Applications of Propargyl Esters of Amino Acids in Solution-Phase Peptide Synthesis

Propargyl esters are employed as effective protecting groups for the carboxyl group during solution-phase peptide synthesis. The propargyl ester groups can be introduced onto free amino acids by treating them with propargyl alcohol saturated with HCl. The reaction between propargyl groups and tetrathiomolybdate is exploited to deblock the propargyl esters. The removal of the propargyl group with the neutral reagent tetrathiomolybdate ensures that most of the other protecting groups used in peptide synthesis are untouched. Both acid labile and base labile protecting groups can be removed in the presence of a propargyl ester. Amino acids protected as propargyl esters are employed to synthesize di- to tetrapeptides in solution-phase demonstrating the possible synthetic utilities of the methodology. The methodology described here could be a valuable addition to currently available strategies for peptide synthesis

Propargyloxycarbonyl as a protecting group for the side chains of serine, threonine and tyrosine

Propargyloxycarbonyl group is used as a protecting group for the hydroxyl groups of serine, threonine and tyrosine. The propargyloxycarbonyl derivatives of these hydroxy amino acids are stable to acidic and basic reagents commonly employed in peptide synthesis. The deprotection of the O-Poc derivatives using tetrathiomolybdate does not affect commonly used protecting groups such as N-Boc, N-Cbz, N-Fmoc, methyl and benzyl esters. The di-and tripeptides synthesized using O-Poc derivatives of serine, threonine and tyrosine are stable, isolable compounds and give the hydroxy peptides in good yields when treated with tetrathiomolybdate

An improved procedure for the synthesis of dehydroamino acids and dehydropeptides from the carbonate derivatives of serine and threonine using tetrabutylammonium fluoride

Dehydroamino acids are important precursors for the synthesis of a number of unnatural amino acids and are structural components in many biologically active peptide derivatives. However, efficient synthetic procedures for their production in large amounts and without side reactions are limited. We report here an improved procedure for the synthesis of dehydroalanine and dehydroamino butyric acid from the carbonate derivatives of serine and threonine using TBAF. The antiselective E-2 elimination of the carbonate derivatives of serine and threonine using TBAF is milder and more efficient than other available procedures. The elimination reaction is completed in less than 10 min with various carbonate derivatives studied and the methodology is very efficient for the synthesis of dehydroamino acids and dehydropeptides. The procedure thus provides an easy access to key synthetic precursors and can be used to introduce interesting structural elements to designed peptides. Copyrigh

Enantioselective Synthesis of 2‑Aminomethyl and 3‑Amino Pyrrolidines and Piperidines through 1,2-Diamination of Aldehydes

An efficient method for the synthesis of 1,2-diamines from aldehydes through proline-catalyzed asymmetric α-amination followed by reductive amination is reported. The products resemble those obtained through direct asymmetric diamination of terminal alkenes. The methodology is used to synthesize 2-aminomethyl and 3-amino pyrrolidines and piperidines in high yields and with a good enantioselectivity. The usefulness of the method is demonstrated through the synthesis of a 2-aminomethyl iminocyclitol

Diastereoselective Synthesis of 1‑Deoxygalactonojirimycin, 1‑Deoxyaltronojirimycin, and <i>N</i>‑Boc-(2<i>S</i>,3<i>S</i>)‑3-Hydroxypipecolic Acid via Proline Catalyzed α‑Aminoxylation of Aldehydes

An efficient synthesis of deoxygalactonojirimycin and deoxyaltronojirimycin through the use of proline catalyzed asymmetric α-aminoxylation of a higher homologue of Garner’s aldehyde, derived from l-aspartic acid, is reported. The method is also used for a highly diastereoselective synthesis of the <i>N</i>-Boc derivative of (2<i>S</i>,3<i>S</i>)-3-hydroxypipecolic acid. The configuration of the proline catalyst used for the asymmetric aminoxylation step ultimately controls the absolute configuration of three adjacent stereogenic centers in the final products

An efficient synthesis of dehydroamino acids and dehydropeptides from O-Cbz and O-Eoc derivatives of serine and threonine

A simple and efficient method for the synthesis of dehydroamino acids from serine and threonine is reported. Various O-Cbz and O-Eoc derivatives of serine and threonine are prepared using CbzCl and EocCl, respectively, and are subjected to an anti-selective elimination on treatment with $K_2CO_3$ in DMF at 65° C to afford dehydroalanine and dehydroamino butyric acid derivatives, respectively, in excellent yields. The high stability of these carbonate derivatives of serine and threonine allows their use in normal peptide synthesis as protected serine and threonine residues. Peptides synthesized by incorporating O-Cbz or O-Eoc derivatives undergo ready elimination under the reported conditions, to give the corresponding dehydropeptides in excellent yields. The reaction conditions are mild enough not to cause the racemization of other stereogenic centers present in the peptide

An improved procedure for the synthesis of dehydroamino acids and dehydropeptides from the carbonate derivatives of serine and threonine using tetrabutylammonium fluoride

Dehydroamino acids are important precursors for the synthesis of a number of unnatural amino acids and are structural components in many biologically active peptide derivatives. However, efficient synthetic procedures for their production in large amounts and without side reactions are limited. We report here an improved procedure for the synthesis of dehydroalanine and dehydroamino butyric acid from the carbonate derivatives of serine and threonine using TBAF. The antiselective E2 elimination of the carbonate derivatives of serine and threonine using TBAF is milder and more efficient than other available procedures. The elimination reaction is completed in less than 10 min with various carbonate derivatives studied and the methodology is very efficient for the synthesis of dehydroamino acids and dehydropeptides. The procedure thus provides an easy access to key synthetic precursors and can be used to introduce interesting structural elements to designed peptides

Base catalyzed cyclization of N-aryl and N-alkyl-O-propargyl carbamates to 4-alkylidene-2-oxazolidinones

The base catalyzed cyclization of N-aryl and N-alkyl-O-propargyl carbamates is studied in detail. The effect of various bases and solvents on the efficacy of this cyclization reaction is analyzed and a new base-solvent system (LiOH in DMF) for effective cyclization of these carbamates is reported. A number of differentially substituted O-propargyl carbamates were cyclized to the corresponding 2-oxazolidinones under these conditions. The reaction conditions reported here are mild and no side reactions were observed in any of the substrates studied. A propargyl carbonate group was unaffected during the course of the cyclization of the O-propargyl carbamate group. The propargyl carbamates were prepared from the corresponding alkyl or aryl amines and the corresponding propargyl chloroformate, resulting in oxazolidinones diversely substituted at the nitrogen atom. N-Aryl-O-propargyl carbamates cyclized readily to the corresponding oxazolidinones with LiOH in DMF, whereas N-alkyl-O-propargyl carbamates reacted slowly under the same conditions. O-Propargyl carbamates substituted at the 1-position tend to cyclize faster whereas those substituted at 3-position cyclize considerably slower than the unsubstituted carbamates