathway is determined by the structure of the intermediate quasiphosphonium compound responsible for the formation of the Arbuzov product as well as for the occurrence of the amonalous reaction yielding vinyl phosphate.     

Solvent-Free Microwave-Assisted Organic Reactions Preparation of β-Keto Esters

Microwave technique has been utilised in the preparation of β-keto esters. Two different procedures are described: transesterification of β-keto esters and ring opening of 2,2,6-trimethyl-1,3-dioxin-4-one.     

Efficient Synthesis of γ‐Keto Esters from Enamines and EDA

Abstract

The reaction of enamines with ethyl diazoacetate (EDA) catalyzed by dirhodium and copper complexes provided γ‐keto esters in good yields. The influences of catalyst, reaction solvent, temperature, and structure of enamines on this transformation were investigated.