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Biomedical subjects

Andrew E Greene

Publications and source records attributed to Andrew E Greene.

At least 19 recordsLinked to original sources
PubMed2007

1-(2,4,6-triisopropylphenyl)ethylamine: a new chiral auxiliary for the asymmetric synthesis of gamma-amino acid derivatives.

The title compound has proven to be an excellent chiral auxiliary for nitrones in SmI2-mediated reductive coupling with alpha,beta-unsaturated esters. A variety of such nitrones, prepared from aldehydes and enantiopure N-hydroxy-1-(2,4,6-triisopropylphenyl)ethylamine, afforded gamma-N-hydroxyamino esters in high yields and diastereomeric purity. These adducts, readily available as either enantiomer, could be transformed into gamma-N-acetoxyamino esters, N-Boc-gamma-amino esters, and gamma-lactams.

Amino Acids↗
PubMed2006

High-pressure Diels-Alder approach to natural kainic acid.

The first Diels-Alder based synthesis of (-)-kainic acid is described. Danishefsky's diene and a vinylogous malonate derived from 4-hydroxyproline combine under high pressure to afford a key bicyclic intermediate with virtually no loss of enantiopurity. This adduct can be converted into the natural product with complete stereocontrol. [reaction: see text].

Bridged Bicyclo Compounds↗
PubMed2006

Novel, efficient total synthesis of natural 20(S)-camptothecin.

Enantiopure 20(S)-camptothecin has been prepared from a known hydroxypyridone through a novel approach that involves a Claisen rearrangement, an asymmetric nucleophilic ethylation, a Heck coupling and a Friedländer condensation as the key transformations.

Camptothecin↗
PubMed2006

Reaction of nitrones with silyl ketene acetals: a DFT study.

Theoretical calculations at the DFT level indicate that the reaction of a nitrone with a silyl ketene acetal proceeds, contrary to previous suggestions, through a classical 1,3-dipolar cycloaddition, followed by a silyl group transfer step to give the open-chain product. Introduction of a diffuse basis set is necessary to describe properly nitrones. The influence of a Lewis acid has been studied.

Acetals↗
PubMed2005

New asymmetric approach to natural pyrrolizidines: synthesis of (+)-amphorogynine A, (+)-amphorogynine D, and (+)-retronecine.

Three natural pyrrolizidines, (+)-amphorogynines A and D and (+)-retronecine, have been prepared from a common lactam intermediate. This central compound, in turn, was synthesized in diastereomerically enriched form through a highly selective [2 + 2]-cycloaddition of dichloroketene with a chiral enol ether, followed by Beckmann ring expansion and reduction. Subsequent stereocenters were then cleanly introduced through internal induction.

Molecular Structure↗
PubMed2005

A novel, expeditious synthesis of racemic camptothecin.

[reaction: see text] A novel and efficient synthesis of racemic camptothecin, starting from a readily accessible hydroxy pyridone, is presented. Key steps include a Claisen rearrangement of a functionalized allylic ether, a hindered Heck coupling, and a Friedländer condensation.

Antineoplastic Agents, Phytogenic↗
PubMed2004

Insight into the reactivity of olefins in the Pauson-Khand reaction.

The reactivity of different Co(2)(CO)(6)-acetylene complexes in the Pauson-Khand reaction is strongly dependent on the nature of the olefin. Theoretical calculations at both the DFT and ONIOM levels are concordant with experimental observations and suggest how the olefin-cobalt interactions in the complex could have a major effect on the relative reactivity of the olefins. This study rationalizes for the first time the experimentally observed reactivity differences of cyclohexene, cyclopentene, and norbornene.

Journal Article↗
PubMed2003

New approach to bicyclo[5.3.0]decanes: stereoselective guaiane synthesis.

[reaction: see text] A conceptually new and highly versatile approach to bicyclo[5.3.0]decanes, based on dichloroketene cycloaddition-diazoalkane ring expansion, is disclosed, and its relevance to natural product synthesis is demonstrated through the preparation of three guaiane sesquiterpenes. A concise total synthesis of a guaian-8,12-olide, 6-deoxygeigerin, highlights the effectiveness of the new methodology.

Journal Article↗
PubMed2003

On early events in the Pauson-Khand reaction.

[reaction: see text]. The Magnus Pauson-Khand (PK) mechanism has been studied for the first time by electrospray ionization coupled to tandem mass spectrometry. It has been found that loss of CO from the PK complex precedes olefin coordination and insertion.

Journal Article↗
PubMed2003

Dichloroketene-chiral olefin-based approach to pyrrolizidines: highly stereocontrolled synthesis of (+)-amphorogynine A.

[reaction: see text] A highly stereoselective route to (+)-amphorogynine A, a novel pyrrolizidine recently isolated from the New Caledonian plant Amphorogynine spicata, has been realized. The key step in the approach is a diastereoselective [2 + 2] dichloroketene-chiral enol ether cycloaddition (dr >or= 93:7) to access a dichlorocyclobutanone intermediate, which is converted into the alkaloid natural product via a pyrrolidinone derivative.

Chemical Phenomena↗
PubMed2002

Synthesis of C-3' methyl taxotere (docetaxel).

Protected (3R,4S)-N-Boc-3-hydroxy-4-methyl-4-phenylazetidin-2-one has been synthesized stereoselectively and used to esterify protected 10-desacetylbaccatin III to give, following removal of the protecting groups, novel C-3' methyl taxotere (docetaxel).

Combinatorial Chemistry Techniques↗