Reaction In Text Research Articles

A convenient method for the efficient removal of ruthenium byproducts generated during olefin metathesis reactions.

[reaction in text] An efficient method for removing ruthenium byproducts generated during olefin metathesis reactions with Grubbs catalysts is described. Treatment of the crude reaction products with triphenylphosphine oxide or dimethyl sulfoxide, followed by filtration through silica gel, was found to be a practical and effective method to remove colored ruthenium byproducts.

Palladium-Mediated Intramolecular Carbonylative Annulation of o-Alkynylphenols To Synthesize Benzo[b]furo[3,4-d]furan-1-ones

[reaction in text] The carbonylative annulation of o-alkynylphenols mediated by PdCl(2)(PPh(3))(2) and dppp in the presence of CsOAc at 55 degrees C in acetonitrile under a balloon pressure of CO generates functionalized benzo[b]furo[3,4-d]furan-1-ones in good yields. This novel synthetic approach provides a highly efficient method for diversification of the benzofuran scaffold for combinatorial synthesis.

Tandem cationic aza-cope rearrangement-Mannich cyclization approach to the core structure of FR901483 via a Bridgehead iminium ion.

[reaction in text] An approach to the potent immunosuppressant FR901483 is described. This route utilizes a tandem cationic aza-Cope rearrangement-Mannich cyclization to generate the core structure of this compound. In addition, this is the first demonstration of this tandem reaction passing through a bridgehead iminium ion.

The first total synthesis of (+/-)-linderol A, a tricyclic hexahydrodibenzofuran constituent of Lindera umbellata bark, with potent inhibitory activity on melanin biosynthesis of cultured B-16 melanoma cells.

[reaction in text] The first total synthesis of (+/-)-linderol A, a hexahydrodibenzofuran isolated from Lindera umbellata bark, with potent inhibitory activity on melanin biosynthesis of cultured B-16 melanoma cells was achieved via a 20-step of reaction in 7.64% overall yield starting from 4,6-dimethoxysalicylaldehyde.

Transmembrane Ion Conductance by an Acyclic Bolaamphiphile

[reaction in text] An acyclic bolaamphiphile forms ion channels in vesicles and planar bilayer membranes that are closely similar to the channels formed by related bismacrocyclic compounds. Thus the function of these ion channels does not depend on synthetically difficult macrocyclic subunits.

Peptide bond formation mediated by 4,5-dimethoxy-2-mercaptobenzylamine after periodate oxidation of the N-terminal serine residue.

[reaction in text] A thiol linker-attached peptide was prepared from a nonprotected peptide via an N(alpha)()-alpha-oxoacyl peptide. Selective oxidation of the N-terminal serine with sodium periodate gave the N(alpha)-glyoxyloyl peptide, reductive amination of which with 4,5-dimethoxy-2-(triphenylmethylthio)benzylamine gave an N(alpha)-4,5-dimethoxy-2-mercaptobenzyl glycyl peptide after removal of the trityl group. The N(alpha)-4,5-dimethoxy-2-mercaptobenzyl peptide can be condensed with a peptide thioester, and the linker is removable. This strategy provides a useful method for the synthesis of peptides using recombinant proteins.

A convergent strategy for the synthesis of beta-carba-galacto-disaccharides.

[reaction in text] A convergent strategy for the synthesis of beta-carba-galacto-disaccharides is illustrated by the preparation of 1 and 4, from a central "glycone" component 22, and the corresponding "aglycone" segments, monosaccharide alcohols, 23a or 23b. The key step is the formation of the carbasugar ring via an oxocarbenium ion-enol ether cyclization.

The 2-(N-formyl-N-methyl)aminoethyl group as a potential phosphate/thiophosphate protecting group in solid-phase oligodeoxyribonucleotide synthesis.

[reaction in text] The 2-(N-formyl-N-methyl)aminoethyl deoxyribonucleoside phosphoramidite 1 has been synthesized and used in the solid-phase synthesis of an octadecathymidylic acid as a cost-efficient monomer for potential application in the preparation of therapeutic oligonucleotides. The 2-(N-formyl-N-methyl)aminoethyl group can be cleaved from oligonucleotides according to a unique thermolytic cyclodeesterification process at pH 7.0. In addition to being cost-effective, the use of 1 simplifies oligonucleotide postsynthesis processing by eliminating the utilization of concentrated ammonium hydroxide in oligonucleotide deprotection.

Chiral auxiliary based approach toward the synthesis of C-glycosylated amino acids.

[reaction in text] In a chiral auxiliary based method C-glycosylated amino acids can be obtained by a 1,3-dipolar cycloaddition of a chiral glycine equivalent and C-1 allyl- or vinyl-derived carbohydrate building blocks as the key step. The products are formed regio- and diastereoselectively. Reductive cleavage of the N-O bond of the isoxazolidine and of the chiral auxiliary leads to C-glycosylated amino acids. The use of (-)-menthone to (+)-menthone as the auxiliary leads to the corresponding diastereomers.

Synthetic Studies toward Diazonamide A. A Novel Approach for Polyoxazole Synthesis

[Reaction in text]The indole-bisoxazole fragment of diazonamide A was prepared by a Chan-type rearrangement of a tertiary amide. This approach represents a remarkably direct strategy for polyoxazole synthesis.

A new convergent route to aldohexoses from a common chiral building block.

[reaction in text] A diastereocontrolled route to the eight aldohexoses has been developed starting from a common cyclohexanoid chiral building block.

Enantioselective synthesis of (-)-roccellaric acid.

[reaction in text] A new strategy for the synthesis of anti-4,5-disubstituted gamma-butyrolactones starting from inexpensive furan-2-carboxylic methyl ester was developed. By applying this methodology, the enantioselective synthesis of (-)-roccellaric acid ((-)-17) was accomplished using a copper(I)-catalyzed asymmetric cyclopropanation, a tin(IV)-catalyzed retroaldol/lactonization sequence of cyclopropanols, and a ruthenium-catalyzed intermolecular metathesis reaction as key steps.

Desymmetrization of 4-dimethylsiloxy-1,6-heptadiynes through sequential double silylformylation.

[reaction in text] Desymmetrization of dimethylsilyloxyalkadiynes (1) by Rh-catalyzed intramolecular silylformylation affords 5-exo-(formylmethylene)oxasilacyclopentanes 2 in high yields. Novel sequential double silylformylation of 1a also provides desymmetrization, giving 3-(3-silyl-2-formylprop-2-enyl)-5-exo-(formylmethylene)oxasilacyclopentanes 4 in excellent yields. Reduction of 2a and 4 with NaBH(4) gives the corresponding 5-exo-(hydroxymethylmethylene)oxasilacyclopentanes 3a and 5, respectively.

Catalytic amination of 2-substituted pyridines with hydrazine derivatives.

[reaction in text] Protected pyridylhydrazine derivatives were prepared in a one-step palladium-catalyzed amination reaction using chelating phosphine ligands. 2-Pyridyl chlorides, bromides, and triflates were effective electrophiles in these reactions. Di-tert-butyl hydrazodiformate was an excellent hydrazine substrate, and the resulting products were deprotected under mild conditions. Catalytic amination provides a direct route to protected bifunctional hydrazinopyridine linkers that are suitable for metal-bioconjugate syntheses.

A novel synthesis of enantiomerically pure 5,5,5,5',5',5'-hexafluoroleucine.

[reaction in text] A novel, short, and efficient synthesis of (S)-5,5,5,5',5',5'-hexafluoroleucine (6) in greater than 99% ee starting from the protected oxazolidine aldehyde 1 is described. The enantiomeric excess of the product was calculated from an NMR analysis of a dipeptide formed by reaction with a protected L-serine derivative. Furthermore, a racemic sample of N-acylated hexafluoroleucine was enzymatically resolved by treatment with porcine kidney acylase I and was found to have the same optical rotation as a synthetic sample of 6.

Double allylation reactions of (2-azaallyl)stannanes: synthesis of N,N-bis(3-butenyl)amines and their conversion to 2,3,6,7-tetrahydroazepines via ring-closing metathesis.

[reaction in text] Treatment of (2-azaallyl)stannanes (i) with 2.2 equiv of allylmagnesium bromide afforded good yields of N,N-bis(3-butenyl)amines derivatives (ii), which were subjected to ring-closing metathesis to afford 2,3,6,7-tetrahydroazepines (iii). Thus, (2-azaallyl)stannanes are the synthetic equivalents of amine alpha,alpha'-dications.

Total synthesis of (-)-ratjadone.

[reaction in text] A convergent asymmetric synthesis of (-)-ratjadone (1) has been achieved, confirming the assignments of stereochemistry for the naturally occurring antifungal metabolite.

Photochemistry of tosylstilbenoids in the preparation of complex heterocyclic compounds. Synthesis of a cyclopropafuroindolone analogue of the dna-alkylating section of the antitumor compound CC-1065.

[reaction in text] A novel photocyclization of tosylstilbenoids is used in the preparation of a cyclopropafuroindolone analogue of the DNA-alkylating unit of the antitumor compound CC-1065.

A novel enantioselective synthetic route to omuralide analogues with the potential for species selectivity in proteasome inhibition.

[reaction in text] The building blocks shown can be combined for an enantioselective construction of the simplified omuralide analogue 4 in nine steps, with the use of (R)-atrolactic acid as a recoverable chiral controller.

Bocdene and mocdene derivatives of catechols and catecholamines.

[reaction in text] Catechols react chemoselectively, in the presence of either alcohols, 1,2-diols, or simple phenols, with tert-butyl propynoate and with methyl propynoate to give 2-Boc-ethylidene (Bocdene) and 2-Moc-ethylidene (Mocdene) acetals, respectively, in 96-100% yields within 30 min at room temperature, provided that 150 mol % of DMAP is added. Cleavage of these acetals with pyrrolidine readily takes place (at room temperature!) in 95-100% yields. By taking advantage of the features of Bocdene acetals, novel catecholamine-related phosphate mimetics have been prepared.