SciCombinator

Discover the most talked about and latest scientific content & concepts.

Journal: Organic letters

28

Multicomponent reactions are powerful tools for organic chemistry, and among them, the Ugi reaction provides remarkable improvement in many fields of organic chemistry such us combinatorial chemistry, medicinal chemistry, and peptide chemistry. A new, enzyme-catalyzed example of the Ugi three-component reaction is presented. The studies include the selection of an enzyme as well as determination of the scope and limitations of the newly described reaction. The presented method combines the enzyme promiscuity and multicomponent reaction advantages in the first one-pot formation of dipeptide 1.

Concepts: Chemical reaction, Chemistry, Organic chemistry, Peptide synthesis, Ugi reaction, Multi-component reaction, Passerini reaction, Multiple component reactions

28

A formal total synthesis of the spiroketal containing cytotoxic myxobacteria metabolite spirangien A (1) is described. The approach utilizes a late introduction of the C20 alcohol that mirrors the biosynthesis of this compound. The key steps involved a high yielding cross metathesis reaction between enone 6 and alkene 7 to give E-enone 4 and a Mn-catalyzed conjugate reduction α-oxidation reaction to introduce the C20 hydroxyl group. Acid treatment of the α-hydroxyketone 4 gave spiroketal 19 which was converted into known spirangien A (1) advanced intermediate spiroketal 3.

Concepts: Alcohol, Functional group, Total synthesis, Olefin metathesis, Functional groups, Richard R. Schrock, Hydroxyl, Alkane metathesis

28

A solvent switchable rotaxane equipped with a pyrene stopper and with two ferrocenyl units on the macrocycle is reported, in which three different states, two nondegenerate and one degenerate, can be obtained in different solvents at room temperature. This is accompanied by high contrast changes in fluorescence intensity of the pyrene stopper by the presence of the ferrocenyl moieties on the macrocycle, which quench the emission of pyrene more efficiently with proximity.

Concepts: Fluorescence, Oxygen, Light, Fluorescence spectroscopy, Solubility, Solvent, Rotaxane, Degeneracy

28

The constitution of the aglycon of nudicaulin has been revised to be a pentacyclic indole alkaloid. The relative and absolute configurations of the two diastereomers, nudicaulins I (3a) and II (3b), have been assigned by NMR, conformational analyses, and interpretation of the experimental ECD spectra by quantum-chemical calculations.

Concepts: Papaver, Configuration management, Constitution, Papaver nudicaule

28

The first catalytic asymmetric isatin-involved Povarov reaction has been established. This method provides an unprecedented approach to access the enantioenriched spiro[indolin-3,2'-quinoline] scaffold with concomitant creation of two quaternary stereogenic centers in high yields and excellent stereoselectivities (all >99:1 dr’s, up to 97% ee).

Concepts: Stereochemistry, Imine, Quinoline, Povarov reaction

28

An efficient total synthesis of (-)-epothilone B has been achieved in ca. 8% yield over 11 steps from 9 (or 10 steps from 7/8), which features a bissiloxane-tethered ring closing metathesis reaction to approach the trisubstituted (Z) double bond and forms a new basis for further development of an industrial process for epothilone B and ixabepilone.

Concepts: Total synthesis, Paclitaxel total synthesis, Olefin metathesis, Chemical synthesis, Epothilone, Process management, Ixabepilone, Sorangium cellulosum

28

A novel Claisen rearrangement in which the Breslow intermediate is engaged as a hydroxy-substituted N,S-ketene acetal to provide complex 3° alcohols without the use of organometallic reagents is reported. The reaction constitutes an unprecedented reactivity mode for the Breslow intermediate.

Concepts: Alcohol, Chemical reaction, Claisen rearrangement, Rearrangement reactions, Claisen condensation

28

The pentasaccharide part of the potent neuritogenic ganglioside GAA-7 has been synthesized for the first time. The unique branched terminus constituting partially modified sialic acids and N-acetylgalactosamine was successfully established by stereoselective double-sialylation using 8-O-methyl-N-Troc-sialic acid as a donor. The final 4 + 1 coupling reaction provided a high yield of pentasaccharide, which was deprotected to deliver the target molecule.

Concepts: Oxygen, Sialic acid, Chemical reaction, Salt, 2004 singles

28

In a new version of the Fischer indole synthesis, primary and secondary alcohols have been catalytically oxidized in the presence of phenylhydrazines and protic or Lewis acids to give the corresponding indoles. The overall reaction can be accomplished in one step, and the use of alcohols instead of aldehyes or ketones as starting materials has several advantages in terms of a large selection of reagents, easy handling, and safety of the process.

Concepts: Alcohol, Carbon dioxide, Enzyme, Chemical reaction, Hydrogen, Indole, Bartoli indole synthesis, Fischer indole synthesis

28

The racemic modification of the Aspidosperma alkaloid limaspermidine (1) has been prepared in ten steps including one involving a Raney-cobalt-mediated tandem reductive cyclization of nitrile 8 to give the tetracyclic system 9b. Compound (±)-1 has been converted over two steps into (±)-1-acetylaspidoalbidine [(±)-13].

Concepts: Chemical synthesis, Alkaloid, Reserpine